New Insights into Obesity

The December 2010 issue of the Nutrition Action Health Letter, published by the Center for Science in the Public Interest, featured an interview with Eric Ravussin, head of the Nutrition Obesity Research Center of the highly regarded Pennington Biomedical Research Center in Baton Rouge, LA. The discussion centered on new clues as to why we gain weight, and revealed the following:

• Leptin, a hormone discovered in 1994, is produced by fat cells and  tells the brain when the cells are full.
• When people diet and lose weight, leptin levels drop sharply, causing food cravings and weight regain.
• Loss of 10-20% of body weight slows the metabolism and rate of caloric burn.
• Injecting leptin can bring the metabolism back up.
• However, most overweight people are resistant to leptin, just as Type II diabetics are resistant to insulin.
• Using drugs to shut down hunger mechanisms doesn’t work well because the human body has developed several redundant systems to stimulate eating as protection against starvation.
• People have natural ranges of body fat depending on their genes that control energy intake and expenditure.
• Nutrition in the womb and infancy can affect propensity for overweight and obesity by switching different genes on and off.
• Brown adipose tissue, which burns calories to produce body heat, previously thought to exist only in infants, was recently discovered in adults.
• By maintaining homes at a steady comfortable temperature throughout the year, we don’t burn calories via brown fat to keep warm in winter, and we miss the appetite-suppressing effect of heat in the summer.
• A common cold virus (adenovirus-36) makes experimental animals gain a lot of weight. Antibodies to this virus, an indication of exposure, are much more common in obese than in normal-weight people.
• Gut bacteria can be a factor. Transplanting feces from a fat animal to a lean one results in weight gain for the latter, while transplanting from the lean to the fat animal makes the fatter one leaner. Similar transplants in humans have reduced insulin-resistance of people with metabolic syndrome, a set of symptoms indicative of heart-disease risk characterized by excess fat around the waist, low HDL, and elevated blood pressure, blood triglycerides, and fasting blood glucose.

Ravussin feels that we should tax soft drinks and other unhealthy foods while subsidizing healthy foods, create areas where kids can safely play, and make physical education mandatory so that everyone, not only the athletically-gifted, engages in physical activity,