Carbohydrate and Fiber

Many studies have examined the role of sucrose and sugars in the etiology of type 2 diabetes.

A few have suggested a positive association, but the majority of studies have shown no association. Some have even suggested an inverse association between diabetes incidence and sucrose intake (11,14). Poor assessment of dietary intake, inability to disentangle dietary and other confounding factors, as well as overinterpretation of data derived from observational studies characterize many of these studies. Despite the lack of direct evidence for the role of sugars in the etiology of type 2 diabetes, it is conceivable that excessive sucrose intake might predispose to obesity, and thus sucrose indirectly may be a predisposing factor for type 2 diabetes.

This has been suggested particularly in those who prefer to consume large amounts of sugar-sweetened beverages (22,23).

There is support for the suggestion that foods rich in slowly digested starch or high in fiber might be protective. Countries with high intakes of these foods have low rates of type 2 diabetes. In a cross-sectional study of normoglycemic men, intake of pectin was inversely associated with postprandial blood glucose levels, independent of total energy intake and body mass index (BMI) (5). In the Health Professionals’ Follow-up study and the Nurses’ Health study, diets low in cereal fiber and with high-glycemic loads were associated with an increased risk of type 2 diabetes after adjustment for other risk factors (13).

In the Iowa Women’s Health study the risk of self-reported diabetes was highest in the group with the lowest whole-grain intake. In contrast, a higher consumption of refined grains was associated with an increased risk of type 2 diabetes after adjustment for age and total energy intake.

The ratio of whole grain to refined grain was related to a significantly lower risk of diabetes, suggesting a potential benefit for replacing refined grains with whole grains (24).

It is of interest that, in the studies quoted, cereal fiber appeared to contribute most to the protective effect; however, experimental studies have repeatedly demonstrated a more marked beneficial effect of soluble fibers than insoluble fibers on several measures of carbohydrate and lipid metabolism. Thus, fiber from fruit and vegetables might have been expected to have exerted a more marked protective effect than cereal fiber.

Although further research is needed to investigate the effects of different types and sources of fiber, it seems to be prudent to encourage an increased consumption of total dietary fiber from different sources:  whole grains, fruits, vegetables, and legumes.