Exercise plus IF better than IF alone at improving body composition and cardiometabolic health

A systematic review and meta-analysis conducted by researchers from the Chinese University of Hong Kong and Hong Kong Baptist University has shown that combining exercise with intermittent fasting (IF) is associated with greater reductions in fat mass and waist circumference (WC) as well as more substantial improvements in cardiometabolic health parameters in overweight and obese individuals than IF alone.

Exercise plays a crucial role in supporting endocrine health by regulating metabolic hormones like insulin and cortisol, which may amplify the benefits of IF by improving insulin sensitivity and reducing stress-related hormonal responses. [Rev Endocr Metab Disord 2023;24:251-266] “Understanding whether exercise provides significant additional benefits when combined with IF would allow interventions to be tailored more effectively for individuals with overweight or obesity,” postulated the researchers.

The present systematic review and meta-analysis included 12 articles derived from 10 studies involving a total of 616 participants (mean age, 40 years; female, 87.3 percent) with overweight or obesity (mean body-mass index [BMI], 33.6 kg/m²) from Australia, Brazil, Norway, Thailand, Tunisia, and US, which compared the effects of exercise plus IF vs IF alone on various anthropometric, body composition and glycaemic outcomes. [Curr Obes Rep 2025;14:54]

Interestingly, the analysis showed no significant difference in body mass or BMI changes between the combined intervention and IF alone. However, the combined strategy was associated with a lower level of fat mass vs IF alone (mean difference [MD], -0.93 kg; p=0.01), which was supported by a moderate certainty of evidence. The analysis also showed, with a low level of certainty, that the combined strategy led to a greater reduction in WC (MD, -2.51 cm; p<0.001). “These findings indicate that while IF primarily drives overall weight loss, exercise plays a distinct role in optimizing body composition through targeted fat mass reduction,” commented the researchers.

The combined strategy was associated with lower insulin level than IF alone (MD, -3.10 µIU/mL; p<0.001), as well as lower values for homeostatic model assessment for insulin resistance (HOMA-IR), which was evaluated as an outcome measure in eight studies involving a total of 269 individuals (standardized MD, -0.57; p<0.001). The evidence was of a low level of certainty for both assessments.

IF diets have certain therapeutic effects on blood glucose in patients with metabolic syndrome and significantly improve insulin resistance. [Int J Endocrinol 2022;doi:10.1155/2022/699990] In adults with overweight or obesity, exercise enhances glycaemic control by boosting insulin sensitivity and glucose uptake in muscles. [Nat Rev Mol Cell Biol 2023;24:607-632] “Physical activity induces muscle contractions that prompt glucose transporters to translocate to the cell surface, facilitating insulin-independent glucose entry. Furthermore, exercise activates AMP-activated protein kinase, a key enzyme that enhances insulin signalling and mitochondrial function, collectively improving the body's capacity to regulate blood sugar levels and reduce insulin resistance,” explained the researchers. [Nat Rev Endocrinol 2017;13:133-148]

The addition of exercise to IF led to a lower resting heart rate (-2.68 bpm; p=0.01; low certainty) and an elevated VO_{2 max} (1.80 ml/kg/min; p=0.036; very low certainty). “While IF alone may maintain cardiorespiratory fitness [CRF] in healthy adults, its impact on individuals with overweight or obesity remains ambiguous. Notably, higher CRF levels can help protect against obesity-related cardiovascular complications, highlighting the clinical significance of incorporating exercise into weight management programmes,” concluded the researchers. [BMJ Open Sport Exerc Med 2024;10:e001831; Curr Obes Rep 2020;9:571-581]