March 23, 2010
By: Marion Nestle
Recent publications have found no correlation between intake of saturated fat and coronary heart disease (CHD)—see, for example, the recent meta-analysis in the American Journal of Clinical Nutrition—but the debate over the role of saturated fat continues.
In the same issue of the Journal, another study reports that reducing saturated fat only works if you replace it with something better. If you replace saturated fat with carbohydrates, the effects on heart disease will be even worse.
The fat story is not simple (in my chapter on fats and oils in What to Eat, I explain the biochemistry of food fats). The main reason for the complexity is that different kinds of fats do not occur separately in foods.
Without exception, food fats are mixtures of three kinds of fatty acids: saturated (no double bonds and solid at room temperature), monounsaturated (one double bond), and polyunsaturated (two or more double bonds and liquid at room temperature). Food fats just differ in proportions of the three kinds.
Meat, dairy, and egg fats are generally saturated. Plant fats and oils are generally unsaturated.
How to make sense of the saturated fat story? A joint panel of experts from the World Health Organization and the Food and Agriculture Organization just produced a new review of the evidence (click here for a PDF). The panel evaluated CHD morbidity and mortality data from epidemiological studies and controlled clinical trials. It found:
• Convincing evidence that replacing saturated fat with polyunsaturated decreases the risk of CHD.
• Probable evidence that replacing saturated fat with largely refined carbohydrates (starch and sugar) has no benefit and even may increase the risk of CHD.
• Insufficient evidence on whether replacing saturated fat with monounsaturated fats or whole grain carbohydrates affects the risk of CHD, but a trend suggesting that these might decrease CHD risk.
• Possible positive relationship between saturated fat and increased risk of diabetes.
• Insufficient evidence for establishing any relationship of saturated fat with cancer.
The panel’s recommendations:
1 – Replace saturated fat with polyunsaturated fats (omega-3 and omega-6) in the diet, and
2 – Limit saturated fat to 10 percent of daily calories or less.
Translation: Replace more of your animal fats with vegetable fats.
Historical note: These are precisely the same recommendations that have been standard in the U.S. for at least 50 years. This was good advice in the late 1950s, and it still is.