Low-carb diets such as Atkins may eventually cause a heart attack if people stay on them for too long.
The diet - which involves eating almost no carbohydrates, but large amounts of fat and protein - could be causing damage to the arteries, eventually leading to a heart attack or stroke.
Researchers say the damage could be done by following the diet for just 12 weeks, although their findings are based on tests of mice and so they may not necessarily be replicated in humans.
They noted that the mice suffered from atherosclerosis, a build-up of plaque in the arteries, while they were on the diet, and they also lost the ability to form new blood vessels.
(Source: Proceedings of the National Academy of Sciences, 2009; doi: 10.1073/pnas.0907995106).