A study from the Harvard T.H. Chan School of Public Health, published in the Journal of the American College of Cardiology, shows that what truly protects the heart is not the amount of carbohydrates or fats we consume, but the quality of the foods that make up the diet.
The researchers conclude that low-carb or low-fat diets only reduce the risk of coronary disease when they are based on healthy foods, primarily plant-based and with unsaturated fats. On the other hand, versions that include ultra-processed products or unhealthy animal sources can even increase heart risk.
What “quality” in the diet means
The study differentiates between healthy and unhealthy versions of low-carb and low-fat diets:
- Healthy: rich in whole grains, fruits, vegetables, legumes, nuts, seeds, and olive oil.
- Unhealthy: based on refined carbohydrates, saturated fats, and low-quality animal proteins.
According to Zhiyuan Wu, lead author, “it’s not just about cutting carbs or fats, but about the quality of the foods we choose to build those diets.”
Study methodology
The analysis included data from nearly 200,000 health professionals in the United States, followed for over 30 years. Their diets, metabolic profiles, and risk of coronary disease were evaluated, along with blood biomarkers such as cholesterol and triglycerides.
The results showed that healthy diets were associated with a 15% lower risk of coronary disease, higher levels of HDL (“good”) cholesterol, and lower levels of triglycerides.
Implications for public health
The study helps to demystify the idea that reducing fats or carbohydrates is enough to care for the heart. What matters is what type of fats and carbohydrates are consumed. For example:
- Unsaturated fats (olive oil, nuts, seeds) are protective.
- Whole carbohydrates (whole grains, legumes) reduce cardiovascular risk.
- Ultra-processed foods and low-quality animal fats increase the risk.
Researcher Qi Sun, co-author of the study, emphasized: “Promoting an overall healthy eating pattern, rather than strict macronutrient restriction, should be the central strategy for primary prevention of heart diseases.”
Harvard’s research confirms that diet quality is more important than the quantity of macronutrients. To protect the heart, it is not enough to follow low-carb or low-fat diets: it is essential to prioritize plant-based, whole foods and unsaturated fats, avoiding ultra-processed and unhealthy animal products.
