In this ecological study, Pavel Grasgruber and colleagues reassessed the relationship between diet and cardiovascular disease using food consumption and health outcome data from more than 40 European countries, dramatically expanding the scope of analysis beyond the seven countries selected by Ancel Keys in his influential Seven Countries Study. Whereas Keys based his conclusions on a small, non-random subset of nations, the authors examined all countries for which reliable data were available, allowing the diet–heart hypothesis to be tested against a far more comprehensive and representative dataset.

When viewed across this broader population, the relationships claimed by Keys do not hold. Higher consumption of total fat and animal protein was generally associated with lower cardiovascular mortality and better cardiometabolic markers, while higher reliance on carbohydrates—particularly cereal-based carbohydrates—tracked with worse outcomes. Although the authors acknowledge the limits of ecological data, they conclude that Keys’ original findings were highly dependent on selective country inclusion, and that expanding the dataset fundamentally alters the conclusions, calling into question the evidentiary basis for decades of low-fat dietary guidance.

https://pmc.ncbi.nlm.nih.gov/articles/PMC5040825/