If you’re concerned about cardiac health and unsure whether a low-fat or low-carbohydrate diet is better, new research offers reassurance: healthy versions of either dietary approach are linked to a lower risk of heart disease.
A long-term observational study, involving nearly 200,000 adults, found that both low-fat and low-carb diets rich in plant-based foods, whole grains, and unsaturated fats were associated with a reduced risk of coronary heart disease. Coronary heart disease develops when plaque builds up inside the heart’s arteries, hindering blood flow and potentially leading to chest pain, heart attack, or cardiac arrest.
Conversely, diets high in refined carbohydrates and animal-based fats and proteins were associated with a higher risk of the condition, according to findings published , in the Journal of the American College of Cardiology.
“It’s the quality of your diet that matters,” not simply the amount of fat or carbohydrates consumed, explained Dr. Qi Sun, a specialist in nutrition and epidemiology at the Harvard T.H. Chan School of Public Health, and lead author of the study.
While the study focused specifically on coronary heart disease, Dr. Sun noted that the findings may not necessarily apply to other cardiovascular conditions like heart failure or arrhythmias.
Researchers analyzed the self-reported eating habits of health professionals participating in three long-running cohort studies initiated in the 1970s and 1980s: the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-up Study. The Nurses’ Health Study originally enrolled women aged 30 to 55, while the Nurses’ Health Study II included somewhat younger women. The Health Professionals Follow-up Study tracked male health professionals between the ages of 40 and 75.
After excluding participants who reported a history of diabetes, cardiovascular disease, or cancer at the start of the studies, the final study population comprised 198,473 individuals.
Participants provided dietary information every two to four years through questionnaires. Researchers categorized low-fat and low-carb diets into five groups – total, healthy, unhealthy, animal-based, and vegetable-based – and assessed adherence to each diet based on reported food intake.
Over more than 30 years of follow-up, 20,033 participants developed confirmed coronary heart disease.
Among those following a healthy low-carb diet, individuals with the highest adherence demonstrated a 15% lower risk of coronary heart disease compared to those with the lowest adherence. A similar benefit was observed with a healthy low-fat diet, showing a 13% risk reduction among those who adhered most closely.
A healthy low-carb or low-fat diet, according to the researchers, emphasizes foods like whole grains, fruits (excluding juice), vegetables (excluding potatoes for low-carb diets), and plant-based proteins and fats (with reduced fat intake in the low-fat approach).
“Those are relatively large risk reductions” for a lifestyle change, said Kristina Petersen, an associate professor of nutritional science at Penn State, who was not involved in the study.
Conversely, participants whose low-carb diets were classified as the least healthy had a 14% increased risk of developing coronary heart disease compared to those with the most diligent adherence to an unhealthy low-carb diet. The increased risk associated with the least healthy low-fat diet was 12%.
Unhealthy diets were defined as those relying heavily on refined grains and animal sources of protein and fat.
Dr. Clyde Yancy, chief of cardiology at Northwestern University’s Feinberg School of Medicine, praised the study’s strengths, citing its large size, long duration, and detailed analysis of different low-fat and low-carb diet categories.
The study’s methodology extended beyond self-reported questionnaires. Researchers analyzed blood samples from over 11,000 participants, examining metabolites – small molecules like amino acids, cholesterol, and triglycerides – associated with both positive and negative health outcomes, including coronary heart disease. This analysis confirmed the study’s findings, demonstrating that individuals with healthier diets exhibited a favorable metabolite profile and a significantly reduced risk of heart disease, while those with unhealthier diets showed the opposite pattern.
“The strength of this approach is that metabolites are objective measures and ‘cannot lie,’ and so give greater confidence in the study’s findings,” Dr. Sun explained.
Dr. Dariush Mozaffarian, a cardiologist and director of the Food is Medicine Institute at Tufts University, who was not part of the study, echoed these sentiments, stating that the study “confirms what we’ve learned over the last 20 years.”
He emphasized that focusing on the quality of foods, rather than solely on fat, carbohydrates, or protein, is key to reducing heart disease risk. Quality, he and Petersen agreed, means prioritizing nutrient-dense foods like fruits, vegetables, whole grains, nuts, and legumes, while limiting foods high in added sugar, saturated fat, and salt.
The study did have some limitations. While researchers accounted for factors beyond diet that could influence heart health – such as physical activity, smoking status, family history, and body mass index – they acknowledged that this adjustment is not perfect. The study participants were all health professionals, a group generally more health-conscious and with better access to healthcare, which may limit the generalizability of the findings.
The study’s results align with some, but contradict others, of the recommendations from the dietary guidelines. While the guidelines encourage consumption of fresh fruits, vegetables, nuts, legumes, and whole grains, they also recommend including red meat and full-fat dairy products, which are high in saturated fats.
“In this study, we see that if you choose a low-carb diet that is heavily based on animal foods – so fatty meats and animal fats in the form of butter or tallow – then that would increase your risk of coronary heart disease,” Petersen said. Specifically, individuals who most closely adhered to an animal-based low-carb diet had a 7% increased risk of developing coronary heart disease.
Dr. Yancy concluded that combining a high-quality diet with regular exercise, avoiding smoking, and maintaining healthy blood pressure and cholesterol levels can reduce the likelihood of developing heart disease, including a heart attack, by as much as 75% or 80%.
