Vigorous- Versus Moderate-intensity Exercise to Reduce Liver Fat in Adults With Obesity and NAFLD

Summary

Non-alcoholic fatty liver disease (NAFLD) arising from obesity has become a global health concern. Although exercise is a cornerstone approach for managing NAFLD, detailed exercise prescription guidelines are unavailable. According to World Health Organization (WHO) recommendations, 1 minute of vigorous-intensity physical activity can achieve equivalent health benefits to 2 minutes of moderate-intensity physical activity. It is not known whether this relationship is applicable to exercise prescribed as an adjunct therapy in NAFLD treatment. The answer has public health implications because people living with NAFLD can potentially opt for safe higher-intensity exercise requiring less of a time commitment, whereas those in older age groups or with comorbidities, for whom vigorous exercise is unsuitable, can adopt a moderate-intensity regimen of longer duration to acquire equivalent therapeutic outcomes. Adults with obesity and NAFLD will be randomly allocated to a supervised vigorous- or moderate-intensity walking group or usual care control group. Each exercise group will receive a 16-week intervention comprising three walking sessions weekly, whereas the usual care group will receive general health education as the attention control. The per-session walking time will be 25 minutes for the vigorous group and 50 minutes for the moderate group, equating to the same weekly exercise volume and caloric expenditure for each group according to the WHO's minimum physical activity recommendation. Outcome measures, including liver fat, visceral and body fat, body anthropometry, intervention adherence, psychological measures, health-related quality of life, medication usage, adverse events, habitual physical activity, and diet, will be examined by assessors blinded to the group allocation at baseline, 16 weeks (post-intervention), and 42 weeks (26-week post-intervention follow-up). Data will be analyzed by generalized estimating equations and linear contrasts. The proposed study will provide evidence on the presumed equivalent benefits of vigorous- and moderate-intensity exercise, with a follow-up period allowing assessment of the efficacy, safety, adherence, and sustainability of each. The findings will inform practitioners of the role of exercise intensity in reducing liver fat and refine the exercise guidelines for NAFLD patients.

Eligibility

Inclusion Criteria:

* Cantonese, Mandarin, or English-speaking Chinese,
* aged 18-69,
* centrally obese according to the Asia-specific cut-off (waist circumference 90 cm for males, 80 cm for females) and BMI ≥23 (i.e., overweight as defined by the Hong Kong government),
* with NAFLD (defined as \>5% intrahepatic triglycerides assessed by 1H-MR spectroscopy),
* able to perform the prescribed exercise program. Both men and women will be included to enhance generalizability.

Exclusion Criteria:

* regular exercise training (\>3 sessions of \>60 min of moderate-intensity exercise training weekly) in the past 6 months,
* medical history of cardiovascular disease, chronic pulmonary or kidney disease, heart failure, cancer, and/or liver disease except NAFLD,
* somatic conditions that limit exercise participation (e.g., limb loss),
* impaired mobility due to chronic disease (e.g., chronic arthritis/osteoarthritis, neurological, musculoskeletal, and autoimmune diseases),
* daily smoking habit,
* excess alcohol consumption (daily ≥20 g of alcohol for men and ≥10 g for women) in the past 1 year,
* consumption of certain drugs (e.g., tamoxifen and estrogen) known to be secondary causes of steatosis,
* surgery and therapy for morbid obesity in the past 6 months and during the study period (e.g., gastric bypass, gastric band, sleeve gastrectomy, gastric reduction duodenal switch, or dietitian-prescribed dietary program).

Conditions3

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