Wednesday, May 18, 2011

EAT TO GROW : Can Soy Mess Up Metabolism? by Jerry Brainum

How soy affects thyroid function in men

One frequent criticism of soy products is that they interfere with thyroid function. Isoflavones, which are found in soy, are known to adversely affect thyroid-gland function in animals by inhibiting an important enzyme called thyroid peroxidase. Researchers from Canada and Seattle teamed to explore the effects of soy intake on thyroid functioning in young men.1

Thirty-five healthy men, average age 27, supplemented their diets with one of the following:

1) Milk protein isolate

2) Low-isoflavone soy protein isolate

3) High-isoflavone soy protein isolate

They used the supplements for 57 days, separated by four-week washout periods when they took no supplements. The results: None of the soy-based supplements had any adverse effect on any measure of thyroid hormone activity.                                            

1 Dillingham, B.L., et al. (2004). Soy isoflavone consumption does not influence serum thyroid hormones in young men. (Presented at Experimental Biology 2004, April 2004, in Washington, D.C.)

©,2011 Jerry Brainum.Any reprinting in any type of media, including electronic and foreign is expressly prohibited.     

Have you been ripped off  by supplement makers whose products don’t work as advertised? Want to know the truth about them? Check out Jerry Brainum's book Natural Anabolics, available at


The Applied Ergogenics blog is a collection of articles written and published by Jerry Brainum over the past 20 years. These articles have appeared in Muscle and Fitness, Ironman, and other magazines. Many of the posts on the blog are original articles, having appeared here for the first time. For Jerry’s most recent articles, which are far more in depth than anything that appears on this blog site, please subscribe to his Applied Metabolics Newsletter, at This newsletter, which is more correctly referred to as a monthly e-book, since its average length is 35 to 40 pages, contains the latest findings about nutrition, exercise science, fat-loss, anti-aging, ergogenic aids, food supplements, and other topics. For 33 cents a day you get the benefit of Jerry’s 53 years of writing and intense study of all matters pertaining to fitness,health, bodybuilding, and disease prevention.


See Jerry's book at


Want more evidence-based information on exercise science, nutrition and food supplements, ergogenic aids, and anti-aging research? Check out Applied Metabolics Newsletter at