Frank B Hu Am J Clin Nutr 2010:91:1541.

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Highlights…

The diet-heart paradigm that high intake of saturated fat and cholesterol increases the risk of atherosclerosis and ischemic heart disease (IHD) has been the driving force behind national and international dietary recommendations for prevention of IHD

Diets that are typically low in fat (particularly saturated fat) and high in complex carbohydrates, has led to substantial decline in the percentage of energy intake from total and saturated fats in the United States, BUT it has spurred a compensatory increase in consumption of refined carbohydrates and added sugars—a dietary shift that may be contributing to the current twin epidemics of obesity and diabetes.

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Depending on chemical structure, carbohydrates are traditionally classified as simple or complex (polysaccharide). The latter are considered to be a healthy alternative to dietary fats. However, many complex carbohydrates (e.g., baked potatoes and white bread) produce even higher glycemic responses than do simple sugars (5). Thus, the term complex carbohydrates is not useful in characterizing the quality of carbohydrates. More useful indicators of carbohydrate quality include the amount and type of fiber, the extent of processing, and glycemic index (GI) and glycemic load (GL).

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Typically, foods with more compact granules (low-starch gelatinization) and high amounts of viscose soluble fiber (e.g., barley, oats, and rye) are digested at a slower rate and have lower GI values than do highly processed refined carbohydrates (e.g., white bread). These refined carbohydrates are more rapidly attacked by digestive enzymes due to grinding or milling that reduces particle size and removes most of the bran and the germ.

Multivariate analyses showed that saturated fat intake was not associated with risk of MI compared with carbohydrate consumption— a finding consistent with the results from a recent pooled analysis and a meta-analysis.

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However, replacement of saturated fat with high-GI-value carbohydrates significantly increased the risk of MI (relative risk per 5% increment of energy from carbohydrates: 1.33; 95% CI: 1.08, 1.64), whereas replacement with low-GI-value carbohydrates showed a nonsignificant inverse association with IHD risk (relative risk per 5% increment of energy from carbohydrates: 0.88; 95% CI: 0.72–1.07).

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It is the first epidemiologic study to specifically examine the effects of replacing saturated fats with either high- or low-quality carbohydrates, and it provides direct evidence that substituting high-GI value carbohydrates for saturated fat actually increases IHD risk.

The obesity epidemic and growing intake of refined carbohydrates have created a ‘‘perfect storm’’ for the development of cardiometabolic disorders. For this reason, reduction of refined carbohydrate intake should be a top public health priority. Several dietary strategies can be used to achieve this goal. These include replacing carbohydrates (especially refined grains and sugar) with unsaturated fats and/or healthy sources of protein and exchanging whole grains for refined ones.

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A very-low-fat, high-carbohydrate diet (e.g., percentage of energy, 20% from fat and 70% from carbohydrates), once typical in traditional Asian populations, has the potential to be cardioprotective if most of the carbohydrates come from minimally processed grains, legumes, and vegetables and if the population is lean and active (and thus has low insulin resistance).

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Although intake of saturated fat should remain at a relatively low amount and partially hydrogenated fats should be eliminated, a singular focus on reduction of total and saturated fat can be counterproductive because dietary fat is typically replaced by refined carbohydrate, as has been seen over the past several decades.