Sugar and addictive pleasure

You probably know that ingesting too much sugar is not good for your body. However, did you know that more than harming your health, sweets can be more addictive than cocaine? Exactly, sugar addiction is real. It makes someone dependent by “hijacking” the brain’s reward pathways. Recent neurochemical and behavioral evidences show how sugar acts in the organism, transforming a something pleasurable into dependency.

RAISA JAKUBIAK

UC Berkeley


Animals act on instinct. However, some human behaviors are not only instinctive, but also pleasurable. This occurs as an encouragement to repeat actions like eating or sexual intercourse, ensuring not only the survival of individuals, but also of the species as a whole. After all, who would be crazy enough to go to a barbecue party, knowing that afterwards you could feel bloated and have a hangover, if no rewards are included? – an irrational decision based on psychological rewards.

That is exactly what drives our consumption of sugar: a natural reward. The origin of the reward system lies in our evolutionary past. Without the Internet or ingredient tables to consult, our ancestors learned to “read” the flavors as different signs sent by food found in nature. Typically, whereas sour indicates that something is not yet ready to be eaten, or bitter can be an alert for potential poison, sweet foods are naturally related as a good source of carbohydrates. Although carbs are treated as villains in popular restrictive diets like Atkins, they are fundamental for the organism to operate properly. In addition to being the most abundant bimolecular class on Earth, their oxidation is the main source of energy for most non-photosynthetic cells. Organisms can more quickly break down carbohydrates into energy since they are easier to metabolize than fat and amino acids. They also play a role as structural elements from the cell wall and markers in the organism.

Although the name “carbohydrate” suggests that these molecules are only carbon and hydrogen scientists today know about carbs which also contain nitrogen, sulfur and phosphorous in their composition. They can be divided into three classes concerning the number of glycosidic bonds (bonds between the monomers, which number will influence in the difficulty to be digested): monosaccharaides (the most basic unit in a carbohydrate), oligosaccharides (responsible for cell adhesion and cell recognition) and polysaccharides (responsible for cell structure and energy storage) [2].  Not each of them present sugary flavor and some have complex structures, sometimes even to the point that they are non-digestible like cellulose, but we still generally associate carbs with sugar.

 

SWEET PLEASURE PHYSIOLOGY

The evolution process favored the development of what we call the mesolimbic system, or mesolimbic pathways, which is responsible for modulating and decoding the neural stimulations we understand as rewarding. Basically, when we do something that is perceived as pleasurable, a bundle of neurons called the ventral tegmental area releases dopamine as a signal to the nucleus accumbens, a structure in the brain[1]. The connection between the nucleus accumbens and the prefrontal cortex decide what your next step is going to be: “Will I have another bite of this marvelous Boston Cream, with soooo much chocolate on top and filled with this delicious cream, or should I stop?” or “Should I really have one more Insomnia Cookie?”. Moreover, the prefrontal cortex is also responsible for activating hormones which helps you decide if something is tasty or not, saving this information for future stimuli.

 

ADDED SUGAR

What do we eat today? The truth is that, besides the sugar found in natural food eaten by our ancestors, there is added sugar in almost all processed food we ingest – even when it is something salty! Given the quick and dynamic routine the majority of the population, it is more likely that we will choose something practical over something healthy to eat. Having to prepare a full meal after arriving home late and tired is something unthinkable for many people.

Even if you lower the sweets intake hoping to lose weight, escaping from added sugars is not an easy task. With preservatives added to most foods, today it is very difficult to find processed food without any form of added sugar [3]. Food companies usually fill their products with sugar and fat so the flavors are attractive to the consumers – and even addictive.

Daily sugar intake actually changes certain genes’ expression and the availability of dopamine receptors both in the midbrain and frontal cortex.

Just like nicotine and cocaine, sugar triggers the release of dopamine neurotransmitter in the nucleus accumbens. If you only eat sweets occasionally and have a healthy day-to-day diet, this will be no problem. However, if you regularly eat sweets, in the long run, this daily sugar intake actually changes certain genes’ expression and the availability of dopamine receptors both in the midbrain and frontal cortex. While sugar elevates the concentration of one type of excitatory receptor called D1, it lowers the number of inhibitory D2 receptors [1].

Basically, regular sugar intake leads to a long term decrease in dopamine signaling. This means that the reward pathways of the brain are continuously heavily excited, and the individual feels the need of higher doses of sugar to be able to excite the receptors [4]. Just like drug addicts, the individual needs more and more sugar to reach the same pleasure state he reached before.

Since added sugars are disguised in almost every processed food, it is no surprise that it is so difficult to lose weight and overcome the sugar compulsion. Unlike with drug addiction, sugar constantly stimulates the brain with every single meal, many times without our own knowledge. Take cream crackers, for example: they are salty, and are the best friends of many people in diets. But instead of being a healthy snack, if you read the ingredients carefully you will see that they are fulfilled not only with fat, but also with alarming quantities of added sugars.

 

WITHDRAWAL AND BEHAVIOR EVIDENCE

Have you ever heard that if you are addicted to a substance, you are prone to go to something heavier? This idea is called cross-sensitation - the notion that one addicting substance can lead someone to develop an addiction for another. Together with compulsion, withdrawal, desire, and cross-sensitation form the “pillars” of addictive behavior [1].  You basically crave for something and, if you have it, you will take too much and indulge in pleasure. If you don’t have it, you fall in depression or become aggressive. Several experiments on addiction with animal models have been conducted in order to observe these stages of addiction, and results indicate that all four of them are present in addicted individuals.

Rats began to behave like those under drug addiction, with a more eagar compulsion towards the sugar solution...they also presented passive and depressive behaviors.

In one experiment, for example, rats were not fed for a period of 12 hours a day. During the next 12 hours, they were given unlimited access both to a sugary solution and chow. After following this pattern for a month, rats began to behave like those under drug addiction, with a more eager compulsion towards the sugary solution rather to chow. They also presented passive and depressive behaviors. When put under a stressing situation, like having to swim to be safe, they just stood there floating instead of trying to escape [4].

Finally, current research suggests that sugar deprivation can lead to compulsive behavior. Rats were trained to receive water from a container after pressing a lever. Then they were returned to their cages, where sample rats received water with sugar and control rats received just water. After 30 days, the sample rats pressed the lever many times more than the control group, indicating anxiety and compulsion. Besides being anxious to ingest sugar, the addicted rats ate way more than they needed to survive [5].

These are extreme examples, after all most of us don’t fast for 12 hours and finish them by eating three cakes and a whole bottle of soda. However, they certainly introduce alarming evidence of how sugar induces dependency in our organisms.  The scary thing is that we cannot deny that the results are very similar to some behaviors we observe in our sweet-toothed friends.


References

[1] Jordan Gaines Lewis, “Here’s what happens to your brain when you give up sugar for Lent”, The Conversation (2015)

[2] “Carboidratos: Estrutura, Propriedades e Funções”, Wilmo E. Francisco Junior, Química Nova Vol. 37

[3] Added Sugar in the Diet, Harvard School of Public Health

[4]» Avena NM1, Rada P, Hoebel BG., “Evidence for sugar addiction: behavioral and neurochemical effects of intermittent, excessive sugar intake”, Neurosci Biobehav Rev. 32, p 20-39 (2008)

[5]» Mangabeira V., Garcia-Mijares M., Silva MT., “Sugar withdrawal and differential reinforcement of low rate (DRL) performance in rats” Physiol Behav. 139, p 468-73 (2015)