Is Soy Really Making You Fat?

I get a lot of fitness and nutrition related emails.  I mean, a LOT of them.  Lately, my virtual mailbox has been filled with scary headlines like,

"What NEVER To Eat at 6:12PM If You Don't Want To Become Jabba The Hut Overnight"

and

"If You Eat This One Unique Food That Everyone Says Is Healthy, You Will Regret It Forever."

Or something like that.  I'm paraphrasing.

One of the foods that has been popping up left and right as the Evillest Evil of all Evils is soy.  Many of the people I know won't touch soy with a ten-foot pole.  Amongst it's many other alleged crimes, soy now supposedly contributes significantly to obesity. 

Look at them, just sitting there, plotting your demise.

Now, I don't eat a lot of soy.  But I do eat it in moderate amounts-- some tempeh here, some sprouted tofu there, and the occasional mock meat at a restaurant (although as a general rule I try to stay away from highly processed soy like mock meats, for much the same reasons that I try to stay away from highly processed foods in general).  So this piqued my interest, and I decided to dig a little deeper.

Know what I found?

Nothing.

That's right-- Nothing.  Nada.  Zip. 

There is, to my knowledge, NO objective, peer-reviewed, reputably-published research out there showing a link to soy and obesity.  The closest I could find was this article:

http://ebm.rsmjournals.com/content/233/9/1066.full#sec-30

which, in fact, states:

"The results of in vitro studies clearly suggest that isoflavones may have inhibitory effects on adipose tissue enlargement in vivo, and the experiments using rodents and humans demonstrate that some of the beneficial effects may actually apply in vivo. However, in vivo, especially in humans, the actions of soy isoflavones appear to depend on a complicated interaction between many factors, such as the presence of soy protein and particular intestinal bacteria. 

Although no clinical studies have recorded a reduction in body weight, the isoflavones may help prevent obesity-associated diseases by improving the plasma lipid profile. With respect to this, more research is needed to elucidate the biological mechanisms of soy isoflavones and to address the potential side effects associated with increased intake of these compounds."

In other words, soy has been shown to have promise to actually have the opposite effect.  

I also found this article:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1838825/,

which contains this very interesting table:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1838825/table/T1/ , and concludes the following:

"In conclusion, an increasing body of evidence from nutritional intervention studies in animals and humans indicates that dietary soy protein has beneficial effects on obesity. Consumption of soy protein can favorably affect satiety and reduce excess body fat in obese animals and humans. Soy protein ingestion also improves insulin resistance, the hallmark of obesity. Dietary soy protein and some of its constituents also reduce plasma lipids and fat accumulation in liver and adipose tissue, which may reduce the risks of atherosclerosis and lipotoxicity and possibly other obesity-related complications."

I also found this article:  http://care.diabetesjournals.org/content/30/4/967.full

which concludes:  "Short-term soy nut consumption reduced some markers of inflammation and increased plasma nitric oxide levels in postmenopausal women with the metabolic syndrome."

In the mean time, I found NOTHING linking soy to obesity.  Now, I'm not all-knowing, and I may have missed something.  So if someone would like to step up and show me the objective, peer-reviewed, reputably-published research linking soy consumption to adipose tissue retention, I'd really like to see it.

There are lots of other "Evil Foods" on the list, and I will get to them at a later date.  In the meantime, enjoy your (hopefully minimally processed) soy in moderation (as long as it doesn't affect you adversely, and as long as your thyroid isn't a problem), and don't believe everything that shows up in your mailbox.

Questions?  Comments?  Post 'em here.  I'm sure I've upset a lot of people by saying nice things about soy.  I apologize.