A major new study that followed nearly 200,000 people for several decades has found that when it comes to heart health, the quality of the food you eat matters just as much—if not more—than whether you follow a low-carbohydrate or low-fat diet.
The study suggests that focusing on healthy, high-quality foods is the most important factor in protecting the heart.
For many years, low-carb and low-fat diets have been promoted for weight control and better blood sugar or cholesterol levels. But doctors and scientists have continued to ask whether these diets actually lower the risk of heart disease.
To explore this, researchers from the Harvard T.H. Chan School of Public Health looked at the long-term diets and health outcomes of people enrolled in three large studies: the Health Professionals Follow-Up Study, the Nurses’ Health Study, and the Nurses’ Health Study II. Together, these studies tracked about 200,000 men and women for up to 30 years.
The researchers asked participants to regularly complete detailed food questionnaires. Then they scored how healthy their diets were—based on the types of carbohydrates, fats, and proteins they ate.
Foods like fruits, vegetables, whole grains, nuts, and legumes were considered healthy. On the other hand, refined grains, sugary foods, and animal-based saturated fats were classified as unhealthy.
The results were clear: people who followed either a low-carb or low-fat diet made up of healthy, plant-based, and minimally processed foods had a lower risk of heart disease.
Their risk of developing coronary heart disease dropped by about 15%. But people who followed low-carb or low-fat diets that were full of unhealthy, processed foods saw an increased risk of heart disease.
To better understand how these diets affected the body, the researchers also looked at blood samples from more than 10,000 participants. They studied hundreds of different blood metabolites, which are small molecules that reflect how the body processes nutrients. This helped them see how diet quality influences the body’s metabolism.
The researchers concluded that it’s not enough to simply reduce carbs or fats. What matters more is the quality of the foods that supply these nutrients.
For example, a low-carb diet based on vegetables, beans, nuts, and whole grains is very different from one based on processed meats and refined grains. The same goes for low-fat diets—eating healthy fats from plants is very different from eating lots of sugary, fat-free snacks.
Lead researcher Dr. Zhiyuan Wu said that the key takeaway is to improve the quality of your food. Regardless of whether you eat fewer carbs or fats, focusing on whole and unprocessed foods can significantly lower your risk of heart disease.
For people wanting to eat healthier, the advice is simple: eat more fruits, vegetables, whole grains, nuts, and legumes. Cut back on processed foods, refined grains, sugary drinks, and snacks with added sugar. It also helps to read food labels and avoid foods with hidden sugars or low-quality ingredients.
The researchers plan to continue studying how diet quality affects other diseases like type 2 diabetes and cancer. They also hope to understand how genetics and lifestyle choices interact with diet to affect health. This could help doctors give more personalized advice in the future.
This long-term study highlights the importance of not just following a diet trend but paying attention to what’s on your plate. High-quality food choices—whether part of a low-fat or low-carb diet—are essential for a healthy heart.
If you care about heart health, please read studies about how eating eggs can help reduce heart disease risk, and herbal supplements could harm your heart rhythm.
For more health information, please see recent studies about how drinking milk affects risks of heart disease and cancer, and results showing strawberries could help prevent Alzheimer’s disease.
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