More Evidence That a High-Fiber Diet May Prevent Type 2 Diabetes

Commentary

The current study by the European InterAct Consortium adds to the available evidence supporting the association of dietary fiber and risk of diabetes. Higher intake of dietary fiber, especially cereal fiber, has been consistently associated with a lower risk of diabetes [2,3].

This study showed that a high intake of total fiber (primarily cereal and vegetable fiber) was associated with an 18% lower risk of type 2 diabetes (adjusted for dietary and lifestyle factors). While there was no association after adjusting for BMI, their meta-analysis of 18 studies did support the an inverse association between total fiber and cereal fiber intake and risk of type 2 diabetes.

What is it about fiber that is protective? With regard to whole grains, a rich source of fiber, potential mechanisms have been identified [5], including the possible impact of improved postprandial glucose response. However, whole grains are rich in nutrients and phytochemicals, and new hypotheses for the health-protective mechanisms of whole grains beyond fiber are being proposed [6]. In addition, the beneficial effect of fiber seen in this and other studies may be partly mediated by a lower BMI. Dietary fiber may affect appetite and energy intake through a range of processes.

It should be noted that although the effect of whole-grain foods for the prevention of type 2 diabetes is strongly supported by numerous epidemiological studies, a 2008 systematic review by the Cochrane Collaboration [4], which included 1 low-quality RCT and 11 cohort studies, stated that the evidence is too weak to be able to draw a definite conclusion about the preventive effect of this dietary factor.

Strengths of the study included its prospective design and large sample size. Limitations of the study include that dietary intake was assessed only at baseline and measurement error through the use of a questionnaire may have occurred. Although food-frequency questionnaires are widely used, they are subjective estimates and subject to recall bias, and some researchers have questioned their value for use in epidemiologic studies [7]. In addition, the authors note that the inverse association for total fiber and cereal fiber intake in the meta-analysis could be due to residual confounding as fiber intake has been associated with healthier diet, lower BMI, and greater physical activity.

Applications for Clinical Practice

The prevalence of type 2 diabetes has increased rapidly during the past decades in the United States. Dietary guidelines recommend the consumption of whole grains to prevent chronic diseases. The results presented in the current study strengthen the evidence supporting cereal fiber as an important determinant of type 2 diabetes risk. Randomized controlled trials are needed and should elucidate this matter.