Network meta-analysis reaches nutrition research

Excerpt

Network meta-analysis (NMA) is increasingly recognized as a promising evidence synthesis method commonly allowing stronger conclusions on the comparative effectiveness of healthcare interventions than conventional pairwise meta-analysis [1]. Its strength arises from the fact that it allows to synthesize both direct and indirect evidence from randomized trials. It is hence timely that Hui et al. recently published an NMA in the European Journal of Nutrition [2], comparing the effects of different whole grains (oat, brown rice, barley, and wheat) and brans (oat bran and wheat bran) on blood lipids (total cholesterol, LDL-C, HDL-C, and triacylglycerols), using data from 55 trials. NMA allows inference on every possible pairwise comparison of interventions within a connected network. For example, in the paper by Hui et al. [2], oat bran and barley have not been directly compared in a randomized trial, but each has been compared with wheat (Fig. 1). As such, an indirect comparison between oat bran and barley can be obtained. Sometimes, the relative effects estimated by the network may rely to a notable extent on indirect comparisons (i.e., for which no trials were ever conducted); the influence of direct and indirect evidence on the results can be seen using the contribution matrix [3, 4]. In fact, in the NMA by Hui et al., the contribution of direct evidence to the relative effects estimated by the network was very low ranging from 0.3% (oat vs. wheat) to 15.9% (wheat vs. control). …