A large-scale, decades-long study involving nearly 200,000 men and women has found that the quality of food, rather than the quantity of carbohydrates or fats, is the primary determinant of heart health. The research, conducted by Harvard University scientists and recently highlighted by Dutch media, challenges conventional dietary wisdom that often focuses on restricting specific macronutrients.
The study, which tracked participants for approximately 30 years, revealed that both low-carbohydrate and low-fat diets can be beneficial for the heart, provided they emphasize healthy food choices. Diets heavily reliant on processed foods, high levels of animal protein, or saturated fats, and lacking in fruits, vegetables, and whole grains, offered less protection against cardiovascular disease, even when categorized as “low carb” or “low fat.”
“Simply focusing on nutrients, without looking at the quality of food, may not lead to health benefits,” said Zhiyuan Wu, an epidemiologist who led the research. The findings, published February 11, 2026, in the Journal of the American College of Cardiology, suggest that the overall composition of a diet is more crucial than adhering to strict macronutrient ratios.
Participants who consumed a varied and healthy diet, rich in macronutrients and prioritizing plant-based foods, exhibited higher levels of high-density lipoprotein (HDL) cholesterol – often referred to as “good” cholesterol – in their blood. They also demonstrated lower levels of harmful fats and inflammatory markers. Significantly, these individuals experienced a substantially reduced risk of developing coronary heart disease, the leading cause of heart attacks.
According to Wu, the results indicate that healthy low-carbohydrate and low-fat diets likely activate overlapping biological mechanisms that support cardiovascular health. “By focusing on the overall quality of the diet, people gain more flexibility to choose an eating pattern that suits them and protects their heart,” he stated.
The study’s findings align with a growing body of evidence emphasizing the benefits of minimally processed foods and increased consumption of whole grains, vegetables, and healthy fats, such as those found in nuts and olive oil. Restrictive diets that primarily focus on counting calories, carbohydrates, or fats appear to be less important than previously thought. A related Harvard study, published in 2018, found that a moderate carbohydrate intake (50% to 55% of daily calories) was associated with lower mortality rates over a 25-year period.
Yale cardiologist Harlan Krumholz described the recent study as a potential turning point in the dietary debate. “What really matters for the heart is the quality of the food,” Krumholz said. “Whether a diet is lower in carbohydrates or lower in fat, the emphasis on plant-based foods, whole grains, and good fats is associated with healthier hearts and blood vessels.”
The study relied on self-reported dietary data from healthcare professionals, which may introduce a degree of bias, as participants may have reported healthier lifestyles and had better access to healthcare than the general population. However, the study’s large scale and duration – encompassing over 5.2 million person-years of data – provide substantial weight to its conclusions.
A separate Harvard study from December 2023 indicated that low-carb diets emphasizing plant-based proteins and healthy fats resulted in slower long-term weight gain compared to those primarily composed of meat and unhealthy fats.
