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Soy Protein Isolates vs. Soy: What’s the Truth?

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On Monday, October 26, 2015, the World Health Organization (WHO) made an announcement that the consumption of processed meats and red meats may be a definite factor in the development of cancer. It is great to see the WHO release this announcement.

Soy Is Healthy

We wish that a definite announcement of the safety of soy and the problems with soy protein isolates would be stated so clearly. Soy is healthy. Soy protein isolates are not. Many of the favorite meat replacement foods, often called “mock meats”, are made with a substance which may be harmful in the development of cancer, osteoporosis and other diseases. This substance is often found in vegan protein powders as well. This substance is called soy protein isolates. This substance is only a portion of what makes up the entire soy food. Separating the protein in soy from the whole soy food creates an imbalance, and in this form, a potentially dangerous substance. However, soy in its natural form (and not with the protein separated) is a healthy food.


Countless people around the world have eaten soy for thousands of years, and are healthier as a result.

Soy Protein Isolates = Meat Protein

Soy protein isolates mimic the amino acids in meat. They are treated by the body in the same manner as meat protein. This results in an over stimulation and production of IGF-1 (Insulin-Like Growth Factor 1). IGF-1 is the messenger to the cells of the body to produce more cells. This is important for normal body function as cells in our body reproduce themselves about every three weeks, removing old cells and replacing them with new ones. However an abnormal stimulation of this process has been linked to the development of cancer. Eating large amounts of soy protein isolates, such as those found in many “mock meats”, may stimulate this process to work on cancer cells and cause them to grow at abnormal rates. We all have cancer cells in our bodies all the time. If our body functions properly it eliminates these cancer cells before they grow into more cancer cells. It is this stimulation of abnormal growth of cancer cells that is the problem. This is the process which causes cancers to grow and spread in the human body.


Eliminating sources of chemicals which will stimulate production of IGF-1 is important in the prevention of cancer. IGF-1 has also been shown to be a deterrent to the absorption of calcium. This can be an issue for anyone who might be susceptible to osteoporosis or its precursor, osteopenia. Additionally, prolonged high levels of IGF-1 have been shown to elevate blood sugar levels. A prolonged elevated blood sugar level is often a precursor to type-2 diabetes. Therefore, it is important for multiple reasons to limit foods that will promote the creation of IGF-1 whether they are in the form of animal products or as an additive to vegan or other products in the form of soy protein isolates.

Distinction Between SPI and Soy

Note that some organizations continue to state that soy is an unhealthy food and causes cancer. At best, this is a gross misunderstanding and confusion between actual soy and soy protein isolates. At worst, it is an attempt to smear the reputation of a truly beneficial food. We cannot help but notice that some groups that disparage soy are heavily funded by various aspects of the meat industry. As the old saying goes, “follow the money” to find the truth.

Soy protein isolates are quite different from soy foods. Soy consumed in less processed forms such as soy beans, tofu, tempeh, edamame or soymilk does not present the health risk that is present when consuming large amounts of highly processed soy protein isolates. Quite the opposite!   Soy foods are very good sources of protein and other substances.

For more information on soy and the health benefits please see Is Soy Safe. 








Author: Glenn McCarthy

Glenn McCarthy was an avid competitive runner for over 40 years, running 15 marathons with an average finish time of 2:46. He is a certified coach with the Road Runners Club of America and has coached distance runners for many years using the Lydiard method. Glenn is a long-time vegan who loves to cook. He has two grown daughters and two grandsons and lives in Colorado with his wife who is also vegan.