Dietitians and doctors plead with increasingly obese Americans to eat less and exercise more, often to no avail. Now, one diet researcher is pointing to growing evidence that fewer food choices could be part of the answer.
"We're all eating more calories, and you have to ask yourself why that is," says Susan Roberts, PhD, who runs dietary and metabolism research at a Tufts University in Boston.
According to Roberts, one reason for Americans' increased caloric intake (search) — as much as 350 more calories per day on average than 15 years ago — is that we have too many food choices, especially of bad foods, and that animals, especially humans, find that variety irresistible.
Researchers are quick to point out that there are many proven reasons behind the 60 percent-plus rate of overweight and obesity in the U.S. population. In addition to eating more, technological improvements mean that we have to exercise less to work, do chores, or do just about anything else.
"Individuals are now left with a stark choice of whether or not to fill the gap with voluntary physical activity" such as joining a gym or blocking of time each day for a run, says Elizabeth Frazao, an assistant deputy director with the U.S. Department of Agriculture Economic Research Service.
But at the same time, inexpensive, high-fat, high-calorie foods abound in restaurants, vending machines, and on dinner tables. Americans love this abundance of food choices — a stubborn fact that haunts advocates and dietitians trying to push lighter eating.
But Roberts points to evidence showing that simply limiting the variety of available foods, therefore limiting food choices, can be effective in limiting consumption.
"The more varied your diet, the more calories you consume," she told an audience at a national obesity prevention conference sponsored by the USDA.
More Food Choices Makes Us Eat More
As many as nine studies suggest that mere choice makes humans eat more, even when the food choices are seemingly meaningless. Experimenters in one trial got subjects to eat 14 percent more on average per meal just by offering them two different pasta shapes instead of one.
The studies have been confirmed dozens of times in animals, Roberts says. And a 2001 University of Buffalo study backed up the conclusion by analyzing 39 animal and human trials.
Part of the reason for the variety effect is that humans and other mammals just like food more when it differs from what they just ate. One study showed that people reliably ate more when sausages, bread, chocolate, and bananas were each served in four consecutive courses than when they were served four times together on a plate, the Buffalo researchers wrote.
Few suggest that asking or forcing food manufacturers to market fewer food choices is the answer. But Roberts says researchers have paid relatively little attention to effective ways of helping people design meals or tailor shopping so that their evolutionary drive to eat less kicks in.
"I think we should be putting more effort into looking at this," she says.
By Todd Zwillich, reviewed by Charlotte E. Grayson, MD
SOURCES: Susan Roberts, PhD, USDA Human Nutrition Research Center, Tufts University. Elizabeth Frazao, PhD, assistant deputy director for women, infants and children research, Economic Research Service, USDA. Psychological Bulletin, May 2001; vol 127:pp 325-334.
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