Eating 100 fewer calories a day—roughly three bites of a fast-food hamburger—could prevent the 1.8 to 2.0 pounds that the average person gains per year, according to new estimates by James Hill and colleagues. Their article appears in the 7 February issue of the journal Science, published by the American Association for the Advancement of Science.
While 100 fewer calories isn’t enough to bring about weight loss, it represents a specific, manageable strategy that people can use to stop the current trend in our ever-fattening population, according to Hill, a researcher at the University of Colorado Health Sciences Center. This is the most urgent priority in addressing the obesity epidemic, he said.
“We asked ourselves, ‘what’s it going to take to start turning the tide?’” Hill said. “The first measure of success is to stop weight gain. That might not be so overwhelming, since we can break it down into concrete steps.”
Hill and his colleagues studied data collected by the National Health and Nutrition Examination Survey (NHANES) and the Coronary Artery Risk Development in Young Adults (CARDIA) study. Obesity is generally defined as having a body mass index, or “BMI,” (a measure of body weight based on height and weight) of 30 or more. Worldwide, over 300 million are obese, according to the World Health Organization.
The NHANES data showed that the prevalence of obesity increased from 23 percent to 31 percent between 1988 and 1994 in the United States. Hill’s team calculated that if weight gain continues at the present rate, 39 percent of the U.S. population will be obese in 2008.
Stopping this so-called “obesity epidemic” will require two types of approaches, according to Hill. The long-term approach would be to mount a social change campaign, akin to those for smoking cessation, seat belt use, and recycling, to build an environment more supportive of healthy lifestyles.
The short-term goal of stopping weight gain requires first pinpointing what Hill calls the “energy gap”: the amount of calories we consume but do not burn off.
“We all know you’ve got to eat less and exercise more, but, well, how much? That’s what we’ve laid out,” Hill said.
Using the NHANES and CARDIA data, Hill and his colleagues estimated that individuals are gaining, on average, 14-16 pounds in eight years. That breaks down to an average of 1.8 – 2.0 pounds each year.
Assuming that each pound of body weight gained represents 3500 calories, the researchers calculated that 90 percent of the population is gaining up to 50 extra calories a day. The body doesn’t store excess energy with 100 percent efficiency, however. Hill’s team figured that for every 100 extra calories consumed, at least 50 would be stored as fat.
“Nobody really ever talks about numbers, but that’s what we need. Something around 100 calories a day is do-able,” Hill said.
To close the energy gap, people could walk an extra mile a day, either all at once or divided up across the day, Hill suggested. Since it takes most people approximately 2000-2500 steps to complete a mile, they could slightly adjust their lifestyles to fit in those extra steps.
“When we look at what’s causing the obesity epidemic, it doesn’t look like it’s our biology gone bad. It’s the environment, acting on our ancient biology,” Hill said. “We need to look at what’s happening to changes in energy intake and physical activity, and then determine the extent of the problem.”
Even if we can close the energy gap, slimming the population down will still be a challenge. A key part of this task, Hill believes, will be a fundamental change in how people think about being physically fit.
“I think most people who are fit are making conscious efforts to be that way. So, we need to do a better job of teaching people those skills,” Hill said.