Abstract
Background: In previous meta-analyses of prospective observational studies, we investigated the association between food groups and risk of chronic disease. Objective: The aim of the present network meta-analysis (NMA) was to assess the effects of these food groups on intermediate-disease markers across randomized intervention trials. Design: Literature searches were performed until January 2018. The following inclusion criteria were defined a priori: 1) randomized trial (≥4 wk duration) comparing ≥2 of the following food groups: refined grains, whole grains, nuts, legumes, fruits and vegetables, eggs, dairy, fish, red meat, and sugar-sweetened beverages (SSBs); 2) LDL cholesterol and triacylglycerol (TG) were defined as primary outcomes; total cholesterol, HDL cholesterol, fasting glucose, glycated hemoglobin, homeostasis model assessment insulin resistance, systolic and diastolic blood pressure, and C-reactive protein were defined as secondary outcomes. For each outcome, a random NMA was performed, and for the ranking, the surface under the cumulative ranking curves (SUCRA) was determined. Results: A total of 66 randomized trials (86 reports) comparing 10 food groups and enrolling 3595 participants was identified. Nuts were ranked as the best food group at reducing LDL cholesterol (SUCRA: 93%), followed by legumes (85%) and whole grains (70%). For reducing TG, fish (97%) was ranked best, followed by nuts (78%) and red meat (72%). However, these findings are limited by the low quality of the evidence. When combining all 10 outcomes, the highest SUCRA values were found for nuts (66%), legumes (62%), and whole grains (62%), whereas SSBs performed worst (29%). Conclusion: The present NMA provides evidence that increased intake of nuts, legumes, and whole grains is more effective at improving metabolic health than other food groups. For the credibility of diet-disease relations, high-quality randomized trials focusing on well-established intermediate-disease markers could play an important role.
Key Findings
The 2016 Global Burden of Disease study suggested that nearly 20% of all deaths worldwide were accountable to dietary risk factors and previous meta-analyses of prospective observational studies suggest a lower disease risk for the consumption of food groups of plant origin compared to certain groups of animal origin and sugar-sweetened beverages (SSBs). The current review suggests that Network meta-analyses (NMA) can be used to “close the gap” between evidence from prospective observational studies and RCTs. The aim of the current review was to investigate the hypothesis that increased intake of foods of plant origin is more effective at the primary prevention of metabolic disturbances and diseases than intake of other food groups. This paper performed a search for randomized studies comparing at least two food groups from refined grains, whole grains, fruits and vegetables, nuts, legumes, eggs, dairy, fish, red meat and SSBs with primary outcomes including LDL cholesterol and triacylglycerol (TG) and secondary outcomes including total cholesterol, HDL cholesterol, fasting glucose, blood pressure amongst others. The study included 66 trials in the review covering 3595 participants and performed an NMA for each outcome along with the determination of the surface under the cumulative ranking curve (SUCRA) for ranking outcomes. For secondary outcomes, nuts had the highest SUCRA value (92%) for total cholesterol reduction while fish had the highest SUCRA value (91%) for HDL cholesterol improvement. Whole grains showed the highest SUCRA value (87%) for improvements in fasting glucose, fruit and vegetables had the highest value (91%) for improvements in systolic blood pressure with red meat (74%) having the highest value for diastolic blood pressure improvements. Across all outcomes, the study found that nuts (66%), legumes (62%) and whole grains (62%) had the highest SUCRA values with SSBs (2%) showing the worst value. This is further support for flaxseed – as a quasi whole grain – in a healthy diet.