Soy has been promoted as a health food for many decades. Due to its high protein content, soy is also very popular among vegans and vegetarians. So is soy really a health food? Are all soy products the same? What is the latest research regarding soy and disease?
Soy is cheap to grow and cheap to process, so it is truly a food manufacturer’s dream. The industry has marketed soy as an ancient health food. They claim that Asian cultures have eaten soy for thousands of years and associate their longevity and health with the consumption of soy. But if you examine the diets of Asian cultures closely, you will discover that:
- first, they only use soy as a condiment and do not eat it as a main item or in large quantities,
- second, they eat fermented soy which is remarkably different from the unfermented soy that Americans typically eat, such as the following:
Examples of Unfermented Soy Foods
soy ice cream
soy protein isolate in energy bars and protein powders
textured vegetable protein (TVP)
edamame (green soybeans)
soy hot dog or sausage
soy nut butter
In traditional Asian diets, people eat soy which has been fermented, that means the soy food has been cultured with beneficial bacteria, yeast, or mold. This type of soy is entirely different from the unfermented, processed soy products (like the ones listed above) that are sold in American grocery stores.
Why Unfermented Soy Is Not Recommended
Humans do not have a history of eating much unfermented soy. It was not until the last fifty years that we have introduced a variety of processed, unfermented soy foods.
If you are getting more than 35 grams of soy protein each day from unfermented soy, you should be aware of the following anti-nutrients that are present in this type of soy and their potential effects on your health.
Phytic acid that impairs mineral absorption. Plant seeds, such as nuts, edible seeds, beans/legumes, and grains contain phytic acid. Soy is particularly high in phytic acid, which impairs the absorption of iron, zinc, manganese, magnesium, and calcium. Mineral deficiencies caused by phytic acid are rarely a concern among meat-eaters because their diets are more diverse. However, vegans and vegetarians who consume a lot of high phytic acid foods at every meal can be at increased risk of developing mineral deficiencies overtime.
Oxalates that have been linked to kidney stones. Calcium oxalate stones are the most common type of kidney stones. Oxalate is a natural substance found in many foods but highest in spinach, wheat bran, nuts, beer, coffee, soybeans, and chocolate. Oxalate cannot be metabolized by the body and is excreted through urine. When there is too much oxalate and too little urine, the oxalate can bind to calcium in the urine and form crystals that stick together into a solid mass (kidney stone). To prevent calcium oxalate stones:
- Drink enough fluids like water.
- Reduce sodium in the diet as salt causes more calcium to be excreted in the urine.
- Eat high calcium foods with oxalate-rich foods (e.g. spinach salad with cheese) so that the oxalate can bind with calcium in the stomach and intestines rather than in the kidneys.
- Cut down on the oxalate-rich foods.
Goitrogens that suppress the thyroid gland. Goitrogens may prevent the thyroid from getting the necessary amount of iodine and disrupt the normal production of thyroid hormones. Raw vegetables from the cruciferous family (e.g. broccoli, kale, cabbage) and soy contain goitrogens. An overconsumption of soy may eventually lead to an underactive thyroid creating symptoms like weight gain, mood swings, feeling cold, fatigue, insomnia, and an inability to concentrate and remember details. To overcome this problem, make sure your iodine intake (eg. seaweed, seafood, dairy) is adequate when consuming soy.
Trypsin inhibitors that interfere with digestion. Trypsin is a digestive enzyme needed to properly digest protein. Trypsin inhibitors are a plant’s defense mechanism. By having this harmful component, wild animals learn that any food with trypsin inhibitors is a food to avoid. Soybeans are rich in trypsin inhibitors, hence, taking in too much soy may lead to gastric distress like bloating and gas in some individuals.
Lectins that clump red blood cells. Plants produce damaging proteins called lectins as self-defense against hungry animals. Soy contains a specific class of lectins called hemagglutinin that promotes clotting in the blood and impairs blood flow. Hemagglutinins can also tear holes in the gut lining, allowing bacteria to get into the bloodstream and causing autoimmune and allergic problems for people who are sensitive to lectins..
