There are several studies to back up both claims, but a new review out of Harvard found that—as the age-old saying goes—quality matters more than quantity. The study, published in JAMA Internal Medicine, found that eating more of a certain macronutrient didn’t raise someone’s risk of death, but eating unhealthy versions of them did.
Specifically, the researchers found that eating a “healthy” low-carb diet—one filled with mostly plant proteins and unsaturated fats—reduced people’s all-cause mortality risk by 9 percent. On the other hand, diets high in animal proteins and saturated fats were associated with a 7 percent increase of mortality risk.
If you’re following a low-fat diet, be sure to stick to whole grains and non-starchy vegetables, which reduces your all-cause mortality risk by 11 percent. Eating low-quality carbs, like white bread and sugary snacks, increases your all-cause death risk by 6 percent, the researchers found.
“The debate on the health consequences of low-fat or low-carbohydrate diets is largely moot unless the food sources of fats or carbohydrates are clearly defined,” Zhilei Shan, a postdoctoral researcher in Harvard’s Department of Nutrition and lead author of the study, said in a release.
Close to 40,000 U.S. adults were examined from 1999 to 2014 for the study, with periodic check-ins conducted by the researchers. While some of the adults were on low-carb or low-fat diets, the eating regimens themselves did not increase or decrease their mortality risk.
“These findings suggest that the associations of low-carbohydrate and low-fat diets with mortality may depend on the quality and food sources of macronutrients,” the study’s authors wrote.
This study doesn’t necessarily disprove the reported benefits of low-carb or low-fat diets, but it does mean that cooking up a plate of bacon and eggs and calling it “keto” is probably not the best idea.