Obesity

Obesity is an incredibly important issue that we touched on at the end of the last block. It's an epidemic that is sweeping across Westernizing nations, targeting young and old, and increasing morbidity and mortality. So many diverse factors play into the equation: genetics, nutrition, exercise, hormones. And it's a problem that is so resistant to change. Here, I am going to focus on two obesity-related issues that fascinated me.

The first is the identification of the fat hormone leptin and its receptor. These were experiments done in the 1950s on mice with mutations that caused them to be severely obese. I think the experiments were very elegant for their time. Researchers used a technique called parabiotic pairs, connecting two mice so that they share the same bloodstream (it's a little strange, and I don't know the details). If you take a parabiotic pair of a normal mouse and an obese ob/ob mouse (image above), then the ob/ob mouse will lose weight to a normal weight. The researchers concluded that something in the normal mouse "rescued" the obese mouse, and this hormone traveled through the bloodstream. If you take a parabiotic pair of a normal mouse and an obese db/db mouse, then the normal mouse will lose weight, but the db/db mouse will remain obese. Researchers deduced that the receptor for the hormone was knocked out in the db/db mouse so the db/db mouse had elevated levels of the hormone, which caused the normal mouse to lose weight. So they were able to characterize two mice with separate etiologies of obesity, one involving the hormone and one involving the receptor. Pretty cool.

The other interesting thing about obesity is that not all fat is equal. Visceral or intra-abdominal fat ("the beer belly") is harmful to the person's health, but subcutaneous fat is not. This presents itself strikingly in Japanese sumo wrestlers. Sumo wrestlers eat and exercise. So they build up an incredible amount of weight, but all that fat is subcutaneous. As a result, sumo wrestlers don't get type II diabetes, no matter how heavy they are. On the other hand, a huge percentage of obese people in the U.S. develop type II diabetes because they have visceral fat. Interestingly enough, when sumo wrestlers retire and stop working out, the rate of obesity-related morbidity and mortality shoots up.