سویا یکی از بقولات است. نیام و دانه آن (لوبیا) غذای میلیونها نفر را فراهم میکنند و در تهیه مواد شیمیایی نقش عمده دارند. سویا احتمالاً حاصل اهلیسازی گیاهی وحشی در شرق آسیا است. روغن استخراج شده از دانههای سویا یکی از مهمترین انواع روغنها است. این روغن حاوی اسید لینولئیک بسیار بالایی است و به همین دلیل از آن نمیتوان برای تهیه روغن سرخ کردنی استفاده کرد. دانه سویا از لحاظ اسید آمینه میتونین نسبت به کنجد فقیر است اما از لحاظ اسید آمینه لیزین در سطح بالایی قرار دارد سویا بیش از سایر دانهها به پروتئین حیوانی شباهت دارد. روغن سویا ۴۹ درصد لینولئیک اسید و ۲۵ درصد اسیداولئیک دارد. میزان پروتئین دانه سویا بسیار بیشتر از سایر دانههای روغنی است. ارقام زیر نشان دهنده تفاوت عمده سویا با سایر دانههای روغنی به لحاظ میزان روغن و پروتئین است. میزان پروتئین سویا۳۰-۵۰ درصد، کلزا۱۸-۲۵ درصد، آفتابگردان ۱۵-۲۵ درصد، گلرنگ ۱۵-۲۵ درصد، کنجد ۱۹-۲۵ درصد، بادام زمینی ۲۵-۳۵ درصد میباشد
میزان روغن در سویا۱۸-۲۵ درصد، کلزا۴۰-۵۰ درصد، آفتابگردان۲۵-۵۰ درصد، گلرنگ۴۰-۵۰ درصد، کنجد۲۵-۴۵ درصد، بادام زمینی۴۵-۶۵ درصد میباشد.
همان طور که ملاحظه میشود میزان پروتئین سویا دو برابر سایر دانههای روغنی است و البته درصد روغن آن نیز از سایر دانههای روغنی رایج کمتر است. وجود پروتئین زیاد سبب شده است که کنجاله روغن کشیده شده آن برای تغذیه انسان بسیار مناسب باشد.
محصولات ساخته شده از سویا[ویرایش]
مواد مغذی موجود در یک فنجان ۸۸ گرم آرد سویا بدون چربی:
کالری ۲۹۰ - کربوهیدرات ۳۴ گرم - پروتئین ۴۱ گرم - کلسیم ۲۱۲ میلی گرم - چربی ۱ گرم - اشباع ۰ - فسفر ۵۹۳ میلی گرم - کلسترول ۰ میلی گرم - آهن ۸٫۱ میلی گرم - سدیم ۱۸ میلی گرم - تیامین ۰٫۶۱ میلی گرم - پتاسیم ۲۰۹۷ میلی گرم - ریبو فلاوین ۰٫۲۲ میلی گرم - الیاف غذایی ۲ گرم - نیاسین ۲٫۳ میلی گرم - ویتامین آ ۴ RE ویتامین ث ۰ میلی گرم
لوبیا روغنی با نام علمی Glycine max گیاهی است از تیره نخود (لگومینوز) که به صورت بوتهای استوار و با شاخ بر گ زیاد رشد میکند. ریشه سویا مستقیم و با انشعاب زیاد است. اما در شرایط ایران ریشه در عمق ۳۰ سانتیمتر خاک پراکنده است. روی ریشه سویا نوعی باکتری همزیست بنام Rhizobium japonicum مشاهده میشود. باکتریهای ریزوبیوم، کربوهیدراتها و سایر مواد غذایی را از آوند آبکشی گرفته و انرژی دریافتی را صرف تبدیل نیتروژن هوا به یون آمونیوم و در نهایت اسیدهای آمینه میکند. مقداری از نیتروژن تولید شده که مازاد مصرف باکتری است در اختیار گیاه قرار میگیرد و مقداری نیتروژن هم از تجزیه بافت گرههای مرده (قطع در اثر پیری و رشد ثانویه ریشه) آزاد گردیده و در اختیار گیاه قرار میگیرد. عمق ریشه سویا در مرحله گلدهی ۲ برابر ارتفاع ساقه است ولی وزن خشک ریشه کمتر از اندامهای هوایی است. رشد ریشه تا زمان تشکیل دانه ادامه پیدا میکند و سپس قبل از ورود دانه به مرحله رسیدگی فیزیولوژیک متوقف میشود. باکتری ریزوبیوم ژاپونیکوم به صورت طبیعی در خاکهای ایران وجود ندارد و باید باکتریها همراه بذر به خاک اضافه شود. برگهای سویا در هنگام رسیدگی معمولاً ریزش میکنند که این یک صفت مطلوب برای برداشت است. سویا دارای دو فرم رشد محدود و نامحدود است. در گیاهان با فرم محدود گلها در ابتدای گرههای فوقانی به ظهور رسیده و به طرف پایین ادامه مییابد. در ارقام رشد نامحدود گل دهی در گرههای پایینی آغاز گردیده و به طرف بالا پیش میرود. در سویا اشکال رشد نامحدود بزرگ ترین بر گها در وسط بوته قرار دارند و در بخشهای بالایی و پایینی بوته از سطح برگها و طول دمبرگ کاسته میشود. در ارقام رشد محدود برگها ی قسمت انتهایی بوته دارای سطح برگ کمتر و دمبرگ کوتاهتر میباشند، ولی نزدیک شدن به طرف پایین بوته، سطح بر گها و طول دمبر گ افزایش مییابد. در ارقام سویا دارای رشد محدود دانههایی که در قسمت پایین بوته تولید میشوند نسبت به دانههایی که در قسمت بالای بوته تولید میشوند کوچکتر هستند. آرایش بر گها در بوته میتواند عملکرد را تحت تاثیر قرار دهد و ارقام دارای برگهای عمودی نسبت به ارقام دارای بر گهای ا فتاده کارایی بالاتری از نظر فتوسنتزی دارد. در سویا هر چه فاصله غلاف بندی ازسطح خاک بیشتر باشد، به همان اندازه برداشت مکانیزه راحت تر خواهد بود و غلاف به جای مانده بر روی بوته در حداقل خواهد بود. فاصله اولین غلافهای بوته از سطح خاک غالباً تابع ژنوتیپ و تراکم بوته است و در تراکم بالا غلاف در سطح بالاتری از سطح خاک تشکیل میشود. در سویا تعداد ساقههای فرعی در ارقام دیررس زیاد بوده و بلعکس، در ارقام زودرس تعداد آنها کمتر است. با افزایش ساقههای فرعی در بوته، عملکرد دانه نیز افزایش خواهد یافت. از طرف دیگر بین رسیدگی محصول و ارتفاع بوته همبستگی مثبت وجود دارد به طوری که ارقام پاکوتاه زودرس و ارقام پابلند دیررس تر میباشند. گرده افشانی در لوبیا روغنی خودگشنی است و میزان دگرگشنی وابسته به فعالیت حشرات از ۱٪ تجاوز نمیکند. وزن هزار دانه سویا ۶۰ تا ۲۰۰ گرم و با میانگین ۱۵۰ گرم است (بذر ارقام مختلف سویا اندازههای متفاوتی دارند مثلاً بذر کلارک درشت و رقم هیل ریز است) و روغن در پروتئین در لپهها ذخیره میشود.
