Not All Proteins Are Created Equal, Part II (Soy Proteins - The Good, The Bad and The Ugly)

Before discussing which proteins to use, when, and why, let's take a look at soy protein and its benefits.

Studies show that soy offers benefits that casein and whey don't provide. This is one of the reasons why many supplement manufacturers now combine all three proteins as a means of harvesting the benefits associated with each one.

Studies have shown that soy may protect against cardiovascular disease, provide prevention against or relief from post-menopausal symptoms in women, and even stimulate thyroid function in rats. We also know that Soy Protein Isolates are high in branched-chain amino acids, glutamine, and Arginine. Since soy is a legume, soy is low in methionine, an essential amino acid. Therefore, it may be necessary to combine it with another protein that contains methionine in adequate amounts and that is why many protein manufacturers use soy as an ingredient in their blends (so that the many differing proteins will complement each other-whey and casein will make up for the aminos soy is missing and vice versa).

Another benefit of using soy is that it is priced low in comparison to casein, whey, and milk derived proteins. Soy also has the potential to help women in their postmenopausal years; studies on the long term use have not been done as extensively with men. However, soy contains phytoestrogens, which can act in both an estrogenic and anti-estrogenic fashion. It is the phytoestrogens that allow soy to exert its protective benefits on postmenopausal women.

Please note that until more is understood about the effect of phytoestrogens in men, taking more than 60 grams of soy protein per day may not be a good idea.  This is especially true for children of both sexes as giving an estrogen mimicking substance to them may lead to gynocomastia in males (breast development) as well as hormonal imbalances and faster development in females. If the statement above, that soy has been shown to stimulate thyroid function in rats, has you thinking of its possible fat loss qualities, think again, as recent evidence indicates that soy may actually lower thyroid hormone levels in people (in contrast to rats).

Another thing to consider is that vegetable proteins do not contain tertiary bonds as animal proteins do. In order for humans to be able to digest, absorb, and make use of soy protein, it must first be broken down or "isolated." This pre-digestion process is done via solvents, which are known to leave a residue. The solvents used to isolate or break down the soy protein create residual "non-solvent" amino acids consisting of free form amino acids stuck to non free form amino acids.

The importance of this is that free form amino acids are absorbed by the enterocytes (intestinal lining cells) via active diffusion. Active diffusion is another form of "lock and key" interaction between a receptor embedded in the enterocytes' cell membrane and a specific amino acid. The amino acid binds to the receptor and gets "actively sucked into" the enterocyte where it then gets sent to the liver via the portal vein for release into the general circulation. The problem with soy isolates is that the "non-solvent" amino acids (consisting of free form amino acids stuck to non-free form amino acids) bind to the enterocyte receptors and also get "actively sucked into" the enterocyte; however, because these aminos have non-free form amino acids stuck to their opposite end, these also get pulled into the receptor causing intestinal perforation and damage due to their much larger molecular size. Not a good thing, causing bleeding and compromising gut health as well as promoting a lower or suppressed immune system. Recently soy has been thought to contribute to Irritable Bowel Syndrome (IBS), thought to be caused by intestinal lining perforations such as those mentioned above. In my opinion, the benefits of using soy do not outweigh the risks.  However, I will leave this for a future discussion¡­

© 2007 Lucho Crisalle, RD, internationally recognized expert in nutrition created the What Works! Ezine. Go to www.exerciseandnutritionworks.com to get your copy of our FREE REPORT "The Truth About FAT LOSS And The Way To A Leaner You - REVEALED!