Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. In this meta-analysis, both high-intensity interval training and moderate-intensity continuous training showed a significant improvement in maximum fat oxidation compared to controls in patients with overweight and obesity.

2. Furthermore, there was a significant dose-response effect between exercise intensity and maximum fat oxidation during moderate-intensity continuous training.

Evidence Rating Level: 1 (Excellent)

High body mass index (BMI) is well-known to increase the risk and worsen the prognosis of a multitude of diseases. With the increasing prevalence of overweight and obesity in the population, finding solutions ways to combat high BMI has become crucial. Exercise—such as high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT)—are potential therapeutic interventions. Maximum fat oxidation (MFO) is a measurement describing the optimal use of fat as a fuel source that is linked to weight loss maintenance, metabolic health, and fitness levels. With critical knowledge gaps of how HIIT or MICT influence MFO in individuals with overweight and obesity, this systematic review and meta-analysis aimed to gain clarity on this relationship and potential exercise factors that may influence exercise prescription.

Of 790 publications screened, 13 were included, with a total of 519 individuals—136 participated in HIIT, 235 participated in MICT, and 148 were in the control group. Inclusion criteria were adults aged 18-60 years with BMI >25 kg/m2, studies that were randomized controlled trials, completion of either HIIT or MICT, measurement of MFO, and studies that included a non-exercise control group. Exclusion criteria were individuals who participated in a structured training protocol for at least three months prior to the study. The review was conducted in compliance with the PRISMA guidelines. The effects of HIIT and MICT on MFO were represented as a mean difference (MD) and standard mean difference (SMD). The primary outcome measure was an increased MD of MFO in an exercise intervention when compared to the control group.

The results demonstrated that both HIIT and MICT showed significantly increased MFO in people with overweight or obesity when compared to the control group. Furthermore, a dose-response relationship was established between the exercise intensity of individuals in the MICT group and the effect on MFO. It was not possible to show this relationship in the HIIT group due to heterogeneity and the limited number of HIIT studies. Finally, there was no significant difference between the effect of MICT vs. HIIT interventions on MFO in the study population. However, this review included studies of varying exercise intervention modalities, making comparison and generalizability difficult. Nonetheless, this systematic review was the first to examine the effect of MICT and HIIT on MFO in adults with overweight and obesity.

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