The Obesity Epidemic in the US Is Due Solely to Increased Food Intake

Fran Lowry

May 15, 2009

May 15, 2009 (Melbourne, Australia) — The amount of food Americans eat has been increasing since the 1970s, and that alone is the cause of the obesity epidemic in the US today [1]. Physical activity--or the lack thereof--has played virtually no role in the rising number of expanding American waistlines, according to research presented at the 2009 European Congress on Obesity in Amsterdam last week.

The finding is contrary to the widely held assumption that decreased physical activity is an equally important driver of overweight and obesity in the US, said lead author Dr Boyd Swinburn (Deakin University, Melbourne, Australia).

If Americans want to get serious about winning the battle of the bulge, they are going to have to cut down on the amount of food they eat, Swinburn, who is director of the World Health Organization Collaborating Centre for Obesity Prevention, told heartwire .

But, he warned, that won't be easy. "The food industry has done such a great job of marketing their products, making the food so tasty that it's almost irresistible, pricing their products just right, and placing them everywhere, that it is very hard for the average person to resist temptation. Food is virtually everywhere, probably even in churches and funeral parlors."

I Eat [Too Much], Therefore I'm Fat

How much this rise in obesity has been driven by excess calorie intake and how much by decreased physical activity has been a topic of debate for years but has been difficult to pin down, Swinburn said. He and his colleagues estimated those proportions by devising a series of equations that took into account energy intake, energy expenditure, and body size in 963 children and 1399 adults. They also analyzed the US Department of Agriculture (USDA) food-supply data to determine how much food had actually been delivered to the US population between 1970 and 2002.

Using that information, they then predicted the increases in weight in children and adults between 1971 and 1976 and between 1999 and 2002. If the predicted weight equaled the observed weight, increased food consumption was presumed to be the cause of the weight increase. If the predicted weight was higher or lower than the weight that was actually observed, it was assumed that changes in physical-activity levels were the cause.

As shown in National Health and Nutrition Examination Survey (NHANES) data, the mean weight gain in children was as the researchers had predicted--4.0 kg--and therefore attributed to increased calorie consumption alone. In adults, the predicted increase in mean weight--10.8 kg--was higher than the observed mean weight gain--8.6 kg--and this implied that increased physical activity might have moderated the effect to some extent.

"Americans have been eating more; the USDA data clearly show this. But US epidemiological data shows that physical-activity levels haven't really changed all that much. So I think we have to be much more focused on the energy-intake side of the energy-balance equation in understanding what the drivers of obesity are and also in working out what the solutions are," Swinburn commented. "We still need to continue to promote increases in physical activity, because exercise has a lot of positive physiologic benefits, but our level of expectation about the impact of physical activity on weight gain has to be a bit more tempered."

The Food Industry Is Driving Overconsumption

Promoting physical activity has been the favored approach to solving the problem of obesity by politicians and the food industry, said Swinburn. "It's relatively uncontroversial, there are no commercial competitors, it's a positive thing to do, so politicians, egged on by the food industry, heavily promote the physical-activity side of the equation."

Swinburn said that the food industry has been "extraordinarily successful" in promoting excessive intake of calories. "They've worked their marketing out to the nth degree. They've got the products that we like to eat, they've got the price right--in fact the price of junk food has been coming down for years and is getting cheaper and cheaper. Food is everywhere. In the 1970s, in Australia, when you went to a petrol station you used to buy petrol. Now it's a chocolate and fast-food station. The food industry has done all they can to sell their products, and they're doing it extremely well."

The food industry has also mastered promotion, especially to the most vulnerable and impressionable members of society--children. "Over the past 30 years they have become very sophisticated in marketing and advertising that is particularly iniquitous in relation to kids. They are adept in the way they turn kids into liking, preferring, demanding, and pestering for the foods that they advertise."

Study Says What Needs to Be Said, Say AHA, ACC

Spokespersons for the American Heart Association and the American College of Cardiology praised the study, even though its results are not surprising. "This is a nice study. It reflects many of the things that we have predicted, but I'm glad to see that it has been presented and that it is going to be published somewhere," said AHA spokesperson Dr Gerald Fletcher (Mayo Clinic Jacksonville, Florida).

Lower-caloric, healthier foods are also more expensive, and this can pose a problem for families with two or three kids when they go to the supermarket to shop. "The less expensive foods are those the industry can provide, with lots of calories. It's a socioeconomic problem as much as anything," Fletcher said.

ACC spokesperson Dr Matthew Sorrentino (University of Chicago), agreed that Swinburn and colleagues verified what experts in the obesity field had long suspected.

"The main cause of the obesity epidemic in this country is the wide availability of high-caloric foods and the fact that we are eating way too many calories in the course of a day. Exercise has much less impact."

Sorrentino said that about 90% of weight loss is achieved by cutting calories; only about 10% of weight loss is achieved by significantly increasing physical activity.

There needs to be a population-based approach to teach people how to count and cut calories, choose whole foods instead of packaged foods, and increase their awareness of just how fattening going out for dinner can be.

"Studies have shown that when you go out to eat, most individuals will eat on average 500 more calories per meal than they would eat at the same meal at home. There are now huge varieties of fast food, in packages and in fast-food restaurants, and they are usually calorically dense, full of carbohydrates, and sweetened, so they taste good and you want more. Years ago, you had to prepare food; now they're all prepared for you."

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