Beltsville -- For years, you diet without success while your friend eats fries and double cheeseburgers without gaining a pound. But you console yourself by thinking it's not your fault: Your friend's body just burns up calories faster, right?
Wrong. The truth is, you don't exercise enough and you sneak a lot more cookies than you're willing to admit, even to yourself.
That's the inescapable conclusion of U.S. Department of Agriculture researchers who have spent the last three years studying more than 100 people in USDA's calorimeter, an unusual live-in laboratory designed to monitor food intake and measure human energy.
"Our tests found no metabolic magic: We've yet to see any evidence that there is any difference in people's efficiency in the way food is metabolized," said Paul Moe, research leader in the Energy and Protein Nutrition Laboratory here.
"In other words, sorry folks, there is no free lunch."
Although the review invalidates a long-cherished excuse for overweight Americans -- blaming your genetic metabolism instead of the Twinkies -- USDA's researchers say The Box, as the calorimeter is affectionately nicknamed, cannot lie.
The same can't always be said for human beings, who tend to fib or forget when it comes to food. "We find people are either eating much more or much less than they recall, leaving out exercise and convincing themselves that the number of calories they eat has no impact," Mr. Moe said.
The calorimeter, a 9-by-10-foot metal box, with eight-foot-high ceilings, provides no room for excuses. The floor, walls and ceiling are embedded with 80,000 sensors that pick up heat -- one measure of the
energy a body expends. The box also measures oxygen input and carbon dioxide output to calculate total energy expenditure.
Once in the box, a subject lives for 24 hours in a totally controlled environment, with a constant temperature of about 72 degrees. TV is available -- but it can be viewed only through the window, so that the set won't affect the temperature.
Meals arrive through a slot in the door. Exercise on a stationary bike in the corner is carefully monitored for 20-minute periods. A bed in the corner allows for a snooze.
The controlled environment allowed the researchers to conclude that people eating the same food and getting the same exercise in the same environment seem to metabolize or "burn up" the calories at very close to the same rate.
"There is some difference among subjects, related to the variation in spontaneous movement or what we call the fidget factor," Mr. Moe said. "However, the differences are rather
small -- it's not enough to make the difference in a 1,200-calorie diet vs. an 1,800-calorie diet."
The USDA researchers noted little change in metabolism rates on a low-fat vs. a high-fat diet, which is good news for dieters. That means if you cut the fat and eat more carbohydrates --
which, because they're bulkier, will probably mean you eat fewer calories before you feel full -- your body will burn those calories at its usual rate, so you can lose weight.
"The good news is that if you reduce calories, exercise and start eating like a 120-pound person, you can become a 120-pound person," said Mr. Moe. "The bad news is, once you lose the weight, you can't go back to what you were eating like a 150-pound person or you'll gain it right back."
Added Joan Conway, a researcher at the lab, "In the end, we may decide that up to 30 percent of what you weigh is determined by genetics, but the biggest part is all in how you manage it."