What You Eat Matters More Than Cutting Carbs, Fat

• A new study suggests that food quality matters more than fat or carbs for heart health.
• A low carb, low fat diet could lack heart-protective nutrients and have too much of certain nutrients associated with heart disease risk.
• A balanced diet with high quality, unprocessed foods is best for your heart.

When it comes to heart health, the quality of the food you eat could matter a lot more than simply cutting carbohydrates or fats.

A new study suggests that rather than focusing solely on macronutrient counts, emphasizing whole, minimally processed, and plant-based foods while limiting refined grains, added sugars, and animal products can significantly reduce the risk of coronary heart disease.

The researchers’ findings highlight a shift toward more personalized and nuanced dietary guidance for cardiovascular health.

For years, low-carbohydrate (low carb) and low fat diets have dominated nutrition advice as methods to improve health, manage weight, and reduce risks of chronic diseases such as heart disease.

However, the scientific community has debated how much these diets truly protect the heart, especially when the quality of foods consumed within these diets varies greatly.

Researchers at Harvard T.H. Chan School of Public Health shed light on this important question, concluding that food quality is just as critical, if not more so, than merely restricting carbs or fats.

Researchers tracked participants’ dietary habits and heart disease outcomes over 25 years. Detailed food frequency questionnaires allowed the team to assign scores based on the healthfulness of the foods consumed within low carb and low fat diets.

They found a clear association between low carb and low fat diets that emphasize high quality foods (i.e., whole grains, fruits, vegetables, nuts, and legumes) and a roughly 15% lower risk of developing coronary heart disease.

Conversely, diets low in carbs or fat but high in unhealthy foods like refined grains, sugary snacks, processed meats, and animal fats carried a higher risk of heart disease.

“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,” Lead study author Zhiyuan Wu, PhD, a postdoctoral research fellow in the Department of Nutrition at Harvard, explained in a press release.

This suggests that simply cutting carbs or fats without considering the source and quality of these macronutrients can be counterproductive.

To deepen their understanding, the research team also measured blood metabolites — a wide range of biological markers related to metabolism — in a subset of over 10,000 participants.

This allowed them to observe how different diet qualities influenced metabolic regulation and lipid profiles in the body. The findings showed that healthy and unhealthy versions of low carb and low-fat diets distinctly affected plasma lipid species and other metabolites, which are important indicators of cardiovascular health.

Interestingly, the study differentiated between various types of low carb and low fat diets. For example, “animal-based” low carb diets, which tend to be higher in saturated fats and proteins from animal products, were linked to increased heart disease risk.

On the other hand, “vegetable-based” or plant-focused low carb diets showed more favorable outcomes.

Similarly, unhealthy low fat diets that rely heavily on refined carbohydrates and added sugars also increased risk, whereas healthy low fat diets emphasizing whole foods lowered it.

Yaa Boakye, a registered dietitian nutritionist, personal trainer, and nutrition consultant, said it’s helpful to think of food quality like a grading rubric for your body. Boakye wasn’t involved in the study.

“Imagine asking a student to write a book report without providing the grading rubric; they may complete the assignment, but without clear direction, their work might miss the mark,” she told Healthline.

Boakye noted that food quality is akin to the rubric in that your body uses it to interpret what you eat.

“It is not enough to check off a box labeled ‘low carb’ or ‘low fat’ — we need to examine what is actually in the food: fiber content, added sugars, sodium, micronutrients, and anti-inflammatory or proinflammatory compounds,” she explained, adding that carbohydrates, fats, and proteins are only broad categories.

“A carbohydrate could be a refined white roll or a fiber-rich lentil; a fat could be processed trans fat or cold-pressed olive oil,” she said. “Food quality helps us zoom in on these differences.”

Boakye added that when individuals simply follow a low fat or low carb diet without considering these nuances, they tend to overlook important nutrients that have consequences for heart health.

“High sodium levels, added sugars, lack of fiber, and insufficient antioxidants are all red flags that often go unnoticed,” she said, adding that you could be meeting your macro targets but still consuming a diet conducive to hypertension, poor cholesterol profiles, or systemic inflammation.

“A ‘low fat’ diet lacking magnesium, potassium, and omega-3s could backfire, while a ‘low carb’ plan omitting prebiotic-rich plants or colorful fruits might hinder gut health and indirectly stress the cardiovascular system,” she added.

She advised following the plate model, which involves filling one-half of your plate with vegetables and fruit, one-quarter with lean proteins (including meat, fish, beans, or lower-fat cheese), and one-quarter with whole grains.

“Making this your plate automatically reduces the amount of carbohydrate you eat and reduces the fat that you’re eating because it removes a lot of excess fats that can enter someone’s diet through eating higher fat foods,” she told Healthline.

Smart further noted that vegetables and fruit contain fiber, which helps keep you full so you’re less tempted to snack between meals.

They also contain vital nutrients like vitamins, minerals, and antioxidants, which help protect your heart and blood vessels. According to Smart, whole grains also contain fiber and B vitamins.

“All this fiber helps better control blood sugar,” she said. “Poorly controlled blood sugar contributes to heart disease by damaging blood vessels, so better blood sugar control reduces heart disease risk.”

Smart added that eating lean proteins like lean meats, beans, and legumes helps keep your saturated fat intake low.

She added that a diet filled with high quality foods will naturally include fewer highly processed foods, which reduces your intake of sodium, saturated fat, and excess calories.

“Reducing the amount of highly processed foods you eat helps to protect your cardiovascular health by helping to control blood pressure and reduce your risk of developing atherosclerosis (hardening of the arteries) and helps to prevent excess weight gain,” Smart concluded.