09:08am Wednesday 16 October 2019

Exercise more beneficial on an empty stomach, research shows

Dr Jason Gill and Nor Farah of the Institute of Cardiovascular and Medical Sciences conducted a study to compare the effects of exercise performed before and after breakfast on fat loss and metabolic health.

Ten overweight men who were not regular exercisers took part in the study. Each man underwent three trials, 1-2 weeks apart, involving performing no exercise then eating breakfast; walking briskly for 60 minutes before eating breakfast; or doing the same walk after eating breakfast.  

Participants were given lunch three-and-a-half hours after breakfast and the amount of fat their body burned, and the levels of fat, sugars and insulin in the blood were measured over an eight-and-a-half hour period on each occasion.

Over the course of the day with no exercise the men were left with an average of 49kcal unburnt fat while exercising after breakfast burned 216kcal more of fat on average than the control trial and 298kcal more than the control group when exercising before breakfast.

The results indicated that both timings of exercise increased fat burning over the day and improved the metabolic profile in the blood. But, exercise before breakfast resulted in greater fat loss and larger reductions in the level of fat in the blood.

The important figures is the total over the course of the day.  Fat balance over the course of the day (i.e. the difference between fat eaten and fat burnt) in the control (no exercise trial) was +204 kJ (+ 49 kcal); in the exercise after breakfast trial was -697 kJ (-167 kcal); and in the exercise before breakfast trial was -1043 kJ (-249 kcal).  Thus in the exercise after breakfast trial, individuals had a lower fat balance by 216 kcal (i.e. they would have lost 216 more calories of fat) compared to control and in the exercise before breakfast trial, they had a lower fat balance of 298 kcal compared to control; and 82 kcal compared to exercise after breakfast.

Dr Gill said “Any exercise you do is beneficial, but the indications are that there might be an extra benefit associated with exercising before eating, compared to after. However, further study is needed to determine whether the present findings extend over the long term.

“In the end, we would like to encourage everyone to do some form of exercise everyday – the difference between exercising before compared to after breakfast was much smaller than the difference between exercising at either time compared to not exercising at all.”

The research paper, ‘Effects of exercise before or after meal ingestion on fat balance and postprandial metabolism in overweight men’ is published in the latest edition of the British Journal of Nutrition.

For more information contact the Media Relations Office at the University of Glasgow 0141 330 3535 or email media@glasgow.ac.uk

Notes to Editors

‘Effects of exercise before or after meal ingestion on fat balance and postprandial metabolism in overweight men’, Nor M.F Farah and Jason M.R. Gill  – British Journal of Nutrition

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