A massive new study tracking nearly 200,000 people over decades reveals that the quality of the food you eat matters just as much as whether you follow a low-carb or low-fat diet.
Diets rich in whole grains, fruits, vegetables, nuts, and legumes significantly reduce heart disease risk, while those heavy in processed and animal-based foods do the opposite, even if they meet the “low-fat” or “low-carb” label.
Diet Quality Matters More Than Macronutrient Focus
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.
Healthy vs. Unhealthy Versions of Diets
“We found that what you eat on low-carb or low-fat diets matters just as much as the diet itself,” said Zhiyuan Wu, PhD, 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 presented the findings at NUTRITION 2025, the flagship annual meeting of the American Society for Nutrition held in Orlando.
Decades-Long Data from Nearly 200,000 People
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.
Defining High- and Low-Quality Nutrients
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.
Diet Quality Directly Tied to Heart Risk
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 diet, 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.”
Practical Tips for Healthier Eating
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.
Meeting: NUTRITION 2025
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13 Comments
The most important factors for heart health is #1 don’t smoke #2 stop burning fossil fuels and producing dangerous air pollution and keep your BMI below 25. You can argue low carb and low fat all day long. I was diabetic (insulin resistance is the worst of the metabolic risk factors) and cured myself with a very low carb diet high fat diet. The one thing that no one can refute is keeping your BMI below 25 is the best single thing you can do to promote heart health.
Your a1c might be good but have you had a glucose tolerance test recently? I would be curious to see your first phase insulin response. In all likelihood your insulin resistance is still high since muscle and liver insulin resistance is caused by excess fat in the diet that accumulates in these tissues and interferes with efficient function of the insulin receptor/glucose transporter. You only mask the problem by not putting any glucose or starch into the system. To fix the problem you have to get fat out of your muscles and liver.
Fossil fuels got nothing to do with you diabetes. Stop ping fossil fuel use is extremely STUPID. There is no VIABLE substitute for them. No fossil fuel use would create an gigantic unextended consequences. There is NO. CURE for Diabetes. It calls into question this guys intelligence
Low fat whole food plant based with a special emphasis on adequate servings of dark leafy greens will ALWAYS beat ANY low-carb diet. If you restrict carbohydrates you can only make up the necessary calories from fat and protein. Excess protein is bad for health, and excess fat of any kind is bad for health, although saturated and trans are the worst. They lack fiber and micronutrients that are found in abundance in plants.
Agree! I have seen what low-carb diets does to people, constipation, hair loss, and bad breath. The list goes on. Most people don’t realize how unhealthy milk from animals is. Nature grows all we need to thrive. It is a win win for the animals, the planet, and humans.
To enjoy better health: eliminate all seed oils; stop eating foods with added sugar; remove all foods that contain refined (white) flower; and significantly increase you exposure to natural sunlight.
Stop spreading seed oil FUD.
New scientific study substantiates omega−6 linoleic acids reduce inflammation.
https://www.sciencedaily.com/releases/2025/06/250621103446.htm
Defining what is healthy and unhealthy BEFORE doing the study sounds like a completely unscientific way to do a study!
Conference paper. I want to see the peer reviewed work
People posting comments clearly have no clue on nutrition and diet. They act like they’re “experts” but their claims have been debunked many times.
Seed oils are fine. Sugars are not dangerous if consumed sparingly. Low-carb/keto diets promote higher risk of mortality in the long run compared to those who stick with balanced diets.
Diabetics telling us that they’re better on keto are not useful for those who are healthy to begin with and diabetics are always at risk of dying sooner than later. That’s the way it is.
People avoiding gluten when they’re not celiacs or gluten sensitive – they have no clue how ridiculous they are. They’re missing good protein. People saying we need tons of protein are ridiculous as well – they won’t be utilized if the body doesn’t need it. It’s like taking vitamin B complex – they go straight to urine.
Eat well – that means plenty of vegetables, grains, fruits, nuts/seeds, and eat dairy and meats in small amounts. The rest of “foods” are optional but can be harmful if taken in excess – you’d be taking too many calories unless you expend the calories equally.
A 15% reduction in risk from a non-RCT study does not settle the debate about low-carb vs. Iow-fat. Yet another sham study coming out of Harvard and published on this silly website. Come back when you cut risk in half, or more.
I’ve never seen so many ‘experts’ with different opinions as I do in the area of nutrition. The secret to a healthy, long life is inheriting good genes.
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