When I talk to fellow nonscientists about my job here at SiS, I find that many folks are most interested in topics that span the murky divide between things like nature and nurture, the conscious and unconscious, what we can control and what we cannot. Basically, which parts of us are governed by things like active decision-making and willpower, and what is simply controlled by our biology.
To get even murkier, that distinction is not cut and dried. Most things are controlled by...both. One of the best examples of this is weight loss. At first glance, it really should just be simple math - control your intake, burn more calories than you consume on a daily basis, and you will lose weight. At the very root of the issue, this is true.
But there are complicating biological factors, as covered by NPR's Morning Edition today. Even though our active minds might be telling our body one thing, hormones could be telling it something different. One of these hormones, called leptin, is produced by fat cells. When you start dieting and begin depleting your fat reserves, leptin levels drop. This tells your brain to brace itself for starvation. While our conscious brain knows this isn't true - we're not starving at all, just trying to become more healthy - our biology overrides and slows down our metabolism, which makes losing weight even more difficult. Then, to kick us while we're down, the brain sends a signal to stimulate the appetite. So, while one part of our brain is sending you to bed without dessert, the other is sending you screaming to McDonald's. Thanks, biology.
The researcher interviewed for the piece, Donna Ryan of the Pennington Biomedical Research Center in Baton Rouge, said that this biological disconnect amounts to what she calls a "caloric handicap" for people who diet. Essentially, if someone loses 50 pounds to hit a goal of 150, that person can't eat the same amount of calories in a day to maintain that weight as a friend who has always weighed around 150. So it's not about hitting a target once and then resuming past behaviors; it's about adopting a lifelong strategy of healthy eating and exercising. This, of course, requires a lot of willpower.
If you'd like to learn more about our frenemy leptin, check out this video from the Center for Genetic Medicine's Silverstein Lecture Series. It features Jeffrey Friedman, a professor at The Rockefeller University who first discovered the hormone.