Both time-restricted eating, a type of intermittent fasting that means you can only eat during a specific time window of the day, and high-intensity interval training (HIIT) have been shown to be beneficial for cardiometabolic health in people overweight and at risk of serious diseases. Now, a randomized controlled trial has wanted to test whether the combination of these two approaches is more effective than either of them separately. The results, published in the journal Cell Metabolism, show that together improved glycemic control long-term average compared to a no-intervention control group. Furthermore, it induced two-fold reductions in fat mass and visceral fat area compared to each intervention alone.
“Time-restricted eating and HIIT alone have received increasing attention as effective and feasible strategies for at-risk populations,” said Trine Moholdt, head of the Exercise, Cardiometabolic and Reproductive Health Research Group at the Norwegian University. of Science and Technology (NTNU) and the lead author of the study. “We wanted to compare the effects of the combination of both and their effects separately and determine if they would act synergistically to improve health in people at risk of cardiometabolic disease. This finding highlights the importance of changing dietary and physical activity habits for people who want to rapidly improve their health and reduce their risk of disease,” she says.
The trial had four arms: HIIT alone, intermittent fasting alone, the intermittent fasting-HIIT combination, and a control group. A total of 131 women were enrolled, with 32 or 33 in each arm. All were overweight or obese and had risk factors for cardiometabolic diseases such as type 2 diabetes and cardiovascular disease.
Time-restricted feeding consisted of consuming all daily calories within a 10 hour time window. HIIT training was defined as exercise performed at 90% of maximum heart rate for 35 minutes, three times per week. The physical activity sessions were supervised by the researchers and the participants were asked to record their first and last calories each day.
The interventions lasted 7 weeks. Various measurements were taken both before and after the study, including the participants’ blood pressure, body mass index, blood fat and cholesterol levels, and blood glucose and insulin levels.
The researchers found that participants who combined intermittent fasting and HIIT were able to improve your glycemic control long-term average measured by glycosylated hemoglobin (HbA1c) test. They could also effectively reduce fat mass and the visceral fat and increase your cardiorespiratory fitness measured as maximal oxygen uptake. However, there were no statistically significant differences in blood lipids, appetite hormones, or vital signs after any of the interventions compared to the control group.
Another important finding of the study was that adherence was high. “Compliance rates with general lifestyle recommendations are low, and our diet and exercise strategies may serve as an alternative,” said first author Kamilla La Haganes, a doctoral student at NTNU. In fact, after the study ended, 18 participants in the control group also chose to try one of the study interventions.
“We recommend this type of program for people who want a relatively easy way to change their diet and exercise habits and improve their health. Time-restricted feeding is a time efficient method to lose weight and less tedious compared to daily calorie counting, and HIIT is tolerable and safe for previously sedentary people and can be completed in 30 to 40 minutes,” advises Moholdt.
A limitation of the study was that the intervention period was only 7 weeks. Longer-term investigations are needed to determine effects and viability over longer periods of time. It was also carried out during the Covid-19 lockdown, which affected the lifestyle of the participants and could have influenced the results.
The researchers are currently inviting participants for follow-up testing 2 years after completing the study to find out if they have continued with the interventions. They also plan to determine if the combination of time-restricted eating and HIIT it will induce the same health benefits and have equally good adherence rates in a completely home-based setting. That study will include both men and women. “Together, these two new studies will give us more information about long-term feasibility and also about the possibility of implementation in a real-world environment. In addition, we can investigate if there are sex differences in response to these interventions, “Haganes concludes.