For heart health, food quality may matter more than cutting carbs or fat

A new study that followed almost 200,000 people for several decades has found that when it comes to heart health, the quality of food consumed matters as much as following a low-carbohydrate or low-fat diet. The results suggest that choosing healthy, high-quality foods is key to protecting the heart.

In the past two decades, low-carbohydrate and low-fat diets have been promoted for their potential health benefits, such as weight management and improved blood sugar and cholesterol levels. However, the impact of these diets on reducing heart disease risk has remained an ongoing debate.

“We found that what you eat on low-carb or low-fat diets matters just as much as the diet itself,” said Zhiyuan Wu, Ph.D., a postdoctoral fellow in the lab of Qi Sun, MD, ScD, at Harvard T.H. Chan School of Public Health.

“Healthy versions of these diets—those rich in plant-based foods and whole grains—were linked to better heart health outcomes and improved metabolic function. In contrast, low-carb and low-fat diets emphasizing unhealthy foods were associated with a higher risk of heart disease.”

Wu will present the findings at NUTRITION 2025, the flagship annual meeting of the American Society for Nutrition held May 31–June 3 in Orlando.

The study included 43,430 men in the Health Professionals Follow-Up Study (1986–2016), 64,164 women in the Nurses’ Health Study (1986–2018) and 92,189 women in the Nurses’ Health Study II (1991–2019). The researchers followed the nearly 200,000 study participants for several decades, tracking their dietary habits and whether they developed heart disease.

Based on information from detailed questionnaires completed by the study participants, the researchers assigned scores indicating how healthy or unhealthy their food choices were within low-carbohydrate and low-fat diets.

The researchers classified carbohydrates, fats and proteins from foods such as whole grains, fruits, vegetables, nuts and legumes as high-quality nutrients, or healthy, while carbohydrates from potatoes and refined grains as well as saturated fats and proteins from animal-based foods were categorized as low-quality, or unhealthy.

For more than 10,000 of the study participants, the researchers also measured hundreds of blood metabolites to assess how diet quality influenced their metabolic regulation. “This approach allowed us to better understand the biological effects of these diets and strengthened our findings,” said Wu.

The analysis showed that study participants who followed a healthy low-carbohydrate or low-fat diet had a lower risk of developing coronary heart disease, while those on unhealthy versions saw an increased risk. These healthy diet patterns, whether low-carbohydrate or low-fat diets, lowered the risk of developing heart disease by about 15%.

“Our findings suggest that improving food quality is crucial for improving heart health,” said Wu. “Regardless of whether someone follows a low-carbohydrate or low-fat diet, emphasizing whole, minimally processed and plant-based foods and limiting refined grain, sugar and animal foods, can significantly reduce the risk of coronary heart disease.”

For those looking to improve their diet, the researchers suggest focusing on adding more whole grains, fruits, vegetables, nuts and legumes while cutting back on processed meats, refined carbs and sugary foods. They note that it is also important to check food labels and be mindful of added low-quality ingredients, such as added sugars in juices and processed snacks.

Moving forward, the researchers aim to explore additional factors that may influence the relationship between diet quality and heart health. For example, they want to look at how genetic factors, lifestyle choices and other metabolic markers may further shape these associations.

They are also interested in how low-carbohydrate or low-fat diets may impact other health outcomes, such as type 2 diabetes and cancer. This knowledge could help tailor dietary recommendations for individuals based on their unique health profiles.

A new study that followed almost 200,000 people for several decades has found that when it comes to heart health, the quality of food consumed matters as much as following a low-carbohydrate or low-fat diet. The results suggest that choosing healthy, high-quality foods is key to protecting the heart.

In the past two decades, low-carbohydrate and low-fat diets have been promoted for their potential health benefits, such as weight management and improved blood sugar and cholesterol levels. However, the impact of these diets on reducing heart disease risk has remained an ongoing debate.

“We found that what you eat on low-carb or low-fat diets matters just as much as the diet itself,” said Zhiyuan Wu, Ph.D., a postdoctoral fellow in the lab of Qi Sun, MD, ScD, at Harvard T.H. Chan School of Public Health.

“Healthy versions of these diets—those rich in plant-based foods and whole grains—were linked to better heart health outcomes and improved metabolic function. In contrast, low-carb and low-fat diets emphasizing unhealthy foods were associated with a higher risk of heart disease.”

Wu will present the findings at NUTRITION 2025, the flagship annual meeting of the American Society for Nutrition held May 31–June 3 in Orlando.

The study included 43,430 men in the Health Professionals Follow-Up Study (1986–2016), 64,164 women in the Nurses’ Health Study (1986–2018) and 92,189 women in the Nurses’ Health Study II (1991–2019). The researchers followed the nearly 200,000 study participants for several decades, tracking their dietary habits and whether they developed heart disease.

Based on information from detailed questionnaires completed by the study participants, the researchers assigned scores indicating how healthy or unhealthy their food choices were within low-carbohydrate and low-fat diets.

The researchers classified carbohydrates, fats and proteins from foods such as whole grains, fruits, vegetables, nuts and legumes as high-quality nutrients, or healthy, while carbohydrates from potatoes and refined grains as well as saturated fats and proteins from animal-based foods were categorized as low-quality, or unhealthy.

For more than 10,000 of the study participants, the researchers also measured hundreds of blood metabolites to assess how diet quality influenced their metabolic regulation. “This approach allowed us to better understand the biological effects of these diets and strengthened our findings,” said Wu.

The analysis showed that study participants who followed a healthy low-carbohydrate or low-fat diet had a lower risk of developing coronary heart disease, while those on unhealthy versions saw an increased risk. These healthy diet patterns, whether low-carbohydrate or low-fat diets, lowered the risk of developing heart disease by about 15%.

“Our findings suggest that improving food quality is crucial for improving heart health,” said Wu. “Regardless of whether someone follows a low-carbohydrate or low-fat diet, emphasizing whole, minimally processed and plant-based foods and limiting refined grain, sugar and animal foods, can significantly reduce the risk of coronary heart disease.”

For those looking to improve their diet, the researchers suggest focusing on adding more whole grains, fruits, vegetables, nuts and legumes while cutting back on processed meats, refined carbs and sugary foods. They note that it is also important to check food labels and be mindful of added low-quality ingredients, such as added sugars in juices and processed snacks.

Moving forward, the researchers aim to explore additional factors that may influence the relationship between diet quality and heart health. For example, they want to look at how genetic factors, lifestyle choices and other metabolic markers may further shape these associations.

They are also interested in how low-carbohydrate or low-fat diets may impact other health outcomes, such as type 2 diabetes and cancer. This knowledge could help tailor dietary recommendations for individuals based on their unique health profiles.