Opioids are a naturally occurring chemical in the brain which blocks pain, slows breathing, and can cause a general calming and anti-depressing effect. When they’re produced naturally in the body they’re called endogenous opioids. The most famous endogenous opioid is Dopamine and it has an effect on the ‘pleasure’/’reward’ area of the brain (calling it an area is a massive simplification as it’s a pathway which runs though various areas…..I am of course also talking about neurochemistry so this whole thing will also be a massive simplification!)

A classic study by Olds and Milner (1954) showed the importance of this pleasure pathway on behaviour. They wired an electrode into a pleasure centre of the brain and gave the rats the power to activate it themselves. Rats would press a lever to receive a reward of mild electrical stimulation to this part of the brain. The rats would continue to press the lever over other possible rewards such as food, drink or sexual activity and would even cross a grid with a painful electric current passing through it to reach the lever and receive the pleasurable stimulation.

This same process of pleasure is how drugs such as heroin work; they basically pretend to be natural opioids and ‘hi-jack’ the system constantly providing pleasure. This over time, however, leads to desensitisation where the person needs to take more and more of the drug in order to get the same enjoyment. This is by a process called ‘down regulation’ where the receptors of the nerve cells in the brain get so bombarded with the excessive chemical that the receptors either shut down or reduce in number to stop that ‘flood’, this means the person has to take even more of the drug.

What has all of this got to do with food?…and Obesity?

In a recent study Tuulari et al (2017) looked at endorphin release in the brain after eating pizza (and a tasteless nutritional drink as a control group) and found that it released a significant amount of these opioids across the brain. They note that interestingly enough even more were released for the tasteless nutritional drink, possibly because it was being digested quicker and so ended up releasing more opioids to suggest ‘satiation’ rather than ‘pleasure’. Since dysfunction in this opioid system have previously been found to link to morbid obesity this study suggests that overeating may lead to overstimulation of this system (a similar effect to drug addiction but to a smaller degree).

Karlsson et al (2015) found even more links between food/obesity and drug addiction- their study suggests that a similar process of down regulation occurs in the brains of those with morbid obesity, as they found a negative correlation with BMI and amount of a specific receptor (MOR receptor). This suggests the more obese someone was then the less of this receptor they had, suggesting that downregulation reduces the pleasure/euphoria of the food itself which then leads to more overeating in order to compensate for the decreased hedonic response.

All of this suggests we may be able to use this knowledge of the processes of drug addiction to help treat obesity which is governed by a similar process (or possibly offer people tasteless nutritional drink as a substitute for tasty food….which I’m sure people are totally up for).

https://www.ncbi.nlm.nih.gov/labs/articles/28747384/

https://www.ncbi.nlm.nih.gov/pubmed/25740524