The long-standing debate over the optimal macronutrient composition of a healthy diet – whether to prioritize low-carbohydrate or low-fat approaches – may be shifting. New research suggests that the quality of those carbohydrates and fats, rather than their quantity, is the key determinant of heart health. A study published , in the Journal of the American College of Cardiology (JACC), found that both low-carbohydrate and low-fat diets could be associated with a lower risk of coronary heart disease (CHD) when built around high-quality, plant-based foods. Conversely, the same dietary patterns rich in refined carbohydrates and animal products were linked to a higher risk.
For decades, Americans have been presented with conflicting dietary advice, often centered on manipulating carbohydrate and fat intake. This new research, analyzing data from nearly 200,000 participants across three large-scale studies – the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow-up Study – offers a more nuanced perspective. Researchers followed participants for a combined total of over 5.2 million person-years, documenting over 20,000 cases of CHD.
The study categorized diets not simply as “low-carb” or “low-fat,” but as “healthy” or “unhealthy” versions of each. Healthy low-carbohydrate diets emphasized plant-based foods, whole grains, and unsaturated fats. Healthy low-fat diets followed a similar pattern. Unhealthy versions, however, were characterized by high intakes of refined carbohydrates, animal-based fats, and proteins.
“Our findings help debunk the myth that simply modulating carbohydrate or fat intake is inherently beneficial, and clearly demonstrate that the quality of foods constructing low-carbohydrate and low-fat diets is what’s most important to protect heart health,” explained Zhiyuan Wu, PhD, the study’s first author and a postdoctoral research fellow in the Department of Nutrition at Harvard T.H. Chan School of Public Health.
The researchers found a significantly lower risk of CHD among those adhering to the healthy versions of both diet patterns. In contrast, those consuming unhealthy low-carb or low-fat diets experienced a higher risk of CHD. Further analysis revealed that the healthy diet patterns were also linked to more favorable metabolic profiles, including lower triglycerides, higher levels of high-density lipoprotein (HDL) cholesterol (often referred to as “good” cholesterol), and reduced levels of inflammation.
These findings align with a growing body of evidence emphasizing the importance of food quality over strict macronutrient ratios. As Alice Lichtenstein, a nutrition expert at Tufts University who was not involved in the study, noted, “the quality of the foods, and not so much if a diet is high or low in a certain macronutrient, is what’s important.”
The study’s results also resonate with the recently updated Dietary Guidelines for Americans, which increasingly emphasize the consumption of real, whole foods and limiting ultra-processed products. These guidelines, while sparking some debate regarding recommendations on whole-fat dairy and animal protein, generally advocate for dietary patterns rich in fruits, vegetables, and whole grains.
The research team utilized food frequency questionnaires to assess dietary patterns and created indices to differentiate between healthy and unhealthy versions of low-carbohydrate and low-fat diets. Metabolomic analyses – the study of small molecules within the body – provided further support for the findings, revealing biomarker profiles associated with the healthy dietary patterns.
It’s important to note that the study did not examine extremely restrictive diets, such as the ketogenic diet. The dietary patterns analyzed represented more moderate approaches commonly observed in the study population. Wu clarified that the observed risk reduction was comparable across the healthy versions of both diet types, even though they emphasized different macronutrients.
This research doesn’t necessarily advocate for one diet over another, but rather underscores the critical importance of food choices within any dietary framework. Whether someone chooses to follow a low-carbohydrate or low-fat approach, prioritizing plant-based foods, whole grains, and healthy fats appears to be the most effective strategy for protecting heart health. The emphasis, according to Wu, should be on “focusing on the overall quality of the diet,” allowing individuals to choose foods they enjoy while still prioritizing cardiovascular well-being.
The findings suggest a shift in focus for both public health recommendations and individual dietary choices. Instead of fixating on counting carbohydrates or restricting fats, the emphasis should be on building a diet around nutrient-dense, minimally processed foods. This approach, supported by the latest research, offers a more sustainable and effective path towards a healthier heart.
