Popular diets offering different advice about carbohydrates and fat seem to be similarly effective for weight loss — as long as people stick to them, according to a new review of past studies.
Researchers looked at data from nearly 50 studies, which involved about 7,300 participants altogether, to compare the effectiveness of several diet types, including those that advocate either limiting fat or carbs — two different and highly debated approaches to weight loss.
The results showed that there was little difference between low-fat and low-carb diets in terms of weight loss. People who followed either type of diet for six months lost an average of about 18 lbs. (8 kilograms), compared with people who didn't follow any specific diet, according to the study published today (Sept. 2) in the journal JAMA.
The researchers also found that behavioral support and exercise enhanced the effects of diets, resulting in more weight loss.
The findings may reassure overweight or obese people, reminding them that "there is no need for a one-size-fits-all approach to dieting," and that they can pick a diet that is the least challenging for them to stick to, the researchers said. [Busted! The 7 Biggest Diet Myths]
"Given that the diets are relatively equal, individuals should choose the diet that they think that they can best adhere to," said study co-author Bradley Johnston, an assistant professor of clinical epidemiology at McMaster University in Hamilton, Ontario. "For example if someone tends to be vegetarian, it might make sense for them to choose a low-fat diet."
The researchers noted that although these diets seemed to work well in the short term, further study is needed to understand their long-term effects on weight loss and their influence on the general health of people.
Any diet could do?
Two low-fat diets were examined in the reviewed studies — the Ornish and Rosemary Conley diets, which dictate that less than 20 percent of daily calories should come from fat, 10-15 percent from protein and about 60 percent from carbs. Low-carb diets in the study included diet brands Atkins, South Beach and Zone, all of which advised dieters to eat less than 40 percent of their daily calories from carbs, about 30 percent from proteins and 30-55 percent from fat.
The analysis also included diets recommending a moderate amount of fat, carbs and protein, such as Weight Watchers, Biggest Loser, Jenny Craig, Nutrisystem and Volumetrics. People on these diets also lost weight, but on average they shed about 4 lbs. (1.8 kg) less than people following low-carb or low-fat diets, according to the study. [Lose Weight Smartly: 7 Little-Known Tricks That Shave Pounds]
The researchers also found differences among some diet brands. For example, people who followed the Atkins diet for six months lost, on average, 3.8 lbs. (1.7 kg) more than people on the Zone diet.
But these differences are too small to be important factors in choosing a diet, Johnston said. However, there may be more important differences among the diet types that go beyond their effectiveness for weight loss.
"We didn't look at other health outcomes, such as blood sugar and so forth," Johnston said. "We are hoping to look at that as our next question."
Studies have suggested that low-fat diets and low-carb diets could have different effects on blood sugar, blood pressure and cholesterol, but those findings haven't been conclusive. One new study, published today in the Annals of Internal Medicine, found that people on low-carb diets lost more body fat and showed reduced risk factors for heart disease compared with people who followed low-fat diets.
Although this may suggest a low-carb diet is the healthier choice of the two, making health-care decisions based on a single study can result in errors, Johnston said. "We need to take all the evidence together," he said.
Balance is key
The new findings bolster evidence that it matters less what particular diet composition people follow and more whether a person sticks with that diet, said Linda Van Horn, a professor of preventive medicine at Northwestern University Feinberg School of Medicine in Chicago, who wrote an editorial about the new study.
"The bottom line in weight loss is that you have to eat less calories than you need in order to drive a change in your weight, so whatever diet that's going to help a person accomplish that is the one that they might want to follow," Van Horn said.
However, weight loss diets that focus on certain food groups and eliminate others can be unhealthy in the long run.
"Find a diet you like, stick to it, but more importantly, find a diet you like that is also meeting all of your nutrient needs," Van Horn said. "There are important nutrients found in all of the food groups, and all of them contribute to your health. So the idea of consuming only foods that are high in protein or low in carbohydrates might mean that you are avoiding certain foods, especially fruits vegetables and whole grains that have a wealth of good nutrition."