Diet quality may be more important than carbs or fat for heart health

A large U.S. study found that people who followed healthier versions of low-carb and low-fat diets had lower rates of coronary heart disease. Although the two approaches differed in how much carbohydrate or fat they contained, both were linked to better outcomes when they emphasized plant foods and limited refined carbohydrates.

The results suggest there may be room for personal preference in eating style. What mattered most, researchers said, was the quality of the foods used to shape each diet, which helped separate patterns associated with lower heart disease risk from those tied to higher risk.

The Harvard-led research team published the findings in the Journal of the American College of Cardiology. It analyzed data from three long-running studies of nurses and other health professionals, involving 198,473 adults and more than 30 years of follow-up.

Participants completed food questionnaires describing what they ate. Using those responses, the researchers assigned scores based on the amount and type of carbohydrate and fat in the diet, as well as the sources of protein and other nutrients.

Someone could rank well on a lower-carbohydrate diet by eating more plant protein and unsaturated fats while cutting back on refined carbohydrates. Another person might consume a similar amount of carbohydrates but depend more on animal fats or proteins, leading to a different diet-quality score.

The same idea applied to lower-fat diets. Eating patterns that included whole grains and other plant foods appeared more favorable than diets that reduced fat but relied heavily on refined carbohydrates.

Researchers are also looking at AI-guided food swaps as a way to improve diet quality.

During follow-up, the team recorded 20,033 cases of coronary heart disease, a condition in which the arteries supplying the heart become narrowed or blocked. Healthier versions of both diet patterns were linked with lower risk, while less healthy versions were linked with higher risk.

The researchers also examined blood molecules to see whether the eating patterns lined up with other biological differences. The healthier diets were associated with lower triglycerides, higher HDL cholesterol, and reduced inflammation.

These biomarkers may help explain how diet relates to disease over time, but they do not identify which specific changes caused the differences in coronary heart disease across the groups.

Because the study observed people’s existing habits, other lifestyle or health factors may have influenced the results. The diets were self-reported, and the findings may be less directly applicable to people on very restrictive diets or to populations outside the health professions.

Within the range of diets studied, both eating styles had healthier and less healthy versions. That is why carbohydrate or fat intake alone says relatively little about what someone actually eats from day to day.

Source: Harvard T.H. Chan School of Public Health and American College of Cardiology.