فعالیتهای به نژادی سویا منجر به تولید ارقام متفاوتی از نظر طول دوره رشد شده است که سبب شده آن را در عرضهای جغرافیایی متفاوت و ار تفاع مختلف از سطح دریا کاشت. با این که سویا گیاهی روز کوتاه است اما بسیاری از ارقام دیگر به طول روز حساسیت ندارند. لوبیا روغنی بر حسب طول روز و در نتیجه زودرسی به ۱۳ گروه شامل ۰۰۰،۰۰،۰،I،II،III،IV، V،VI،VII،VIII، IX و X قرار دارند. ارقام ۰۰۰ و ۰۰ کانولا بی تفاوت به طول روز و بسیار زودرس و گروه X بسیار حساس به طول روز و دیر رس است. گروههای V تا VIII در تیپ رشد محدود قرار دارند و گروههای ۰۰ تا IV رشد نامحدود هستند. در ارقام رشد نامحدود تعداد شاخههای جانبی زیاد بوده و یکنواختگی رسیدگی کمتری از انواع رشد محدود دارند.
به جز طول روز، شدت نور نیز نقش زیادی در رشد و عملکرد سویا دارد به طوری که آزمایشها انجام گرفته نشان میدهد که وجود سایه و کمی شدت نور سبب کاهش عملکرد سویا تا ۴۰ درصد میشود. ارقام کلارک ۶۳، ویلیامز و استیل در گروه رشد نامحدود قرار دارند. در ایران بیشتر از ارقام گروه II مانند هارکو و استیل به عنوان زودرس و ارقام گروه III مانند ویلیامز، کلارک ۶۳ و هابیت به عنوان میان رس و ارقام گروه V مانند لی و هیل به عنوان دیررس استفاده میشود. سویاهای دیررس حساس ترین گیاهان زراعی به طول روز هستند.
لوبیا روغنی گیاهی گرمادوست است این گیاه درجه حرارتهای بالا را حتی بیش از ذرت تحمل میکند البته این بدین معنا نیست که در درجه حرارتهای زیاد عملکرد خوبی خواهد داشت زیرا بسیاری از غلافها در درجه حرارتهای زیاد ریزش میکنند اما بوته زنده میماند و در اثر درجه حرارتهای بسیار زیاد از بین نمیرود هر چند عملکرد مطلوبی هم تولید نمیکند. حداقل دما برای رشد لوبیا روغنی ۱۰ درجه سانتی گراد و دمای ۲- دمای کشنده آن است. دمای بالاتر از ۳۵ درجه در طول دوره رشد برای آن مناسب نیست و بذرهای که در درجه حرارتهای بالا تولید میشوند کیفیت مطلوبی ندارند. سویا حساس به خشکی است و بذر آن در مرحله سبز شدن حساس به آب ایستادگی می باشدالبته سویا حساسیتی به رطوبت نیبی هوا (خشکی هوا) ندارد.
لوبیا روغنی سرمای خفیف را در مرحله گیاهچه و مرحله رسیدگی دانه (کمی بیش از ذرت) تحمل میکند. کشت دیم لوبیا روغنی در مناطق با بارندگی سالانه ۱۰۰۰ میلیمتر امکانپذیر است (مانند شمال ایران). این گیاه به باد مقاوم است. سویا به عنصر بر و شوری خاک بسیار حساس است.
در غلظت بالای CO2 تثبیت ازت هم افزایش مییابد. به صورت معمول غلظت CO2 جو ppm320 میباشد اما پیش بینیها نشان میدهد که این غلظت تا سال ۲۰۵۰ به ppm600 افزایش یابد. آزمایشها انجام گرفته نشان میدهد که در غلظت ppm600 CO2 در سویا ۵۰درصد افزایش عملکرد دیده میشود و این افزایش عملکرد بیشتر در نتیجه افزایش تعداد غلاف در بوته است و اثر زیادی بر روی اندازه دانهها ندارد. از طرف دیگر بذرهایی که والد آنها شرایط غلظت بالای CO2 رشد کرده بود نسبت به بذرهای معمولی ریشه چه قوی تری تولید میکردند. عوامل مؤثر بر تثبیت ازت در سویا ۱-دما:سویا به عنوان یک گیاه گرمسیری برای فعالیت باکتری همزیست به دمای بین ۲۵ تا ۳۰ درجه سانتی گراد نیاز دارد. وقتی دمای خاک به کمتر از این حد کاهش یابد، تشکیل گره در سویا کاهش مییابد و در دمای ۱۰ درجه سانتی گراد تشکیل گره مختل میشود.
۲-میزان ازت خاک:گره زایی در سویا به وسیله نیترات زیاد بازداری میشود مطالعات نشان داده است که تاخیر بیشتری در تشکیل گره به واسطه نیترات در مقایسه با آمونیوم و اوره حاصل میشود.
۳-دسترسی به آب: دسترسی به آب اثر عمدهای بر تشکیل گره و تثبیت نیتروژن دارد، گره زایی با افزایش محتوای آب خاک تا زمانی که غرقابی شدن روی میدهد افزایش مییابد. تنش آبی به طور قابل توجهی تعداد رشتههای سرایت تشکیل شده را کاهش میدهد و از گره زایی جلوگیری میکند.
۴-غلظتهای بالای نمک: در غلظتهای بالای نمک در آب فعالیت گره به صورت منفی به واسطه بازداری اسمزی گرهها کاهش مییابد.
۵-اسیدیته پایین: اسیدیته معمولاً گره زایی کاهش میدهد و اسیدیته کمتر از ۶ سبب کاهش گره بندی فعالیت ریزویبوم میشود. در صورتیکه اسیدیته خاک مورد کشت ما کمتر از این میزان باشد می باست با دادن آهک اسیدیته خاک را بالا برد تا مناسب فعالیت باکتری شود و هم از سمیت ناشی از آلمینیوم و منگنز در خاکهای اسیدی جلوگیری کرد.
۶-افزایش CO2: تحقیقات نشان داده با افزایش CO2 تثبیت ازت هم افزایش مییابد. علت اینکه افزایش CO2 باعث افزایش فتوسنتز میشود این است قند بیشتری در اختیار باکتری قرار میگیرد. باکتریهایی که بر روی گیاه قرار دارند در عوض ترکیبات مورد نیازشان را از گیاه میگیرند
۷-عوامل زراعی: عواملی چون آتش زدن مزرعه، آب ایستادگی، سله ممتد و خشکی موجب کاهش فعالیت باکتری میشود.
۸-فشردگی خاک: فشردگی خاک سبب کاهش رشد ریشه و رشد گرههای تثبیت ازت شده میگردد. قدرت نفوذ پذیری ریشه سویا رابطه معکوس با فشردگی خاک دارد و فشردگی خاک سبب کاهش وزن و تعداد گرهکهای تثبیت از ت میشود.
۹-تغذیه: کمبود عناصری چون کبالت، کلسیم، منیزیم، فسفر مولبیدن و آهن سبب کاهش یا عدم تشکیل گرههای باکتریایی سویا میشود. عناصر سنگین مانند کادمیوم میتوانند سبب از بین رفتن گرههای باکتریایی شود
۱۰-آفات و بیماریها:گرهها ممکن است سطوحی از ویروس را داشته باشند که فعالیت گره را مستقیماً تحت تاثیر قرار میدهند. گرههای ریشه ممکن است به وسیله حشرات یا لاروهای حشرات خورده شوند.
