If you’ve got plans to spend the entire weekend sat down scoffing food, there is no reason to feel guilty – as long as you exercise on the Friday.

University of Texas Southwestern researchers have found exercising ‘semi-intensely’ just once can ‘reap benefits that last for days’. 

Tests on mice showed their metabolism was boosted for 48 hours – meaning a gym session on a Friday could allow you to indulge for an entire weekend.

A person’s metabolism sets the rate they burn calories, with a fast one aiding weight loss. 

The researchers analysed the effect of exercise on two types of brain networks that make up the melanocortin brain circuit, found in both mice and humans.

One of the networks, POMC, is associated with reduced appetite, lower blood sugar levels and greater calorie burning.

While the other, NPY/AgRP, makes people hungrier and lowers their metabolism, according to the researchers led by Dr Kevin Williams.

The rodents’ brain circuit activity was monitored after they completed varying training regimens, which ranged from none to one, five and ten days of exercise.   

Results, published in the journal Molecular Metabolism, showed that just a single bout of exercise boosted the activity of POMC while inhibiting NPY/AgRP. 

This caused the animals to have a reduced appetite for up to six hours, as well as burning calories quicker. 

A single bout of exercise was defined as three 20-minute treadmill runs for the rats. 

‘This result may explain at the neural circuit level why many people don’t feel hungry immediately after exercise,’ Dr Williams said. 

The effects are thought to last longer the more a person trains. 

This is the first time the melanocortin brain circuit has been linked to exercise. Previous studies suggest it can be altered through feeding or fasting.   

‘It doesn’t take much exercise to alter the activity of these neurons,’ Dr Williams said.

‘Based on our results, we would predict that getting out and exercising even once in a semi-intense manner can reap benefits that can last for days, in particular with respect to glucose metabolism.’ 

The longer-term effects of exercise were particularly seen in POMC, which improves blood sugar metabolism when activated.  

The researchers believe their findings offer new insight into how the brain influences fitness and could result in therapies that boost metabolism. The blood sugar results may also lead to new diabetes treatments, they added.

‘This research is not just for improving fitness,’ Dr Williams said. 

‘It is possible that activating melanocortin neurons may hold therapeutic benefits for patients one day, especially for diabetics who need improved blood-glucose regulation.’

Exercise stimulates insulin sensitivity, which encourages glucose to be taken up by muscles and halts its production by the liver. 

In 2015, 30.3million Americans, or 9.4 per cent of the population, had diabetes, according to the American Diabetes Association.

It is estimated that more than one in 17 people in the UK has the condition, whether diagnosed or not, Diabetes UK states. In both the US and UK, around 90 per cent of patients have type 2, which is associated with being overweight or obese.  

Dr Williams’ laboratory is preparing a second study that aims to identify how exercise triggers changes in the melanocortin brain circuit. 

This comes after research released at the end of last month suggested type 2 diabetes and heart disease can be diagnosed by simply shining a light on your skin.

Scientists from the University of Groningen found those with higher levels of certain proteins – called AGEs – face a greater risk of the two conditions and even premature death. AGEs reflect fluorescent light and can be picked up by illuminating the skin.