Soy & Phytoestrogens

Last week I finished reading an article from Hormones and Behavior about the metabolism of hunger and sex drive. Within it, I learned some more interesting factoids about the consequences of ingesting soy. I think I drink a lot of soy, and I also eat tofu occassionally, so I am interested.

I'm still trying to wrap my head around the wide-ranging article, to fit the pieces together myself, so I'll just report some of the more interesting elements of the story.

1 - Fat cells have estrogen receptors! Mice without working estrogen receptors become obese.

2 - Body fat distribution is more critical to long term cadiovascular health than body fat content or BMI. Gluteofemoral fat deposits are cardioprotective. So, if you have an hourglass figure (narrow waist with wide hips and fleshy butt and hips - an hourglass/pear figure rather than an apple) you're at reduced risk of heart disease. Also, women with a .70 waist to hip ratio (the hourglass figure) have higher fertility.

3 - Insulin levels are associated with visceral (deep belly) fat, whereas leptin levels are associated with subcutaneous gluteofemoral (butt, hips, thigh) fat. Hormones of the HPA axis (hypothalamus - pituitary - adrenal glands), such as cortisol, are also implicated in body fat distribution. Stress may cause you to put on more visceral fat.

4 - Eating disorders (of which the author seems to be primarily interested in obesity) may arise from changes in neural sensitivity to estrogen that occur early in brain development.

5 - These changes might be intitiated by exposure to phytoestrogens in our diet and pollutants.

So, evidently, consuming soy is cardioprotective and reduces the risk of developing obesity only when consumed as an adult. BUT - and this is a big but - consumption of soy during pregnancy or exposure of a fetus to soy and phytoestrogens actually increases the risk of cardiovascular problems and obesity.

Pregnant women and infants should not consume soy or any products containing phytoestrogens because the phytoestrogens bind to the body's estrogen receptors in the brain, various internal organs, and particular body cells like fat cells. This leads to organizational changes in the infant's brain that masculinize a female's body fat distribution after puberty: more visceral fat around the waist, less around the hips and butt. This places her at greater risk of developing heart disease and obesity.

The paper, however, focused on an evolutionary theory that there are brain mechanisms dependent on hormones that serve to signal an animal when it's time to eat vs. mate. The author explored the metabolic control of hunger inhibition, arguing that such a mechanism is adaptive because it would "bring the cessation of hunger and eating long enough to find and court potential mates." She suggests that the hormone leptin, known as a hunger hormone because high levels of it inhibit appetite, should come to be viewed as a sex hormone too. Evidently, leptin enhances sex behavior - in rats and mice. It stimulates the preference of having sex over eating. The author also argues that the hormone neuropeptide Y which is known as an appetite stimulant, should also come to be viewed as a sex hormone that stimulates the preference for food over sex.