اثرات سویا بر سلامتی[ویرایش]
مضرات سویا و موارد منع مصرف[ویرایش]
لوبیا سویا بکر تقریبا خوراکی بی خطری میباشد و میتوان در رژیم غذایی بزرگسالان، کودکان و یا حتی نوزادان استفاده نمود. با اینحال آلرژی به سویا معمول بوده و اگر شما یا سایر اعضای خانوادتان به سویا حساسیت دارید، نمیبایست آن را مصرف کنید. نشانههای حساسیت به سویا متفاوت بوده و میتواند شامل آب ریزش بینی، التهاب دستگاه گوارش و یا افت فشار ناگهانی شود.
"Soy" redirects here. For other uses, see Soy (disambiguation).
Glycine max, commonly known as soybean in North America or soya bean in British English, is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses. The plant, classed as an oilseed rather than a pulse by the UN Food and Agriculture Organization, produces significantly more protein per acre than most other uses of land.
Fat-free (defatted) soybean meal is a significant and cheap source of protein for animal feeds and many packaged meals. For example, soybean products, such as textured vegetable protein (TVP), are ingredients in many meat and dairy substitutes. The beans contain significant amounts of phytic acid, dietary minerals and B vitamins. Soy vegetable oil, used in food and industrial applications, is another product of processing the soybean crop. Traditional non-fermented food uses of soybeans include soy milk from which tofu and tofu skin are made. Fermented soy foods include soy sauce, fermented bean paste, natto and tempeh.
The main countries growing soybeans are the United States (32% of world total, 2016 forecast), Brazil (31%) and Argentina (18%).
The English words "soy" and "soya" are ultimately derived from the Japanese pronunciation of shōyu (醤油?), the Sino-Japanese word for soy sauce, by way of the German adaptation of the same word, soja.
The genus Glycine Willd. is divided into two subgenera, Glycine and Soja. The subgenus Soja (Moench) F.J. Herm. includes the cultivated soybean, Glycine max (L.) Merr., and the wild soybean, Glycine soja Sieb. & Zucc. Both species are annuals. Glycine soja is the wild ancestor of Glycine max, and grows wild in China, Japan, Korea, Taiwan and Russia. The subgenus Glycine consists of at least 25 wild perennial species: for example, Glycine canescens F.J. Herm. and G. tomentella Hayata, both found in Australia and Papua New Guinea. Perennial soybean (Neonotonia wightii) originated in Africa and is now a widespread pasture crop in the tropics.
Like some other crops of long domestication, the relationship of the modern soybean to wild-growing species can no longer be traced with any degree of certainty. It is a cultural variety with a very large number of cultivars.
Like most plants, soybeans grow in distinct morphological stages as they develop from seeds into fully mature plants.
The first of stage of growth is germination, a process that first becomes apparent as a seed's radicle emerges. This is the first stage of root growth and occurs within the first 48 hours under ideal growing conditions. The first photosynthetic structures, the cotyledons, develop from the hypocotyl, the first plant structure to emerge from the soil. These cotyledons both act as leaves and as a source of nutrients for the immature plant, providing the seedling nutrition for its first 7 to 10 days.
The first true leaves develop as a pair of single blades. Subsequent to this first pair, mature nodes form compound leaves with three blades. Mature trifoliolate leaves, having three to four leaflets per leaf, are often between 6–15 cm (2.4–5.9 in) long and 2–7 cm (0.79–2.76 in) broad. Under ideal conditions, stem growth continues, producing new nodes every four days. Before flowering, roots can grow 1.9 cm (0.75 inch) per day. If rhizobia are present, root nodulation begins by the time the third node appears. Nodulation typically continues for 8 weeks before the symbiotic infection process stabilizes. The final characteristics of a soybean plant are variable, with factors such as genetics, soil quality, and climate affecting its form; however, fully mature soybean plants are generally between 51–127 cm (20–50 in) in height and have rooting depths between 76–152 cm (30–60 in).
Flowering is triggered by day length, often beginning once days become shorter than 12.8 hours. This trait is highly variable however, with different varieties reacting differently to changing day length. Soybeans form inconspicuous, self-fertile flowers which are borne in the axil of the leaf and are white, pink or purple. Depending of the soybean variety, node growth may cease once flowering begins. Strains that continue nodal development after flowering are termed "indeterminates" and are best suited to climates with longer growing seasons. Often soybeans drop their leaves before the seeds are fully mature.
The fruit is a hairy pod that grows in clusters of three to five, each pod is 3–8 cm long (1–3 in) and usually contains two to four (rarely more) seeds 5–11 mm in diameter. Soybean seeds come in a wide variety sizes and hull colors such black, brown, blue, yellow, and green. Variegated and bicolored seed coats are also common.
The hull of the mature bean is hard, water-resistant, and protects the cotyledon and hypocotyl (or "germ") from damage. If the seed coat is cracked, the seed will not germinate. The scar, visible on the seed coat, is called the hilum (colors include black, brown, buff, gray and yellow) and at one end of the hilum is the micropyle, or small opening in the seed coat which can allow the absorption of water for sprouting.
Remarkably, seeds such as soybeans containing very high levels of protein can undergo desiccation, yet survive and revive after water absorption. A. Carl Leopold, son of Aldo Leopold, began studying this capability at the Boyce Thompson Institute for Plant Research at Cornell University in the mid-1980s. He found soybeans and corn to have a range of soluble carbohydrates protecting the seed's cell viability. Patents were awarded to him in the early 1990s on techniques for protecting "biological membranes" and proteins in the dry state.
Many legumes (alfalfa, clover, lupins, peas, beans, lentils, soybeans, peanuts and others) contain symbiotic bacteria called Rhizobia within nodules of their root systems. These bacteria have the special ability of fixing nitrogen from atmospheric, molecular nitrogen (N2) into ammonia (NH3). The chemical reaction is:
Ammonia is then converted to another form, ammonium (NH4+), usable by (some) plants by the following reaction:
This arrangement means that the root nodules are sources of nitrogen for legumes, making them relatively rich in plant proteins.
Together, protein and soybean oil content account for 56% of dry soybeans by weight (36% protein and 20% fat, table). The remainder consists of 30% carbohydrates, 9% water and 5% ash (table). Soybeans comprise approximately 8% seed coat or hull, 90% cotyledons and 2% hypocotyl axis or germ.
Further information: Soy protein
Soybeans are an exceptional source of essential nutrients, providing in a 100 gram serving (raw, for reference) high contents of the Daily Value (DV) especially for protein (36% DV), dietary fiber (37%), iron (121%), manganese (120%), phosphorus (101%) and several B vitamins, including folate (94%) (table). High contents also exist for vitamin K, magnesium, zinc and potassium (table).
For human consumption, soybeans must be cooked with "wet" heat to destroy the trypsin inhibitors (serine protease inhibitors). Raw soybeans, including the immature green form, are toxic to all monogastric animals.
Most soy protein is a relatively heat-stable storage protein. This heat stability enables soy food products requiring high temperature cooking, such as tofu, soy milk and textured vegetable protein (soy flour) to be made.
