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Exercising on an empty stomach burned 70% more fat, study found

Exercising on an empty stomach helped people to burn about 70% more fat than those who exercised two hours after eating, a study found.

    Exercise bike
    The amount of fat burned during the 30-minute cycle increased by about 70% from 4.5g to 7.7g

    Sports scientists at Nottingham Trent University also found that the participants – who undertook both fasted and fed exercise in the evening – did not overcompensate for the calories skipped earlier in the day.

    While studies have suggested the benefits of exercise could be increased when done in the morning following an overnight fast, the team’s own research found that evening exercise, between 4pm and 8pm, is the most popular time for people due to other commitments.

    Therefore, the researchers designed the study so that participants cycled on an exercise bike at 6.30pm at moderate intensity for 30 minutes, before completing a time trial to cycle as far as they could in 15 minutes.

    Participants did this twice on separate days – once after a seven hour fast and once after eating a meal two hours earlier.

    The researchers also measured how much food participants ate at dinner, after exercising.

    The results showed that, similar to exercise after an overnight fast, fasted exercise in the evening increased the amount of fat burned during exercise.

    The amount of fat burned during the 30-minute cycle increased by about 70% from 4.5g to 7.7g.

    And, while calorie intake at dinner was about 100 kcal greater for those doing fasted exercise, calorie intake over the whole day was on average 440 kcal less, when exercise was performed fasted.

    The researchers also found, however, that despite these benefits participants covered slightly less distance during the 15 minute time trial performance, had a lower motivation to exercise and enjoyed the exercise less when done fasted.

    “We wanted to explore the impact of fasted exercise in the early evening which we’d found was the most popular time for people to exercise during the week,” said Tommy Slater, a sports science researcher in Nottingham Trent University’s School of Science and Technology.

    “Fasting before evening exercise might benefit some elements of health due to increasing the amount of fat burned during exercise, or by reducing the number of calories that are eaten during the day. If done regularly it may improve the way the body deals with spikes in blood sugar after eating.

    “However, despite these benefits, fasting during the day does appear to reduce people’s exercise performance, motivation and enjoyment, which may make it harder for some people to stick with it in the longer term.

    Dr David Clayton, an expert in nutrition and exercise physiology at Nottingham Trent University, said: “Combining exercise and fasting can be a potent way to increase the benefits of exercise, so we would like to assess this over a longer period of time and explore other ways in which we can make fasting easier and more convenient for people.”

    The study, which included Manchester Metropolitan University and Loughborough University, is reported in the International Journal of Sport Nutrition and Exercise Metabolism.

    • Notes for editors

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      Nottingham Trent University (NTU) received the Queens Anniversary Prize for Higher and Further Education in 2021 for cultural heritage science research. It is the second time that NTU has been bestowed the honour of receiving a Queen’s Anniversary Prize for its research, the first being in 2015 for leading-edge research on the safety and security of global citizens.

      The Research Excellence Framework (2021) classed 83% of NTU’s research activity as either world-leading or internationally excellent. 86% of NTU’s research impact was assessed to be either world-leading or internationally excellent.

      NTU was awarded The Times and The Sunday Times Modern University of the Year 2023 and ranked second best university in the UK in the Uni Compare Top 100 rankings (2021/2022). It was awarded Outstanding Support for Students 2020 (Times Higher Education Awards), University of the Year 2019 (Guardian University Awards, UK Social Mobility Awards), Modern University of the Year 2018 (Times and Sunday Times Good University Guide) and University of the Year 2017 (Times Higher Education Awards).

      NTU is the 5th largest UK institution by student numbers, with nearly 39,000 students and more than 4,400 staff located across five campuses. It has an international student population of 7,000 and an NTU community representing over 160 countries.

      Since 2000, NTU has invested £570 million in tools, technology, buildings and facilities.

      NTU is in the UK’s top 10 for number of applications and ranked first for accepted offers (2021 UCAS UG acceptance data). It is also among the UK’s top five recruiters of students from disadvantaged backgrounds and was the first UK university to sign the Social Mobility Pledge.

      NTU is ranked 4th most sustainable university in the world and 1st in the UK for sustainability-themed Education and Research in the 2021 UI Green Metric University World Rankings (out of more than 900 participating universities).

    Published on 7 November 2022
    • Category: Press office; Research; School of Science and Technology