Eating a low-carb, high-fat diet for years doesn't raise the risk of heart disease, a long-term study suggests, easing fears that the popular Atkins diet and similar regimens might set people up for eventual heart attacks.

The study of thousands of women over two decades found that those who got lots of their carbohydrates from refined sugars and highly processed foods nearly doubled their risk of heart disease.

At the same time, those who ate a low-carb diet but got more of their protein and fat from vegetables rather than animal sources cut their heart disease risk by 30 percent on average, compared with those who ate more animal fats.

The findings came from researchers at Harvard University's schools of medicine and public health who reviewed records of 82,802 women in the ongoing Nurses' Health Study over 20 years. The women were not dieting to lose weight.

Conventional wisdom says risk of heart disease should increase for those eating the lowest-carb, highest-fat diet, said lead author Thomas Halton.

"It didn't, which was a little eye-opening," he said.

Halton said that may be because the women eating the fewest carbs were compared directly to the group eating the highest-carb, lowest-fat diet.

"Neither diet is ideal," he said. "You need to take the best of both."