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.

Non-alcoholic fatty liver disease (NAFLD) arising from obesity has become a global health concern. As well as being a risk factor for cardiovascular disease, diabetes, and chronic kidney disease, it has also been identified as a precursor to severe liver disease. Given that there is no available licensed drug for the treatment of NAFLD, the proposed research seeks to contribute to the treatment and management of NAFLD by comparing two walking exercise regimens as a lifestyle intervention. Using a robust randomized controlled equivalence trial design, it will seek an answer to this research question: Does vigorous-intensity exercise induce equivalent benefits in reducing liver fat relative to moderate-intensity exercise at matched weekly exercise volumes aligned with the World Health Organization's (WHO) minimum physical activity recommendation, and can the two regimens improve NAFLD to a similar degree? Our results are expected to provide scientific evidence-based conclusions revealing the optimal exercise intensity for NAFLD treatment in patients with obesity. The proposed study is novel, with worldwide implications for NAFLD management. The walking programs will be delivered in accordance with the WHO's minimal physical activity recommendations, thereby putting into practice the standardized WHO physical activity guidelines, even for unfit beginners for whom minimal exercise is a more feasible goal. The project thus has two objectives:

1. To examine the therapeutic efficacy of a walking exercise intervention, at either moderate- or vigorous-intensity, for reducing liver fat in adults with obesity and NAFLD. The two exercise intensities to be tested are based on the operational definition of the WHO, and the weekly exercise volumes are aligned with the WHO's minimum physical activity recommendation.

   It is important to elucidate the practical value of the therapeutic efficacy of the walking exercise intervention, at either moderate- or vigorous-intensity, because inactive patients with obesity begin exercise training programs with lower, more achievable goals to learn how to train safely and then adapt progressively, thereby building a sense of self-efficacy and self-confidence to continue adherence. Hence, the proposed research has practical value, as it will provide research evidence on the WHO's minimum exercise guidelines, ultimately contributing to the management and treatment of NAFLD among obese adults.

2. To compare the equivalence of the head-to-head therapeutic efficacy of moderate-intensity exercise versus vigorous-intensity exercise with matched weekly exercise volumes for reducing liver fat in adults with obesity and NAFLD.

This study has important scientific and practical value because it will address an unanswered scientific question: Does vigorous-intensity exercise induce equivalent benefits for reducing liver fat in comparison with moderate-intensity exercise at matched weekly exercise volumes? Its findings will be of practical public health significance to people living with obesity and NAFLD, as they will have the option to engage in vigorous-intensity exercise for a shorter duration or moderate-intensity exercise for a longer duration, following the WHO's physical activity recommendation (75 minutes of vigorous-intensity or 150 minutes of moderate-intensity exercise weekly). This flexibility aligns with the concept of "personalized medicine" and is likely to facilitate patient adherence to an exercise program. If the results show a moderate-intensity exercise regimen with a longer per-session exercise duration to demonstrate an equivalent therapeutic response, the study will also be of important clinical value, especially for patients in older age groups or those with comorbidities, who may be frail and unable to participate in vigorous-intensity exercise. The proposed research is thus expected to provide new evidence to refine the exercise guidelines for NAFLD patients, thereby guiding these patients and their healthcare professionals as to the intensity of weekly exercise that is most suited to their personal circumstances and lifestyles.

The investigators will test two hypotheses: 1) a 16-week moderate- or vigorous-intensity walking intervention, when delivered at the minimum amount of physical activity recommended by the WHO, significantly reduces liver fat in adults with obesity and NAFLD compared with a usual care control group (to be tested through designed superiority comparisons between the moderate/vigorous groups and control group), and 2) the therapeutic efficacy of vigorous-intensity exercise for reducing liver fat is equivalent to that of moderate-intensity exercise at matched weekly exercise volumes (i.e., 75 minutes of vigorous-intensity physical activity versus 150 minutes of moderate-intensity physical activity weekly) (to be tested through designed equivalence comparison between the vigorous and moderate groups).

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).

The data of individual participants that underlie the results reported in this trial, after de-identification including text, tables, figures, and appendices, as well as study protocol and statistical analysis plan, will be shared after 3 months of study publication. Data will be shared with researchers who provide a methodologically sound proposal for academic purposes. Proposals should be directed to pmsiu@hku.hk to gain access and for data request, a data-access agreement needs to be signed.

Beginning 3 months and ending 3 years following the publication of the article.

Data will be shared with researchers who provide a methodologically sound proposal for academic purposes. Proposals should be directed to pmsiu@hku.hk to gain access and for data request, a data-access agreement needs to be signed.

Random allocation will be performed after subjects have completed the baseline assessments. Subjects and the research personnel delivering the walking program and health education cannot be blinded to group allocation, but the latter will not be involved in the outcome assessments. All personnel involved in the outcome assessments will be blinded to the group allocation, and subjects will be instructed not to disclose their allocation during the assessments. The research personnel conducting the statistical analysis cannot be fully blinded to the treatment allocation for the between-group comparisons but will be blinded to subjects' identity.