Sun, Feb 16, 2014 - Page 9 News List

Chemistry behind our cravings

Researchers believe that liking food and craving it are different things — meaning our brains are more sophisticated than previously thought when it comes to making us eat certain things

By Amy Fleming  /  The Guardian

Illustration: June Hsu

Do you ever get that thing where you compulsively eat something even though there is something a bit disgusting about it? You think: This over-boiled egg smells really sulfuric, so I should gobble it up before I change my mind. I often crave sardines straight out of the tin. It is not that I do not enjoy eating them, but the fish-oiliness quickly becomes cloying and I can not let my eyes linger too long on all those innards.

It is common sense, really: Oily fish may not be as palatable as chocolate, but I need its nutrients and so I am driven to keep eating it. The currently popular scientific hypothesis on how our brain’s reward system works when it comes to eating could help explain this.

What precisely do we mean when we talk about rewards in the brain?

Rewards are when neurochemicals make us feel good in response to a stimulus, leading us to go back for more or work to obtain more, said Michigan University neuroscientist Kent Berridge.

LIKING FOOD VERSUS WANTING FOOD

Until the 1990s, most neurologists believed that reward was synonymous with pleasure, and that the neurochemical that gave us pleasure was dopamine. If something triggered pleasure, we would seek it again, simple as that.

However, then Berridge accidentally discovered that there are two essential prongs to the reward system, which are now commonly referred to as liking and wanting.

He first did this by suppressing dopamine in rats and then assessing their facial expressions when something sweet was put into their mouths.

The rats with no dopamine did not want food, but surprisingly, they still enjoyed sweetness when it was administered.

So it seemed that they needed dopamine to actively want something, but liking (the pleasure part) was a separate thing. Numerous studies in humans have since backed this up.

Of course the two prongs are closely entwined — we naturally learn to want foods by having liked them. However, they do not always work in tandem. Furthermore, our conscious minds can overrule what the reward system (of which we have little or no awareness) and our taste buds (of which we are keenly aware) are telling us.

Alcohol and coffee taste like hellfire at first, but when motivated by peer pressure or aspirations to be grown up, we persist, and eventually learn to like and want them after enjoying the effects of caffeine and ethanol.

THE PLEASURE CHEMICALS

If dopamine triggers wanting, then what produces liking? Hard drugs, that is what.

Two types of brain chemical are released when we enjoy a food: opiates such as endorphin and enkephalin, along with what Berridge describes as “natural marijuana compounds called endocannabinoids.”

THE SUGARY ANALGESIC

Sweet-tasting substances have well-known analgesic effects on young children. According to Julie Mennella at the Monell Chemical Senses Center in Philadelphia, this is why “it’s now standard care of many hospital nurseries to give sugar water during heel prick or circumcision.”

This is not about the children being distracted by a nice taste.Research is ongoing, but sugar water is helpful probably due to the pleasure chemicals. Mennella has used what is known as the “cold pressor test” (a standard pain tolerance gauge in which the subject holds their hand in freezing water as long as they can), to study the analgesic effects on different children.

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