Diet Quality Trumps Low-Carb vs Low-Fat Debate for Heart Health, 30-Year Study Finds
A 30-year study of nearly 200,000 adults found that diet quality matters more than macronutrient ratios for heart health, with both healthy low-carb and low-fat diets reducing coronary heart disease risk equally.
A massive study following more than 198,000 U.S. adults for over 30 years has found that both low-carbohydrate and low-fat diets can significantly reduce the risk of coronary heart disease, provided they are built from healthy, whole-food sources. The findings, published Feb. 11 in the Journal of the American College of Cardiology, suggest that diet quality matters more than composition when it comes to reducing coronary heart disease risk.
The researchers examined data from around 200,000 people in 3 cohort studies with more than 30 years of follow-up: the Nurses' Health Study, the Nurses' Health Study II, and the Health Professionals Follow-Up Study. After enrollment, participants received mail questionnaires every 2 to 4 years that inquired about diet, lifestyle factors, medication use, and chronic disease diagnoses.
Based on responses to food frequency questionnaires, the researchers indexed "healthy" and "unhealthy" low-carb and low-fat diets. They defined unhealthy diets as those favoring animal proteins and fats, potatoes, refined grains, and added sugars. Healthy diets were defined as those inclined toward vegetable proteins and fats, nonstarchy vegetables, whole fruits, legumes, and whole grains.
About 20,000 cases of coronary heart disease occurred over the follow-up period. The healthy versions of both low-carb and low-fat diets were associated with similarly lower relative risks of coronary heart disease, whereas the unhealthy versions were linked with similarly higher risks. The study showed that the "unhealthy" low carb dieters had a 14% greater risk of CHD, and the "healthy" low carb dieters had a 15% lower risk of CHD.
Healthy diets were also linked with improved lipid and inflammatory biomarkers, including lower triglyceride, higher high-density lipoprotein cholesterol, and lower high-sensitivity C-reactive protein levels.
An analysis of metabolites in plasma from a subset of participants supported the findings. Whether eating patterns were low carb or low fat, diets with healthy macronutrient sources were associated with favorable metabolomic profiles, such as higher levels of indolepropionic acid and lower levels of valine, whereas the opposite was true for unhealthy versions.
Healthy versions of both diets, which emphasized plant-based foods, whole grains and unsaturated fats, were linked to lower triglycerides (fats in the blood), higher HDL "good" cholesterol, and reduced levels of inflammation. In contrast, diets high in refined carbohydrates (like white bread and sugary snacks) and animal-based fats showed unfavorable biomarker profiles that contribute to clogged arteries.
A postdoctoral research fellow at Harvard T.H. Chan School of Public Health and lead author of the study noted that past studies often produced conflicting results because they didn't distinguish between a "healthy" low-carb diet (full of vegetables and nuts) and an "unhealthy" one (heavy on bacon and butter). The 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.
The study combined dietary data, metabolomic data, as well as clinical risk biomarker data and disease outcome data, which allowed researchers to directly link what people eat and how the human body responds to this diet and the risk of developing coronary heart disease.