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Soy: Should We Be Eating It?

Soy has been part of the Asian diet for thousands of years and has comparatively recently been introduced to western and other diets, where its use is more as a surrogate food, for instance, as a meat replacement.​1​

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Due to their high protein content, and the apparent lack of ethical considerations, soy-based foods are popular among those following vegetarian and vegan diets. Soy chunks for instance contain about 50% protein across brands, though they also contain about 33% carbs, so not a great choice for low-carb meals. Tofu on the other hand has about 8% protein and less than 2% carbs. Interestingly soy milk has lower protein at about 3% and more carbs at 6%. As per the American Dietetic Association, soy protein has the highest quality among plant proteins.​1​ (Nutrition Data Sources: USDA Food Data Central and food labeling)

To my mind, there are five health-related issues that one usually associates with soy-based products:

  1. Effects on sex hormones
  2. Disruption of thyroid gland function
  3. Lowered disease risk
  4. Anti-oxidant effects
  5. Other Outcomes

Effects On Sex Hormones

Reports of most phytoestrogen-related effects of soy-based foods in men, such as reduced libido and erectile dysfunction among others, in addition to adverse effects in menopausal women, appear to be anecdotal in nature. ​1,2​

Each gram of soy based protein has 3.5mg of isoflavones, which have chemical structures similar to estrogen allowing them to bind to estrogen receptors, albeit in a weaker manner than estrogen. This is said to cause estrogen-like effects, giving them the label, phytoestrogens or estrogens of plant origin. Research however has proven that the structures of the two substances are different enough to result in very different outcomes and the results do not merit equation of soy based foods with phytoestrogens.​2​

Disruption Of Thyroid Gland Function

While some studies point to the goitrogenic properties of soy, with small studies finding associations between the consumption of soy based foods and increased TSH in women, by and large, the possibility of alteration of thyroid via the consumption of soy based foods isn’t deemed very high.

Patients of hypothyroid however should avoid soy as it may inhibit absorption of their medication. ​1​

Lowered Disease Risk

Diets rich in phytoestrogens are linked to lowered risk of Coronary Heart Disease in addition to conferring some benefits to:​1,3,4​

  • Hormone dependent prostate, colon and breast cancers
  • Menopausal symptoms
  • Osteoporosis
  • Obesity
  • Cognitive dysfunctions and
  • Overall risk of non-communicable diseases

Anti-oxidant Protective Effects

For more about anti-oxidants, click here. The available data on this front appears mixed, with various aspects of anti-oxidant behavior being analyzed, such as DNA oxidation, fat oxidation, endogenous oxidation and total anti-oxidant capacity. The outcome was not in favor of soy-based foods having significant anti-oxidant activity, though related outcomes did not worsen after the intake of soy-based foods. ​5​

There may be effective anti-oxidant outcomes combined with a reduction in inflammation in patients of Chronic Kidney Disease (CKD). ​6​

Additional Beneficial Effects and Concerns

Soy based foods could benefit kidney function, alleviate hot flashes, improve depressive symptoms and skin health. Animal studies seem to indicate adverse effects as the outcome of the consumption of isoflavones, whereas human studies appear to have beneficial outcomes.​2,6​

Conclusion

Apart from hypothyroidism or being on a low carb diet, soy sounds like a very acceptable food with a variety of benefits.

References

  1. 1.
    Rizzo G, Baroni L. Soy, Soy Foods and Their Role in Vegetarian Diets. Nutrients. Published online January 5, 2018:43. doi:10.3390/nu10010043
  2. 2.
    Messina M. Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature. Nutrients. Published online November 24, 2016:754. doi:10.3390/nu8120754
  3. 3.
    Blanco Mejia S, Messina M, Li SS, et al. A Meta-Analysis of 46 Studies Identified by the FDA Demonstrates that Soy Protein Decreases Circulating LDL and Total Cholesterol Concentrations in Adults. The Journal of Nutrition. Published online April 22, 2019:968-981. doi:10.1093/jn/nxz020
  4. 4.
    Ramdath D, Padhi E, Sarfaraz S, Renwick S, Duncan A. Beyond the Cholesterol-Lowering Effect of Soy Protein: A Review of the Effects of Dietary Soy and Its Constituents on Risk Factors for Cardiovascular Disease. Nutrients. Published online March 24, 2017:324. doi:10.3390/nu9040324
  5. 5.
    Rizzo G. The Antioxidant Role of Soy and Soy Foods in Human Health. Antioxidants. Published online July 18, 2020:635. doi:10.3390/antiox9070635
  6. 6.
    McGraw NJ, Krul ES, Grunz-Borgmann E, Parrish AR. Soy-based renoprotection. WJN. Published online 2016:233. doi:10.5527/wjn.v5.i3.233

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