With the new year in full swing and plenty of people trying out different diets to feel better about their health, you may be wondering how exactly to track the “rules” of the diets. Low-carb and low-fat are two popular methods of dieting, focusing more on the amount of carbs or fat in what you’re eating than the food itself.

As it turns out, the quality of the food may be more important than the quantity. New research from the Harvard T.H. Chan School of Public Health found that low-carb and low-fat diets were only effective if the food was healthy as well.

Researchers studied 37,000 adults over the age of 20, examining data from the US National Health and Nutrition Examination Survey. Diets were analyzed based on levels of fat, protein, and carbohydrate consumption.

When comparing low-carb diets with high-carb diets in terms of life expectancy, scientists didn’t notice any strong differences. When they compared the quality of the carbohydrates, however, there was a big difference in mortality rates. According to the research, people who practiced low-carb diets but also filled their plates with “whole grains, non-starchy vegetables, whole fruits, and nuts” had a much lower risk of premature death as compared to other participants. In fact, people who practiced low-carb or low-fat diets but consumed low-quality food actually had higher rates of premature death.

While we know it’s important to watch exactly what we’re putting in our bodies, this study proves that when implemented correctly and nutritiously, a low-carb diet can boost longevity.

Just because someone is on a low-carb diet, however, does not mean that they are necessarily being healthy. According to the study, “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 brings into conversation the important aspect of certain diets like these: The sources of carbs and fats aren’t well-enough defined to thrive off of only counting carbs or calories. Head researcher Zhilei Shan, Ph.D., says, “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.”

This research may be especially relevant to those just starting on the keto diet—while limiting your daily carb intake may keep you in ketosis, it’s also essential to make sure you’re utilizing those few carbs to get nutrients—things like fruits, veggies, nuts, and grains.