Ask the Diet Doctor: The Last Word on Soy Protein Isolate

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Q: Should I avoid soy protein isolate?

A: Soy has become a very controversial and complicated topic. Historically Asian populations have consumed large amounts of soy products while also having the longest and healthiest lives in the world. Research regarding soy protein and cardiovascular health became so robust that it was awarded a health claim, allowing food companies to state that "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of (name of food) provides X grams of soy protein."

But for every health benefit of this complete plant-based protein source, you'll also hear of a potential detrimental effect, including an increased risk of certain cancers, disturbed hormonal balance, disrupted thyroid function, or intake of pesticides and toxins.

Easing some concerns, the Agency for Healthcare Research and Quality (AHRQ) released a nearly 400-page report on the effects of soy and soy isoflavones (antioxidants found in soy), concluding that, "For all outcomes, including adverse events, there is no conclusive evidence of a dose-response effect for either soy protein or isoflavone." However, because soy products come in such a wide variety-whole soy, fermented soy, soy protein isolate, and others-confusion continues to ensue.

Soy protein isolate in particular has been increasingly placed under a health microscope regarding its safety, due to its widespread use to increase protein content of various foods or to enhance texture. There are three common concerns to be aware of.

1. Metal contamination. Soy protein isolate is extracted from defatted soy flour. It is made of almost pure protein, since the isolation process yields a product that is 93 to 97 percent protein, leaving minimal fat and carbohydrates. The concern about the isolation process centers on the fact that aluminum found in the giant vats used to isolate the soy protein may leach into the protein itself, increasing the likelihood of heavy-metal poisoning. This is completely speculative, as I have yet to see an analysis of soy, whey, or any protein isolate showing heavy metal contamination from the containers used during the isolation process.

2. Pesticide risk. Ninety percent of genetically modified soy is resistant to glyphosate, the pesticide found in Round Up. A concern raised about eating products with soy protein isolate is that you will consume excessive amounts of this chemical. The good news? Glyphosate is not well absorbed by the human GI tract, the potential negative effects on humans are dose-dependent, and the level of that dose is very controversial.

The other good news (or maybe bad news) is that when it comes to glyphosate, soy protein isolate isn't your main problem. Glyphosate is everywhere, which is the really bad news! It is like BPA, which I've covered previously. Research published in 2014 in Food Chemistry and Environmental & Analytical Toxicology highlighted the fact that the worldwide use of glyphosate has made it abundant in our ambient environment and food supply. While the amount of glyphosate in a serving of soy protein isolate has not been quantified, it is very unlikely soy it is your primary, only, or even a significant source of exposure of this pesticide.

3. Concentrated isoflavones. One of the most controversial areas of soy, isoflavones are antioxidants that are famous for mimicking estrogen in the body. This effect has been seen as a benefit, with research showing that 75 or 54 milligrams a day (mg/d) of soy isoflavones can increase bone mineral density and decrease the frequency and severity of hot flashes, respectively. However, isoflavones in soy have also been proposed to play a role in increasing risk of breast cancer. The research in this area is complicated and constantly evolving, with negative effects seen in animal studies, but no effects found in human studies.

It's also important to note that soy protein isolate isn't necessarily a concentrated source of isoflavones. According to the USDA Isoflavone Database, one ounce (about one scoop) of soy protein isolate contains 28mg soy isoflavones and three ounces of cooked tofu contain 23mg soy isoflavones. On a per-serving basis, both foods contain about the same dose of isoflavones, but soy protein isolate contains significantly more protein: 23g vs. 8g.

All things considered, eating moderate amounts of soy protein isolate does not provide a health risk. I see the main benefit of soy protein isolate as a nutritional tool to help you meet your daily protein needs. If you abstain from eating dairy protein (whey) right after a workout or if you need to increase the protein at a given meal, use soy protein as you would use any protein supplement.

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