High sugar consumption is believed to be detrimental to health. But giving up sugar is not easy, especially because it can cause a range of unpleasant symptoms. What happens in the brain when we eliminate sugar from our diet? This may surprise you, but sugar consumption (at least in the UK and other developed countries) has been falling steadily over the past decade, despite all the temptations in food. There are many reasons for this, including changing tastes and lifestyles, and the growing popularity of low-carb diets such as keto. A better understanding of the dangers of excess sugar also plays a role.
The benefits of reducing sugar consumption are clear – for example, for those who want to lose weight or take care of their teeth. But when people try to reduce their sugar intake, they often experience unpleasant side effects, including headaches, fatigue, and frequent mood swings. At present, we do not fully understand the reasons for this side effect. However, it is likely that such symptoms can be explained by understanding how our brains respond to sweet foods and what biology tells us about the so-called reward system.
Carbohydrates are a rather large class of organic compounds, including low molecular weight carbohydrates such as sugars. For example, fructose is found in fruit and lactose in milk. Sucrose (table sugar) is found in cane sugar, sugar beets, and maple syrup. Glucose and fructose are found in honey. Mass production of food has led to the addition of sucrose and other sugars to make products more appetizing. But behind this flavor enhancement, which creates the sensation of “mouth watering,” is a profound biological effect on the brain. This effect is so serious that it has even led to heated debates about whether sugar is addictive, like narcotics. The question remains unresolved.
Sucrose activates sweet receptors in the mouth, leading to the release of the hormone dopamine in the brain. Dopamine is a neurotransmitter, a chemical compound that transmits signals between nerve cells in the brain. When we encounter a rewarding stimulus, the brain responds by releasing dopamine, which rewards us for eating a certain food, for example. “The rewarding effects of dopamine are seen primarily in the areas of the brain responsible for the experience of pleasure and reward. Rewards govern our behavior, pushing us to repeat over and over again those actions that lead to the release of dopamine. It is dopamine that can drive us to eat something unhealthy, junk food.
Experiments in animals and humans have shown the power of sugar to activate the neural pathways of the brain’s reward system. In this regard, the intense sweet taste surpasses even cocaine. In addition, sugar affects the brain regardless of whether it enters the body with food (through the mouth) or in the form of injections (as experiments in mice have shown). This means that the effect of sugar does not depend on the involvement of taste receptors. For example, there is compelling evidence that sucrose consumption in rats can alter the structure of dopamine-excitable brain regions. Emotional processing and behavior are also altered in both animals and humans. It is obvious that sugar has a very strong effect on us.
Therefore, it is not surprising that we experience such a “withdrawal” when we refuse to consume it or at least reduce it. Unpleasant symptoms (both mental and physical) are usually reported by those in the early stages of sugar withdrawal. These symptoms include depression, increased anxiety, mental fog, and an irresistible craving for sweet foods accompanied by headaches, fatigue, and dizziness. So, yes, giving up sugar can be uncomfortable, which makes the transition to a different kind of diet difficult for some of us.
Although sugar is found in many products, its consumption is steadily declining in the United States and European countries. The reasons for such symptoms are not well understood, but it is likely that their occurrence is related to these very neural pathways of the reward system in the brain. Although the notion of “sugar addiction” is quite controversial, there is evidence from rat experiments that sugar, like other addictive substances, can induce excessive consumption, irresistible cravings, and anxiety associated with withdrawal. Other animal studies have shown that the condition of a sugar-addicted organism is similar to that of a drug addict. However, most of the research in this area has been done on animals, so it is difficult to determine how true this is for humans.
Reward pathways in the human brain have not been altered by evolution, and it is likely that similar pathways exist in many other organisms. Therefore, it is reasonable to assume that the biological consequences of sugar deprivation that scientists have observed in animals will, to some extent, be characteristic of humans. Based on the symptoms experienced by people who have removed sugar from their diets, it is likely that there are changes in the chemical balance in the brain. In addition to being involved in the reward system, dopamine also regulates hormonal activity, nausea and vomiting reflexes, and anxiety. When sugar is removed from the diet, a rapid decrease in dopamine action in the brain likely interferes with the normal functioning of neural pathways – and this explains the emergence of unpleasant symptoms.
In one of the few studies conducted on this topic, when overweight adults eliminated sugar from their diets, they experienced “sugar cravings” and an irresistible desire for sweets. What to do in such cases? As with any transition to a new diet, the key is to not give up and to stick with it. “If you are serious about giving up sugar for good, it is crucial to get through the first, most difficult weeks. However, it is important to emphasize that sugar by itself is not harmful to a healthy person – it just needs to be consumed in moderation, with a healthy diet and regular physical activity.
This article was first published on The Conversation website and is reprinted here under a Creative Commons license.
James Brown – Associate Professor of Biology and Biomedicine at Aston University in Birmingham, UK.