I have mixed feelings about low-carb diets. On one hand, many patients who can’t stick to other diets find success with them.

But I don’t recommend them for people who have already been diagnosed with heart disease because they include too much saturated fat.

An article in Lancet Public Health suggests that while eating too many carbohydrates may shorten your life span, so might eating too few. The study defined a low-carb diet as one in which 40 percent of calories are derived from carbohydrates; high-carb diets were more than 70 percent of calories.

The sweet spot, they say, appears to be 50 to 55 percent of calories from carbs. The study also found that low-carb diets that replace carbohydrates with proteins and fats from plant sources were associated with lower risk of mortality compared to those that replace carbohydrates with proteins and fat from animal sources.