Perhaps no idea is more controversial in the diet world than the contention — long espoused by the late Dr. Robert Atkins — that people on low-carbohydrate diets can consume more calories without paying a price on the scales.
Over the past year, several small studies have shown, to many experts' surprise, that the Atkins approach actually does work better, at least in the short run. Dieters lose more than those on a standard American Heart Association plan without driving up their cholesterol levels, as many feared would happen.
Skeptics contend, however, that these dieters simply must be eating less. Maybe the low-carb diets are more satisfying, so they do not get so hungry. Or perhaps the food choices are just so limited that low-carb dieters are too bored to eat a lot.
Now, a small but carefully controlled study offers a strong hint that maybe Atkins was right: People on low-carb, high-fat diets actually can eat more.
The study, directed by Penelope Greene of the Harvard School of Public Health and presented at a meeting here this week of the American Association for the Study of Obesity, found that people eating an extra 300 calories a day on a very low-carb regimen lost just as much during a 12-week study as those on a standard lowfat diet.
Over the course of the study, they consumed an extra 25,000 calories. That should have added up to about seven pounds. But for some reason, it did not.
"There does indeed seem to be something about a low-carb diet that says you can eat more calories and lose a similar amount of weight," Greene said.
That strikes at one of the most revered beliefs in nutrition: A calorie is a calorie is a calorie. It does not matter whether they come from bacon or mashed potatoes; they all go on the waistline in just the same way.
Not even Greene says this settles the case, but some at the meeting found her report fascinating.
"A lot of our assumptions about a calorie is a calorie are being challenged," said Marlene Schwartz of Yale. "As scientists, we need to be open-minded."
Others, though, found the data hard to swallow.
"It doesn't make sense, does it?" said Barbara Rolls of Pennsylvania State University. "It violates the laws of thermodynamics. No one has ever found any miraculous metabolic effects."
In the study, 21 overweight volunteers were divided into three categories: Two groups were randomly assigned to either lowfat or low-carb diets with 1,500 calories for women and 1,800 for men; a third group was also low-carb but got an extra 300 calories a day.
The study was unique because all the food was prepared at an upscale Italian restaurant in Cambridge, Massachusetts, so researchers knew exactly what they ate. Most earlier studies simply sent people home with diet plans to follow as best they could.
Each afternoon, the volunteers picked up that evening's dinner, a bedtime snack and the next day's breakfast and lunch. Instead of lots of red meat and saturated fat, which many find disturbing about low-carb diets, these people ate mostly fish, chicken, salads, vegetables and unsaturated oils.
"This is not what people think of when they think about an Atkins diet," Greene said. Nevertheless, the Atkins organization agreed to pay for the research, though it had no input into the study's design, conduct or analysis.
Everyone's food looked similar but was cooked to different recipes. The low-carb meals were 5 percent carbohydrate, 15 percent protein and 65 percent fat. The rest got 55 percent carbohydrate, 15 percent protein and 30 percent fat.
In the end, everyone lost weight. Those on the lower-cal, low-carb regimen took off 23, while people who got the same calories on the lowfat approach lost 17 pounds. The big surprise, though, was that volunteers getting the extra 300 calories a day of low-carb food lost 20 pounds.
"It's very intriguing, but it raises more questions than it answers," said Gary Foster of the University of Pennsylvania. "There is lots of data to suggest this shouldn't be true."
Greene said she can only guess why the people getting the extra calories did so well. Maybe they burned up more calories digesting their food.
Dr. Samuel Klein of Washington University, the obesity organization's president, called the results "hard to believe" and said perhaps the people eating more calories also got more exercise or they were less apt to cheat because they were less hungry.