A Mathematical Model Determines the Root Cause of the Obesity Epidemic

Dr. Carson Chow

Dr. Carson Chow, a Massachusetts Institute of Technology-trained mathematician, physicist and investigator at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), has boiled down the cause of the country’s obesity epidemic to one thing: the overproduction of food in the country.

From the 1940s to 1970s, technological breakthroughs gave way to the “green revolution,” in which crop yields increased substantially. And so did the number of calories available to the average American, by about 1,000 a day.

Indian Country Today Media Network spoke with Dr. Chow about how his NIDDK team developed a mathematical equation to determine why obesity rates have escalated in the past several decades and how body weight responds to food intake.

How did you reach the conclusion that an increase in food caused the obesity crisis?

The U.S. Department of Agriculture keeps track of how much food is available—the food net. Then, we have the model of the average American. Using the food being made available to Americans, we asked, “What happens?” Through simulating the entire country, we found the average person became heavier because of an increase in food availability. There is a causal connection between the increase in food and the obesity epidemic.

How do you define the “average American”?

The average American adult in 1975 weighed about 75 kilograms, which is roughly 156 pounds. That includes men and women, 18 to 65. The average American adult in 2005 weighed about 80 kilograms, which is about 180 pounds.

How does your mathematical equation work?

We’ve been developing a model that predicts how much the body changes given a change in food intake. The model does account for gender and age; however, I have not published anything broken down by the U.S. population.

Starting in 2004, Kevin Hall, a mathematical physiologist [with the NIDDK], developed a model that could predict how your body composition changed in response to food intake. He created a math model of the human body that could predict what a person will weigh, relative to body size and what they eat.

But the model was complicated. We finally boiled it down to a simple equation in 2008.

An interactive version of our model allows people to enter their age, gender and other personal information: It tells them how much less they need to eat, how much more they need to be physically active, and it tells them about how much time it will take them to lose the weight.

What’s the next step?

At this point, we’re collaborating with researchers at the National Institutes of Health to use a model to predict whether people adhere to diets. A lot of people say, ‘I drop by 500 calories a day, and I’m not losing weight.’

If you actually measure and carefully monitor their caloric intake, they are not eating what they think they are eating—they are unaware that they are actually eating more than they think they are [eating].

You told The New York Times it’s easier for a lean person to bounce back after overeating on a single day than an overweight person. Why?

You have to consider that when you’re in energy balance—which means that your body weight is not changing—whatever you’re eating, you’re burning about that same amount everyday. Say you’re eating 2,000 calories a day and burning 2,000 calories a day. How much energy you burn depends a lot on how much you weigh. But what’s more important is how much lean tissue or lean body mass you have. Lean body mass includes water, all protein, bones, these type of things. So how much energy you burn is dependent on lean tissue, lean body mass. When we gain weight, we gain fat and lean body mass. But a thin person will gain a higher proportion of lean to fat than a fat person. When a fat person gains weight, he or she gains mostly fat.

What makes the difference?

It turns out that fat is metabolically less active than lean body mass, and a fat person gains more fat tissue than a lean person.

Is it especially important for an overweight person to count calories?

Calorie count is important for everyone in the sense that the calories you eat do matter. On the other hand, it’s really the average amount you eat over the year that determines how much you are going to weigh. You can vary day to day, but just don’t increase on average. If you are averaging 2,000 calories per day one year, and the next year you average 2,200 calories per year, you will gain weight—probably 20 pounds. It takes about three years for a dieter to reach their new equilibrium weight.

That said, you could eat a little more over a few months, then go back to your normal, base weight.

Essentially, a person could eat 4,000 calories every other day, and average 2,000 calories per day over the course of three years, and maintain the same weight? Is that healthy?

I guess so, but I don’t know. I wouldn’t recommend it. I’m not a medical doctor.

Do you look at good calories versus bad calories?

We don’t look at the differences in food in relation to their risk for cardiovascular disease or diabetes. In fact, although research may seem to indicate that saturated fat leads to a higher incidence of heart disease, we don’t know why this is true from a biological standpoint.

For a lot of things that people think are true or think make sense, there is not really any biological evidence for why.

You have said it is a hardship to eat less. Why do you think people struggle with cutting back their caloric intake—is it psychological or physical?

That, to me, is the question. We don’t have enough data to know. My personal view—not based on any research or data—it’s a brain thing. The mind is used to eating more calories, and this is not a part of the brain we can control. It’s the part that controls appetite, which is close to the part of the brain where we control breathing. When that part is adjusted to eating more calories, it is hard to adjust that switch once adjusted. There is some evidence in animal models that the brain changes once it becomes obese, but we don’t know if that applies to humans.

I do think it is a lot easier to stay where you are than to gain weight or lose it.

Do some people have higher metabolisms than others?

It’s a myth that a thin person has a higher metabolism. A think person does not have a higher metabolism [than a heavier person]. They have a slower metabolism on average. It seems the efficiency of the digestive system is about the same no matter who you are. There may be variations, but if you’re bigger, you don’t process more of the food than if you’re smaller. That’s not the message people want to hear, but it seems to be the case.

What do you suggest the federal government do to reduce obesity rates?

My opinion is that it’s easier to stay where you are than to lose weight. So we should help prevent children from becoming obese by not advertising food to children. This is based on some cost-effective studies out of Australia. If we prevent a child from becoming obese, it is much easier for the child not to become obese as an adult.

Also, this is purely my opinion—this is not a scientific statement—but maybe it would be good if we subsidized the growth of a greater variety of fruits and vegetables, such as making tomato and spinach cheaper. Maybe it would be good if we made those things cheaper compared, to say, a can of coke.

It would be nice if people ate lots of fruits and vegetables, which contain a lot of water and not a lot of calories. Processed food is rid of water and dense in calories. You would need to eat a lot of lettuce to consume a lot of calories. You could graze on spinach, lettuce and kale all day—you can only eat so much. This might sound funny, but sleep is a constraint on how much a person eats. You can’t eat while you’re sleeping.

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