Nuts in Relation to Markers of Adiposity, Overweight, and Obesity: A Series of Systematic Reviews and Meta-analyses of Randomized Controlled Trials and Prospective Cohort Studies

Background: Peanuts and tree nuts (almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pine nuts, pistachios and walnuts) are an important source of unsaturated fatty acids, vegetable protein, and fibre, as well as minerals, vitamins, and phytonutrients. The FDA has permitted health claims for tree nuts for cardiovascular disease risk reduction and the cardiovascular benefits of nuts is acknowledged [FDA, 2015; Bao et al., 2013; Sabate et al., 2010]; however, intake of tree nuts is low in Canada. Based on the 2004 Canadian Community Health Survey (CCHS), <5% of Canadians consumed nuts on any given day with a mean intake of 18 g/day in those consuming nuts [PHAC, 2004]. This intake level is far below the 42 g/day amount recommended by the FDA for cardiovascular risk reduction. One of the barriers to increasing the consumption of nuts is the perception that they may contribute to weight gain more than other "healthy foods" owing to their high energy density. With the rise in overweight and obesity and its downstream cardiometabolic complications, heart and diabetes associations have cautioned against the over consumption of nuts at the same time that they recommend them for heart health [Sievenpiper et al., 2013; Evert et al., 2014; Anderson et al., 2013]. In a series of earlier systematic reviews and meta-analyses, we have shown that nuts improve glycemic control and metabolic syndrome criteria, findings which run contrary to any expected weight gain [Viguiliouk et al., 2014; Blanco Mejia et al., 2014]. Although an earlier systematic review and meta-analysis of controlled trials showed a lack of effect of nut intake on body weight [Flores-Mateo et al., 2013], it remains unclear whether nuts have an increasing, neutral, or even decreasing effect on a broader set of markers of adiposity.

Need for proposed research:The lack of high quality syntheses and knowledge translation to reconcile the benefits of nuts with potential weight gain represents an urgent call for stronger evidence. High quality systematic reviews and meta-analyses of randomized controlled trials and prospective cohort studies represent the highest level of evidence to support dietary guidelines and public health policy development.

Objective: The investigators will conduct a series of systematic reviews and meta-analyses to (1) distinguish the effect of peanuts and tree nuts on body weight and markers of adiposity in randomized controlled trials and (2) assess peanut and tree nut consumption with incident overweight/obesity and changes in weight and markers of adiposity in prospective cohort studies.

Design: Each systematic review and meta-analysis will be conducted according to the Cochrane Handbook for Systematic Reviews of Interventions and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [Higgins et al., 2011; Moher et al., 2009].

Data sources: MEDLINE, EMBASE, and The Cochrane Central Register of Controlled Trials (Clinical Trials; CENTRAL) will be searched using appropriate search terms supplemented by hand searches of references of included studies.