If you’re tackling your diet and exercise routine but not thinking about when you plan them into your day, you may be missing a trick. That’s because a new study has not only found that time-restricted eating is most effective when combined with high-intensity exercise – but also that the timing of these two approaches could enhance the benefits.
Time-restricted diets limit when, but not what you eat. In this study, published in the journal PLoS ONE, it counted as eating within an eight-hour window and then fasting for 16 hours. High-intensity functional training (HIFT), meanwhile, combines aerobic and resistance exercise. It’s similar to high-intensity interval training (HIIT) but is less repetitive and varies impacts on your joints.
The research team from the University of Sfax, Tunisia, found that women with obesity had an improved body composition and better cardiometabolic health after completing a 12-week programme where these two methods were combined. Crucially, the exercise took place just after the eating period had ended.
Good cardiometabolic health indicates all your systems are working well, reducing the risk of cardiovascular issues like heart attacks and metabolic disorders like diabetes.
“Combining exercise (or simply physical activity) and diet is the best strategy to improve metabolic health, irrespective of weight loss,” nutritionist Dr Adam Collins, who was not involved in the study, told BBC Science Focus.
“I think this could be further enhanced by looking at the timing of eating around exercise too. This study has suggested how impactful this can be.”
How to enhance your weight-loss strategy with time-restricted eating
For the study, the scientists randomly assigned 64 women with obesity, aged between 22 and 42 years, to one of three programmes. These were: time-restricted eating only, high-intensity exercise only, or a combination of both.
The high-intensity exercise elements took the form of three 45-55 minute workouts per week at 5pm (so, for those on time-restricted diets, at the start of their fasting period). These workouts involved following an instructor to complete eight sets of eight different exercises in 20-30 second batches with 10 second rest intervals.
Once the 12 weeks had finished, the scientists measured the impacts on the cholesterol levels, blood glucose and lipid levels, as well as other markers of cardiometabolic health.
The results? Well, it’s good news if you are taking any of these three approaches: after 12 weeks, all three groups saw significant weight loss and decreases in waist and hip circumferences – as well as healthier lipid and glucose levels.
But those in the combined diet and exercise group saw bigger changes – and the researchers think this approach could be easier to commit to in the long term.
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“Time-restricted eating is relatively non-invasive, and the combined use of exercise and diet can alleviate reliance on one or the other to exert benefit,” said Collins. “In terms of sustainability, it can be adapted to become more flexible. Similarly, the frequency, type and intensity of exercise can be adjusted to maintain the benefits.”
What’s more, the people in the exercise-only group and the combined diet and exercise group saw a benefit that the diet-only group didn’t: improved blood pressure and better distribution of lean mass and skeletal muscle mass.
The researchers note that the study had a small sample size, but they say that this research could encourage new opportunities in learning more about how diet and exercise can work together to improve health.
“The interesting element to me is the fact that HIFT sessions were done one hour after the eating window and were followed by an extended fast,” Collins said. “I think this could have exaggerated the metabolic effects, particularly in women. This is because the ‘afterburn effect’ of exercise is not blunted by subsequent feeding.”
The afterburn effect is the phenomenon where your body continues to burn energy after your workout has ended.
Collins added: “We have seen in our studies that, in women, this is more subtle and can be blunted by eating carbohydrates after exercise. Hence recovering while 'fasted' could be an enhancing strategy.”
About our expert
Dr Adam Collins is an associate professor of nutrition at the University of Surrey. His areas of focus include obesity, exercise nutrition, body composition and energy metabolism as part of weight loss and maintaining metabolic health. His research has been published in the British Journal of Nutrition; Applied Physiology, Nutrition, and Metabolism; and Research in Endocrinology.
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