Intermittent Fasting Combined with Exercise Boosts Fat Loss and Fitness in People Living with Obesity, 12-Week Trial Finds

Key Takeaways: 

• Over 12 weeks, adults living with obesity who combined intermittent fasting with supervised exercise lost more weight and body fat and improved their cardiorespiratory fitness, compared with standard care.
  
• Liver fat, measured by MRI, fell in all four groups, but no intervention reduced it significantly more than standard care, although around 30% of participants with fatty liver in the combined group no longer met the diagnostic criteria for the condition.
  
• One year after the programme ended, the differences in weight, body composition and liver fat between groups were no longer detectable, which points to the need for longer-term interventions and strategies to maintain the benefits.
  
  
  

Combining fasting and exercise in people living with obesity

A research team led by the Joint University Institute for Sport and Health (iMUDS) at the University of Granada, working with the Granada Institute for Biomedical Research and the Biomedical Research Network Center, has examined the effects of combining intermittent fasting with supervised exercise in people living with obesity. The research forms part of the TEMPUS project.

The study, published in the journal Nature Communications, found that pairing intermittent fasting with supervised exercise led to greater weight loss and body fat loss, as well as improved cardiorespiratory fitness, in people living with obesity. However, the combined approach did not produce a greater reduction in accumulated liver fat than standard care.

Four groups tested over 12 weeks

The trial included 187 adults living with obesity, around half of whom were women. Participants were randomly assigned to one of four groups:

• Standard care
• Intermittent fasting
• Supervised exercise
• Intermittent fasting combined with supervised exercise

For 12 weeks, every group received education on the Mediterranean diet and physical activity.

Participants in the intermittent fasting groups ate all their meals within an eight-hour window each day. Those in the exercise groups followed a supervised programme combining strength training with high-intensity aerobic exercise.

Weight loss outpaces changes in liver fat

The primary aim of the trial was to establish whether these strategies led to a greater reduction in liver fat – measured by MRI – and to improvements in cardiovascular health.

Liver fat decreased in all four groups. However, the researchers found no statistically significant differences between any of the interventions and standard care, nor between the three interventions themselves.

Participants who fasted, whether or not they also exercised, lost more weight than those who only exercised or who received standard care. In both fasting groups, weight loss was on average about 2.2 kilograms (4.9 pounds) greater than in the standard care group.

The combination of fasting and exercise also led to greater body fat loss than either standard care or exercise alone. Meanwhile, both groups that exercised improved their cardiorespiratory fitness, a marker of cardiovascular health.

Antonio Clavero Jimeno, co-lead author of the study and a predoctoral researcher at the University of Granada (UGR), notes that “these results allow us to assess the effects of the interventions beyond weight, also taking into account changes in liver fat deposits, as well as total body fat and physical fitness.”

For healthcare professionals supporting people living with obesity, the findings reinforce the value of looking beyond the scales when assessing dietary and lifestyle interventions. The College of Contemporary Health’s Nutrition & Weight Management Essentials course explores the evidence behind nutritional approaches to weight management, helping clinicians interpret research such as this and apply it in everyday practice.

Differences between men and women

The study, which forms part of Clavero Jimeno’s doctoral dissertation, also looked at how men and women responded to the interventions. Among men, the combination of fasting and exercise led to a greater reduction in liver fat than standard care. This additional difference was not seen among women.

Alba Camacho Cardeñosa, co-lead author of the study and a postdoctoral researcher at ibs.GRANADA, cautions, however, that “for now, these analyses alone do not allow us to conclude that the intervention works differently depending on sex.”

Improvements in participants with fatty liver

Among participants who had fatty liver at the start of the study, approximately 30% of those who combined fasting and exercise no longer met the criteria used to diagnose the condition by the end of the trial. This compared with 6.5% of participants in the standard care group.

Benefits fade after one year

One year after completing the programme, the researchers found no differences between the groups in changes to liver fat. The differences in weight and body composition seen at the end of the 12 weeks were also no longer detectable.

According to the researchers, these findings suggest that longer-term interventions need to be analysed, particularly in people with high levels of liver fat, alongside strategies to help people maintain the benefits they achieve.

CCH insight

This trial shows that combining time-restricted eating with structured exercise can deliver meaningful short-term gains in weight, body fat and fitness, while also highlighting how difficult it can be to sustain those results. For healthcare professionals, translating evidence like this into practical, sustainable support is key. CCH’s Nutrition & Weight Management Essentials course equips clinicians with an evidence-based understanding of nutrition and weight management to support people living with obesity with confidence.

Explore Nutrition & Weight Management Essentials →

Source: Nature Communications