Hunger is the best spice

Ghrelin is a hormone produced in the stomach that appears to stimulate appetite. A recent paper in Cell Metabolism shows that giving ghrelin to volunteers made their brains respond more strongly to food images, reward systems in the brain became more active and they rated their level of hunger higher. An immediate reaction in the blogosphere was to consider the practical applications: Stomach hormone turns hungry people into junkies (New Scientist), Fast Food Joints Add Hormone to Food That Makes You Want to Eat More (Io9). Are we moving towards a future where food will be literally addictive?

There is already a sizeable literature on what influences how rewarding food is. We seem to have three somewhat separate systems regulating food intake: a hunger system controlled by the actual need to eat (as determined by the body and hypothalamus), an appetite system dealing with the psychological desire to eat (linked to how the food looks, expectations, habits, cultural patterns and many other things), and satiety signals (such as a full stomach) making us less willing to eat. We can have appetite for dessert even if we are not hungry and feel rather full. Hunger may be the reason we eat, but appetite tells us what to eat.

The rewards of eating also split into actually wanting the food and liking it. As eating disorders and drug addiction show, people can be driven by strong desires for things they do not enjoy, or enjoy things they do not desire.

In psychology food is known to be a primary reinforcer: if we are given food after an action, we are more likely to do that action again in similar circumstances. However, the strength of reinforcement depends on individual factors and circumstances.

This means that delicious food is already addictive to some extent. When we see it we feel desire for it, and after having enjoyed it we are more likely to seek it out again. Certain tastes are more rewarding than others: infants react very positively to sweet tastes without knowing anything about what they are, and quickly learn to do whatever it takes to get them.

Umami, the fifth taste, is often signalled by glutamate (which can be found in everything from soy to paramesan cheese to tomatoes). Glutamate is a flavor enhancer and can improve appetite, something which has been used to increase eating among elderly people.

Adding ghrelin straight to a meal is unlikely to work both for biological and economical reasons: first, ghrelin is destroyed in the stomach. Drugs that release ghrelin could perhaps be devised, but would fall under drug  and food additive legislation. Second, anybody selling food wants us hungry before we buy: additives that makes us want to eat more will at most make us buy a bit more dessert at the restaurant, but it will not help the fast food chain or convenience store. Perhaps it could give return business, but the risk is that the ghrelin kicks in when we are eating a competitors product and we will remember that instead. Much safer to stick to sugar and glutamate, as well as the classic trick of unit bias.

While hunger-manipulation is unlikely to be a major marketing success it may still turn out to be important. Interest in a ghrelin-antibody anti-obesity treatment is high, and the US military is looking for ways of getting soldiers their food when it suits military operations rather than the bodies. Food that could manipulate hunger and satiety would sell well among the weight-conscious.

Being able to regulate our desires is in many ways a good thing. But we want to make sure the higher-order desires (what we want to want) are running the show, not the lower-order desires (what we want). We cannot avoid wanting food, but we want to avoid overeating and we want to want good food. It is relatively easy for us to collectively decide that adding ghrelin-like substances to food is against what we really want and that such additions should be banned or must be clearly labelled.

Unfortunately that will not solve the deeper problem: we will want the sweet, savoury and delicious food we now can create. It is impossible to effectively ban good cooking and cheap food. Appetite is something deeper and stronger than reason (which after all was developed by evolution in order to make us better at finding stuff to eat).

What we can do is to investigate ways of enhancing our self-control and how to turn our appetite towards what is good for us. Ironically, if we discover effective means to achieve such control the discoveries are likely to be just as risky to us as better ways of being overwhelmed by appetite: any tool that controls motivation is a dangerous tool. Yet it would be so tempting I doubt we could resist it.