Study: Food quality, not carb or fat count, is key to heart health

Food quality trumps carb or fat count for heart health

The type of food you eat on a low-carb or low-fat diet matters more for your heart than simply cutting those macronutrients. A new study in the Journal of the American College of Cardiology found that diets emphasizing wholesome, nutrient-dense foods were linked to a lower risk of coronary heart disease (CHD).

Versions of those same diets built around refined carbs and animal products were tied to a higher CHD risk. The research is one of the largest and most detailed investigations into how diet quality affects long-term heart health.

Study tracks nearly 200,000 people for decades

Researchers analyzed data from 198,473 participants across three major U.S. cohort studies, tracking them for over 5.2 million person-years. During that time, 20,033 cases of CHD were recorded.

Dietary habits were assessed using repeated food frequency questionnaires. The team then created scoring systems to separate healthier and less healthy versions of low-carbohydrate and low-fat diets based on food types and nutrient quality.

What makes a "healthy" version of these diets

"Our findings highlighted that it's not simply about cutting carbs or fat, but it's about the quality of foods people choose to construct those diets," said lead author Zhiyuan Wu, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health.

He noted that past studies on these diets showed mixed findings, likely because people follow them in very different ways. Some prioritize vegetables and whole grains, while others rely on processed foods.

The analysis revealed clear patterns. Healthier low-carb and low-fat diets shared key characteristics:

• High intake of plant-based proteins, healthy fats, and whole grains
• Low intake of refined carbohydrates, saturated fats, and processed meats
• Better scores on measures of diet quality like the Alternate Healthy Eating Index

Unhealthy versions show clear risks

In contrast, unhealthy versions of both diet types were associated with increased CHD risk. These diets were characterized by:

• High intake of animal-based proteins and fats
• High intake of refined carbohydrates
• Lower overall diet quality scores

Participants following unhealthy low-carb diets had the highest observed risk. The study also analyzed metabolomic data, finding that healthier diets were linked to favorable profiles in blood metabolites related to inflammation and insulin resistance.

Implications move beyond diet wars

"These results suggest that healthy low-carbohydrate and low-fat diets may share common biological pathways that improve cardiovascular health," Wu said. He emphasized that focusing on overall diet quality offers flexibility for people to choose eating patterns aligned with their preferences.

The researchers noted several limitations. The findings may not apply to extreme diets like ketogenic plans, and dietary data was self-reported. Participants were also health professionals, who may have greater health awareness than the general public.

Still, the core message is clear. "The findings show that what matters most for heart health is the quality of the foods people eat," said JACC Editor-in-Chief Harlan M. Krumholz. "Whether a diet is lower in carbohydrates or fat, emphasizing plant-based foods, whole grains, and healthy fats is associated with better cardiovascular outcomes."