The effects of Mediterranean diet with and without exercise on body composition in adults with chronic disease: A systematic review and meta-analysis of clinical trials

The Mediterranean diet (MedDiet), with and without energy restriction, has been associated with reduced risk of numerous chronic diseases, including type 2 diabetes and cardiovascular disease. Exercise is well known to improve various health outcomes in individuals with chronic diseases and emerging evidence indicates that combining diet and exercise may be superior to individual interventions. The primary aim of this systematic review and meta-analysis was to assess the effects of all MedDiet interventions (regardless of exercise or energy restriction), as well as MedDiet alone (and in hypocaloric and isocaloric subgroups) on body composition outcomes [weight, waist circumference (WC), body mass index (BMI), body fat (BF), lean mass (LM) and visceral adipose tissue (VAT)] in adults with chronic disease. Secondary aims were to assess the effects of MedDiet plus exercise, including in hypocaloric and isocaloric subgroups, on body composition outcomes. Four electronic databases (ProQuest, Medline, Embase and CINAHL) were searched from inception to January 2025. Randomised controlled trials including MedDiet interventions in adults with chronic diseases that assessed body composition as outcomes were included. Outcomes were pooled using random-effect meta-analysis for MedDiet interventions compared with controls to determine the standardised mean difference. Twenty papers were included in the systematic review and meta-analysis, reporting data from 17 unique studies. Reductions in BMI (SMD = -1.21, P = 0.01) and VAT (SMD = -0.12, P = 0.02) and improvements in LM (SMD = 0.11, P = 0.01) were found in meta-analytic models including all MedDiet interventions (regardless of exercise or energy restriction). MedDiet alone did not result in significant changes in any body composition outcomes. Interventions combining MedDiet plus exercise had statistically significant effects on reducing weight (SMD = -0.19), BMI (SMD = -0.27), WC (SMD = -0.39), BF (SMD = -0.13) and VAT (SMD = -0.12), with all P < 0.05. Although effect sizes were small, the estimated absolute reductions were approximately 2.5 kg in weight, 1.0 kg/m2 in BMI, 3.5 cm in WC and 102 g in VAT, based on SD reported previously in the literature. Subgroup analysis showed that hypocaloric MedDiet plus exercise significantly reduced BMI (SMD = -0.24, P = 0.01), BF (SMD = -0.13, P = 0.01), and VAT (SMD = -0.12, P = 0.02), while isocaloric MedDiet with exercise led to significant reductions in weight (SMD = -0.18, P = 0.04), BMI (SMD = -0.24, P = 0.02), and WC (SMD = -0.32, P = 0.0) relative to controls. MedDiet interventions (regardless of exercise or energy restriction) led to improvements in BMI, LM and VAT. MedDiet in combination with exercise, with or without energy restriction improved all body composition outcomes, with the exception of LM. These novel findings highlight the potential importance of a multimodal intervention, integrating the MedDiet with exercise for chronic disease management. This systematic review and meta-analysis has been registered with PROSPERO (CRD42022358345).