Why Fermented Soy Is Better
Fermented soy is much healthier than unfermented soy. The lengthy fermentation process reduces some of its anti-nutrients, resulting in a form of soy that is:
- rich in probiotics or healthy bacteria that is extremely important for gut health and the immune system,
- lower in phytic acid that prevents the absorption of minerals,
- easier to digest and less likely to cause gastric distress,
- lower in lectins (hemagglutinins) that promote clumping of red blood cells, and
- high in the MK-7 form of vitamin K2, an important nutrient for supporting bone and heart health. (Unfermented soy does not contain vitamin K2.)
Top 4 Fermented Soy Foods
Natto. Fermented soybeans that are sticky and gooey with a strong, distinctive taste. A popular breakfast side dish in traditional Japanese cuisine.
Tempeh. Originated from Indonesia, it is a fermented soybean cake with a firm texture and an earthy flavor.
Miso. Fermented soybean paste with a salty, buttery texture. It is commonly used to make miso soup in Japanese cooking.
Soy sauce. Originated from China, it is a liquid condiment made from fermented soybeans and roasted grain (wheat). Tamari is soy sauce made without the grain, hence, it is gluten-free.
Considerations When Eating Fermented Soy
Quantity may be the key. Asian cultures do not eat a huge amount of soy. They generally use fermented soy foods as a condiment rather than as a main item. The average intake of soy protein in Asian populations is about 10-20 grams per day. This is in stark contrast to how much unfermented soy Americans consume.
The following shows the soy protein content of some common unfermented soy products. Are you eating multiple servings of these everyday?
Unfermented Soy Foods_____Serving Size_____Protein (grams)
Soy protein isolate____________1 oz_____________25
Soy nuts, roasted_____________1/2 cup___________22
Soy burger__________________1 patty___________14
Tofu, firm___________________4 oz_____________14
Edamame, boiled_____________1/2 cup__________12
Soy milk____________________8 oz______________8
Soy nut butter________________2 Tbsp.___________8
Soy cheese__________________1 oz______________6
Soy yogurt__________________4 oz______________4
Furthermore, unfermented soy is a hidden component of the American diet. Research estimates that soy is present in 70% of all supermarket products and widely used in fast food chains.
- Soy is used to bulk up and bind many processed foods so that food firms can put a higher protein value on them.
- The husk of the soybean is used for fiber in breads, cereals, and snacks.
- The big one is soybean oil which is the most consumed vegetable oil in the world. It is used in frying oils, salad dressings, and many processed foods.
- Last but not least, 70% of the soybeans grown in the U.S. are used for animal feed, with poultry being the highest livestock sector consuming soybeans, followed by hogs, dairy, beef, and aquaculture. These soy-fed animals are then eaten by us.
Soy is largely genetically modified. 94% of the soy planted in the U.S. is “Roundup Ready”, which means it is genetically bioengineered to survive heavy application of Monsanto’s toxic Roundup herbicide. In March 2019, a San Francisco federal jury unanimously agreed that Roundup caused a man’s non-Hodgkins lymphoma. The verdict is the second in the U.S. to find a connection between the herbicide’s key ingredient glyphosate and cancer. Therefore, even if you are eating fermented soy, make sure it is organically grown.
Soy is one of the top eight allergens. They are cow’s milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, and soybean. These foods account for about 90% of all food allergies. If you have a soy allergy or sensitivity, watch out for “hidden” soy as it is often used in many processed food products.
Research On Soy And Disease
Soy is unique in that it contains a high concentration of isoflavones or plant estrogens (called genistein and daidzein) that are structurally similar to human estrogen but with weaker effects. They can bind to estrogen receptors in numerous tissues, including those associated with reproduction, as well as bone, liver, heart, and brain. In human tissues, isoflavones can have totally opposite effects – they can either mimic estrogen or block
Soy is a controversial food that has been widely studied for its estrogenic as well as anti-estrogenic effects on the body. Proponents claim that soy can tame hot flashes, prevent osteoporosis, and protect against hormonal cancers. Opponents worry that it may actually increase the risk of cancer, cause thyroid problems, and other health issues.
Up to now, there is yet concrete conclusions about soy, but it is probably due to the wide variation in how the studies have been designed – the types of soy used (fermented vs. unfermented), quantity consumed, and duration of exposure (since childhood vs. adulthood). That said, Asian populations have eaten a traditional diet of fermented soy for thousands of years and have reported a neutral to beneficial effect on many health conditions.
