The quality of a low-carbohydrate or low-fat diet may matter more than the amount of carbohydrates or fat consumed when it comes to reducing heart disease risk, according to a study published Feb. 11 in JACC. Researchers found that versions of both diet patterns emphasizing macronutrients from healthy foods were associated with a lower risk of coronary heart disease (CHD), while versions high in refined carbohydrates and animal products were linked to higher risk and adverse metabolic profiles.

Researchers at Harvard University analyzed data from a 30-year Diet and Health Outcomes Survey of some 20,000 healthcare professionals to assess their associated risk of developing heart disease. By comparing healthcare professionals who followed a low-carbohydrate diet, they discovered that the risk of heart disease could actually increase by 14% if the person regularly consumed processed or low-quality carbohydrates. In contrast, if they consumed good-quality carbohydrates, such as whole grains, this risk decreased by 15%.

This study suggests that “simply reducing carbohydrate or fat intake” is not enough to guarantee good health, explains Zhiyuan Wu, a postdoctoral fellow in Harvard University’s Department of Nutrition and co-author of the study. “Our message is: food quality matters more.”

Zhiyuan Wu, PhD, et al., analyzed data from 198,473 participants across three large-scale cohort studies: the Nurses’ Health Study (NHS), NHSII and Health Professionals Follow-up Study. Participants were followed for a combined total of more than 5.2 million person-years, during which 20,033 cases of CHD were documented. Diet patterns were assessed using food frequency questionnaires, and indices were created to distinguish healthy and unhealthy low-carbohydrate and low-fat diets based on food sources and macronutrient quality.

Key findings include:

1. Healthy versions of both low-carb and low-fat diets, emphasizing plant-based foods, whole grains and unsaturated fats, were associated with a significantly lower risk of CHD.
2. Unhealthy versions of both diets, high in refined carbohydrates and animal-based fats and proteins, were linked to higher risk of CHD.
3. Healthy diet patterns were linked to lower triglycerides, higher HDL cholesterol and lower levels of inflammation.
4. Metabolomic analyses supported these findings, showing favorable biomarker profiles associated with healthy dietary patterns.

“These results suggest that healthy low-carbohydrate and low-fat diets may share common biological pathways that improve cardiovascular health,” Wu said. “Focusing on overall diet quality may offer flexibility for individuals to choose eating patterns that align with their preferences while still supporting heart health.”

“The findings show that what matters most for heart health is the quality of the foods people eat,” adds Harlan M. Krumholz, MD, SM, FACC, Editor-in-Chief of JACC. “Whether a diet is lower in carbohydrates or fat, emphasizing plant-based foods, whole grains, and healthy fats is associated with better cardiovascular outcomes.”

Because it was only an observational study, the researchers were unable to directly prove that certain diets actually contributed to the development of heart disease in the participants. But the fact that this study followed such a large number of people for such a long period is “impressive,” notes Camilla Dalby Hansen, a researcher at the University of Southern Denmark in Odense, who was not involved in the study.

As Zhiyuan Wu explains, the researchers went even further by collecting biological data to help counteract potential self-selection biases stemming from health questionnaires. They took blood samples from over 11,000 participants and were able to measure their metabolites—small molecules present in cells and tissues—which corroborated their previous findings.

“They obtained results with a particularly rigorous or complex methodology,” notes Camilla Dalby Hansen. “The fact that they incorporated metabolites into their analysis delights me. It’s unprecedented and exciting.”

WHOLE FOODS TO CHOOSE

The body needs macronutrients—carbohydrates, proteins, and fats—for energy and good health. These macronutrients are found in many foods: red meat, fruits, oatmeal, fast food, ice cream, and vegetables.

But not all the foods we consume are of the same quality. For example, in their study, the Harvard University researchers distinguish between processed carbohydrates, which are of lower quality, and high-quality ones, such as whole grains.

The study also differentiates between the quality of fat sources. Processed or saturated fats, which are of lower quality and unhealthy, such as those found in red meat, heavy cream, and butter, are not easily metabolized by the body. They are often associated with a higher risk of diseases such as type 2 diabetes and heart disease.

Conversely, good quality fats, like those found in avocados or nuts, are easily broken down and converted into energy. They also contribute to feelings of fullness. “Fats are the most incredible macronutrients,” says Camilla Dalby Hansen. “They’re good for brain health, hormone function, and skin. They also have a cardioprotective effect, [since they clear] your arteries of debris.”

In this study, researchers created different categories of diets considered good and bad for health. The former included more plant-based or high-quality protein and fat, along with quality carbohydrates. The latter were high in lower-quality processed carbohydrates and animal protein and fat, which the study considered a source of unhealthy fats.

The results clearly demonstrate that the difference in the quality of fats and carbohydrates can reduce the risk of disease, even with lower consumption. Specifically, participants consuming high-quality carbohydrates and more plant-based protein and fats had a lower risk of developing heart disease than those who ate refined carbohydrates and larger quantities of animal fats and proteins.

In addition, those whose protein and fat sources were of animal origin were more likely to consume saturated and processed fats, which also increases the risk of cardiovascular disease .

For Camilla Dalby Hansen, one of the study’s limitations is the way it simplifies the categories of “good and bad” foods by classifying animal fats and proteins as unhealthy. “In my opinion, not all animal proteins and fats are bad for your health,” she argues.

Zhiyuan Wu agrees that some low-fat animal proteins, such as yogurt, can have beneficial effects. Other experts emphasize that this study highlights the additional benefits offered by whole grains and plant-based fats and proteins compared to other types of macronutrients.

“The study doesn’t say we shouldn’t consume animal protein, but rather that we should incorporate a significant portion of whole foods and plant-based proteins and fats, such as legumes and beans, into our diet,” explains Jennifer Sacheck, dean of the School of Public Health at Brown University. “Increased consumption of plant-based foods has been shown to offer greater health benefits.”

INDICATORS OF GOOD HEALTH

Blood samples taken during the study also provided insight into the participants’ actual health status. Those following the healthiest diets, low in carbohydrates and fats, had higher levels of good cholesterol and lower triglyceride levels (triglycerides are produced when our bodies have reached a healthy calorie limit). High levels of good cholesterol can protect the body against heart disease by removing bad cholesterol from the arteries.

The researchers also analyzed metabolites, the molecule residues resulting from metabolism by the body. “If you eat certain foods, your metabolome will confirm it,” explains Jennifer Sacheck.

A metabolite, hippuric acid, was found in higher quantities in participants following a healthier diet low in carbohydrates and fats. This metabolite also indicates a diet rich in fruits and vegetables. This finding confirms risk modeling and suggests that healthier diets are biologically better.

Zhiyuan Wu notes that, interestingly, those following a healthy low-carbohydrate diet and those following a healthy low-fat diet showed similar signs of good health. According to him, this proves that we can choose the type of diet we want to follow (in this case, low-carbohydrate or low-fat) as long as we prioritize the consumption of whole foods and quality sources of fats and carbohydrates.

“This allows for greater flexibility in preferences, while still providing even greater protection for cardiovascular health,” he concludes.

Source https://www.acc.org/