After four decades of persistent warnings that saturated fats should be avoided in healthy diets, new research is casting doubt on that claim. An extensive new analysis of nearly 80 studies involving 660,000 people has found no evidence linking the fats found in meat, butter, and cheese to an increased risk of heart disease, reports The New York Times. Researchers also found no firm evidence that unsaturated fats, such as the omega-3 fatty acids in salmon, reduce heart disease rates. Taken together, the findings further muddy the waters in the ongoing debate about what’s best to eat. “These are interesting results that encourage careful reappraisal of our current nutritional guidelines,” says researcher Rajiv Chowdhury of the University of Cambridge. While saturated fats are known to increase LDL, or “bad” cholesterol, the new findings suggest that the relationship between cholesterol and heart disease is more complicated than previously thought. Researchers did confirm, however, that the much maligned trans fats, the partially hydrogenated oils found in processed foods, do have a direct link to heart disease.