The review of current research found that people on Atkins-style low carbohydrate diets tend to lose more weight in the first six months. But they said weight loss for both groups is similar after 12 months.
In addition, they said more research on the long-term effects on health of the low-carbohydrate regime promoted by Atkins was lacking.
"There is no clear evidence that Atkins-style diets are better than any others for helping people stay slim, and despite the popularity and apparent success of the Atkins diet, evidence in support of its use lags behind," write Professor Arne Astrup and colleagues at RVA University in Copenhagen.
The Atkins diet books have sold over 45 million copies over 40 years. Low-carbohydrate diets have been around since the 1860s, but the Atkins books are the most successful to date, perhaps a result of today's obesity epidemic and the range of foods marketed by the Atkins company and others.
While the diet's most substantial following is in the US, a recent survey of major European and US food companies by Reuters Business Insight found a quarter were formulating new products to meet the criteria of the diet. Ad-libitum consumption of butter, fatty meat, and high-fat dairy products are advocated, while carbohydrate intake is restricted to under 30g a day.
The Danish researchers said however that people on Atkins may lose weight because they are bored eating the same foods and not because of the nutritional components of the diet.
The team looked at three studies carried out in the past two years comparing the effects of a low-fat diet with a low-carb one on obese volunteers. All showed the low-carb diet to double the weight loss seen in those with a low-fat intake after six months. But after a year, there was little difference between both groups.
Professor Astrup, who also works as a medical adviser for Weight Watchers, and colleagues write: "Weight loss on the low-carbohydrate diet is probably caused by a combination of restriction of food choices and the enhanced satiety produced by the high protein content."
The study did however show greater improvements in some heart disease risk factors, such as cholesterol levels, in the low-carb diet. But the researchers warned that cutting out fruit, vegetables, whole-grain bread and cereals may actually increase the risk of heart disease and cancer and are to blame for the constipation and headaches reported by Atkins dieters.
"Future studies should focus more on the foods making up the diets and report more markers of nutritional status," they added.
"Although there is no solid evidence to support advising against the short-term use of low-carbohydrate diets…future research that assesses a broader spectrum of risk factors of thrombo-atherosclerotic disease might eventually warn against such diets," continue the researchers in the Rapid Review article.
They also said that the evidence for people who want to keep weight off remains more substantial for a reduced-fat, reduced-calorie diet.
It is thought that one-third of western European consumers are currently overweight and by 2006 this will increase to almost half. The debate continues to rage over whether the Atkins diet will become more than a fad for the food industry but the latest research suggests that further studies may be required for it to maintain momentum.