Scientific Study

The primary aim was to investigate the effects of nut and seed consumption on markers of glucose metabolism in adults with prediabetes. Studies with a randomized controlled trial (RCT) design, comparing the effects of a diet containing nuts or seeds against a diet without nuts or seeds in adults with prediabetes, were considered eligible. Primary outcome measures included fasting plasma glucose (FPG), 2-hour plasma glucose (PG) during oral glucose tolerance test (OGTT) and glycated haemoglobin (HbA1c) concentrations. Studies were identified by searching PubMed and Scopus electronic databases and by checking full texts and reference lists of relevant records. Risk of bias was assessed using the Cochrane Collaboration's tool. We included 5 RCTs involving 371 adults with prediabetes or at risk of diabetes; 3 RCTs investigated the effects of whole nut consumption and 2 the effects of ground flaxseed consumption. Consumption of 57 g/day pistachios or mean intake of 60 g/day almonds for 4 months improved FPG and fasting plasma insulin (FPI) concentrations, insulin resistance, cellular glucose uptake in lymphocytes and β-cell function. Consumption of 56 g/day walnuts for 6 months was not found to affect FPG or HbA1c concentrations. Consumption of 13 g/day flaxseed for 3 months improved FPG and FPI concentrations and insulin resistance. In a second study, however, flaxseed consumption was not found to affect markers of glucose metabolism. The risk of bias was generally low, thus the reported results could be reliable. Further investigation of nut and seed consumption effects in the field of prediabetes is warranted.