Harvard Heart Letter

Understanding the unsaturated fats

Confused about fats? Learn the latest on which fats offer the best health benefits.

There used to be one simple rule—all fat is bad. More recently, we've been told that fat is absolutely essential to our health, especially polyunsaturated fats in plant-derived oils. But, as research piles up, the picture of fats and health has sometimes become blurred.

The role of polyunsaturated fats

Polyunsaturated fats include two types: omega-3 (linolenic acid) and omega-6 (linoleic acid). Both are essential and not made by the body. "For years the recommendation has been to replace saturated fat from animal sources with polyunsaturated fat from plant sources," says Dr. Frank Hu, professor of nutrition and epidemiology at the Harvard School of Public Health. But a research analysis published last year threatened to turn that advice on its ear. The study suggested that polyunsaturated fats, primarily found in vegetable oils, were not necessarily protective against heart disease. In particular, the role of the omega-6 fatty acids was called into question. Some investigators went as far as to speculate that omega-6s might actually promote inflammation leading to arterial disease.

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