As the CEO of a supplement company I often get asked, whey vs soy, which is better? Let’s start with whey. Whey protein contains all nine of the essential amino acids. It is easy to digest and also has a higher concentration of branched chain amino acids than any other protein source (an important feature for muscle enhancement). Whey also has higher values for protein quality. Four measurements are often used to gauge protein quality:
- Protein efficiency ratio
- Biological value (BV)
- Net protein utilization (NPU)
- Chemical score
Protein efficiency is a measurement of animal growth as a result of consuming a fixed amount of protein. The biological value is a measure of the amount of protein the body retains. Net protein utilization is a measure of the amount of amino acids supplied by the protein source. Chemical score is a measure of the concentration of amino acids.
Starting with BV the value is adjusted using a relative scale with whole egg as the standard (BV of 100). How do the BV values compare for soy versus whey?
For BV whey is 104-110 and soy is usually in the mid-70s.
The NPU measures the ratio of protein consumed through a person’s diet, to the amount of nitrogen excreted. The value varies from 0 to 100 and is often interpreted as a percentage. A value of 100 indicates that the body uses 100% of the protein provided. Above the requirement, the excess protein is burned (a great source of carbon for gluconeogenesis) or may support some new protein synthesis in a person who is exercising in a correct manner.
For NPU whey is ~90 and soy is usually in the low 60s.
The protein efficiency ratio measures the gain in body weight divided by the weight of the protein consumed for infant laboratory rats. The FDA uses the protein efficiency ratio to derive the recommended daily allowance of protein seen on food labels. Any protein having greater than a 2.7 protein efficiency ratio calculation is considered an excellent source of protein.
Whey ~3.2
Soy ~2-2.5
Finally, the amino acid or chemical score measures essential amino acids in a protein compared to a reference protein (often egg white). The chemical score rates the protein on the most limiting amino acid. Soy contains less sulfur-containing amino acids such as methionine; thus values range from 0.7 (70%) to 0.9 (90%) depending on how the soy product is modified. Compared to egg white, whey is 110-120%.
So – a summary to this point:
Whey is a better protein source nutritionally; it contains selectively more micronutrients but most whey isolates are lactose rich (~70% by weight), which means it can be hard to tolerate for some. Also, there is the perception by some vegetarians that animal proteins should be avoided.
Are there advantages for soy? There are some:
Glutamine – The higher glutamine content of soy is often touted as a positive attribute (it is about twice per 100 grams that found in whey). Glutamine is a non-essential amino acid, which is used to shuttle ammonia for urea synthesis to allow the carbon chain/skeleton of glutamine to act as a gluconeogenic source. It is suggested or inferred that glutamine supplementation increases growth hormone levels, which leads to the muscle using fatty acids for fuel rather than blood sugar. However, in the majority of trials, the effects are short-lived returning to baseline shortly after cessation of therapy. The assumptions are also based on studies in which the subjects have disorders (e.g., short bowel syndrome). What is forgotten in these types of inferences is that one needs glucose via gluconeogenic to keep the TCA cycle running smoothly (throughout the day in contrast to your mealtime or a particular activity). Thus, a glutamine supplement (or good food source like soy) may mostly be affecting transient changes in metabolism and at the end of the day not make much difference, assuming a good diet is being consumed as a starter. One’s body actually makes a lot of glutamine (in the liver).
Arginine – Arginine is also about 2-3 times higher in soy than whey. Arginine has become popular recently due to its role as a nitric oxide substrate, which increases blood flow, and thus presumably delivers more nutrients to the muscles and promoting growth. Again, the available literature is mixed. Most studies suggest that in endurance events there may be some benefit, but for isotonic muscle/strength training probably little or barely measurable effects. In the popular literature (in contrast to the clinical literature) significant changes in nitric oxide, growth hormone, IGF-1, or insulin are suggested or inferred by merely taking arginine supplements. In this regard, it may help those in which circulation is compromised. One needs about 6-10 grams of arginine for a response. 100 grams of soy comes close to delivering that. In healthy individuals, however, it is difficult to show an effect.
What do opponents for soy protein say about it…
Soy isolates contain phytoestrogens that behave like estrogen, which is the opposite of what anyone trying to build muscle wants. However, phytoestrogens exist in almost all plants and the amounts vary. Nevertheless, the propaganda related to soy is that it can increase estrogen levels in males.
Furthermore, soy is not a “health food” per se given the amount of processing required in making the isolate. Raw soy is both heat stable (saponins, tannins, estrogens, and phytates) and heat-labile (protease inhibitors). Protease inhibitors in soy affect digestibility. They are destroyed by heating but other factors also play a role, such as duration of heating, particle size and moisture conditions. Thus, how soy products are processed will dictate how much of the protease inhibitor remains and other products remain. For example, raw soy flour has ample amounts of trypsin/proteinase inhibitor, but toasted soy flour and soy protein isolate can loss 90% or more. Appreciate that the loss of trypsin/proteinase inhibitor is essential to obtain the protein related values summarized above.
Whey vs Soy Protein conclusion
As supplements go probably both are OK with, of course, a number of caveats for each. If you set aside the lactose issue, whey seems to be the clear winner for non-vegetarians. Those who believe the “Forks Over Knives” arguments will want soy protein, although the isolate is a highly “processed food”.