Time-Restricted Eating Vs. HIIT: which Achieves Greater Fat Reduction for Obesity?

Individuals with obesity and insulin resistance are at increased risk of cardiometabolic conditions, including diabetes, high blood pressure, and other cardiovascular diseases. Lifestyle interventions involving dietary modifications and increasing physical activity levels can reduce cardiometabolic risk, but adhering to these prescriptions is often challenging.

Moreover, these participants showed high levels of adherence to TRE and HIIT alone and in combination.

“Our findings of improved body composition, metabolic health, and high adherence rates suggest that women at high risk for cardiometabolic disorders can improve their health with a combined TRE + HIIT program and that it is safe and feasible for this population.”

Alternative weight loss strategies

Strategies for weight loss and maintenance primarily involve increasing physical activity and dietary changes. However, studies have shown that weight loss strategies such as reducing daily calorie intake and meeting recommended physical activity levels are associated with low levels of adherence.

This has led to an increase in interest in alternative weight loss strategies such as TRE and HIIT.

Time-restricted eating involves restricting the intake of calorie-containing foods to a specific time window, typically between 6 to 12 hours, during the day.

TRE does not limit the types of foods that can be consumed or the intake of calories during the eating window. This could promote better compliance than the standard weight loss strategy of calorie restriction.

“TRE offers a relatively simple method for changing dietary habits by only focusing on meal timing and usually induces a spontaneous reduction in energy intake without deliberate effort,” Dr. Moholdt said.

High-intensity interval training, on the other hand, involves repeated short bouts of high-intensity exercise interspersed with periods of rest or low- intensity activity.

Around 80% of adults in the United States do not meet the current physical activity guidelines that recommend moderate-intensity aerobic exercise for 150 minutes/week. HIIT requires a significantly lower time commitment and produces greater improvements in cardiorespiratory fitness than moderate-intensity training. Thus, HIIT may be a viable and time-efficient strategy for weight loss.

Previous studies have shown that TRE and HIIT in isolation can improve cardiovascular and metabolic health in individuals at risk of cardiometabolic disorders. Moreover, a combination of TRE and HIIT has been shown to facilitate weight loss and reduce body fat levels in trained athletes.

However, there is a lack of evidence on the effects of a combination of TRE and HIIT in individuals with obesity who have a more sedentary lifestyle.

In the present randomized controlled trial, the researchers examined the combined effect of time-restricted eating and HIIT in women of reproductive age with overweight/obesity.

Impact of combined HIIT and TRE

The researchers randomly assigned the 131 women with overweight/obesity enrolled in the study to one of the four groups—combined TRE and HIIT, TRE alone, HIIT alone, and the no-intervention control group. HIIT involved three sessions of treadmill exercise per week that were supervised by the researchers, whereas TRE involved restricting calorie intake to a 10-hour window during the day.

These interventions lasted for a total of seven weeks and the participants were administered an array of assessments to evaluate glycemic control and cardiometabolic health before and at the end of the intervention.

The primary assessment included the glucose tolerance test, which measures the ability of the body to absorb glucose. The researchers also assessed cardiorespiratory fitness and other metabolic markers of glucose metabolism and regulation, body composition, and blood lipid profile at baseline and after the study.

The researchers found that the participants in the isolated and combined TRE and HITT did not show any differences in glucose tolerance in comparison with the control group.

However, participants in the combined TRE and HITT group showed a greater reduction in the levels of glycated hemoglobin, a measure of long-term glycemic control, than either intervention alone. Glycated hemoglobin refers to the hemoglobin in red blood cells bound to glucose and reflects blood glucose levels over the previous 2-3 months.

All three interventions resulted in lower body weight and greater total and visceral fat mass loss than the no intervention control group.

Moreover, the combined TRE and HIIT group showed a two-fold greater decline in total and visceral fat mass than the TRE and HIIT in isolation. This is noteworthy since visceral fat, the fat that surrounds abdominal organs, is a risk factor for diabetes and other metabolic diseases.

The researchers then examined the levels of adherence to these interventions during the seven-week study period. Individuals in the TRE alone and the combined TRE and HIIT groups adhered to the 10-hour eating window for an average of over six days per week during the study.

Similarly, participants in the HIIT alone and combined TRE and HIIT groups completed more than 90% of the exercise sessions. The researchers cautioned that further research is necessary to determine if such high rates of adherence to HIIT can be sustained over a longer period.

“We believe that the high adherence rates reported in our study were due to the close follow-up of the participants and the fully supervised exercise sessions. In most real-world settings, such follow-up is not realistic or available,” Dr. Moholdt explained.

Limitations

This study is one of the largest studies to examine the combined impact of TRE and HIIT. However, the study had a few limitations.

The short study duration of seven weeks might not have been sufficient to detect differences in metabolic health markers and measures of glycemic control due to the three interventions.

Dr. Courntey Peterson, associate professor at the Department of Nutrition Sciences, the University of Alabama at Birmingham, said:

“The study was only seven weeks long, so it may not be enough time to see changes in health, and the study included only women. There’s some suggestive evidence that intermittent fasting has slightly different effects in men vs. women, so we don’t know whether the same is true in men. Also, the study is not large enough to detect all possible improvements in health. Lastly, body fat was measuring was not measured using bioimpedance, which is not the best available test to measure body fat.”

“Participants in TRE reported eating less, so we don’t know if the positive effects of TRE were due to a reduced energy intake or the timing of meals per se,” Dr. Hawley added.

Future directions

The researchers are currently engaged in studies to further examine the impact of TRE combined with HIIT and address some of the shortcomings of their current work.

“Further research should investigate the long-term effects of these interventions and their combination. Furthermore, we believe that the high adherence rates reported in our study were due to the close follow-up of the participants and the fully supervised exercise sessions. In most real-world settings, such follow-up is not realistic or available. We are now investigating whether TRE combined with HIIT undertaken remotely for seven weeks will induce positive health benefits in men and women with overweight or obesity,” Dr. Moholdt said.

“We are also currently inviting women who partook in the study to come in for new lab tests and answer questionnaires about adherence and perceptions of TRE and/or HIIT two years after they completed the intervention period,” she added.

“[A] two-year follow-up study will give us insight into how TRE and HIIT might be maintained after a familiarization period provided through a study setting, and whether any health benefits initially induced by the interventions are maintained over the long term.”— Dr. Trine Moholdt

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