<qa>  What is the name of the study that will be used for crossover trials?Data synthesis: Mean differences will be pooled for the trials and risk ratios for the cohorts using the generic inverse variance method. Random-effects models will be used even in the absence of statistically significant between-study heterogeneity, as they yield more conservative summary effect estimates in the presence of residual heterogeneity. Fixed-effects models will only be used where there is 5 included studies. Paired analyses will be applied for crossover trials. Heterogeneity will be assessed by the Cochran Q statistic and quantified by the I2 statistic. To explore sources of heterogeneity, the investigators will conduct sensitivity analyses, in which each study is systematically removed. If there are 10 studies, then the investigators will also explore sources of heterogeneity by a priori subgroup analyses by age children 18 years of age, adults, health status metabolic syndromediabetes, overweight, normal weight, comparator carbohydrate, mixed macronutrient, animal protein, other, nut type, nut dose, baseline measurements, randomization, study design parallel, crossover, energy balance positive, neutral, negative, duration of follow-up, and risk of bias. Meta-regression analyses will assess the significance of categorical and continuous subgroups analyses. When 10 studies are available, publication bias will be investigated by inspection of funnel plots and formal testing using the Egger and Begg tests. If publication bias is suspected, then the investigators will attempt to adjust for funnel plot asymmetry by imputing the missing study data using the Duval and Tweedie trim and fill method. 