Soybeans are considered by many agencies to be a source of complete protein. A complete protein is one that contains significant amounts of all the essential amino acids that must be provided to the human body because of the body's inability to synthesize them. For this reason, soy is a good source of protein, amongst many others, for vegetarians and vegans or for people who want to reduce the amount of meat they eat. According to the US Food and Drug Administration:
The Protein Digestibility Corrected Amino Acid Score (PDCAAS) of soy protein is the nutritional equivalent of meat, eggs, and casein for human growth and health. Soybean protein isolate has a biological value of 74, whole soybeans 96, soybean milk 91, and eggs 97.
Soy protein is essentially identical to the protein of other legume seeds and pulses. Moreover, soybeans can produce at least twice as much protein per acre than any other major vegetable or grain crop besides hemp, five to 10 times more protein per acre than land set aside for grazing animals to make milk, and up to 15 times more protein per acre than land set aside for meat production.
The principal soluble carbohydrates of mature soybeans are the disaccharide sucrose (range 2.5–8.2%), the trisaccharide raffinose (0.1–1.0%) composed of one sucrose molecule connected to one molecule of galactose, and the tetrasaccharide stachyose (1.4 to 4.1%) composed of one sucrose connected to two molecules of galactose. While the oligosaccharides raffinose and stachyose protect the viability of the soybean seed from desiccation (see above section on physical characteristics) they are not digestible sugars, so contribute to flatulence and abdominal discomfort in humans and other monogastric animals, comparable to the disaccharide trehalose. Undigested oligosaccharides are broken down in the intestine by native microbes, producing gases such as carbon dioxide, hydrogen, and methane.
Since soluble soy carbohydrates are found in the whey and are broken down during fermentation, soy concentrate, soy protein isolates, tofu, soy sauce, and sprouted soybeans are without flatus activity. On the other hand, there may be some beneficial effects to ingesting oligosaccharides such as raffinose and stachyose, namely, encouraging indigenous bifidobacteria in the colon against putrefactive bacteria.
The insoluble carbohydrates in soybeans consist of the complex polysaccharides cellulose, hemicellulose, and pectin. The majority of soybean carbohydrates can be classed as belonging to dietary fiber.
Within soybean oil or the lipid portion of the seed is contained four phytosterols: stigmasterol, sitosterol, campesterol, and brassicasterol accounting for about 2.5% of the lipid fraction; and which can be converted into steroid hormones.
Comparison to other major staple foods
The following table shows the nutrient content of green soybean and other major staple foods, each in respective raw form. Raw soybeans, however, aren't edible and cannot be digested. These must be sprouted, or prepared and cooked for human consumption. In sprouted and cooked form, the relative nutritional and anti-nutritional contents of each of these grains is remarkably different from that of raw form of these grains reported in this table. The nutritional value of soybean and each cooked staple depends on the processing and the method of cooking: boiling, frying, roasting, baking, etc.
All spermatophytes except for the grass/cereal family contain soybean-like 7S (vicilin) and/or 11S (legumin), (S denotes Svedberg, sedimentation coefficients) seed storage globulin proteins. Oats and rice are anomalous in that they also contain a majority of soybean-like protein. Cocoa, for example, contains the 7S globulin, which contributes to cocoa/chocolate taste and aroma;, whereas coffee beans (coffee grounds) contain the 11S globulin responsible for coffee's aroma and flavor.
Vicilin and legumin proteins belong to the cupin superfamily, a large family of functionally diverse proteins that have a common origin and whose evolution can be followed from bacteria to eukaryotes including animals and higher plants.
2S albumins form a major group of homologous storage proteins in many dicot species and in some monocots but not in grasses (cereals). Soybeans contain a small but significant 2S storage protein. 2S albumin are grouped in the prolamin superfamily. Other allergenic proteins included in this 'superfamily' are the non-specific plant lipid transfer proteins, alpha amylase inhibitor, trypsin inhibitors, and prolamin storage proteins of cereals and grasses.
Peanuts, for instance, contain 20% 2S albumin but only 6% 7S globulin and 74% 11S. It is the high 2S albumin and low 7S globulin that is responsible for the relatively low lysine content of peanut protein compared to soy protein.
Further information: List of soybean diseases
Soybeans are a globally important crop, providing oil and protein. In the United States, the bulk of the harvest is solvent-extracted with hexane, and the "toasted" defatted soymeal (50% protein) then makes possible the raising of farm animals (e.g. chicken, hog, turkey) on a large industrial scale. Soybean products are used in a large variety of processed foods.
During World War II, soybeans became important in both North America and Europe chiefly as substitutes for other protein foods and as a source of edible oil. During the war, the soybean was discovered as fertilizer by the United States Department of Agriculture. In the 1960–1 Dillon round of the General Agreement on Tariffs and Trade (GATT), the United States secured tariff-free access for its soybeans to the European market. In the 1960s, the United States exported over 90% of the world's soybeans. By 2005, the top soybeans exporters were Argentina (39% of world soybean exports), United States (37%) and Brazil (16%), while top importers were China (41% of world soybean imports), European Union (22%), Japan (6%) and Mexico (6%).
Cultivation is successful in climates with hot summers, with optimum growing conditions in mean temperatures of 20 to 30 °C (68 to 86 °F); temperatures of below 20 °C and over 40 °C (68 °F, 104 °F) stunt growth significantly. They can grow in a wide range of soils, with optimum growth in moist alluvial soils with a good organic content. Soybeans, like most legumes, perform nitrogen fixation by establishing a symbiotic relationship with the bacterium Bradyrhizobium japonicum (syn. Rhizobium japonicum; Jordan 1982). For best results, though, an inoculum of the correct strain of bacteria should be mixed with the soybean (or any legume) seed before planting. Modern crop cultivars generally reach a height of around 1 m (3.3 ft), and take 80–120 days from sowing to harvesting.
Environmental groups, such as Greenpeace and the WWF, have reported soybean cultivation and the probability of increased soybean cultivation in Brazil has destroyed huge areas of Amazon rainforest, and is encouraging further deforestation.
American soil scientist Andrew McClung, who first showed that the ecologically biodiverse savannah of the Cerrado region of Brazil could grow profitable soybeans, was awarded the 2006 World Food Prize on October 19, 2006. However, even correcting for poor soils soybeans were an unlikely cash crop for the Cerrado. Soy did not fare well in the low latitudes. More than the heat and humidity, it was a lack of seasons that hampered production. In the higher more northerly latitudes, flowering coincides with the summer solstice, when the plants reach their maximum height. The first soybeans planted in the Cerrado, however, flowered early and, deprived of long summer days, remained stunted. For soy agriculture to take root in Mato Grosso it was first necessary to develop a "tropical soybean"—one that would flower later, giving the plants more time to fully mature. The feat was accomplished after years of laborious crossbreeding by scientists within Embrapa, the respected research arm of the Brazilian Ministry of Agriculture.
Human sewage sludge can be used as fertilizer to grow soybeans. Soybeans grown in sewage sludge likely contain elevated concentrations of metals. Soybean plants are vulnerable to a wide range of bacterial diseases, fungal diseases, viral diseases and parasites. One important pest is the corn earworm moth, which is the most common and destructive pest of soybean growth in Virginia.
