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Whey vs. soy protein: which is inferior?

Posted November 2, 2007 at 09:00 AM by Denise Musumeci

Section: His Health, Physical Health, Lifestyle Health, His Nutrition, Healthy Eating, Diets, Supplements

Between the Atkins craze, Weight Watchers, and all the fad diets out there, people feel an increased pressure to lead a healthy lifestyle. However, in our fast-paced society and technology that seems to promote laziness, finding the time to maintain a healthy diet seems impossible to most. This is where proteins come in. Adding protein supplements to your diet greatly increases overall health. With the many varieties out there, how can you find the one that is right for you?

Having long been considered the gold standard of protein supplements, whey is considered a complete protein, meaning that it contains the perfect combination of amino acids essential for muscle growth. According to Christopher Jack at thefinalsprint.com, it also has the largest concentration Branched Chain Amino Acids (BCAAs) of any natural source, which helps delay fatigue and aid in the post-workout recovery process. In addition, whey prevents free radicals by acting as an antioxidant, which helps the immune system and consistently builds muscle.

Soy, on the other hand, has long been thought to make it harder to gain muscle. According David Robson at bodybuilding.com, “Studies have suggested that the phytoestrogens contained in soy protein lead to both unwanted decreases in testosterone, and increases in the female sex hormone estrogen.” In recent years, however, many have replaced whey protein as their primary supplement. How could this be? If whey is much more beneficial than soy, why would one replace what is knows as the ideal protein? Recent research suggests that soy is just as effective in building muscle as whey and contains many of the same benefits.

Compared to other plant-based proteins, soy is the only one that is considered a high quality protein because it contains all of the essential amino acids and a respectable amount of zinc, potassium, and Vitamin E. Soy also has high amounts of arginine, a well known as a stimulant of anabolic hormones that stimulate muscle formation, and glutamine, which is essential during metabolic stress. In addition, soy helps reduce the risk of heart disease, relieves the symptoms of menopause, and reduces the risk of breast and prostate cancer.
When compared to each other, how does soy measure up to whey? A study by Middle Management lays out the facts about each protein to determine which one is more valuable. Some of the factors include Biological Value, Net Protein Utilization, Protein Efficiency Ratio, Amino Acid Score, Protein Digestibility Corrected Amino Acid Score (PDCAAS), Digestibility Percentage, and Essential Amino Acids (per gram).

The Biological Value indicates both how digestible the protein is and how available the protein is for use by the body. Biological value began as a percentage - A whole egg rated at 100% nitrogen absorbed. Whey protein exceeds perfection with 104% digestibility while Soy fell short at a 74% Biological Value. Net Protein Utilization (NPU) is the amount of amino acids converted to protein inside the body versus the amount of amino acids from protein eaten. It measures the ratio of protein consumed through a person’s diet, to the amount of nitrogen emission. The body only uses 94% of whey protein provided but only 61% of soy protein.
The protein efficiency ratio measures the gain in body weight divide by the weight of the protein consumed for infant laboratory rats. The FDA used the protein efficiency ratio to derive the recommended daily allowance of protein seen on food labels. A protein efficiency ratio of 2.7 per calculation is considered an excellent source of protein. Soy fell slightly short of this with a calculation of 2.2 while whey exceeded with a rate of 3.2. The amino acid score (AAS) measures essential amino acids in a protein compared to a reference protein. A value greater than 1 indicates that the protein being considered contains a greater amount of essential amino acids than humans require. Soy’s value just missed the cut with an amino acid score of 0.99 while whey exceeded the standard with a score of 1.14, containing more essential amino acids than the body needs.

Like the AAS, the , Protein Digestibility Corrected Amino Acid Score (PDCAAS) measures the essential amino acids in a protein compared to a reference protein. This reference protein meets the essential amino acid requirements of humans, and is given a PDCAAS of 1.0. Both soy and whey had a score of 1.0.

The protein digestibility percentage (PD%) measures the percentage of protein eaten that is absorbed in the body. Soy protein has a protein digestibility percentage of 94%, while whey has a 99% PD.

While both proteins carry all of the essential amino acids the body needs, which one contains more? Check out the table used in the study by Middle Management:

As the table shows, whey contains more essential amino acids. With the exception of the PDCAAS, whey exceeds soy’s rankings in all categories. While soy is undoubtedly a great contender, whey remains unmatched in protein value. For body builders, whey is the more reasonable choice, but there may be a few exceptions. If you are a vegetarian, soy would substitute whey, since soy is a plant protein and whey is derived from milk. If you typically do not hit the gym very often and are looking for supplements to balance your diet, taking soy protein may be more cost effective. According to bodybuilding.com, soy is around two dollars per pound less and the price of whey is rapidly increasing. If you do hit the gym, the best bet may be to take both soy and whey. A study from PubMed shows that soy and whey protein bar products both promoted exercise training-induced lean body mass gain, but the soy had the added benefit of preserving two aspects of antioxidant function. Soy also digests slower than whey, which provides a prolonged deliberate release of amino acids to muscles.

The theory that soy inhibits muscle growth and is inferior to whey has certainly been disproved, but it is certainly no match for whey. The benefits of soy and studies of the value of alternative protein sources are still being conducted.

Research sources and for more information: [Bodybuilding.com]; [Build-muscle-and-burn-fat.com]; [NIH]
[The Final Sprint.com]; [picture]

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Tags: amino acid score, amino acids, and essential amino acids, biological value, body building, diet, digestibility percentage, excersize, health, net protein utilization, protein, protein digestibility corrected amino acid score (pdcaas), protein efficiency ratio, protein supplements, soy, studies, supplements, whey

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