Which achieves greater fat reduction for obesity?

A closeup of a woman wearing sneakers preparing to lift a kettlebell as part of her HIIT workoutShare on Pinterest
When it comes to improving health, HIIT or time-restricted eating may not be as effective on their own. Nastasic/Getty Images
  • Previous studies have shown that time-restricted eating (TRE) and high-intensity interval training (HIIT) in isolation can reduce cardiometabolic risk in overweight or obese individuals.
  • A recent randomized controlled trial showed that 7 weeks of treatment with TRE in combination with HIIT resulted in greater improvements in long-term glycemic control and body composition in overweight/obese women compared to TRE or HIIT alone.
  • These results suggest that the combination of TRE and HIIT could be a potential long-term strategy to improve cardiometabolic health in obese/overweight women.

Individuals with obesity and insulin resistance are at increased risk for cardiometabolic diseases, including diabetes, hypertension, and other cardiovascular diseases. Lifestyle interventions that include changing diet and increasing physical activity can reduce cardiometabolic risk, but maintaining these regimens is often challenging.

A new study published in cellular metabolism suggests that overweight/obese women who followed a regimen of time-restricted eating (TRE) combined with high-intensity interval training (HIIT) for seven weeks showed greater improvements in metabolic health than either intervention alone.

Additionally, these participants demonstrated high levels of adherence to TRE and HIIT alone and in combination.

The co-author of the study, Dr. Trine Moholdt, researcher in exercise physiology at the Norwegian University of Science and Technology, said:

“Our results 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.”

Strategies for weight loss and maintenance primarily involve increasing physical activity and changing your diet. However, studies have shown that weight loss strategies such as Reducing daily calorie intake and adherence to recommended physical activity levels are associated with low adherence.

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

Time-restricted eating means limiting your intake of calorie-dense foods to a specific window of time, typically between 6 and 12 hours, during the day.

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

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

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

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

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

However, evidence is lacking on the effects of combining TRE and HIIT in obese individuals who have a more sedentary lifestyle.

In the present randomized controlled trial, researchers evaluated the combined effect of time-restricted eating and HIIT in overweight/obese women of childbearing potential.

Researchers randomly assigned the 131 overweight/obese women enrolled in the study to one of four groups — TRE and HIIT combined, TRE alone, HIIT alone, and the no-intervention control group. HIIT involved three treadmill workouts per week that the researchers monitored, while TRE involved restricting calorie intake to a 10-hour window during the day.

These interventions lasted a total of seven weeks, and participants received a series of assessments to assess glycemic control and cardiometabolic health before and at the end of the intervention.

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

The researchers found that participants in the isolated and combined TRE and HITT showed no differences in glucose tolerance compared to the control group.

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However, participants in the combined TRE and HITT group showed greater reductions in values ​​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 sugar levels over the past 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.

In addition, the combined TRE and HIIT group showed two-fold greater reductions in total and visceral fat mass than the TRE and HIIT group alone. This is notable since visceral fat, the fat that surrounds the abdominal organs, is a risk factor for diabetes and other metabolic diseases.

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

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

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

This study is one of the largest studies examining the combined effects of TRE and HIIT. However, the study had some limitations.

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

dr Courttey Peterson, associate professor at the University of Alabama’s Department of Nutritional Sciences at Birmingham, said:

“The study only lasted seven weeks, so there may not be enough time to detect changes in health status, and the study only included women. There is some evidence that intermittent fasting has slightly different effects in men and women, so we don’t know if this is also the case for men. Also, the study is not large enough to capture all possible health improvements. Finally, body fat was not measured using bioimpedance, which is not the best test available to measure body fat.”

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The co-author of the study, Dr. John Hawley, Director of the Physical Activity and Diet Research Program at the Australian Catholic University, Melbourne, agreed with Dr. Peterson’s comments that the study only includes women and said it needs to be replicated in men.

“Participants in TRE reported eating less, so we don’t know if the beneficial effects of TRE were due to reduced energy intake or meal timing itself,” added Dr. Hawley added.

Researchers are currently involved in studies to further investigate the effects of TRE in combination with HIIT and to address some of the shortcomings of their current work.

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

“We are also currently inviting women who participated in the study to come for new laboratory testing and to complete questionnaires about TRE and/or HIIT adherence and perception two years after the completion of the intervention period,” she added.

“[A] A two-year follow-up study will educate us on how TRE and HIIT can be sustained after an acclimatization period provided by a study setting and whether any health benefits initially induced by the interventions are sustained over the long term.”
– dr Trina Moholdt

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