People trying to lose weight may swear by specific diet plans calling for strict proportions of fat, carbs and protein, but where the calories come from may not matter as much as simply cutting back on them, according to a study.
Researchers whose results were published in the American Journal of Clinical Nutrition found there were no differences in weight loss or the reduction of fat between four diets with different proportions of fat, carbohydrates and protein.
"The major predictor for weight loss was 'adherence'. Those participants who adhered better, lost more weight than those who did not," said George Bray, at Pennington Biomedical Research Center in Baton Rouge, Louisiana, who worked on the study.
Earlier research had found that certain diets -- in particular, those with very low carbohydrates -- worked better than others, Bray told Reuters Health in an email, but there had been no consensus among scientists.
Bray and his colleagues randomly assigned several hundred overweight or obese people to one of four diets: average protein, low fat and higher carbs; high protein, low fat and higher carbs; average protein, high fat and lower carbs; or high protein, high fat and lower carbs.
Each of the diets was designed to cut 750 calories a day.
After six months and again at two years after starting the diets, researchers checked participants' weight, fat mass and lean mass.
At six months, people had lost more than 4.1 kg (9 lbs) of fat and close to 2.3 kg (5 lbs) of lean mass, but they regained some of this by the two-year mark.
People were able to maintain a weight loss of more than 3.6 kg (8 lbs) after two years. Included in this was a nearly 1.4 kg (3 lb) loss of abdominal fat, a drop of more than seven percent.
But many of the people who started in the study dropped out, and the diets of those who completed it were not exactly what had been assigned.
For example, the researchers had hoped to see two diet groups get 25 percent of their calories from protein and the other two groups get 15 percent of their calories from protein. But all four groups ended up getting about 20 percent of their calories from protein after two years.
"If you're happier doing it low fat, or happier doing it low carb, this paper says it's OK to do it either way. They were equally successful," said Christopher Gardner, a Stanford University professor uninvolved in the study.
"They did have difficulties with adherence, so that really tempers what you can conclude," he added.
In the end, he said, people should choose the diet that's easiest for them to stick with.