Average Isoflavone Intake in Asia is 25-50 mg/day.
Fermented Soy Foods_______Serving Size____Isoflavone content (mg)
Tempeh, cooked_____________3 oz_____________30
Soy sauce__________________1 Tsbp.___________0.02
Excessive estrogen stimulates the growth and multiplication of breast cancer cells. So it was once thought that soy foods increase the risk of breast cancer because soy contains isoflavones that may mimic our estrogen.
However, it has also been suggested that the lower risk of breast cancer in Asian countries compared to Europe, North America, and Australia/New Zealand is attributed to a lifelong intake of traditional soy foods. So who is right?
So far studies have not provided a clear-cut answer. Some have shown a slight benefit while others show no association. Nonetheless, no research has demonstrated that soy causes breast cancer, even in women who have had the cancer before. In fact, it appears that soy may have a mild estrogen-blocking action in breast tissues, resulting in a slight reduction of breast cancer risk and recurrence of breast cancer.
In addition, the protective effect seems to be more pronounced for women who start eating soy early in life. Women from Asian countries generally start consuming fermented soy foods found in traditional Asian diets at an early age. Fermented soy contains healthy bacteria that can convert isoflavone daidzein to equol. Equol is believed to block potentially negative effects of estrogen. Studies found that 50-60% of adults in Asia possess the equol-producing gut bacteria compared to only 25-30% of adults in Western countries. This may also explain why women from Asia who eat fermented soy seem to derive more benefits than Western women who generally consume unfermented, processed soy.
In theory, the potential estrogenic effects of soy isoflavones could help to tame hot flashes and night sweats that accompany menopause by giving an estrogen-like boost during a time of dwindling estrogen levels. Hence, soy has been a popular alternative treatment though it is not clearly supported by research which shows conflicting results. Nonetheless, in Asian countries where fermented soy is eaten daily, women do report lower rates of menopausal symptoms (10-20%) compared to women in the U.S. (70-80%).
Memory and Cognitive Function
Menopause has been linked with mood changes and memory impairment. Low levels of estrogen in women can reduce the number of estrogen receptors in the brain that are necessary for cognitive functions like memory and learning. The soy isoflavone daidzein has been hypothesized to reduce cognitive decline. Unfortunately, trials have yielded contradictory results with some showing benefits and others no benefit.
Endometrial (Uterine) Cancer
It is thought that the development of endometrial cancer could be related to prolonged exposure to unopposed estrogen, i.e., estrogen not counterbalanced with the hormone progesterone. Excess estrogen relative to progesterone may result in endometrial thickening and ultimately, endometrial cancer. A number of studies have examined whether high intakes of soy with anti-estrogenic activity in uterine tissue could be associated with a lower risk of endometrial cancer. The results are inconclusive.
The decline in estrogen production that accompanies menopause places middle-aged women at risk of osteoporosis (loss of bone mineral density). As estrogen receptors are present in bone, whether the estrogenic properties of soy might play any role in preserving bone health and preventing bone loss has been proposed. To date, the results of observational and intervention studies examining the potential protection of soy against osteoporosis have been inconsistent.
The incidence of prostate cancer is highest in Western countries and lowest in Asian countries, where fermented soy foods are a regular part of the daily diet. Soy isoflavones, specifically genistein and daidzein, are found to collect in prostate tissue and may act as weak estrogens and exert a protective effect against the development of prostate cancer.
Interestingly, observational studies have found an increased risk of prostate cancer in Chinese and Japanese men who move to Western countries and adopt a Western diet, but not in those who continue eating the traditional diet.
Based on a number of studies that showed eating substantial quantities of soy protein daily reduced harmful LDL cholesterol, in 1999, the Food and Drug Administration (FDA) allowed food companies to claim products that are low in saturated fat and cholesterol and contain soy protein “may reduce the risk of heart disease”. The FDA also suggested that eating 25 grams of soy protein per day may lead to reductions of total and LDL cholesterol levels.
However, since then subsequent scientific findings have not presented sufficient evidence to show a clear connection between soy protein and reduction of heart disease risk. In October 2017, after reviewing additional research, the FDA proposed to revoke the heart health claim regarding soy. At present, the agency has yet made a final decision.