Global production of soybeans is forecast to be 324 million tonnes in 2016, a 5% increase from the 2014 world total. The United States, Brazil and Argentina are the world's largest soybean producers and represent more than 80% of global soybean production (table).
In 2014, the average worldwide yield for soybean crops was 2.6 tonnes per hectare. The three largest yields per hectare were in Thailand, Turkey and Italy, having an average nationwide soybean yield of 4.9 tonnes. The most productive soybean farms in the world in 2014 were in Thailand, with a nationwide average farm yield of 6.2 tonnes per hectare.
Soybeans were a crucial crop in East Asia long before written records began. There is evidence for soybean domestication between 7000 and 6600 BCE in China, between 5000 and 3000 BCE in Japan and 1000 BCE in Korea. They are now a major crop in the United States, Brazil, Argentina, India, and China. Prior to fermented products such as fermented black soybeans (douchi), jiang (Chinese miso), soy sauce, tempeh, natto, and miso, soy was considered sacred for its beneficial effects in crop rotation. Soy was introduced to Africa from China in the late 19th century, and is now widespread across the continent.
The closest living relative of the soybean is Glycine soja (previously called G. ussuriensis), a legume native to central China. According to the ancient Chinese myth, in 2853 BCE, the legendary Emperor Shennong of China proclaimed that five plants were sacred: soybeans, rice, wheat, barley, and millet. Cultivation of soybeans took place over long periods of time in the prehistory of modern-day Japan, Korea and Northern China, based on archaeological evidence.
The origin of soy bean cultivation remains scientifically debated. Early Chinese records mention that soybeans were a gift from the region of Manchuria and the Korean peninsula. Recent research, however, indicates that seeding of wild forms started early (before 5000 BCE) in multiple locations through China, Korea and Japan The Great Soviet Encyclopedia claims soybean cultivation originated in China about 5000 years ago. Some scholars suggest that soybean originated in China and was domesticated about 3500 BCE. However, the oldest preserved soybeans resembling modern varieties in size and shape were found in archaeological sites in Korea dated about 1000 BCE Radiocarbon dating of soybean samples recovered through flotation during excavations at the Early Mumun period Okbang site in Korea indicated soybean was cultivated as a food crop in around 1000–900 BCE. Soy bean from the Jomon period in Japan from 3000 BCE are also significantly larger than wild varieties. The cultivation of soybeans began in the eastern half of northern China by 2000 BCE, but is almost certainly much older.  It became an important crop by the Zhou Dynasty (c. 1046 BCE–256 BCE) in China. However, the details of where, when, and under what circumstances soybean developed a close relationship with people are poorly understood. Soy bean was unknown in South China before the Han period From about the first century CE to the Age of Discovery (15–16th century), soybeans were introduced into several countries, such as India, Japan, Indonesia, the Philippines, Vietnam, Thailand, Cambodia, Malaysia, Burma and Nepal. This spread was due to the establishment of sea and land trade routes. The earliest Japanese textual reference to the soybean is in the classic Kojiki (Records of Ancient Matters), which was completed in 712 CE.
Many people have claimed soybeans in Asia were historically only used after a fermentation process, which lowers the high phytoestrogens content found in the raw plant. However, terms similar to "soy milk" have been in use since 82 CE, and there is evidence of tofu consumption that dates to 220.
Soybeans were first introduced to North America from China in 1765, by Samuel Bowen, a former East India Company sailor who had visited China in conjunction with James Flint, the first Englishman legally permitted by the Chinese authorities to learn Chinese. The first 'New World' soybean crop was grown on Skidaway Island, Georgia in 1765 by Henry Yonge from seeds given him by Samuel Bowen. Bowen grew soy near Savannah, Georgia, possibly using funds from Flint, and made soy sauce for sale to England. Although, soybean was introduced into North America in 1765,for the next 155 years, the crop was grown primarily for forage.
It wasn't until Lafayette Mendel and Thomas Burr Osborne (chemist) showed that the nutritional value of soybean seeds could be greatly increased by cooking, wet heat, that soy went from merely a forage to a farm animal feed and became much more appreciated as a human food.
William Morse is considered the 'father' of modern soybean agriculture in America. He and Charles Piper, Dr. C.V. Piper, took what was an unknown Oriental peasant crop in 1910 and transformed it into a 'golden bean' for America becoming one of America's largest farm crops and its most nutritious.
Prior to the 1920 in the USA, the soybean was mainly a forage crop, a source of oil, meal (for feed) and industrial products, with very little used as food. However, it took on an important role after World War I. During the Great Depression, the drought-stricken (Dust Bowl) regions of the United States were able to use soy to regenerate their soil because of its nitrogen-fixing properties. Farms were increasing production to meet with government demands, and Henry Ford became a great leader in the soybean industry.
In 1931, Ford hired chemists Robert Boyer and Frank Calvert to produce artificial silk. They succeeded in making a textile fiber of spun soy protein fibers, hardened or tanned in a formaldehyde bath, which was given the name Azlon. It was usable in the making of suits, felt hats, and overcoats. Though pilot production of Azlon reached 5000 pounds per day in 1940, it never reached the commercial market; Dupont's nylon was the winner in the quest to produce artificial silk. In 1932–33, the Ford Motor Company spent approximately $1,250,000 on soybean research. By 1935, every Ford car had soy involved in its manufacture. For example, soybean oil was used to paint the automobiles, as well as fluid for shock absorbers. Ford's involvement with the soybean opened many doors for agriculture and industry to be linked more strongly than ever before.
Henry Ford promoted the soybean, helping to develop uses for it both in food and in industrial products, even demonstrating auto body panels made of soy-based plastics. Ford's interest led to two bushels (120 pounds) of soybeans being used in each Ford car, as well as products like the first commercial soy milk, ice cream and all-vegetable nondairy whipped topping. The Ford development of so-called soy-based plastics was based on the addition of soybean flour and wood flour to phenol formaldehyde plastics. A prototype vehicle, colloquially titled the "Soybean Car", was built in 1941 out of such plastics.
The soybean first arrived in South America in Argentina in 1882.
Andrew McClung showed in the early 1950s that with soil amendments the Cerrado region of Brazil would grow soybeans. The march of soybeans into deforested areas of the Amazon rain forest would come later.
The soybean first arrived in Africa via Egypt in 1857.
Wild soybeans were discovered in northeastern Australia in 1770 by explorers Banks and Solander. In 1804, the first soyfood product ("Fine India Soy" [sauce]) was sold in Sydney. In 1879, the first domesticated soybeans arrived in Australia, a gift of the Minister of the Interior Department, Japan.
In 1831, the first soy product "a few dozen India Soy" [sauce] arrived in Canada. Soybeans were probably first cultivated in Canada by 1855, and definitely in 1895 at Ontario Agricultural College.
Caribbean and West Indies
The soybean arrived in the Caribbean in the form of soy sauce made by Samuel Bowen in Savannah, Georgia, in 1767. It remains only a minor crop there, but its uses for human food are growing steadily.
The soybean is first in cultivated Transcaucasia in Central Asia in 1876, by the Dungans. This region has never been important for soybean production.
Mexico and Central America
The first reliable reference to the soybean in this region dates from Mexico in 1877.
By the 13th century, the soybean had arrived in Indonesia; it probably arrived much earlier, carried by traders or merchants from southern China.
