Whey protein and soy protein are both commonly used in meal replacement drinks and powders. Whey protein is a byproduct of the cheese-making process, while soy protein is derived from soy beans. While some people believe that soy is superior to whey for building muscle, losing fat, and improving general health, it is more likely that the opposite is true.
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Soy protein tends to be heavily processed, and because of this, it contains antinutrients, which can block the absorption of certain vitamins and minerals. Soy crops are sprayed heavily with pesticides, so they also carry a high toxic load. According to MayoClinic.com, soy is among the top eight most allergenic foods. So even if you aren't allergic to soy, you may suffer adverse reactions if you consume a lot of it.
Whey and soy protein contain a similar amount of protein and calories, but the protein in whey meal replacements has a higher biological availability than soy. This means that when you consume whey, more of the protein can be used by your body to repair damaged muscle tissue than when you drink soy. Soy protein, however, does contain higher amounts of the muscle-building amino acids glutamine and arginine.
The main health concern associated with soy is that some studies have shown it to lower testosterone levels and increase estrogen levels in the body. Testosterone is important for hormone production and general health, and it decreases with aging, meaning that a lower testosterone level could have a negative impact on health and body composition. The increased estrogen levels may be of benefit to postmenopausal women.
While whey appears to be the superior choice, you should always check the ingredients of any supplement you take to make sure you are not adversely reactive to any of the ingredients. Another factor to consider when purchasing a meal replacement supplement is calories. The calories of meal replacement shakes can differ vastly among brands, depending on how much carbohydrate and fat is added to the protein, so always look for one that fits in with your requirements.