A new study suggests that low-carb diet regimens, such as Atkins and Zone I help people lose weight because, simply, they eat less food.
According to researcher Dr. Guenther Boden, a professor of biochemistry at Temple University in Philadelphia, numerous theories have been suggested 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, carbohydrate calories are somehow different from other calories," he says.
To help determine which was correct, Boden's team sequestered 10 obese patients in a controlled, clinical environment where diets were strictly monitored for three weeks. For the first week, the 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 (g) per day to just 20 g a day.
At the same time, a tempting array of fatty, sugary foods was readily available to the patients, all of whom had Type 2 diabetes.
"We told them, 'You can eat as much of anything else as you want, whenever you want," Boden says.
The researchers used the latest technology to assess weight-related outcomes, including body mass loss, water loss and total calories expended.
By the end of the two-week low-carb regimen, patients lost an average of 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 they were on the low-carb regimen.
"Take the carbohydrates away, and I expected the participants would just eat more of the other stuff," says Boden. "But they didn't. In fact, it turned out they ate 1.000 calories less every day," he notes.
Interestingly, that 2,100 calories per day that they consumed on the low-carb regimen "turned out to be exactly the amount of energy they should've been consuming" in order to avoid weight gain, he says. "In other words, they self-corrected their previously excessive appetites down to normal."
As usual with weight loss, diabetes risk factors, such as insulin and blood-glucose levels, began to noticeably improve as well. So did levels of unhealthy blood fats called triglycerides-a finding noted in previous studies that examined 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, does not explain why carb-deprived individuals don't reach for sugars, proteins or fats.
Boden suspects it might be because of a drop in insulin. "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," he says. "I can't prove it, of course, because we still know so very little about appetite."
Dietitian Cathy Nonas, director of the obesity and diabetes program at North General Hospital in New York City, and a spokeswoman for the American Dietetic Association, says the study doesn't tell scientists much that they didn't 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 notes. And that's true of most diets."
Nonas also says previous studies have suggested that cutting back on one type of food doesn't necessarily mean people are going to gorge on another.
However, she is concerned that the Temple study did not include a control group—people the researchers could have used for comparison. "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?"
Dr. George A. Bray, of the Pennington Biomedical Research Center, in Baton Rouge, Louisiana, believes the new study adds to the literature suggesting that low-carbohydrate diets may have a place in the treatment of obesity."
Nonas remains skeptical that any diet that excludes a whole food group can be healthy -or sustainable over the very long term.
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.
The Skinny on Dieting's Newest Terms
There's no standard definition for the terms “low carb," "carb wise" or "carb fit." These are marketing terms designed to sell products. In addition, "low carb" doesn't mean low in fat or calories.
Carefully examine food product labels. Total carbohydrates, as listed on the Nutrition Facts labels, are calculated by subtracting the grams of protein, fat, water and ash (the nonburnable portion of the food, such as minerals) from the total weight of the food.
Net carbs are promoted by food manufacturers to give consumers the impression that a certain food has a low carb count.
Net carbohydrates are the total carbs minus the fiber, glycerin and sugar alcohols.
The idea is that these types of carbohydrates don't raise blood sugar and therefore, shouldn't be included when counting cards in foods. But sugar alcohols actually can raise blood sugar and do add calories.
Good Vs. Bad
Sugar, which offers no nutritional benefit other than calories, is usually considered a bad carbohydrate.
Whole grains, such as oatmeal or brown rice, on the other hand, contain healthful minerals, vitamins and fiber, making them good carbohydrates.
But, remember, too much of any food leads to excess calories and weight gain.
Low-Carb Diets Lower Cholesterol, Too
A low-carbohydrate diet is good for more than weight loss.
Recent study: Obese adults on a low-carb diet had a greater decrease in triglyceride levels (higher levels are a risk factor for heart disease) than those in a low-fat group. They also had a lower decrease in the level of good HDL cholesterol. Diabetics on the low-carb diet had better blood sugar levels. These benefits were in addition to losing more weight in the first six months than participants in the low-fat group. After 12 months, the weight-loss difference was not statistically significant.
Best way to cut carbs: Limit soft drinks and junk food.