Kevin Hall, a mathematical physiologist, and Carson C. Chow, an M.I.T.-trained mathematician and physicist, developed a mathematical model that could predict how body composition changes in response to food intake.
Hall and Chow, an investigator at the National Institute of Diabetes and Digestive and Kidney Diseases, streamlined their model down to one simple equation in an attempt to answer why 1 in 3 Americans are obese.
“I could see the facts on the epidemic were quite astounding,” Chow told Claudia Dreifus with the New York Times.
“Between 1975 and 2005, the average weight of Americans had increased by about 20 pounds,” Chow said.
“Since the 1970s, the national obesity rate had jumped from around 20 percent to over 30 percent. The interesting question posed to me when I was hired was, Why is this happening?”
According to Chow, the conventional wisdom of burning off 3,500 calories to lose a pound of weight is wrong. The body changes as you lose weight.
Chow claims the fatter you get, the easier it is to gain weight. An extra 10 calories a day puts more weight onto an obese person than on a thinner one.
Chow determined time is an important factor in weight loss, and claims it takes about three years for a dieter to reach their new steady state.
“Our model predicts that if you eat 100 calories fewer a day, in three years you will, on average, lose 10 pounds — if you don’t cheat.”
And as long as your average food intake over a year is about the same, dramatic variations in daily food intake will not cause variations in weight, because a person’s body will respond slowly to the food intake.
Chow attributes the obesity epidemic in the United States to an overproduction of food, and dismisses genetics and lack of physical exercise as contributing factors.
“Levels of physical activity have not really changed in the past 30 years,” Chow says.
“As for the genetic argument, yes, there are people who are genetically disposed to obesity, but if they live in societies where there isn’t a lot of food, they don’t get obese. For them, and for us, it’s supply that’s the issue.”
Chow notes that beginning in the 1970s, farmers were encouraged to grow as much food as they could instead of the standard practice of the government paying farmers not to produce food.
Unrestricted production coupled with technological changes and the green revolution made farms much more productive, which in turn caused the price of food to plummet.
According to Chow, his model shows that the increase production explains the increase in weight, and suggests that with such a huge food supply, food marketing got better and restaurants got cheaper.
“The low cost of food fueled the growth of the fast-food industry. If food were expensive, you couldn’t have fast food.”
Chow believes we should stop marketing food to children. “I think childhood obesity is a major problem. And when you’re obese, it’s not like we can suddenly cut your food off and you’ll go back to not being obese. You’ve been programmed to eat more.”
Body Weight Simulator
By visiting an interactive version of Hall and Chow’s model, people can plug in their information and learn how much they’ll need to reduce their intake and increase their activity to lose weight. It will also give them a rough sense of how much time it will take to reach the goal. Applied mathematics in action!