Following a low-carbohydrate, high-protein diet is a more effective way to lose weight than following a low fat diet, say US researchers.
Low-carbohydrate, high protein diet lead to the greatest weight loss
Two studies published in the journal Annals of Internal Medicine found weight loss was greatest when people followed an Atkins-style diet.
Cholesterol levels also seemed to improve more on a low-carb diet compared to a low-fat diet.
However, the research was funded by the Robert C Atkins Foundation.
And critics say there are still serious doubts about the long-term effect on health of adopting such diets.
In the first study, researchers at Duke University Medical Center in Durham, North Carolina, assigned 120 obese volunteers to either a low-carbohydrate, high-protein diet or a low-fat, low-cholesterol, low-calorie diet.
After six months, the people on the Atkins-style diet had lost an average of 26 pounds, compared to an average of 14 pounds in the conventional low-fat diet group.
The low-carbohydrate, high-protein diet also had a good effect on fat levels.
The Atkins dieters lost more body fat, lowered their triglyceride levels and raised their "good" HDL cholesterol levels more than the low-fat dieters.
In the second study, researchers at the Veterans Affairs Medical Center in Philadelphia followed 132 obese adults who were randomised to either low-carbohydrate or low-fat diet groups.
Again, after six months the people following the low-carbohydrate diet lost the most weight and had improved fat levels.
However, at 12 months both groups had lost similar amounts of weight.
The low fat group had continued to lose weight from six to 12 months while the average weight in the low-carbohydrate group had remained steady after six months.
Lead author of the Philadelphia study Dr Linda Stern said: "I think a low-carbohydrate diet is a good choice because much of our overeating has to do with consumption of too many carbohydrates."
But she said more research was needed to see if a low-carbohydrate diet remained safe and effective over the longer term.
In an accompanying editorial, Dr Walter Willett, from the Harvard School of Public Health in the US, said: "We can no longer dismiss very-low-carbohydrate diets."
But he added that such diets should include healthy sources of protein and fat and incorporate regular exercise.
"Patients should focus on finding ways to eat that they can maintain indefinitely rather than seeking diets that promote rapid weight loss," he said.
Dr David Haslam, chairman of the National Obesity Forum, said: "There is no doubt that if low-carbohydrate, high-protein diets are followed properly you will lose weight.
"What's always been questioned is the long term efficacy of such diets and in the short term, with weight loss, there are certain risks in certain patients - like patients with renal problems."
"There's still no long term data about the efficacy and you can't stick on that type of diet for long because it's unpalatable," he said.
Dr Haslam called for more research spanning five to six years rather than months.
He said the best diet was still a healthy, balanced diet cutting out excessive fat.
"One thing the Atkins isn't is balanced. It's not what the body expects and that's why we don't know the long term changes," he said.
Dietzmina Govindji, of the British Dietetic Association, also warned people against thinking Atkins, or other similar diets, were the best way to lose weight.
She said: "Do not be sucked in by the cabbage soup diet and other fad diets.
"The thing to remember about all these quick-fix diets is they do help you lose
weight very, very quickly but often you will put it back on very, very quickly
and they often miss out on whole food groups, so you are not getting the full
range of vitamins and minerals you need."