Soy is More Than Just Good Source of Protein
by Ellie Zografakis, R.D., & Dale Huff, R.D., CSCS
There's no getting away from it - protein supplementation is today’s hot nutritional topic. And everyone has a different take on where that extra protein should be derived.
In the bodybuilding community, the protein source of choice has long been whey protein, with soy protein coming in a distant second. If you count yourself among the whey devotees, here's some information that may encourage you to take another look at soy.
The whey it is
The two most-researched forms of protein supplements are soy protein isolate and whey concentrate.
Soy protein isolate is 90 percent protein on a dry-weight basis, is highly digestible (97 percent) and allows the essential amino acids (valine, isoleucine and leucine, which the body does not produce) to be absorbed across the GI tract.
A water-washed process is used to allow isoflavones to remain intact. All of the gas-producing carbohydrates and fat have been removed.
Whey concentrate is extracted by two processes: microfiltration (proteins are physically separated by a filter) and ion exchange (extracted by specific electronic charges).
Both of these processes are very expensive, which is why whey protein is the most costly protein source on the market. Both soy protein isolate and whey concentrate are high-quality proteins and have a Protein Digestibility Corrected Amino Acid Score (PDCAAS) of 1.0.
Amino acid content
Glutamine, a nonessential amino acid, is the body's primary carrier of nitrogen to skeletal muscle and other tissues. It helps buffer lactic acid buildup in the blood and muscles, boosts muscle protein activity, increases growth hormone levels and strengthens immune capacity. Soy protein isolate typically contains 10.5 grams glutamine/100 grams protein, while whey concentrate contains 4.9 grams glutamine/100 grams protein.
Arginine plays a key role in stimulating the release of anabolic hormones that promote muscle formation, reducing physiological stress, and maintaining a strong and healthy immune system. Soy protein isolate contains 7.6 grams arginine/100 grams protein and whey concentrate contains 2.9 grams arginine/100 grams protein.
Branched chain amino acids
Branched chain amino acids are used as an energy source during exercise. During endurance activity, nitrogen is removed from the BCAA and converted to alanine, which is transported via the bloodstream from the muscle to the liver where it is converted to glucose.
Glucose from the liver returns to muscle to supply energy for fueling exercise. Whey concentrate contains approximately 20 percent BCAAs while soy protein isolate contains 18 percent.
Nearly 40 research studies have examined various types of soy products and found significantly decreased serum concentration of total cholesterol, low-density lipoproteins and triglycerides when animal products are replaced by soy protein in the diet1.
Soy products that contain fat are rich in polyunsaturated fat called linoleic acid, which also has been shown to lower blood cholesterol. Certain phytochemicals found in soy, most notably genistein and daidzein, may offer further protection against cardiovascular disease. To date, little research has been done on whey protein's effect on total cholesterol, LDL or triglycerides.
Research is currently underway to examine the potential for isoflavones to suppress tumor growth. Soy may reduce the risk of prostate cancer in men and breast cancer in women2.
And its high estrogen content may lengthen the menstrual cycle in women, thereby reducing the potential cancer-causing effect of one's own estrogen. No research has been done on whey in relation to cancer prevention.
Phytochemicals also appear to have a modest positive effect on bone health3.
A big concern with recommending additional protein is its potentially taxing effect on the kidneys. Soy protein isolate has been proven to actually decrease the load placed on the kidneys by decreasing proteinuria, renal hypertrophy, and causing less renal histological damage4, 5.
Research on Romanian Olympic rowers, swimmers and kayak-canoers indicates that a soy protein supplement aids in the formation of lean body mass, increases serum hemoglobin, decreases urinary mucoproteins (renal stress due to excretion of higher amounts of mucoproteins is considered a biochemical marker of metabolic fatigue in the athlete) and reduces fatigue after training sessions6.
Soy's ability to reduce the workload of the kidneys and maintain the health of the vascular system, and the preventative properties of isoflavones, genistein and daidzein give soy a distinct advantage over whey protein.
Soy protein is a healthy adjunct to a varied diet high in fiber, fruits and vegetables and moderate in fat, whether your goals are to lose weight or improve sports performance.
1. Anderson, J. et al. (1995). Meta-analysis of the effects of soy protein intake on serum lipids. New England Journal of Medicine, 333, 276-82.
2. Messinal M.J. et al. (1994). Soy intake and cancer risk: A review of the in vitro and in vivo data. Nutr Cancer, 21, 113-131.
3. Arjmandi, B.H. et al. (1996). Dietary soybean protein prevents bone loss in an ovariectomized rat model on osteoporosis. J Nutr, 126, 161-167.
4. Kontessis, P., et al. (1990). Renal, metabolic and hormonal responses to ingestion of animal and vegetable proteins. Kidney Int, 38, 136-144.
5. Williams, A.J. et al. (1987). Effect of varying quantity and quality of dietary protein intake in experimental renal disease of fischer rats. Nephron, 46, 83-90.
6. Dragan, V. et al. (1992). Studies regarding the efficiency of Supro isolated soy protein in Olympic athletes. Rev Roum Physio, 29, 63-70.
This appeared in ACE FitnessMatters, ACE's official magazine.
Click here to order your subscription today.
for ACE's FREE e-newsletter for fitness enthusiasts.