A new study presented at NUTRITION 2025, the American Society for Nutrition’s annual meeting in Orlando, Florida, suggests that food quality matters more for heart health than simply cutting carbs or fat. The research highlights a shift toward more personalized and nuanced dietary advice for preventing coronary heart disease.
Long-Term Study of Nearly 200,000 Participants
Researchers from the Harvard T.H. Chan School of Public Health tracked nearly 200,000 men and women over 25 years. Participants came from three major U.S. cohort studies: the Health Professionals Follow-up Study, the Nurses’ Health Study, and the Nurses’ Health Study II.
Using detailed food frequency questionnaires, the team rated the healthiness of foods within low-carb and low-fat diets. They linked these ratings to heart disease outcomes over the long term.
High-Quality Diets Cut Heart Disease Risk by 15%
The study found that low-carb and low-fat diets emphasizing high-quality foods—such as whole grains, fruits, vegetables, nuts, and legumes—were associated with about a 15% lower risk of coronary heart disease.
In contrast, diets low in carbs or fat but heavy in refined grains, added sugars, processed meats, and animal fats carried a higher risk of heart disease.
Dr. Zhiyuan Wu, the study’s lead author and a postdoctoral fellow in Harvard’s Department of Nutrition, said, “The healthier versions of these diets—those rich in plant foods and whole grains—are linked to better heart health and improved metabolic function. Unhealthy low-carb and low-fat diets show the opposite effect.”
Blood Metabolites Reveal Metabolic Effects
To understand how diet quality affects the body, researchers measured blood metabolites in over 10,000 participants. These biomarkers showed that healthy and unhealthy low-carb and low-fat diets each had distinct impacts on plasma lipid species and other metabolic markers.
These findings underscore the importance of diet quality in metabolic regulation and cardiovascular health.
Animal-Based vs. Plant-Based Low-Carb Diets
The study also distinguished between types of low-carb diets:
Animal-Based Low-Carb Diets: High in saturated fat and protein from animal products. These diets were linked to a higher risk of heart disease.
Plant-Based Low-Carb Diets: Centered on vegetables and plant proteins. These diets showed more favorable effects on heart health.
Similarly, unhealthy low-fat diets high in refined carbs and sugars increased risk, while healthy low-fat diets focusing on whole foods reduced risk.
Expert Commentary on Food Quality
Registered dietitian Yaa Boakye compared food quality to a rubric for the body. “It’s not enough to just check ‘low carb’ or ‘low fat’—we need to examine what the food actually contains: fiber, added sugars, sodium, micronutrients, and anti-inflammatory compounds,” she said.
Boakye noted that carbs can range from refined white rolls to fiber-rich lentils, and fats can range from trans fats to cold-pressed olive oil. Focusing on food quality ensures important nutrients—like fiber, vitamins, and antioxidants—are not overlooked.
How to Eat a Heart-Healthy Diet
Registered dietitian Ayanna Smart recommends a balanced, high-quality diet to support heart health. Her simple plate pattern divides your plate into three parts:
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Half fruits and vegetables
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Quarter lean protein (meat, fish, beans, or low-fat cheese)
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Quarter whole grains
This approach helps manage blood sugar, maintain blood pressure, control weight, and improve cholesterol levels. Smart says that fiber from fruits, vegetables, and whole grains keeps you full and protects your heart.
She added that lean proteins and nuts supply healthy fats that help lower “bad” LDL cholesterol. Reducing highly processed foods also cuts sodium, saturated fats, and excess calories.
“Limiting processed foods can help control blood pressure, protect cardiovascular health, reduce atherosclerosis risk, and prevent weight gain,” Smart said.
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