Gym or junk food: What would you choose?

10 October 2017

Interview with

Natalya Beer, University of Western Australia

Michael Wheeler’s been working up a sweat down at the gym; but did he decide the exercise regime, or did someone else? It’s an important distinction because it could determine how tempted he is afterwards by the junk food in the vending machine...

Michael - Many of us can relate to those days when we manage to get in a tough exercise session but then all we want to do is eat is junk food. But, on other times, completing and exercise session motivates us to eat healthy… our bodies seem to work in mysterious ways. But now researchers from the University of Western Australia have shed some light on the link between exercise and subsequent eating behaviour…

Natalya - We all know the benefits of exercise, but it’s also important to note that sometimes our behaviour after an exercise session can actually counteract some of these benefits.

Michael - That’s Natalya Beer; she’s an exercise researcher at the University of Western Australia…

Natalya - We wanted to see how manipulating people’s psychological approach to exercise would influence the way they approach food after exercise. And specifically we manipulated people’s sense of choice in a workout to then see how much food they would eat afterwards, and the types of food that they would reach for.

Michael - The experiment that Natalya and her colleagues did was to randomise people into two groups prior to completing an exercise session. One group had lots of choice about things like the kind of exercise they did, the exercise intensity, the exercise duration, as well as what music to listen to. Now, for every person in this choice group, there was a matching pair who did a similar exercise session but with no choices available.

The matching pairs were similar in almost every respect, except one had lots of choice and the other had no choice. They were the same gender, they were similar in height, age, weight, fitness, and they expanded a similar amount of energy in the exercise session. The researchers then secretly measured the amount and the type of food that the participants ate after exercise...

Natalya - At no point were they told that we would be measuring their energy intake or their appetite. And when we presented the food buffet to them we actually said that that was a thank you gesture.

Michael - The researchers used a questionnaire to confirm the participants were not aware of the true nature of the study which was to measure what they ate from both the pile of healthy food and the pile of unhealthy food…

Natalya - We provided obvious options such as low fat milk, whole grain bread, whole grain breakfast cereals, fruits, things that we’re quite familiar with being healthy. And then with the unhealthy foods we had quite obvious choices again, so we had muffins, lollies, chocolate biscuits.

Michael - I certainly know what foods I would reach for, but the researchers found something quite interesting. Despite both groups reporting similar ratings of appetite, the group who weren’t given any choice in their exercise session ate more of the unhealthy food and had an energy intake that was about 30% higher than the group who were given lots of choices. So what is going on here?

Natalya - In the instance of this experiment, perhaps exerting self-control by continuing an exercise they don’t particularly enjoy may lower their capacity to be able to exert self-control after that when they’re exposed to foods that they might want to go for. We looked at their blood glucose levels as there are a number of theories out there that suggest that with this lowered self-control, they might also experience low blood glucose levels, but we found quite similar blood glucose levels between the two conditions.

Michael - It’s a clever experiment and the researchers believe there is a lesson to be learned…

Natalya - Well, from what we’ve seen in our study it seems that simple acts of providing choice in an exercise session, if they can influence the way we behave in a positive way after that exercise session, then why not incorporate those aspects. It’s an important consideration for anyone that’s involved in exercising themselves and wants to get the most out of their exercise. But also for people motivating others to exercise to ensure that they’re giving those people they are motivating some choice about what they’re doing and making sure that they enjoy it, and doing it because they would like to as opposed to being forced to do it.


Thank you to DjDust for the apple-crunch sound effect

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