12-Month Once-a-week HIIT Improves Body Adiposity and Liver Fat

Obesity and non-alcoholic fatty liver disease (NAFLD) are two related growing epidemics that are becoming pressing public health concerns. High-intensity interval training (HIIT) is a promising cost-effective and time-efficient exercise modality for managing obesity and NAFLD. However, patients with obesity and NAFLD are generally inactive and unfit, and might feel intimidated by the frequency of the prescribed HIIT (conventionally three times weekly). Previous HIIT studies, mostly over 2-4 month periods, showed that the participants could accomplish this exercise frequency under a controlled laboratory environment, but the long-term adherence and sustainability, especially in a field setting, remains uncertain. The situation is more unclear if we also consider those individuals who refused to participate possibly because of their overwhelming perceptions or low self-efficacy toward HIIT. Thus, logically, HIIT at a lower frequency would be practical and more suitable for patients with obesity and NAFLD, but the minimum exercise frequency required to improve health, especially in the long-term, is unknown. This proposed study aims to examine the effectiveness of long-term low-frequency HIIT for improving body adiposity and liver fat in centrally obese adults. The premise of this proposal is supported by recent findings that HIIT performed once a week could improve cardiorespiratory fitness, blood pressure, cardiac morphology, metabolic capacity, muscle power, and lean mass. This study will provide evidence for the benefits of long-term low-frequency HIIT with a follow-up period to assess its effectiveness, safety, adherence, and sustainability. We expect this intervention will enhance the practical suitability of HIIT in inactive obese adults and will provide evidence for low-frequency HIIT as a new exercise option in the management of obesity and NAFLD.

Inclusion Criteria: 1. Cantonese, Mandarin or English speaking, 2. Aged 18-60, 3. Central obesity, defined as BMI ≥25 (obesity classification adopted by the Hong Kong Government) with waist circumference of ≥90 cm for men and ≥80 cm for women (abdominal obesity according to the International Diabetes Federation's Chinese ethnic-specific criterion), 4. Willing to initiate lifestyle modification but not pharmacologic or surgical means for treating obesity. Exclusion criteria: 1. ≥150 minutes moderate-intensity exercise or ≥75 minutes vigorous exercise weekly, 2. Regular HIIT (≥1 weekly) in the past six months, 3. Medical history of cardiovascular disease, chronic pulmonary or kidney disease, heart failure, cancer, and liver disease except for NAFLD, 4. Somatic conditions that limit exercise participation (e.g., limb loss), 5. Impaired mobility due to chronic diseases (e.g., chronic arthritis/osteoarthritis, neurological, musculoskeletal and autoimmune diseases), 6. Daily smoking habit, 7. Excess alcohol consumption (daily ≥30 g of alcohol for men and ≥20 g for women) in the past six months 8. Surgery, therapy or medication for obesity or weight loss in the past 6 months (e.g., gastric bypass, gastric band, sleeve gastrectomy, gastric reduction duodenal switch, and dietitian-prescribed dietary program). 9. During the study period, subjects identified with major physical changes that would considerably affect their body composition and weight (e.g., anorexia nervosa, bulimia nervosa, and prolonged gastrointestinal and digestive disorders) will be excluded.