Carbohydrates have taken another hit. A new study finds that a low-carb diet results in greater weight loss and better cholesterol readings than a low-fat regimen that promotes a lot of grains and fruits. A Mediterranean diet that incorporates some of each diet yielded results that fell between the two, researchers in Israel report in the July 17 New England Journal of Medicine.
By conducting a trial within a single workplace, the scientists managed to keep 85 percent of the study participants on their respective diets for a full two years, a coup among diet studies. High dropout rates have historically skewed the results of such studies.
While people lost at least some weight on all three diets in this trial, the differences were significant. “The old food pyramid is going to get turned on an angle,” says study coauthor Iris Shai, a nutritional epidemiologist at Ben-GurionUniversity of the Negev. “Maybe now it’s a little more questionable that we should be basing our diets on carbohydrates.”
Shai and her team recruited 322 overweight people with an average age of 52 and randomly assigned them in roughly equal groups to one of the three diets. Most of the participants were men.
The low-fat diet closely adhered to guidelines developed by the American Heart Association, in which people are counseled to eat plenty of low-fat grains, vegetables, fruits and legumes. Dietitians counseled participants to strictly limit fats and meats, to avoid sweets and fatty snacks and to keep their daily calorie intake under 1,800 a day for men and 1,500 for women.
A second group was assigned a Mediterranean diet, which had the same overall calorie limits. But these people could eat fats, mainly olive oil and nuts, in moderation. The Mediterranean dieters also ate poultry and fish but little red meat.
The low-carbohydrate group ate an Atkins diet, in which they could consume all they wanted provided very little of it was carbohydrates. Their carbs topped out at 120 grams per day, but protein and fat intake weren’t limited. The dietitians urged them to choose vegetarian foods when available. All the groups avoided trans fats.
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Because the study participants worked at the same facility and ate lunch at the same cafeteria, they were able to obtain food that fit their assigned diets for the midday meal, the largest of the day.
After two years, low-carb dieters had lost an average of 5.5 kilograms and 3.8 centimeters from their waistline. The weight loss was significantly greater than the 3.3 kilograms lost by the low-fat dieters, who carved 2.8 centimeters off their average waistlines. The Mediterranean dieters showed results between the two.
Dieters in the low-carb group also raised their average HDL cholesterol, the good kind, by 8.4 points, 2 points more than the other groups. LDL, the bad cholesterol, didn’t change significantly in the groups.
Also, the low-carb and Mediterranean dieters lowered their blood levels of triglycerides (fats) significantly more than the low-fat group.
Other studies have tackled the low-fat versus low-carb issue, bringing mixed results. Some found that low-carb diets induced quick weight loss, but that the early gains faded after six months.
“This study clearly is longer than anything we’ve seen so far,” says internist William Yancy Jr. of Duke University and the Veterans Affairs Medical Center in Durham, N.C. Combined, this study and some previous reports “are showing repeatedly that higher-fat diets do not worsen the overall blood cholesterol profile,” he says.
Whether this study will single-handedly change how nutrition experts counsel people remains to be seen. Nutrition guidelines evolve very slowly, says Christopher Gardner, a nutrition scientist at StanfordUniversity. But he notes that the Mayo Clinic Healthy Weight Pyramid has recently changed, with fruits and vegetables now at the bottom, and grains just above in a lesser role.
“This study is totally in line with that,” Gardner says.
But the findings run counter to many food pyramids still touted as the basis of a healthy diet. While the U.S. Department of Agriculture rearranged its pyramid in 2005 to reflect a greater mix of foods, it still promotes plenty of grains and other carbohydrates.
Part of the hesitation to change rests on the fact that scientists are still sorting out exactly how a low-carb diet works. For some reason, low-carb dieters don’t gorge themselves even though the diet allows them to eat all they want, minus the carbohydrates.
In this study, the people who stayed on the low-carb diet reported feeling full, says Shai. “This is a high-protein diet, and high protein means much more satiety.” After drastically reducing carbohydrate intake, a person experiences lower insulin and glucose levels in the blood. That, in turn, curbs an individual’s craving for sweets, she says.
Gardner says low-carb dieters also find eating less interesting. “There’s just a smaller choice of options,” he says. “Foods simply get boring and you don’t want as many of them, once you take away the carbs.”
The explanation may lie in our evolutionary origins, Gardner says. “We evolved in another way,” he says, which was to eat a lot of leafy vegetables and meat proteins. “Since the agrarian revolution, we’ve eaten too many grains with too many calories—and it’s killing us,” he says.
It remains to be seen whether the low-carb diet can reduce long-term health risks, such as heart attacks, Yancy says. For the low-carb dieters, the new study used the Atkins diet. Robert Atkins first proffered the diet in 1972, but the idea didn’t gain much traction with the public until the 1990s, when his regimen and others rapidly found popularity. Other variations include the Zone diet and the SouthBeach diet. The new study was supported in part by the Dr. Robert C. and Veronica Atkins Foundation.