New research appearing in JACC—the American College of Cardiology’s flagship journal—finds that the specific foods chosen in low‑carbohydrate or low‑fat eating plans matter far more than the simple reduction of carbs or fat. When participants prioritized nutrient‑dense, plant‑forward options, their risk of coronary heart disease (CHD) dropped. In contrast, versions built around refined grains, sugary foods, and animal‑based fats were linked to higher CHD rates and poorer metabolic markers.
Low‑carb and low‑fat diets are popular across the United States, yet the long‑term impact of food quality within these patterns has remained unclear. This investigation, one of the largest of its kind, tracked nearly 200,000 adults for more than three decades, linking dietary quality, blood‑based metabolomics, and heart‑disease outcomes.
Why Food Sources Matter in Low‑Carb and Low‑Fat Plans
Scope of the Study
Researchers pooled data from three long‑running U.S. cohorts—the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow‑up Study—totaling 198,473 participants and 5.2 million person‑years of follow‑up. Over that span, 20,033 new cases of CHD were recorded.
Dietary intake was captured with validated food‑frequency questionnaires. The team created scoring systems that distinguished “healthier” from “unhealthier” versions of low‑carb and low‑fat diets based on the presence of whole‑food ingredients and overall nutrient density.
Key Findings
- Low‑carb and low‑fat patterns rich in vegetables, fruits, whole grains, legumes, and unsaturated fats were tied to a markedly lower chance of developing CHD.
- Conversely, versions high in refined starches, sugary drinks, and animal‑based fats and proteins showed a higher CHD risk.
- Participants following higher‑quality diets exhibited lower triglycerides, higher HDL‑cholesterol, and reduced inflammatory markers.
- Metabolomic profiling supported these trends, revealing favorable biomarker signatures among those on wholesome diet patterns.
Dr. Wu explains that the shared biological pathways—improved lipid profiles, better insulin sensitivity, and reduced systemic inflammation—likely drive the cardiovascular benefits observed in both healthier low‑carb and low‑fat diets.
Limitations and Practical Takeaways
Nevertheless, the findings shift the conversation away from the low‑carb versus low‑fat debate toward a focus on food quality. Whether someone reduces carbs or fat, emphasizing plant‑based foods, whole grains, and healthy fats appears to be the recipe for a stronger heart.
“What matters most for heart health is the quality of the foods we eat,” says Dr. Harlan M. Krumholz, Editor‑in‑Chief of JACC. “Choosing nutrient‑dense options, regardless of macronutrient ratios, is associated with better cardiovascular outcomes.”