You are an M.I.T.-trained mathematician and physicist. How did you come to work with obesity? In 2004, while on the school of the math department at the University of Pittsburgh, I married. My wife is a Johns Hopkins ophthalmologist, and she’d not go. So I started looking for work in the Beltway area. Through the grapevine, I noticed that the N.I.D.D.K., a branch of the National Institutes of Health, was building up its mathematics laboratory to study obesity and create math dvds. At that time, I knew next to nothing of obesity. I didn’t even understand what a fat was. I quickly read every scientific paper I can get my hands on. I could start to see the details on the epidemic were quite astounding. Between 1975 and 2005, the normal weight of Americans had improved by about 20 pounds. Because the 1970s, the national obesity rate had jumped from around 20 percent to over 30 percent.
The interesting question presented to me when I was chosen was, Why is this happening? Why would mathematics have the solution? Since to do this experimentally would take years. You can find out much quicker if you did the math. Today, ahead of my coming on staff, the start had used a mathematical physiologist, Kevin Hall. Kevin developed a style that could predict how your body composition changed in response to what you ate. He produced a math model of an individual and then connected in all of the variables’ height, weight, food intake, exercise. The model can predict just what a person may consider, given their human body size and what they take in. However, the design was complicated: countless equations. Kevin and I began working together to boil it down to one easy equation. That’s what applied mathematicians do. We make things simple. Once we had it, the slimmed-down picture proved to be a useful program for addressing a number of issues.
What new information did your picture render? That the traditional wisdom of 3,500 calories less is what it requires to drop a pound of weight is wrong. As you lose the system changes. Interestingly, we also discovered that the fatter you receive, the easier it is to gain weight. An additional 10 calories a day puts more weight onto an overweight person than on a thinner one. Also, there’s a time continuous that’s an important factor in weight loss. That’s because if you reduce your caloric intake, after a while, your body reaches equilibrium. It actually takes around three years for an individual to achieve their new “steady state.” Our model predicts that if calories are taken 100 by you less a day, in three years you will, typically, drop 10 pounds’ if you don’t cheat. Yet another finding: Huge variations in your daily diet won’t cause variations in weight, as long as your common food intake over a year is comparable. It is because a person’s system may respond slowly to the food intake.
Did you ever solve the problem presented to you when you were first hired what triggered the obesity epidemic? We think so. And it’s something quite simple, very obvious, something that few desire to hear: The crisis was brought on by the overproduction of food in the United States. Beginning in the 1970s, there is a change in national agricultural policy. Instead of the government paying farmers never to participate in total production, as was the practice, these were encouraged to develop as much food as they could. At the same time, technological improvements and the “green revolution” made our farms much more profitable. The price of food fell, while the amount of calories available to the average American grew by about 1,000 a day.
Well, what do people do when there is extra food around? It is taken by them! That, of course, is a tremendously controversial idea. However, the model implies that increase in food more than explains the increase in weight. In the 1950s, when I was growing up, individuals rarely ate out. Today, Americans dine out with these large restaurant portions and oil-saturated meals about five times a week. Right. A lot have been changed by Society. With this kind of large food supply, food marketing got better and restaurants got cheaper. The low priced of food fueled the development of the fast-food industry. If food were high priced, you couldn’t have junk food. People believe that the epidemic has to be caused by genetics or that physical activity went down. Yet quantities of physical exercise have not really changed in the past 30 years. As for the genetic argument, yes, you will find individuals who are genetically disposed to obesity, but if they reside in societies where there isn’t a large amount of food, they don’t get overweight. For them, and for people, it’s source that’s the issue. Interestingly, we saw that Americans are wasting food at a steadily increasing rate. If Americans were to eat all of the food that’s accessible, we’d be much more obese.