Walnuts have been gathered and cultivated since prehistoric times, with archaeological evidence of human consumption dating back thousands of years in the region spanning modern-day Iran and Central Asia. The walnut's scientific name, Juglans, derives from Latin for "Jupiter's nut" — the Romans considered it food fit for the king of the gods, a reflection of how highly it was regarded.
Walnuts traveled westward along ancient trade routes into Greece and Rome, and eventually across Europe, becoming a staple food and medicinal item across the continent. A long tradition of "doctrine of signatures" thinking — the old folk belief that a plant's appearance hints at its medicinal use — attached itself to walnuts specifically because the wrinkled kernel visually resembles a brain, leading to centuries of traditional use for cognitive and neurological complaints, purely on the basis of that visual resemblance rather than any understanding of its actual chemistry.
Walnut has one of the largest and most consistent evidence bases of any food in this Atlas, specifically for cholesterol and cardiovascular risk factors. A 2025 meta-analysis — the largest to date — pooled 49 randomized controlled trials covering 4,611 participants and found walnut consumption produced statistically significant reductions in triglycerides, total cholesterol, and LDL cholesterol. This wasn't an isolated finding: an earlier 2022 meta-analysis of 13 trials and a separate 2018 meta-analysis of 26 trials (1,059 participants) both reached the same conclusions independently, with closely matching effect sizes across all three reviews.
Across every major review, walnut consistently shows no significant effect on HDL ("good") cholesterol specifically, and researchers note real trial heterogeneity in dose and population. But the sheer consistency of the cholesterol-lowering finding across multiple large, independent meta-analyses spanning nearly a decade of research — rather than a single study or a handful of small trials — is what earns walnut a genuine "Strong" rating, one of the more robust evidence bases covered anywhere on this site.
Eaten raw or roasted, pressed into oil, or ground into pastes; walnut oil has also been used topically in some traditional preparations.