The quality of a low-carb or low-fat diet may matter more than the amount of carbs or fat consumed when it comes to reducing the risk of heart disease, according to a new study published in JACCthe flagship journal of the American College of Cardiology. The researchers found that versions of both dietary patterns that emphasized macronutrients from healthy foods were associated with lower risk of coronary heart disease (CHD), while versions high in refined carbohydrates and animal products were associated with higher risk and adverse metabolic profiles.
Low-carbohydrate, low-fat diets are widely implemented in the US, yet their long-term cardiovascular effects and the role of diet quality in these dietary patterns remain unclear. This study is among the most comprehensive to date to analyze diet quality, metabolic profiles, and CHD risk in nearly 200,000 US adults with more than 30 years of follow-up.
Our findings highlighted that it’s not just about cutting carbs or fat, it’s about the quality of foods people choose to build these diets. The effectiveness of low-carbohydrate, low-fat diets in reducing the risk of cardiovascular disease is a matter of ongoing debate, and previous studies have shown mixed findings.”
Zhiyuan Wu, a postdoctoral researcher at the Harvard TH Chan School of Public Health and lead author of the study
Wu added that one reason for these conflicting findings may be that people can follow the same type of low-carb or low-fat diet using either healthy or unhealthy foods.
“Focusing only on nutrient compositions but not food quality may not lead to health benefits,” he said.
To address these knowledge gaps, researchers analyzed data from 198,473 participants in three large-scale cohort studies: the Nurses’ Health Study (NHS), the NHSII and the Health Professionals Follow-up Study. Participants were followed for a total of more than 5.2 million person-years, during which 20,033 cases of CAD were documented. Dietary 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:
- Healthy versions of both low-carbohydrate and low-fat diets, with an emphasis on plant foods, whole grains, and unsaturated fats, were associated with significantly lower CHD risk.
- Unhealthy versions of both diets, high in refined carbohydrates and animal fats and proteins, were linked to a higher risk of CHD.
- Healthy eating patterns were linked to lower triglycerides, higher HDL cholesterol and lower levels of inflammation.
- Metabolomic analyzes supported these findings, showing favorable biomarker profiles associated with healthy dietary patterns.
“These results suggest that healthy low-carbohydrate, low-fat diets may share common biological pathways that improve cardiovascular health,” Wu said. “Focusing on overall diet quality may provide flexibility for individuals to choose dietary patterns that align with their preferences while supporting heart health.”
Study limitations include that the findings may not be generalizable to more extreme dietary patterns with very low carbohydrate or fat intake, such as ketogenic diets, and should be interpreted within the observed macronutrient consumption limits. Also, dietary intake was self-reported and therefore subject to measurement error. Finally, the study findings may have limited generalizability as the participants consisted of health professionals with higher health awareness and better access to care, however, the underlying biological mechanisms are unlikely to differ drastically between populations.
“This study helps move the debate beyond the long-standing low-carb versus low-fat diet debate,” said Harlan M. Krumholz, MD, Editor-in-Chief of JACC. “The findings show that what matters most for heart health is the quality of the foods people eat. Whether a diet is lower in carbohydrates or lower in fat, an emphasis on plant foods, whole grains and healthy fats is associated with better cardiovascular outcomes.”
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