Fruits and vegetables: important to prevent type 2 diabetes?

The evidence from prospective studies that the consumption of fruits and vegetables reduces the risk of cardiovascular events is overwhelmingly supportive. In contrast, prospective studies have overall produced quite heterogeneous results when evaluating the risk to develop type 2 diabetes. The accompanied meta-analysis in this issue indicates here that – overall – a higher consumption of fruits and vegetables will not help to stem the tide of the diabetes epidemic. While this might be seen as disappointing, we need to keep in mind that observational studies may not be able to capture the true effect of diet on disease risk. Error in measuring participants’ diet could potentially lead to a strongly underestimated effect, as is suggested by one study presented in this issue. The application of more accurate methods to assess dietary intake in epidemiologic studies, e.g. by the use of biomarkers, is a promising approach here to clarify the role of fruits and vegetables. Also, further research is needed to identify mechanisms by which fruits and vegetables may lower diabetes risk. Fruits and vegetables contribute importantly to fiber intake, besides whole grains. Here, a second study in this issue suggests that higher fiber intake reduces hepatic lipid accumulation and sub-chronic inflammation, central mechanisms in the development of insulin resistance.

Nevertheless, most studies evaluating both risk of cardiovascular disease and type 2 diabetes observed quite contradictory associations. Thus, we may still need to acknowledge that the effect of fruits and vegetables on risk of type 2 diabetes may be considerably weaker compared to the effect on cardiovascular risk. However, intervention studies like the PREDIMED-Reus trial strongly suggest that dietary patterns that favour fruits and vegetables at the cost of red meats and include fat predominantly from plant sources are not only heart-healthy but also dramatically reduce the risk of type 2 diabetes.