Tuesday, August 4, 2009

Soy fact vs soy fiction

The FDA has allowed the following claim to be made concerning soy products: “Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease.”

To qualify food must: Contain 6.25 G of soy protein, have less than 3 g fat and 1 g saturated fat, and less than 20 mg of cholesterol and less than 480 mg of sodium. This claim is based on whole soy protein food, not isolated soy constituents. Asian diets contain typically 6-11 g of soy protein/day, which includes 25-50 mg of isoflavones.

Soy is a complete protein. Not really, but that might not be a bad thing.

The FDA claims that soy protein can be a good substitute for animal protein because it contains all the necessary essential amino acids. Soy is high in the non-essential amino acids, but is low in cysteine, methionine, and lysine. However, soy protein, as well as many other vegan proteins, are higher in non-essential amino acids than most animal-derived food proteins, and as a result should preferentially favor glucagon production. (This could help with insulin resistance.)

An unnecessarily high intake of essential amino acids—as in high-meat diets—may prove to be as grave a risk factor for “Western” degenerative diseases as is excessive fat intake.

Soy prevents cancer. Maybe.

Soy contains isoflavones that are phytoestrogens, which may have both benefits and risks. Phytoestrogens interact with many receptors, including estrogen hormone receptors, but the type of interaction and the type of receptor dictates the biologic response. For instance genistein, one of the main soy isoflavones, interacts differently with estrogen receptor alpha and estrogen receptor beta. Genistein was shown to inhibit the growth of MCF-7 breast cancer cells.

Epidemiological studies show that women with traditional diets high in soy have a lower incidence of breast cancer those women with Western diets. There are no studies that show eating high amounts of soy later in life can decrease a women’s risk of breast cancer however.

Soy is safe for breast cancer survivors. Probably NOT.

Currently neither the animal data nor human data is conclusive as to whether soy is safe for breast cancer survivors. Women who are estrogen positive breast cancer survivors are frequently told to restrict their intake of soy products because of the phytoestrogen content.

GMO soy is healthy. If you don’t mind herbicides on your food!

Genetically modified soy is “Roundup Ready”, MEANING Roundup can be sprayed on the crop for weed control. Roundup Ready (RR) varieties of soybean has increased the use of glyphosate for weed control and glyphosate residues were found in soybean leaves and stems, and metabolites of the herbicide were found in the grain. Applications of glyphosate have no effects on phytoestrogen levels in glyphosate-resistant soybeans.

Fermented soy is better for you. Not really.

There is a difference in the isoflavones in non-fermented vs. fermented soy food, but the effect of enzymes and flora activity in the digestive tract makes the difference unimportant.

Soy is a common food allergen. True!

Soy is one of the top food allergens, along with cow’s milk, citrus, nuts, wheat, seafood and egg. Allergenicity of GMO soy may be altered. Hydrolyzed soy protein may not be as antigenic and there may be cross-reactivity with birch pollen and soy.

Soy inhibits the thyroid. Not True!

In 14 human studies, most found little change in thyroid function tests of normal subjects ingesting isolated soy protein. There are a few case studies of soy impacting hypothyroid patients, by reducing thyroid medication absorption. Always also consider iodine deficiency. Iodine deficiency lead to goiter and soy may make an iodine deficiency worse. An interesting not is that Asian soy consumption is often coupled with seaweed, which is naturally high in iodine.

Soy inhibits protein digestion. Possibly.

Raw soy contains Bowman-Birk (BBI) inhibitor of chymotrypsin and trypsin and the Kunitz inhibitor of trypsin (KTI). Heating and processing of the soybean removes most but not all of these inhibitors. On the other hand, several studies suggest that BBI can also function as an anticarcinogen, possibly through interaction with a cellular serine protease.

Soy is safe for infant formulas. Caution is needed.

Infants consuming soy formulas had 10 times higher isoflavone levels in their blood than women receiving soy supplements who show menstrual disturbances. Small, physiologically relevant phytoestrogen exposure levels can alter estrogen-dependent gene expression in the brain and affect complex behavior in a wide range of species. The implications for these findings in humans, and particularly in infants, largely remain uninvestigated but are a subject of increasing public interest.

Soy infant formulas contain BBQ and KTI, protein enzyme inhibitors; infants on soy formula consume about 10 mg of KTI plus BBI per day. The impact of reduced protein digestion due to these enzyme inhibitors in infants is not known.

Soy is a good food. Most likely.

Whole soy foods are a good source of fiber, B vitamins, calcium and omega-3 essential fatty acids. Replacing some high fat animal protein with soy foods is beneficial. Soy can be part of a healthy diet, along with fruits, vegetables, and whole grains, fish and lean meats Introduce soy slowly to the daily diet. Avoid if you have soy allergies.

Soy is a nutraceutical. Most likely.

Soy isoflavones may be helpful for modest cholesterol lowering effects. Soy isoflavones effect on breast cancer is unclear. Soy isoflavones may be helpful for menopausal symptoms. Soy isoflavones may be supportive for postmenopausal bone health.

>> By Dr. Arianna Staruch, ND, ACHS Dean of Admissions

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