Abstract
Background: Given global epidemics of obesity and diabetes, it is clear that adherence to current nutrition and activity guidelines is insufficient. Novel lifestyle interventions such as high intensity interval training (HIIT), intermittent fasting and paleolithic (Paleo) diets may provide alternative options and have proven beneficial for health in controlled studies. However, outcomes from real-world implementation are uncertain. Although HIIT is effective in laboratory settings to improve cardiorespiratory fitness, body composition and measures of metabolic health, it is unknown whether overweight adults will choose to perform HIIT, or can do so safely and effectively while unsupervised. Similarly, although unconventional dietary approaches such as intermittent fasting and Paleo diets produce weight loss and metabolic improvements in controlled trials, there is minimal evidence of long-term efficacy under free-living conditions. The aim of this study was to examine the real-world outcomes from these alternative exercise and dietary approaches in overweight and obese participants after 12 months.
Methods: Within a weight loss intervention evaluating the effect of different support strategies, 250 healthy adults who were overweight or obese chose to undertake unsupervised exercise programmes of HIIT or 30 minutes/day of moderate intensity exercise. Participants could also choose whether to follow intermittent fasting, modified Paleo, or a Mediterranean diet. Eligible participants underwent medical screening to identify health issues relevant to safety during vigorous exercise. HIIT participants received a medical assessment to identify any undiagnosed cardiovascular disease. Following a single supervised HIIT training session, they were advised to independently undertake HIIT three times a week for 12 months. A range of HIIT protocols were offered, with durations of intervals ranging from 30 seconds to 4 minutes, performed at an intensity of 8-10 on a 10-point scale of Rating of Perceived Exertion (RPE), with all HIIT protocols able to be completed within a 20-30 minute session. All participants also received dietary recommendations at baseline during a single education session, which included the exercise advice for those who chose daily moderate intensity exercise. Intermittent fasting participants were instructed to reduce caloric consumption to 25% of their recommended intake on two days each week, and Paleo participants were advised to reduce consumption of any grain-based foods and vegetable oils, and to eat a diet of mainly plant and animal based whole-foods. Those participants opting for the Mediterranean diet were encouraged to include wholegrains, fish, nuts and olive oil, while reducing red meat, sugar and saturated fat. Weight, body composition, blood pressure, aerobic fitness, physical activity, blood indices, dietary intake and psychological outcomes were assessed at 0, 6 and 12 months. Adherence to HIIT was assessed by heart rate monitoring of HIIT sessions over a one-week period every three months.
Results: Up to 19% of HIIT participants had relevant medical issues that could increase health risk during vigorous exercise that were not identified by screening questionnaires. One hundred and four participants (42%) chose to try HIIT and these participants were not leaner, fitter, or more active (all P>0.05) at baseline than those choosing moderate intensity daily exercise (n=146). Most HIIT participants (84.6%) could perform adequately intense HIIT during the initial supervised training session, but adherence to at least twice weekly unsupervised sessions decreased over time to only 19.6% by 12 months. There were no differences between exercise groups in weight (adjusted difference; 95% CI: -0.44kg; -2.5, 1.6), visceral fat (-103cm3; -256, 49), or MVPA (1 minute; -6, 8) at 12 months. However, within the HIIT cohort, adherent participants (23%) showed greater reductions in weight (-2.7kg; -5.2 -0.2) and visceral fat (-292cm3; -483, -101) than non-adherent participants. Intermittent fasting was the most popular dietary intervention (54%), but dietary choice did not result in differences in weight or body composition at 12 months. However, those following intermittent fasting had poorer glycaemic control and a worse lipid profile than those following the Mediterranean diet at 12 months.
Conclusions: Although HIIT was initially a popular choice, adherence declined rapidly over time, with less than one-quarter of participants undertaking regular unsupervised HIIT at 12 months. However, those who did adhere to HIIT experienced greater weight loss, visceral fat reduction and metabolic improvements than non-adherent participants, demonstrating that HIIT can be a useful alternative for some overweight people. Intermittent fasting was a popular diet choice, but when compared to a Mediterranean diet resulted in slightly worse metabolic outcomes after 12 months. These findings support current recommendations to consume diets rich in unprocessed whole-foods.