The much vaunted Atkins diet and similar weight loss regimes could be bad for your health and possibly lead to memory loss.
US research on mice suggests low-carbohydrate diets high in protein and fat could also double the chances of developing atherosclerosis, a clogging up of the arteries that can lead to heart attack and stroke.
The findings showed that the diet led to an impaired ability of the body to form new blood vessels and therefore recuperate after a heart attack.
In order to determine the effects on humans, the study, published in the Proceedings of the National Academy of Sciences, tested two different diets on mice in the laboratory.
The first were on an average western diet of 43 per cent carbohydrate, 42 per cent fat and 15 per cent protein and the second on a low carbohydrate, high-protein diet of 12 per cent carbohydrate, 43 per cent fat and 45 per cent protein.
After six weeks those on the low carbohydrate diet had nearly double the clogging of the arteries (5.4 per cent) compared with the normal diet (2.2 per cent).
The difference was maintained after 12 weeks, with the mice suffering 15.3 per cent and 8.8 per cent clogging of the arteries.
A control group of mice on a high carbohydrate diet - making up 65 per cent of calories - suffered the least furring of the arteries.
The study found that the increased risk came despite normal indicators of heart disease risk, such as cholesterol, being unchanged in the animals fed the low-carb diet.
"It's very difficult to know in clinical studies how diets affect vascular health," said Professor Anthony Rosenzweig, Director of Cardiovascular Research at BIDMC.
"They tend to rely on easily measured serum markers [such as cholesterol], which have been surprisingly reassuring in individuals on low-carbohydrate/high-protein diets, who do typically lose weight.
"But our research suggests that, at least in animals, these diets could be having adverse cardiovascular effects that are not reflected in simple serum markers.
"This issue is particularly important given the growing epidemic of obesity and its adverse consequences. For now, it appears that a moderate and balanced diet, coupled with regular exercise, is probably best for most people."