Exercise, appetite and weight management: understanding the compensatory responses in eating behaviour and how they contribute to variability in exercise induced weight loss
This paper [1] was published in the British Journal of Sports Medicine in March this year (2012). Unlike some of the research papers we?(Fitness Newspaper) have?summarised before, this article doesn?t report on a single study but instead provides a comprehensive review of a number of different studies that have all investigated how energy intake (EI) changes as a result of exercise. There?s an awful lot of information in this paper ? far too much for us to cover fully here. However, we felt that there were some important take-home points from his article that were worth mentioning?
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Exercise, weight loss and Compensatory Eating
The paper starts off by summarising research that has investigated how exercise contributes to weight loss ? Exercise is often used (and recommended) as a means of controlling weight. However, the evidence suggests that, even when exercise is closely monitored and supervised, there is significant variability in weight change ? some individuals lose a lot of weight, some don?t lose any, and some even gain weight!
The authors note that although compliance to an exercise programme is an important issue (obviously if people aren?t doing the recommended exercise they?re unlikely to lose any weight), an issue of perhaps even greater importance (and interest)?is the issue of ?compensatory responses? ? i.e. changes in physiology and behaviour which undermine the ability of exercise to promote weight loss:
Compensatory Responses that Might Affect the Amount of Weight Lost Through Exercise
1. Gastric emptying
Exercise can have an impact on the rate of gastric emptying (the rate at which food passes through the stomach), and this in turn can have an impact on feelings of hunger or satiety (fullness). It?s possible that physical activity increases the rate of gastric emptying and therefore increases hunger, and consequently results in greater energy intake. However, exercise of different intensities and durations has been shown to have different effects on the rate of gastric emptying, and other factors also influence the rate of gastric emptying (such as meal content, meal frequency etc.) so it?s hard to disentangle the exact effects of exercise.
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2. Appetite Peptides
Appetite peptides are molecules that stimulate or inhibit eating. For example, Ghrelin is a peptide secreted from the stomach which increases appetite and stimulates eating, whereas Cholecystokinin (CCK) and polypeptide YY peptides decrease appetite and inhibit eating. Like gastric emptying, the evidence of the effects of exercise on the secretion of these peptides is limited, and habitual diet (what people normally eat) can also have a significant impact on the proportions of these peptides that are produced.Consequently, what people are eating might undermine any beneficial effects of exercise on appetite control.Furthermore, gastric emptying may also have an impact on peptide secretion! So basically, gastric emptying, exercise and diet can all impact on appetite peptides, and the how these three factors interact is not fully understood.
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3. Substrate Oxidation
In this context, substrate oxidation essentially refers to whether the body is relying on fat as it?s prime energy source or on carbohydrate (glycogen). It is though that a greater reliance on fatty acid oxidation increases feelings of fullness (satiety) after eating and hence lowers energy intake, and research has shown that greater carbohydrate oxidation can increase energy intake. Again, however, the effect of exercise on substrate oxidation (whether the body relies more on oxidising fat or carbohydrate) is not well understood, as the evidence out there is limited and contradictory ? with some research showing that it increases carbohydrate oxidation and some showing that it increases fat oxidation. Furthermore, again, habitual diet can also impact on the substrate oxidation, and the how exercise and diet interact to affect substrate oxidation is unclear.
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4. Food and Taste Preferences
Yet again, the research in this area is mixed, with some studies finding that exercise does affect taste perception and others that it doesn?t. However, these mixed findings could be the result of individual differences between the participants in the studies ? with exercise making food taste better to some individuals (and hence leading to them eating more after exercise), but less good to others.
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5. Behavioural Traits
There is evidence to suggest that aspects of people?s personalities can influence their eating response to exercise. For example, people who report that they engage in ?emotional eating? (i.e. eating in response to negative affect/emotion) tend to overcompensate for the energy expended during exercise by eating too much. Conversely, people who report opportunistic eating (i.e. eating just because food is available) tend to show a reduction in energy intake after exercise.
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So What?
So what does this all tell us? Basically there are three take-home points from this research paper:
1. Not everyone loses weight with exercise ? some people lose a lot of weight, some lose very little and some actually gain weight, and the difference in weight lost is likely a consequence of the degree to which each individual engages in ?compensatory eating?.
2. A number of factors can affect compensatory eating in response to exercise - gastric emptying, appetite peptides, substrate oxidation, taste preferences and behavioural traits can all influence the effect that exercise has on an individual?s appetite and eating behaviour.
3. Exercise is still worthwhile - finally, and perhaps most importantly, the authors of this paper note that the beneficial effects of exercise on health (such as improved blood pressure, blood glucose tolerance, blood cholesterol, VO2max, etc.) are evident even when they do not coincide with weight loss!
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Ultimately, everyone will experience significant health benefits by increasing their activity. However, some people might find it harder to control their appetite / eating if they engage in too much exercise and/or exercise of the ?wrong? intensity (whatever that might be). Therefore, until research sheds more light on what kind of exercise and how much is ?best?, anyone trying to lose weight would probably be wise to keep a close eye on their diet, make a note of how their appetite changes in response to exercise, and adjust what they do as best they can so that they can reap the health benefits of an active lifestyle without overeating.
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References
[1] King et al. (2012) Exercise, appetite and weight management: understanding the compensatory responses in eating behaviour and how they contribute to variability in exercise induced weight loss. Br. J. Sports Med. 46, pp315-322.
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Source: http://www.fitnessnewspaper.com/2012/11/19/latest-research-exercise-appetite-and-weight-management/
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