ABSTRACT
Objective: To systematically summarise and evaluate the existing evidence on the effect of diet on the management of type 2 diabetes and prevention of complications. Design: Umbrella review of systematic reviews with meta-analyses of randomised controlled trials. Data sources: PubMed, Embase, Epistemonikos, and Cochrane, from inception up to 5 June 2022. Eligibility criteria for selecting studies: Systematic reviews with meta-analyses of randomised controlled trials reporting summary effect estimates on the effect of diet on any health outcome in populations with type 2 diabetes were included in the review. Only meta-analyses with randomised controlled trials with the duration of at least 12 weeks were eligible for inclusion. Summary data were extracted by two investigators independently. Summary effect estimates with 95% confidence intervals were recalculated with a random effects model if the information provided was insufficient. Methodological quality was assessed with the A MeaSurement Tool to Assess systematic Reviews (AMSTAR) 2 tool and the certainty of evidence with the Grading of Recommendations Assessment, Development, and Evaluations (GRADE) approach. Results: 88 publications with 312 meta-analyses of randomised controlled trials were included. Methodological quality was high to moderate in 23% and low to very low in 77% of the included publications. A high certainty of evidence was found for the beneficial effects of liquid meal replacement on reducing body weight (mean difference -2.37 kg, 95% confidence interval -3.30 to -1.44; n=9 randomised controlled trials included in the meta-analysis) and body mass index (-0.87, -1.32 to -0.43; n=8 randomised controlled trials), and of a low carbohydrate diet (<26% of total energy) on levels of haemoglobin A1c (-0.47%, -0.60% to -0.34%; n=17 randomised controlled trials) and triglycerides (-0.30 mmol/L, -0.43 to -0.17; n=19 randomised controlled trials). A moderate certainty of evidence was found for the beneficial effects of liquid meal replacement, plant based, Mediterranean, high protein, low glycaemic index, and low carbohydrate diets (<26% total energy) on various cardiometabolic measures. The remaining results had low to very low certainty of evidence. Conclusions: The evidence indicated that diet has a multifaceted role in the management of type 2 diabetes. An energy restricted diet can reduce body weight and improve cardiometabolic health. Beyond energy restriction, dietary approaches such as plant based, Mediterranean, low carbohydrate (<26% total energy), or high protein diets, and a higher intake of omega 3 fatty acids can be beneficial for cardiometabolic health in individuals with type 2 diabetes. Systematic review registration: PROSPERO CRD42021252309.
ABSTRACT
BACKGROUND: Physical activity is a cornerstone in diabetes management; however, evidence synthesis on the association between physical activity and long-term diabetes-related complications is scarce. PURPOSE: To summarize and evaluate findings on physical activity and diabetes-related complications, we conducted a systematic review and meta-analysis. DATA SOURCES: We searched PubMed, Web of Science, and the Cochrane Library for articles published up to 6 July 2021. STUDY SELECTION: We included prospective studies investigating the association between physical activity and incidence of and mortality from diabetes-related complications, i.e., cardiovascular disease (CVD), coronary heart disease, cerebrovascular events, heart failure, major adverse cardiovascular events, and microvascular complications such as retinopathy and nephropathy, in individuals with diabetes. DATA EXTRACTION: Study characteristics and risk ratios with 95% CIs were extracted. Random-effects meta-analyses were performed, and the certainty of evidence and risk of bias were evaluated with use of the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) and Risk Of Bias In Non-randomised Studies - of Interventions (ROBINS-I) tools. DATA SYNTHESIS: Overall, 31 studies were included. There was moderate certainty of evidence that high versus low levels of physical activity were inversely associated with CVD incidence, CVD mortality (summary risk ratio 0.84 [95% CI 0.77, 0.92], n = 7, and 0.62 [0.55, 0.69], n = 11), and microvascular complications (0.76 [0.67, 0.86], n = 8). Dose-response meta-analyses showed that physical activity was associated with lower risk of diabetes-related complications even at lower levels. For other outcomes, similar associations were observed but certainty of evidence was low or very low. LIMITATIONS: Limitations include residual confounding and misclassification of exposure. CONCLUSIONS: Physical activity, even below recommended amounts, was associated with reduced incidence of diabetes-related complications.
