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By Anne Harding

TUESDAY, June 28, 2011 (Health.com) — Over the past several decades Americans have steadily gotten fatter. Although our increasingly sedentary lifestyles are partly to blame, a big reason for our national weight gain is that we're simply eating more.



The average portion size has increased, too, but only by about 12 percent. And, surprisingly, the average number of calories per 1-gram serving of food (known as "energy density") actually declined slightly over that period, which suggests that calorie-rich food has played a relatively minor role in our expanding waistlines.

"The real reason we seem to be eating more [calories] is we're eating often," says the lead author of the study, Barry Popkin, Ph.D., a professor of nutrition at the University of North Carolina at Chapel Hill. "The frequency of eating is probably, for the average overweight adult, becoming a huge issue."


"It's all about making people think they want to have something in their hands all the time," he says. "Why are we snacking all the time and munching all the time? [Food] is there, it's available all the time, it's tasty. It's not very healthy, but it's tasty. It's sweet, it's salty, it's fatty—it's all the things we love."


"You never used to see food staring you in the face when you went to…a drugstore," says Young, who was not involved in the new research. "It's in your face and it's cheap. You go get a magazine, you can get a candy bar."

Next page: Study based on national surveys



Christopher Gardner, PhD, the director of nutrition studies at Stanford University's Prevention Research Center, in Palo Alto, Calif., says that although the new findings ring true, the survey-based approach Popkin and his colleague used has some inherent limitations.

Despite being nationally representative, the surveys didn't follow the same individuals over time, and in some cases also used different questions and methods, Gardner points out. Moreover, they relied on the participants' memory of what they'd eaten in the previous 24 hours, which can be unreliable.

"When people try to describe the portion sizes they are consuming, they are often inaccurate," Gardner says, adding that similar inaccuracies may crop up when recalling and calculating the energy density of specific foods. In fact, he says, the number of meals and snacks may be easiest of all to remember and track, which may have somewhat exaggerated its importance to total calorie intake.


In our food-filled environment, Young says, "We need to be conscious of when we eat, how much we eat, and what we eat."

Young recommends sticking with three meals a day and choosing healthy snacks (such as fruits and vegetables) rather than processed foods. "And keep your portions in check," she says.