A long-running analysis of nearly 200,000 U.S. health professionals found that both low-carbohydrate and low-fat eating patterns were associated with lower coronary heart disease risk when they emphasized high-quality foods such as whole grains, plant-based sources, and unsaturated fats. Versions of these diets built around refined carbohydrates and animal-based fats and proteins were associated with higher risk, according to a study published in the Journal of the American College of Cardiology (JACC).
Researchers analyzed data from 198,473 participants across three cohorts: the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow-up Study. Participants were followed for 5,248,916 person-years, during which 20,033 cases of coronary heart disease (CHD) were documented.
Dietary intake was assessed using food frequency questionnaires, and the team constructed multiple scoring systems to distinguish between different types of low-carbohydrate and low-fat diets based on the sources and quality of macronutrients—such as plant-based versus animal-based foods and whole grains versus refined carbohydrates.
In the analysis, healthier versions of both low-carbohydrate and low-fat diets—patterns higher in plant-based foods, whole grains, and unsaturated fats—were associated with lower CHD risk. In contrast, less healthy versions characterized by refined carbohydrates and higher intakes of animal-based fats and proteins were associated with higher CHD risk.
“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 Zhiyuan Wu, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health and the study’s lead author.
The study also linked higher-quality diet patterns to more favorable cardiometabolic profiles, including lower triglyceride levels, higher HDL cholesterol, and lower levels of high-sensitivity C-reactive protein, a marker of inflammation. The researchers reported that metabolomic analyses produced biomarker patterns consistent with the healthier diet scores.
Wu said the results may help explain why earlier research on low-carbohydrate and low-fat diets has produced mixed findings, noting that people can follow these eating patterns in very different ways, ranging from diets centered on vegetables and whole grains to those relying heavily on refined grains, processed foods, and animal fats.
The authors cautioned that the results are based on self-reported diet data, which can introduce measurement error, and that the cohorts consist largely of health professionals, which may limit how well the findings generalize to the broader population. They also said the findings should be interpreted within the ranges of macronutrient intake observed in the study and may not apply to more extreme dietary approaches such as ketogenic diets.
“These results suggest that healthy low-carbohydrate and low-fat diets may share common biological pathways that improve cardiovascular health,” Wu added.
Harlan M. Krumholz, MD, editor-in-chief of JACC, said the findings reinforce a broader message: “The findings show that what matters most for heart health is the quality of the foods people eat. Whether a diet is lower in carbohydrates or fat, emphasizing plant-based foods, whole grains, and healthy fats is associated with better cardiovascular outcomes.”
