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Why Do Low-Carb Diets Cause Weight Loss?

Diets Work Because People Eat Less, New Study Shows
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WebMD Health News

March 14, 2005 - Low-carb weight loss dietsLow-carb weight loss diets do work, at least in the short term, but why?

A meticulously conducted short-term study may have the answer. Temple University researchers reported that participants in a new study lost weight when they restricted carbohydrates simply because -- drum roll, please -- they ate fewer calories.

The researchers found no evidence to support other popular theories for why low-carb diets work, such as the idea that calories from carbs are somehow burned less efficiently than calories from other sources.

"It had nothing to do with water being shed or with carbohydrates being somehow different in the way that they are metabolized by the body," lead researcher Guenther Boden, MD, tells WebMD.

"The people in our study ate less. It was a simple as that."

"Some very prominent researchers have bought into the idea that you can cut carbohydrates without cutting calories and lose weight. We found that people lost weight because they took in fewer calories."

Impact of Low-Carb Diets on Calories

A whole lot fewer calories. The 10 obese study participants, who all had type 2 diabetes, cut their calorie intake by a third while on the most carbohydrate-restrictive phase of the low-carb diet.

Because the subjects were housed in a hospital research center for the length of the 21-day study, investigators were able to track every calorie that was eaten and burned. They also measured fat- and water-derived weight loss, blood sugar control, and cholesterol levels.

The participants ate their regular diets for the first seven days. They then followed the low-carb diet for the next two weeks, limiting carbohydrates to just 20 grams a day but eating unlimited amounts of protein and fat.

Prior to starting the low-carb diet, the subjects ate an average of 3,100 calories a day. While on the low-carb diet, they ate about 2,100 calories, even though they were told to eat as much of the permitted foods as they wanted.

The participants lost an average of 3.6 pounds while on the low-carb diet, their blood sugar level normalized and their cholesterol levels also improved.

The study is published in the March 15 issue of Annals of Internal Medicine.

"In my opinion this study proves conclusively that the weight loss in the Atkins diet is due to reduced calorie intake, period," Boden says.

Can Carbohydrates Stimulate Appetite?

Boden says he was amazed to find that the participants did not compensate for eating fewer carbs by eating more of other foods. He added that they seemed happy with the low-carb diet and did not complain of hunger.

"They ate 1,000 fewer calories a day and did not miss them," he says. "That told me that it was the carbs that fueled their excessive appetites in the first place. In my opinion, carbohydrates do stimulate appetite."

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