South Asia and Indian Subcontinent
By the 1600s, soy sauce spread from southern Japan across the region through the Dutch East India Company (VOC). The soybean probably arrived from southern China, moving southward into northern India.
In 1873, Professor Friedrich J. Haberlandt first became interested in soybeans when he obtained the seeds of 19 soybean varieties at the Vienna World Exposition (Wiener Weltausstellung). He cultivated these seeds in Vienna, and soon began to distribute them throughout Central and Western Europe. Most of the farmers who received seeds from him cultivated them, then reported their results back to him. Starting in Feb. 1876, he published these results first in various journal articles, and finally in his magnum opus, Die Sojabohne (The Soybean) in 1878. In northern Europe lupin/lupine is known as the "soybean of the north"
A Hitler Youth manual from the 1930s promoted soy beans, which it called "Nazi beans" as an alternative to meat.
Austria and Switzerland
In 1861, soybeans were first cultivated in Switzerland.
In Austria, at the Vienna World Exposition of 1873, Prof. Friedrich Haberlandt, of the Royal College of Agriculture in Vienna (Wiener Hochschule für Bodenkultur), gathered a number of soybean varieties from the Chinese, Japanese, Mongolian, Transcaucasian and East Indian expositions. In 1875 he first grew the soybeans in Vienna, then in early 1876 he sent samples of seeds to seven cooperators in central Europe, who planted and tested the seeds in the spring of 1876, with good or fairly good results in each case.
The soybean was first cultivated in France by 1779 (and perhaps as early as 1740). The two key early people and organizations introducing the soybean to France were the Society of Acclimatization (starting in 1855) and Li Yu-ying (from 1910). Li started a large tofu factory, where the first commercial soyfoods in France were made.
1935 - Soybeans are first introduced to Greece by Anton Brillmayer, an Austrian soybean breeder (Brillmayer. 1947. "Die Kultur der Soja in Oesterreich," p. 14-18).
1939 - By now, soybeans have been cultivated in Greece (Matagrin. 1939. "Le Soja et les Industries du Soja," p. 47-48).
An entire book has been published on the history of soybeans and soyfoods in Greece.
The soybean was first cultivated in Italy by 1760 in the Botanical Garden of Turin. During the 1780s it was grown at at least three other botanical gardens in Italy.
Spain and Portugal
In 1603, "Vocabvlario da Lingoa de Iapam", a famous Japanese-Portuguese dictionary, was compiled and published by Jesuit priests in Nagasaki. It contains short but clear definitions for about 20 words related to soyfoods - the first in any European language.
In 1880, the soybean was first cultivated in Portugal in the Botanical Gardens at Coimbra (Crespi 1935).
In about 1910 in Spain the first attempts at Soybean cultivation were made by the Count of San Bernardo, who cultivated soybeans on his estates at Almillo (in southwest Spain) about 48 miles east-northeast of Seville.
Further information: Genetically modified soybean
Soybeans are one of the "biotech food" crops that have been genetically modified, and genetically modified soybeans are being used in an increasing number of products. In 1995, Monsanto company introduced glyphosate-tolerant soybeans that have been genetically modified to be resistant to Monsanto's glyphosate herbicides through substitution of the Agrobacterium sp. (strain CP4) gene EPSP (5-enolpyruvyl shikimic acid-3-phosphate) synthase. The substituted version is not sensitive to glyphosate.
In 1997, about 8% of all soybeans cultivated for the commercial market in the United States were genetically modified. In 2010, the figure was 93%. As with other glyphosate-tolerant crops, concern is expressed over damage to biodiversity. A 2003 study concluded the RR gene had been bred into so many different soybean cultivars, there had been little decline in genetic diversity, but "diversity was limited among elite lines from some companies".
The widespread use of such types of GM soybeans in the Americas has caused problems with exports to some regions. GM crops require extensive certification before they can be legally imported into the European Union, where there is considerable supplier and consumer reluctance to use GM products for consumer or animal use. Difficulties with coexistence and subsequent traces of cross-contamination of non-GM stocks have caused shipments to be rejected and have put a premium on non-GM soy.
A 2006 United States Department of Agriculture report found the adoption of genetically engineered (GE) soy, corn and cotton reduced the amount of pesticides used overall, but did result in a slightly greater amount of herbicides used for soy specifically. The use of GE soy was also associated with greater conservation tillage, indirectly leading to better soil conservation, as well as increased income from off-farming sources due to the greater ease with which the crops can be managed. Though the overall estimated benefits of the adoption of GE soybeans in the United States was $310 million, the majority of this benefit was experienced by the companies selling the seeds (40%), followed by biotechnology firms (28%) and farmers (20%). The patent on glyphosate-tolerant soybeans expired in 2014, so benefits can be expected to shift.
Among the legumes, the soybean is valued for its high (38–45%) protein content as well as its high (approximately 20%) oil content. Soybeans are the second-most valuable agricultural export in the United States, behind corn. Approximately 85% of the world's soybean crop is processed into soybean meal and soybean oil, the remainder processed in other ways or eaten whole.
Soybeans can be broadly classified as "vegetable" (garden) or field (oil) types. Vegetable types cook more easily, have a mild, nutty flavor, better texture, are larger in size, higher in protein, and lower in oil than field types. Tofu and soy milk producers prefer the higher protein cultivars bred from vegetable soybeans originally brought to the United States in the late 1930s. The "garden" cultivars are generally not suitable for mechanical combine harvesting because there is a tendency for the pods to shatter upon reaching maturity.
Main article: Soybean oil
Soybean seed contains 18-19% oil. To extract soybean oil from seed, the soybeans are cracked, adjusted for moisture content, rolled into flakes and solvent-extracted with commercial hexane. The oil is then refined, blended for different applications, and sometimes hydrogenated. Soybean oils, both liquid and partially hydrogenated, are exported abroad, sold as "vegetable oil", or end up in a wide variety of processed foods.
Main article: Soybean meal
Soybean meal, or soymeal, is the material remaining after solvent extraction of oil from soybean flakes, with a 50% soy protein content. The meal is 'toasted' (a misnomer because the heat treatment is with moist steam) and ground in a hammer mill. Ninety-seven percent of soybean meal production globally is used as livestock feed. Soybean meal is also used in some dog foods.
One of the major uses of soybeans globally is as livestock feed, predominantly in the form of soybean meal. Spring grasses are rich in omega-3 fatty acids, whereas soy is predominantly omega-6.
Food for human consumption
In addition to their use in livestock feed, soybean products are widely used for human consumption. Common soybean products include soy sauce, soy milk, tofu, soy meal, soy flour, textured vegetable protein (TVP), tempeh, soy lecithin and soybean oil. Soybeans may also be eaten with minimal processing, for example in the Japanese food edamame (枝豆 edamame?), in which immature soybeans are boiled whole in their pods and served with salt.
In China, Japan, and Korea, soybean and soybean products are a common part of the diet. Tofu (豆腐 dòufu) is thought to have originated in China, along with soy sauce and several varieties of soybean paste used as seasonings. Japanese foods made from soya include miso (味噌), nattō (納豆), kinako (黄粉) and edamame (枝豆), as well as products made with tofu such as atsuage and aburaage. In Korean cuisine, soybean sprouts (콩나물 kongnamul) are used in a variety of dishes, and are the base ingredient in doenjang, cheonggukjang and ganjang. In Vietnam, soybeans are used to make soybean paste (tương) in the North with the most popular products are tương Bần, tương Nam Đàn, tương Cự Đà as a garnish for phở and gỏi cuốn dishes, as well as tofu (đậu hũ or đậu phụ or tàu hũ), soy sauce (nước tương), soy milk (nước đậu in the North or sữa đậu nành in the South), and đậu hũ nước đường (tofu sweet soup).
