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Sugar-sweetened soda drinkers feel more guilty after inadvertent 'bad' deeds

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By Ben Bouckley+

Last updated on 17-Jul-2014 at 16:18 GMT

Randy Aquilizan/Flickr
Randy Aquilizan/Flickr

An intriguing French study suggests that students who drank sugary lemonade before completing a ‘guilt inducing’ task felt more guilty than peers who consumed a stevia-sweetened zero-calorie alternative.

Though the authors apply their insights to blood glucose levels in general, and don’t propose we all guzzle sugary soft drinks to act ethically, their research is interesting given sugar’s current bad press.

“Guilt is an unpleasant emotional feeling that helps us know we did something wrong, and reminds us to do better next time,” write Hanyi Xu, Laurent Begue, Laure Sauce and Brad Bushman, introducing their study published in the journal Appetite.

Although it’s bad for the individual, they add, it’s actually quite good for society – a moral emotion that can inspire moral behaviors such as working harder to help others.

What’s the link to sugar-sweetened soda? Well, Xu et al. argue that higher-order cognitive resources involved in experiencing guilt are energy taxing.

“Once energy has been expended performing one task, there is little energy left to perform a subsequent task,” they write.

“Previous research has shown that depleting tasks reduce guilt, and the less guilty people feel, the less helpful they are,” Xu et al. add.

Restoring blood glucose improves self-control

Since the brain relies in part on glucose to engage in higher-order cognitive processing (consuming 25% of our energy), Xu et al. say restoring blood glucose improves self-control including emotional regulation.

“Thus, restoring blood glucose should also restore guilt feelings that have been depleted. Once guilty feelings are restore, subsequent helpful behaviour should also increase," they write.

Based in Grenoble, the academics recruited 94 students (83% of whom were female) with an average age of around 20 years for the study. They told the students that their ‘alimentary habits and task performance’ would be studied.

The study design is complex. So in sum, 46 subjects drank 100ml of lemonade sweetened with sugar (140 calories) while 48 drank the same lemonade in a zero-calorie, stevia-sweetened version.

After a pause to allow for glucose absorption in the bloodstream, subjects then played a game where they had to identify how many faces (17, 19 or 21) there were in 10 different pictures.

Unpleasant 100db 'blast' of noise

With only five seconds to choose, they had to guess. The catch? They were told that each time they made a mistake the next participant (who they had no contact with) would receive a 5 second 'blast' of an unpleasant 100db noise.

To induce guilt, all subjects were told at the end of the test that they’d made nine errors, while their predecessor had made just five – they then filled in questionnaires using accepted guilt measures.

Xu et al. said glucose beverage drinkers felt significantly more guilty than those students who drank the stevia-sweetened placebo beverage.

“The good news is that a ‘spoonful of sugar’ can restore guilt. Of course, we are not advocating a sugary diet to make society a kinder, gentler place to live,” the authors write.

Eating vegetables also raised glucose levels, they add, where it provides energy that the brain can use to regulate emotions.

“Vegetables just take longer to raise glucose levels, and we needed a fast-acting substance in our lab. Sweet blood appears to sweeten behavior,” Xu et al. write.

Title: ‘Sweetened blood sweetens behaviour. Ego depletion, glucose, guilt and pro-social behavior’

Authors: Xu, H., Begue, L, Sauve, L., Bushman, B.J.

Source: Appetite, 81 (2014) 8-11, published online May 29 

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