Low fat or low carb, Atkins or Ornish, Jenny Craig or Weight Watchers – which diet is best for weight loss? Two new studies offer ammunition for those who say the popular low-carb approach is superior and for those who say all diets are pretty much the same.
But some experts say the bottom line remains unchanged: The best diet for you may be one you can stick to longest and adapt in the healthiest way.
In the first study, published Monday in the Annals of Internal Medicine, 148 obese adults were put on either low-fat or low-carb diets. The low-fat dieters tried especially to limit saturated fat, the kind found in meat, whole milk and butter. The low-carb dieters were told to go ahead and eat more fat and protein, but to cut back on white bread, sugary cereals and other high-carb fare.
While there were no calorie goals, the groups reported cutting statistically similar amounts, about 500 to 700 calories a day. Researchers say they cannot be sure how accurate those counts were.
Results after a year: The low-carb group lost an extra 8 pounds (12 vs. 4), shed more body fat and got a bonus — greater improvements in cholesterol counts and other measures of cardiovascular health.
"That is contrary to popular thought," and should be reassuring to people who want to try the approach, says study co-author Lydia Bazzano, a researcher at Tulane University School of Medicine, New Orleans.
Bazzano says it's important to note that low-carb participants "were not eating butter and burgers at every meal." While they ate more saturated fat, they also ate more of the unsaturated fats found in olive oil, canola oil, nuts and avocados, she says.
The second study, published Tuesday in the medical journal JAMA, mined data from 48 previous studies on brand-name diets such as Atkins (low carb), Ornish (low fat) and Weight Watchers (labeled a "moderate" approach).
It found people on either low-fat or low-carb diets for a year lost an average of 16 pounds more than people on no diets. Those on diets with moderate amounts of fats and carbs lost an average of 12 pounds more than non-dieters.
In practical terms, the results were quite similar, says lead author Bradley Johnston, an epidemiologist at the Hospital for Sick Children Research Institute, Toronto, and McMaster University, Hamilton, Ontario.
"All of the diets can lead to important reductions in weight, but there's no important differences between the diets," he says.
Frank Hu, a nutrition researcher at the Harvard School of Public Health who was not involved in either new study, says the 48-study review is "problematic." He says it relies on studies in which compliance with diets was often low and in which dropout rates were often high. By contrast, about 80% of participants completed the Tulane study and most appeared to do a "pretty good" job of following the diets, Hu says.
The JAMA review also looked at the diets only from a short-term weight-loss standpoint, says Linda Van Horn, a registered dietitian at Northwestern University Feinberg School of Medicine, Chicago. She wrote an editorial accompanying the study.
"There are many, many fad diets out there that will certainly get a person to lose weight," she says.
Whether they are healthy or will work for a lifetime are different questions, she says.
Neither of the new studies addresses long-term weight maintenance, says James Hill, an obesity researcher at the University of Colorado School of Medicine, Denver. Increased exercise, discouraged in the Tulane study, may be one key, he says. Hill says people who are very active may need more carbohydrates than those who are not.
Hu says no one diet can claim to be healthiest or right for everyone.
"It's possible to have a healthy low-fat diet, one rich in fruits, vegetables, nuts, legumes and whole grains, but not loaded with sugar and white bread, and also possible to have a healthy low-carb diet, one not loaded with bacon and sausage," he says. "What matters most is that the individual can stick to the diet over the long term."