Soy flour refers to soybeans ground finely enough to pass through a 100-mesh or smaller screen where special care was taken during desolventizing (not toasted) to minimize denaturation of the protein to retain a high protein dispersibility index, for uses such as food extrusion of textured vegetable protein. It is the starting material for production of soy concentrate and soy protein isolate.
Soy flour is made by roasting the soybean, removing the coat, and grinding into a flour. Soy flour is manufactured with different fat levels. Alternatively, raw soy flour omits the roasting step.
Soy flour has 50% protein and 5% fiber. It has higher levels of protein, thiamine, riboflavin, phosphorus, calcium, and iron than wheat flour. It does not contain gluten. As a result, yeast-raised breads made with soy flour are dense in texture. Among many uses, soy flour thickens sauces, prevents staling in baked food, and reduces oil absorption during frying. Baking food with soy flour gives it tenderness, moistness, a rich color, and a fine texture.
Soy grits are similar to soy flour except the soybeans have been toasted and cracked into coarse pieces.
Section reference: Smith & Circle (1972, p. 442)
Soy-based infant formula
Soy-based infant formula (SBIF) is sometimes given to infants who are not being strictly breastfed; it can be useful for infants who are either allergic to pasteurized cow milk proteins or who are being fed a vegan diet. It is sold in powdered, ready-to-feed, and concentrated liquid forms.
Some reviews have expressed the opinion that more research is needed to determine what effect the phytoestrogens in soybeans may have on infants. Diverse studies have concluded there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula. One of these studies, published in the Journal of Nutrition, concludes that there are:
Meat and dairy alternatives and extenders
Soybeans can be processed to produce a texture and appearance similar to many other foods. For example, soybeans are the primary ingredient in many dairy product substitutes (e.g., soy milk, margarine, soy ice cream, soy yogurt, soy cheese, and soy cream cheese) and meat alternatives (e.g. veggie burgers). These substitutes are readily available in most supermarkets. Soy milk does not naturally contain significant amounts of digestible calcium. Many manufacturers of soy milk sell calcium-enriched products, as well. Soy is also used in tempeh: the beans (sometimes mixed with grain) are fermented into a solid cake.
Soy products also are used as a low-cost substitute in meat and poultry products. Food service, retail and institutional (primarily school lunch and correctional) facilities regularly use such "extended" products. Extension may result in diminished flavor, but fat and cholesterol are reduced. Vitamin and mineral fortification can be used to make soy products nutritionally equivalent to animal protein; the protein quality is already roughly equivalent. The soy-based meat substitute textured vegetable protein has been used for more than 50 years as a way of inexpensively extending ground beef without reducing its nutritional value.
The soybean is used to make a product similar to peanut butter, called SoyNut Butter and with the slogan "I.M. Healthy" printed on the label.
Soybeans are also used in industrial products, including oils, soap, cosmetics, resins, plastics, inks, crayons, solvents, and clothing. Soybean oil is the primary source of biodiesel in the United States, accounting for 80% of domestic biodiesel production. Soybeans have also been used since 2001 as fermenting stock in the manufacture of a brand of vodka. In 1936, Ford Motor Company developed a method where soybeans and fibers were rolled together producing a soup which was then pressed into various parts for their cars, from the distributor cap to knobs on the dash board. Ford also informed in public relation releases that in 1935 over five million acres (20,000 km2) was dedicated to growing soybeans in the United States.
According to the American Cancer Society, "Studies in humans have not shown harm from eating soy foods. Moderate consumption of soy foods appears safe for both breast cancer survivors and the general population, and may even lower breast cancer risk." They caution however that soy supplements should be avoided.
Soybean oil is one of the vegetable oils that contain a significant amount of the essential omega-3 fatty acid alpha-linolenic acid (18:3n−3, ALA). Other plant oils containing significant amount of ALA include chia, flax, hemp, canola and walnut. Soybean oil has an omega-6:omega-3 ratio of 7:1.
Saponins, a class of natural surfactants (soaps), are sterols that are present naturally in a wide variety of food-plants, including vegetables, legumes, and cereals–ranging from beans and spinach to tomatoes, potatoes and oats. Whole soybeans contain from 0.17 to 6.16% saponins, 0.35 to 2.3% in defatted soy flour and 0.06 to 1.9% in tofu. Legumes such as soybean and chickpeas are the major source of saponins in the human diet. Sources of non-dietary saponins include alfalfa, sunflower, herbs and barbasco.
Soy contains isoflavones like genistein and daidzein. It also contains glycitein, an O-methylated isoflavone which accounts for 5–10% of the total isoflavones in soy food products. Glycitein is a phytoestrogen with weak estrogenic activity, comparable to that of the other soy isoflavones.
Main article: Isoflavones
Soy's content of isoflavones are as much as 3 mg/g dry weight. Isoflavones are polyphenol compounds, produced primarily by beans and other legumes, including peanuts and chickpeas. Isoflavones are closely related to flavonoids found in other plants, vegetables and flowers.
Soybeans contain the isoflavones, genistein and daidzein, which are phytoestrogen compounds implicated as potentially beneficial factors in cardiovascular diseases and numerous other conditions. No beneficial effects, however, have been shown in clinical research to lower the risk of cardiovascular diseases, including high blood cholesterol levels, prostate cancer or respiratory infections.
Cholesterol and heart diseases
One review concluded that soy protein is correlated with significant decreases in serum cholesterol, LDL (bad cholesterol) and triglycerides. However, HDL (good cholesterol) did not increase by a significant amount. Soy phytoestrogens (isoflavones: genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels.
The FDA granted the following health claim for soy: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease." One serving, (1 cup or 240 mL) of soy milk, for instance, contains 6 or 7 grams of soy protein. Solae resubmitted their original petition, asking for a more vague health claim, after their original was challenged and highly criticized. Solae also submitted a petition for a health claim that soy can help prevent cancer. They quickly withdrew the petition for lack of evidence and after more than 1,000 letters of protest were received. On 18 February 2008, Weston A. Price Foundation submitted a petition for removal of this health claim. 25 g/day soy protein was established as the threshold intake because most trials used at least this much protein and not because less than this amount is inefficacious. In fact, there is evidence suggesting that lower amounts are indeed efficacious.
An American Heart Association (AHA) review of a decade long study of soy protein benefits casts doubt on the FDA allowed "Heart Healthy" claim for soy protein and does not recommend isoflavone supplementation. The review panel also found that soy isoflavones have not been shown to reduce post-menopausal "hot flashes" and the efficacy and safety of isoflavones to help prevent cancers of the breast, uterus or prostate is in question. However, AHA concludes that "many soy products should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat".
