Low-Carb Diets Work for Weight Loss

A new study involving obese individuals suggests the reason the Atkins, Zone, and other low-carb regimens help people lose weight is that dieters do not substitute fatty or sugary foods for the carbohydrates they lack, says a study reported in the Annals of Internal Medicine.

Instead, they simply eat less food.

"Take the carbohydrates away, and I expected the participants would just eat more of the other stuff," says researcher Dr. Guenther Boden, a professor of biochemistry at Temple University, in Philadelphia.

"But they didn't," he says. "In fact, it turned out they ate 1,000 calories less every day."

Less Carbs Does Not Mean More Fat Instead

The findings may help allay concerns these diets raise heart risks linked to increased fat consumption.

According to Dr. Boden, numerous theories have been floated as to how low-carbohydrate diets trigger weight loss.

"The possibilities were: People eat less, they expend more calories, they don't really lose body mass but instead they lose water, and a fourth possibility - very popularly expressed - that carbohydrate calories are somehow different from other calories," he says.

To help determine the correct answer, his team sequestered 10 obese patients, all diagnosed with type 2 diabetes, in a controlled, clinical environment where diets were strictly monitored for three weeks.

Dr. Boden's team also used the very latest technology to assess weight-related outcomes such as body mass loss, water loss, and total calories expended.

For the first week, participants ate their usual mixed diet. But during the last two weeks the researchers restricted their intake of carbohydrates from an average of 300 grams per day to just 20 grams a day.

At the same time, a tempting array of fatty, sugary, and other foods was readily available to all.

"We told them 'Look, you can eat as much of anything else as you want, whenever you want,' " Dr. Boden notes.

The result: By the end of the two-week low-carb regimen, patients lost an average of 1.65 kilograms (3.6 pounds) and reduced their daily caloric intake by nearly 1,000 calories - from an average of 3,111 calories before they began the diet, to just 2,164 calories while on the low-carb regimen.

"In other words, they self-corrected their previously excessive appetites down to normal," Dr. Boden explains.

And that magic number of around 2,100 calories per day "turned out to be exactly the amount of energy they should've been consuming to start with" to avoid weight gain, he adds.

As happens naturally with weight loss, diabetes risk factors such as insulin and blood-glucose levels began to noticeably improve. So did levels of unhealthy blood fats called triglycerides - a finding noted in previous studies that looked at the effects of low-carb diets on cardiovascular health.

The study, which was funded by grants from the National Institutes of Health and the American Diabetes Association, still leaves unanswered the question of why carb-deprived individuals do not reach for sugars, proteins, or fats.

"The only thing that makes sense to me is a drop in insulin," Dr. Boden says. "I've been treating diabetics for decades, and every time I start them on insulin they gain weight. So I am sure insulin has something to do with appetite."

"I can't prove it, of course," he adds, "because we still know so very little about appetite."

Dietitian Cathy Nonas is director of the obesity and diabetes program at North General Hospital in New York City, and a spokeswoman for the American Dietetic Association. She said the study does not tell scientists much they did not already know about low-carb diets.

"If you look at all of the Atkins data that's ever been done, including USDA White Papers and so forth, people lose weight on the Atkins diet because they eat lower amounts of calories," she says. "And that's true of most diets."

And Nonas says previous studies have suggested that cutting back on one type of food does not necessarily mean people are going to gorge on another.

She is also concerned that the new study did not include a control group - participants the researchers could have used for comparison purposes.

"The problem here," she says, "is that we don't have a study where you also looked at taking away meat, for example - would we have seen similar, greater, or less change in weight?"

But another expert believes the new study "adds to the literature suggesting that low-carbohydrate diets may have a place in the treatment of obesity."

Study Sound, Expert Says

In his editorial comment, Dr. George A. Bray, of the Pennington Biomedical Research Center in Baton Rouge, La., called the Temple research "nicely done."

Long-term studies focused on the Atkins diet have found short-term weight loss that often exceeds that seen in other diets, Dr. Bray writes, "but the differences vanished after 12 months." He believes low-carb regimens should be simply added to a growing list of relatively safe weight-loss options for America's overweight and obese.

Nonas remains skeptical that any diet that excludes a whole food group can be healthy - or sustainable - over the very long term, however. And she believes Americans need only look abroad to find an ideal dietary model for life.

"All of the societies with low levels of the kinds of diseases [that plague us] have diets with lots of vegetables and fruits, a small amount of whole grains, portion-control, and a much higher fiber intake," she says. "And fiber isn't something that's been high on the list in any of these studies."

Always consult your physician for more information.