Math and obesity, a calorie is not a calorie

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A CONVERSATION WITH CARSON CHOW -

http://www.nytimes.com/2012/05/15/science/a-mathematical-challenge-to-obesity.ht\

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A Mathematical Challenge to Obesity

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Temchine for The New York Times

FIGHTING OBESITY Carson Chow at a supermarket. Dr. Chow, a mathematician, has

found that a food glut is behind America's weight problem.

By CLAUDIA

DREIFUS<http://topics.nytimes.com/top/reference/timestopics/people/d/claudia_dre\

ifus/index.html?inline=nyt-per>

Published: May 14, 2012

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Carson C. Chow deploys mathematics to solve the everyday problems of real life.

As an investigator at the National Institute of Diabetes and Digestive and

Kidney Diseases<http://www2.niddk.nih.gov/>, he tries to figure out why 1 in 3

Americans are overweight.

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We spoke at the recent annual meeting of the American Association for the

Advancement of Science<http://www.aaas.org/>, where Dr. Chow, 49, gave a

presentation on " Illuminating the Obesity Epidemic With

Mathematics<http://aaas.confex.com/aaas/2012/webprogram/Session4438.html>, " and

then later by telephone; a condensed and edited version of the interviews

follows.

You are an M.I.T.-trained mathematician and physicist. How did you come to work

on obesity?

In 2004, while on the faculty of the math department at the University of

Pittsburgh, I married. My wife is a s Hopkins ophthalmologist, and she would

not move. So I began looking for work in the Beltway area. Through the

grapevine, I heard that the N.I.D.D.K., a branch of the National Institutes of

Health<http://topics.nytimes.com/top/reference/timestopics/organizations/n/natio\

nal_institutes_of_health/index.html?inline=nyt-org>, was building up its

mathematics laboratory to study obesity. At the time, I knew almost nothing of

obesity.

I didn't even know what a calorie was. I quickly read every scientific paper I

could get my hands on.

I could see the facts on the epidemic were quite astounding. Between 1975 and

2005, the average weight of Americans had increased by about 20 pounds. 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? "

Why would mathematics have the answer?

Because to do this experimentally would take years. You could find out much more

quickly if you did the math.

Now, prior to my coming on staff, the institute had hired a mathematical

physiologist, Hall. developed a model that could predict how your

body composition changed in response to what you ate. He created a math model of

a human being and then plugged in all the variables - height, weight, food

intake,

exercise<http://health.nytimes.com/health/guides/specialtopic/physical-activity/\

overview.html?inline=nyt-classifier>. The model could predict what a person will

weigh, given their body size and what they take in.

However, the model was complicated: hundreds of equations. and I began

working together to boil it down to one simple equation. That's what applied

mathematicians do. We make things simple. Once we had it, the slimmed-down

equation proved to be a useful platform for answering a host of questions.

What new information did your equation render?

That the conventional wisdom of 3,500

calories<http://health.nytimes.com/health/guides/nutrition/diet-calories/overvie\

w.html?inline=nyt-classifier> less is what it takes to lose a pound of weight is

wrong. The body changes as you lose. Interestingly, we also found that 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.

Also, there's a time constant 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 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.

Another finding: Huge variations in your daily food intake will not cause

variations in weight, as long as your average food intake over a year is about

the same. This is because a person's body will respond slowly to the food

intake.

Did you ever solve the question posed to you when you were first hired - what

caused the obesity epidemic?

We think so. And it's something very simple, very obvious, something that few

want to hear: The epidemic was caused by the overproduction of food in the

United States.

Beginning in the 1970s, there was a change in national agricultural policy.

Instead of the government paying farmers not to engage in full production, as

was the practice, they were encouraged to grow as much food as they could. At

the same time, technological changes and the " green revolution " made our farms

much more productive. The price of food plummeted, while the number 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? They eat it! This, of

course, is a tremendously controversial idea. However, the model shows that

increase in food more than explains the increase in weight.

In the 1950s, when I was growing up, people rarely ate out. Today, Americans

dine out - with these large restaurant portions and oil-saturated foods - about

five times a week.

Right. Society has changed a lot. 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.

People think that the epidemic has to be caused by

genetics<http://health.nytimes.com/health/guides/specialtopic/genetics/overview.\

html?inline=nyt-classifier> or that physical activity has gone down. Yet levels

of physical activity have not really changed in the past 30 years. 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.

Interestingly, we saw that Americans are

wasting<http://health.nytimes.com/health/guides/symptoms/muscle-atrophy/overview\

..html?inline=nyt-classifier> food at a progressively increasing rate. If

Americans were to eat all the food that's available, we'd be even more obese.

Any practical advice from your number crunching?

One of the things the numbers have shown us is that weight change, up or down,

takes a very, very long time. All diets work. But the reaction time is really

slow: on the order of a year.

People don't wait long enough to see what they are going to stabilize at. So if

you drop weight and return to your old eating habits, the time it takes to crawl

back to your old weight is something like three years. To help people understand

this better, we've posted an interactive version of our model at

bwsimulator.niddk.nih.gov<http://bwsimulator.niddk.nih.gov/>. People can plug in

their information and learn how much they'll need to reduce their intake and

increase their activity to lose. It will also give them a rough sense of how

much time it will take to reach the goal. Applied mathematics in action!

What can Americans do to stem the obesity epidemic?

One thing I have concluded, and this is just a personal view, is that 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. It's a

hardship to eat less. Obama's initiative is helpful. And childhood

obesity rates seem to be stabilizing in the developed world, at least. The

obesity epidemic may have peaked because of the

recession<http://topics.nytimes.com/top/reference/timestopics/subjects/r/recessi\

on_and_depression/index.html?inline=nyt-classifier>. It's made food more

expensive.

You said earlier that nobody wants to hear your message. Why?

I think the food industry doesn't want to know it. And ordinary people don't

particularly want to hear this, either. It's so easy for someone to go out and

eat 6,000 calories a day. There's no magic bullet on this. You simply have to

cut calories and be vigilant for the rest of your life.

A version of this interview appeared in print on May 15, 2012, on page D2 of the

New York edition.

S. Kalman PhD, RD, FACN

Director, BD - Nutrition & Applied Clinical Trials

Miami Research Associates

6141 Sunset Drive - Suite 301

Miami, FL. 33143

Direct -

Office ext. 5109

Fax

Email: dkalman@...

Web: www.miamiresearch.com<www.mraclinicalresearch.com/>

Linked In: http://www.linkedin.com/in/douglaskalmanphdrd