The Great Fat Debate: How Much Is Unhealthy?

Experts have redefined the role of fat in healthy eating, but before you grab a chunk of cheese or another pat of butter, understand the differences between the various types of fat in your diet.

For decades, guidelines recommended limiting total dietary fat to no more than 30% of daily calories, and then to a range of 20% to 35% of calories. The thinking was this would lower saturated fat and cholesterol intake, both of which were thought to increase heart disease risk. But many people restricted all types of fat, including healthy ones, like the unsaturated fats found in nuts, vegetable oils and fish.

What's more, packaged food manufacturers rushed to replace fat with unhealthy processed carbohydrates like sugar and refined grains. But research analyzing observational studies and clinical trials has found that replacing saturated fat with the refined carbohydrates found in so-called low-fat processed foods doesn't lower heart disease risk.

On the other hand, choosing polyunsaturated fats for either saturated fat or carbohydrates does. Polyunsaturated fats include both plant and marine sources of unsaturated fats, such as olive oil and fatty fish. This is true even when calories from these sources account for 35% or more of the daily diet.

The Dietary Guidelines Advisory Committee now suggests optimizing healthy fats and avoiding low-fat or even non-fat products that have high levels of refined grains and added sugars. This means that most fat calories should come from unsaturated fats, especially polyunsaturated oils. The upper limit for saturated fat is still 10% of daily calories. This includes animal fats like butter, cream, beef tallow and lard, and tropical oils such as palm, palm kernel and coconut oils.

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