Effects of Hazelnut Consumption on Blood Lipids and Body Weight: A Systematic Review and Bayesian Meta-Analysis

Hazelnuts are rich in monounsaturated fatty acids and antioxidant bioactive substances: their consumption has been associated with a decreased risk of cardiovascular disease events. A systematic review and a meta-analysis was performed to combine the results from several trials and to estimate the pooled (overall) effect of hazelnuts on blood lipids and body weight outcomes. Specifically, a Bayesian random effect meta-analysis of mean differences of Δ-changes from baseline across treatment (MDΔ) (i.e., hazelnut-enriched diet vs. control diet) has been conducted. Nine studies representing 425 participants were included in the analysis. The intervention diet lasted 28-84 days with a dosage of hazelnuts ranging from 29 to 69 g/day. Out of nine studies, three randomized studies have been meta-analyzed showing a significant reduction in low-density lipoprotein (LDL) cholesterol (pooled MDΔ = -0.150 mmol/L; 95% highest posterior density interval (95%HPD) = -0.308; -0.003) in favor of a hazelnut-enriched diet. Total cholesterol showed a marked trend toward a decrease (pooled MDΔ = -0.127 mmol/L; 95%HPD = -0.284; 0.014) and high-density lipoprotein (HDL) cholesterol remained substantially stable (pooled MDΔ = 0.002 mmol/L; 95%HPD = -0.140; 0.147). No effects on triglycerides (pooled MDΔ = 0.045 mmol/L; 95%HPD = -0.195; 0.269) and body mass index (BMI) (pooled MDΔ = 0.062 kg/m²; 95%HPD = -0.293; 0.469) were found. Hazelnut-enriched diet is associated with a decrease of LDL and total cholesterol, while HDL cholesterol, triglycerides and BMI remain substantially unchanged.