Innovative study could lead to new anti-obesity treatments and insight into why exercise puts you off your food
1 October 2008
Scientists observing how rats come to dislike certain flavours have developed techniques that could lead to both new anti-obesity drugs and an understanding of the phenomenon known as ‘activity anorexia’. New research, published today in Behavioural Neuroscience, by Biotechnology and Biological Sciences Research Council (BBSRC) funded scientists at Cardiff University and the University of Sydney have found how to distinguish between rats avoiding a flavour because it simply tastes bad as opposed to avoiding it because it has negative connotations for them.
It is crucial that treatments to reduce obesity in humans actively work to reduce appetite and body mass index and do not just make patients averse to certain foods. The research is important in distinguishing between these effects. Similarly, the work has implications for understanding why elite athletes come to dislike the taste of the foods they eat when in training. The team has found that rats can also suffer from ‘activity anorexia’ and that exercise actively caused the rats to dislike the flavours they experienced prior to running.
Dr Dominic Dwyer, Cardiff University’s School of Psychology said: "We used three different scenarios where rats were given a saccharin flavoured drink followed by some event and we measured the pattern of licking on the drink bottle as well as their overall consumption of the drink. We wanted to know whether their experience in each scenario led them to dislike the taste of the drink, or whether they continued to like the taste but they avoided it for some other reason.
"We know that if the rats dislike the taste of their drink then they don’t lick for as long in one go, they produce only small numbers of licks in each bout. If they like the taste but are avoiding the flavour for some other reason then they reduce the total amount consumed without reducing the size of individual licking bouts."
When saccharin was followed by either access to a running wheel or by temporary drug-induced nausea the rats not only avoided saccharin afterwards, but also reduced the size of their licking bouts. In contrast, when saccharin was followed by amphetamine, which is briefly unpleasant for the rats but doesn’t cause nausea, consumption was reduced but the size of licking bouts was unaffected. The similarity between the effects if nausea and running suggest that nausea induced by intense exercise can cause food and drink consumed during training to taste unpleasant, perhaps explaining the phenomenon of ’activity anorexia‘ where athletes ‘go off’ certain foods they consumed during periods of intense training.
Using the technique of monitoring licking patterns Dr Dwyer and his colleagues were able to distinguish between flavour avoidance based on illness that tends to result in the flavour tasting unpleasant, and flavour avoidance based on other aversive consequences where the flavour doesn’t taste bad but the avoidance is based on apprehension of the consequences it predicts.
Dr Dwyer continued: "Obviously you can’t ask rats whether they feel sick or whether they like the taste of something. Previous studies have got around this by observing the facial reactions of the rats when drinking – they produce very characteristic facial patterns when they drink something they don’t like, just like human infants screwing up their faces! The problem is that this method is very time consuming to use. Our method is more efficient and we’ve shown that it produces the same results. We can take this on now to use it to asses the effects of potential obesity treatments to ensure that they don’t induce any sort of taste aversion."
The results of this work indicate that this ‘lick analysis’ method provides a way that animal behaviour can inform our understanding of humans, and help to identify new diet drugs that reduce food consumption without creating aversions to particular flavours. Examining the effects of activity also suggests that one way to prevent ‘activity anorexia’ would be to mask foods consumed during training with a completely novel flavour so that any aversion forms to that novel flavour and not to the underlying foodstuff.
Dr Alf Game, Acting Director of Science and Technology, BBSRC said: "Rising obesity in the UK is a major challenge. Research to understand the underlying mechanisms of how and why we choose to eat certain foods and avoid others is vital in order that we can find out the best way to mitigate against this serious public health problem. This work clearly highlights a number of important considerations to make when we think about developing treatments in the future and offers a powerful method by which to test novel drugs."
Notes to editors
This work is published in Behavioral Neuroscience DOI: 10.1037/a0012703.
The Biotechnology and Biological Sciences Research Council (BBSRC) is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £420M in a wide range of research that makes a significant contribution to the quality of life for UK citizens and supports a number of important industrial stakeholders including the agriculture, food, chemical, healthcare and pharmaceutical sectors. http://www.bbsrc.ac.uk
Dr Dominic Dwyer, School of Psychology, Cardiff University
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