The AHA did not conduct a formal statistical analysis of the 22 studies upon which they based their estimate of the potency of soy protein. When such an analysis was conducted, Jenkins et al. found that the AHA had considerably underestimated the hypocholesterolemic effects of soy protein. Further, when the analysis was limited to the 11 studies that provided evidence that the control and soy diets were matched, soy protein was found to lower LDL by 5.2 percent. This estimate is in line with the results of other recently published meta-analyses. Furthermore, recent research suggests that soy protein decreases postprandial triglyceride levels, which is increasingly viewed as important for reducing coronary heart disease risk.
Main article: Phytic acid
Soybeans contain a high level of phytic acid, which has many effects including acting as an antioxidant and a chelating agent. The beneficial claims for phytic acid include reducing cancer, minimizing diabetes, and reducing inflammation. However, phytic acid is also criticized for reducing vital minerals absorption due to its chelating effect, especially for diets already low in minerals.
Main article: Soy allergy
Allergy to soy is common, and the food is listed with other foods that commonly cause allergy, such as milk, eggs, peanuts, tree nuts, shellfish. The problem has been reported among younger children, and the diagnosis of soy allergy is often based on symptoms reported by parents and results of skin tests or blood tests for allergy. Only a few reported studies have attempted to confirm allergy to soy by direct challenge with the food under controlled conditions. It is very difficult to give a reliable estimate of the true prevalence of soy allergy in the general population. To the extent that it does exist, soy allergy may cause cases of urticaria and angioedema, usually within minutes to hours of ingestion. In rare cases, true anaphylaxis may also occur. The reason for the discrepancy is likely that soy proteins, the causative factor in allergy, are far less potent at triggering allergy symptoms than the proteins of peanut and shellfish. An allergy test that is positive demonstrates that the immune system has formed IgE antibodies to soy proteins. However, this is only a factor when soy proteins reach the blood without being digested, in sufficient quantities to reach a threshold to provoke actual symptoms.
Soy can also trigger symptoms via food intolerance, a situation where no allergic mechanism can be proven. One scenario is seen in very young infants who have vomiting and diarrhoea when fed soy-based formula, which resolves when the formula is withdrawn. Older infants can suffer a more severe disorder with vomiting, diarrhoea that may be bloody, anemia, weight loss and failure to thrive. The most common cause of this unusual disorder is a sensitivity to cow's milk, but soy formulas can also be the trigger. The precise mechanism is unclear and it could be immunologic, although not through the IgE-type antibodies that have the leading role in urticaria and anaphylaxis. However it is also self-limiting and will often disappear in the toddler years.
Main article: Phytoestrogens
Soybeans contain isoflavones called genistein and daidzein, which are one source of phytoestrogens in the human diet. Because most naturally occurring phytoestrogens act as selective estrogen receptor modulators, or SERMs, which do not necessarily act as direct agonists of estrogen receptors, normal consumption of foods that contain these phytoestrogens should not provide sufficient amounts to elicit a physiological response in humans.
Plant lignans associated with high fiber foods such as cereal brans and beans are the principal precursor to mammalian lignans which have an ability to bind to human estrogen sites. Soybeans are a significant source of mammalian lignan precursor secoisolariciresinol containing 13–273 µg/100 g dry weight. Another phytoestrogen in the human diet with estrogen activity is coumestans, which are found in beans, split-peas, with the best sources being alfalfa, clover, and soybean sprouts. Coumestrol, an isoflavone coumarin derivative is the only coumestan in foods.
Soybeans and processed soy foods are among the richest foods in total phytoestrogens (wet basis per 100 g), which are present primarily in the form of the isoflavones daidzein and genistein. When compared to human breast fed or cow milk formula fed diets, which contain isoflavone levels of 0.005-0.01 mg/day, soy-based infant formulas contain isoflavone levels of 6–47 mg/day that constitute several orders of magnitude greater than they receive from other sources of nutrition.
A 2001 literature review suggested that women with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products, based on the effect of phytoestrogens to promote breast cancer cell growth in animals. A 2006 commentary reviewed the relationship with soy and breast cancer. They stated that soy may decrease the risk of breast cancer, but cautioned that the impact of isoflavones on breast tissue needs to be evaluated at the cellular level in women at high risk for breast cancer.
A high consumption of omega-6 polyunsaturated fatty acids, which are found in most types of vegetable oil including soybean oil, may increase the likelihood that postmenopausal women will develop breast cancer. Another analysis suggests an inverse association between total polyunsaturated fatty acids and breast cancer risk. A 2011 analysis of the literature said: "Our study suggests soy isoflavones intake is associated with a significant reduced risk of breast cancer incidence in Asian populations, but not in Western populations."
Because of the phytoestrogen content, some studies have suggested that soybean ingestion may influence testosterone levels in men. However, a 2010 meta-analysis of 15 placebo controlled studies showed that neither soy foods nor isoflavone supplements alter measures of bioavailable testosterone or estrogen concentrations in men. It has been hypothesized that soy foods and enterolactone may increase the development of prostate cancer although no significant associations were observed for the soy isoflavones. Furthermore, soy consumption has been shown to have no effect on the levels and quality of sperm. A 2009 meta-analysis of the research on the association between soy consumption and prostate cancer risk in men concluded that "consumption of soy foods is associated with a reduction in prostate cancer risk in men."
Because of mixed results from animal studies and epidemiological studies, a (relatively definitive but expensive) controlled study of the impacts of soy on cognitive skills was performed; it found no impact.
Though there is some evidence that estrogen can help protect and repair the brain after injury in rats, there is also evidence that phytoestrogens may be harmful for the recovery of rats in other situations that have sustained brain injury.
Similarly, epidemiological evidence of humans eating soya products is currently divided: a study of Japanese men between 1965 and 1999 demonstrated a positive correlation between brain atrophy and consumption of tofu meals.
A 2001 literature review noted that disturbing data on soy's effect on the cognitive function of the elderly existed. In 2008, an epidemiological study of 719 Indonesian elderly individuals found that tofu intake was associated with worse memory, but tempeh (a fermented soy product) intake was associated with better memory.
The cover article in the Center for Science in the Public Interest's September 2014 newsletter reported that a controlled study at USC prompted by suggestive epidemiological evidence found no impact on cognitive skills of years of soy vs milk protein diet enrichment.
Though raw soy flour is known to be correlated with pancreatic cancer in rats the cooked flour has not been found carcinogenic. Whether soy might promote pancreatic cancer in humans is unknown because studies have not yet attempted to single out soy intake and the incidence of pancreatic cancer in humans, and the amount of soy fed to the rats is proportionately far larger than what humans would normally consume. However, the soy isoflavone genistein has been suggested as a chemopreventive agent against pancreatic cancer, by interfering with the chemical pathways that promote the creation and growth of tumors.
The Cancer Council of New South Wales, Australia has released a statement saying scientific research suggests that overall the moderate consumption of soy products does not appear to present a risk to women with breast cancer, and there is equivocal evidence that consuming large amounts of soy products may have a protective effect against developing breast and prostate cancer. However, the Council does not recommend taking soy dietary supplements as there is no evidence they are either effective or safe at preventing or treating cancers.
Soybeans and soy products contain significant amounts of purines, a class of organic compounds. For people who suffer from gout, eating foods containing moderate or high levels of purines may make the condition worse. The U.S. National Institutes of Health (NIH) recommends that gout sufferers limit consumption of soy products (although also suggesting that soy may have health benefits by reducing the risk for heart disease). However, other researchers have found little or no association between consumption of purine-rich vegetables (including beans) and gout.
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