We like to think of ourselves as rational actors when it comes to making decisions, we take in information, process it and choose the path that we think will lead to a desirable outcome (if we aren’t deep-seated masochists I suppose). Regular readers of this blog and others that espouse a sceptical viewpoint will know that this isn’t really the case. We are influenced by a large number of factors from implicit biases, to environmental factors, and errors of thinking. The hope is that if we are aware of these factors we can go some way toward mitigating their effects and making choices that are both rational and lead to improving our lives.

Well, here’s another one for you. You may have guessed by the title of this post that it involves food and risk taking behaviour. A paper published last month in PLoS ONE out of the University College London looked at how hunger and food intake affected choices that had a monetary reward. The actual experimental design ran something like this, subjects fasted for 14 hours they then performed tasks that in effect were an idealised lottery, the tasks were performed before, directly after and an hour after a standardised meal. Over this time the subjects also had blood samples taken to measure hormones that correlate with hunger and energy reserves.

The task subjects had to perform consisted of choosing one of a pair of “lotteries” where there was a 25% chance of receiving one of four monetary amounts. Each pairing was designed so that there was always a difference in risk between the two  (see the picture it’s hard to explain).

Paired Lottery doi:10.1371/journal.pone.0011090.g002

How the subjects performed on the tasks was measured to determine the amount of risk aversion. In other words, humans have a tendency to normally prefer less risky choices. The effect of of hunger and especially immediate satiation (right after eating the meal) is to decrease this risk aversion and to make the subjects more risk neutral.

This way of referring to the subject matter is a little counter intuitive and can take a bit of getting used to, the bottom line is that the researchers looked for the point at which the subjects were equally likely to choose the “safe” bet which promised an certain average reward, and a “risky” bet that may lead to a higher average pay off but a lower chance of receiving it. Thus risk aversion has been reduced. By varying the reward amounts the researchers can measure the degree of risk aversion in each subject as the trial proceeds.

Actually the correlation is more complex than I would have thought, not only is the fact that calories are received taken into account but also the amount of calories. It seems that the size of the meal (in terms of calorific intake) is assessed to determine if it meets the rate of food intake required to meet baseline energy requirements. If it does risk aversion is increased (less risky behaviour) if not the risk aversion is decreased.

In hormonal terms this meant that a greater drop in the hormone associated with hunger was correlated with greater risk aversion but a smaller drop meant an increase in risk taking behaviour. The study authors also note that the adiposity of an individual (eg higher BMI) correlated with the size of the hormonal decrease after eating with higher BMI subjects experiencing a smaller drop and a corresponding greater increase in risk taking behaviour.

In effect we not only look at the reward in terms of the gain we will receive compared to our external resources (cash in the bank, say) but also in relation to our internal resources (metabolic requirements for example). This makes sense if we consider that for most of our history true advantage was not measured in abstract accumulation of “wealth” which we would recognise today but in available energy, including that within our bodies. That’s just a speculation of course, I’m no expert in this area.

What is the take home message of this research then? Well first off we should be careful to realise that risk taking behaviour is not limited to single domains in our lives. If you take away from this that only financial decisions are affected then that is too narrow an interpretation. In the final analysis though, no matter our eating habits or body size, we should endeavour to think over important decisions carefully and be aware of the changeable nature of our biology and it’s effects on our thinking.

Symmonds M, Emmanuel JJ, Drew ME, Batterham RL, & Dolan RJ (2010). Metabolic state alters economic decision making under risk in humans. PloS one, 5 (6) PMID: 20585383

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