【Background】
There have been numerous reports on the impact of dietary factors on the development of type 2 diabetes. However, there have not comprehensively examined the strength and validity of the association. In this study, we aimed to evaluate the existing evidence using an umbrella review that collectively analyzes the results of a systematic review with meta-analysis.
【Methods】
PubMed, Web of Science, and Embase were searched until August 2018 to select reports of meta-analyses of observational studies on the association between the risk of incidence type 2 diabetes and diet behaviours, dietary quality, food groups, foods, beverages, alcoholic, macronutrients, and micronutrients.
Quality of evidence was assessed using a modified version of NutriGrade. We scored the risk of various types of bias, the accuracy of estimates, heterogeneity (whether it can be integrated quantitatively), directness (e.g., whether there were differences in study populations or interventions), and effect size, and divided the quality of evidence into "high," "moderate," "low," and "very low.
【Results】
In the end, 53 meta-analyses including 153 statistics were selected. The statistics included dietary behaviours and diet quality (n = 12), food groups and foods (n = 56), beverages (n = 10), alcoholic beverages (n = 12), macronutrients (n = 32), and micronutrients (n = 31).
There were four foods for which the quality of evidence for developing type 2 diabetes was high. The only food that lowered risk was whole grains, with a 13% reduction in risk for every 30g increase in whole grain intake per day. The three foods that increased the risk were red meat, processed meat, and bacon. The risk increased by 17%, 37%, and 107% for each additional 100g, 50g, and 2 slices per day, respectively.
In terms of beverages, moderate drinking lowered the risk by 25%. Sugar-sweetened beverages raised the risk by 26% for each additional cup per day.
When analyzed by food composition, the quality of evidence was high for only one ingredient: dietary fiber from grains (grain fiber). On the other hand, the quality of evidence was "moderate" for total dietary fiber intake and dietary fiber in fruits and vegetables.
【Discussion and conclusion】
There is high-quality evidence that whole grains and grain fiber reduce the risk of incidence type 2 diabetes. Recommendations to increase intake of whole grains, increase intake of dietary fiber, and reduce intake of foods with a high glycemic index (GI) have been included in various guidelines for the prevention of type 2 diabetes. The results of this study are consistent with these recommendations. The results are consistent with these guidelines.
【Research institution】
Heinrich Heine University (Germany),
German Diabetes Research Center, etc.
Role of diet in type 2 diabetes incidence: umbrella review of meta-analyses of prospective observational studies
BMJ 365, l2368, 2019
