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Dietary carbohydrates

Simin Liu, MD, ScD
Walter C Willett, MD, DrPh
Section Editor
F Xavier Pi-Sunyer, MD, MPH
Deputy Editor
Jean E Mulder, MD


The type and amount of carbohydrate consumption can have important implications for health. Widespread promotion of low fat diets in the 1980s and 1990s led to a reduction in the percentage of calories from fat in the United States diet and a concurrent increase in carbohydrate intake. Despite these dietary changes, the prevalence of obesity and type 2 diabetes mellitus continued to rise [1]. Perhaps partly due to unsatisfactory outcomes with low fat diets, a large segment of the population that wants to lose weight is increasingly following many popular diets that emphasize low or no carbohydrates for weight loss.

In the scientific community, serious concern has also been raised over dietary recommendations for high carbohydrate, low fat diets. High carbohydrate diets reduce high-density lipoprotein (HDL) cholesterol and raise blood concentrations of glucose, insulin, and triglyceride and blood pressure, contributing to a now well-recognized metabolic profile called insulin resistance syndrome that is conducive for the development of coronary heart disease (CHD) and type 2 diabetes mellitus. (See "The metabolic syndrome (insulin resistance syndrome or syndrome X)".)

Because of the differences in chemical structure, physical form, fiber content, and the degree of processing (refining and gelatinization), different forms of carbohydrates are likely to have heterogeneous biological functions and health effects. These effects are discussed here. Overall recommendations for a healthy diet and dietary therapy for obesity are found separately. (See "Healthy diet in adults" and "Obesity in adults: Dietary therapy", section on 'Choice of diet'.)


Carbohydrates are traditionally classified as simple (sugars, ie, mono- and disaccharides) or complex (starches, ie, polysaccharides) on the basis of the number of sugar molecules in their chemical structures. It had been assumed that complex carbohydrates cause smaller rises in blood glucose than simple carbohydrates. Dietary guidelines for individuals with diabetes mellitus that recommend the use of complex rather than simple carbohydrates to control blood glucose levels reflect this assumption [2,3].

A growing body of data, however, contradicts this notion. In the mid-1970s, the first series of studies were published in the English literature showing that various starchy foods differ in their ability to induce plasma glucose and insulin responses [4-7]. These findings initiated a new era of research on the in vivo physiologic effects of carbohydrates. Collectively, these data demonstrate that digestion of carbohydrates, particularly starch, is not a rate-limiting event and is often quite rapid because of the presence of sufficient amylolytic capacity in the intestine [8]. As an example, postprandial glycemic responses to potato and white bread are similar to the response to pure glucose [9,10], indicating that complex carbohydrates may not differ from simple sugars in their effect on plasma glucose level.

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Literature review current through: Nov 2017. | This topic last updated: Sep 11, 2017.
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