If the adverts are to be believed, eating a sugary snack can change you from a “hangry” monster to a calm and cheerful person. On the other hand, many a parent will have experienced tantrums and bad behaviour in their children after consuming too many sweets at a party. Textbooks tell us that the brain consumes large amounts of glucose (a type of sugar obtained from starchy and sugary foods), but does this mean that eating sugar will be good for the brain?


It is true that brains need lots of energy.  At rest a quarter of the body’s total energy consumption is by the brain. It has long been said that the brain relies almost entirely on glucose for this energy and that it struggles to adapt if we restrict our intake of starchy foods. However, more recent work has shown that if we eat less carbohydrate, the amount of glucose used by the brain decreases. So, we don’t have to eat sugar and carbs to fuel the brain.


So, our brains don’t need much sugar at all. What happens in the brain, then, when we do eat a lot of sugar? It has been found that sugar triggers release of the feel-good chemical, dopamine in the brain. Eating a lot of sugar results in high levels of dopamine in the brain, this might be one reason why we crave sweet foods when stressed or after a shock.

 The problem with eating sugary or starchy foods to help us to feel good is that these feelings are short-lived. When we eat a large amount of sugar or carbs, the amount of sugar circulating in the bloodstream increases rapidly but high blood sugar levels are dangerous for our health (see box below) so the body tries to bring these high levels down (which it does by releasing a hormone called insulin). The rapid drop in blood sugar in response to the release of insulin causes the blood sugar levels to go too low. Such peaks and troughs in blood sugar have been shown to adversely affect mood.


 The key to good blood sugar balance, is to prevent the spikes in blood sugar that happen after eating high carbohydrate or high sugar foods. The best way to avoid these problems is to avoid a high carbohydrate diet and always go for slow-release carbs, avoiding refined carbs and sugars. Aim to get your carbs from whole plant foods, including nuts and seeds and perhaps small amounts of beans and non-gluten whole grains.

The amount of carbohydrate that suits your body (and brain) may vary from person to person.


Is sugar truly addictive? The studies on dopamine release in the brain suggests that it may be, at least for some. Studies on sugar intake in animals have found that all of the four major components of addiction: bingeing, withdrawal, craving, and cross-sensitisation (the idea that one addictive substance predisposes someone to becoming addicted to another)  have been observed. The results of brain scans in humans have found the brain regions that relate to appetite and reward can become desensitised such that more sugar/starchy foods are needed before the pleasure is triggered by eating. Hence the sugar addiction becomes even stronger.

Why should we have evolved to find sugar so pleasurable when it appears to be harmful for our health? The theory is that when our ancient ancestors went gathering autumn fruits, eating sour (not yet ripe) or bitter (possibly poisonous) fruits would have been bad for our health, so a preference for sweet foods ensured we only picked and ate the ripe fruits. The sugar found in whole fruit is absorbed slowly due to the fibrous structure, so for our ancestors fruit was a useful and healthy energy source and the pleasure from eating sweet foods gave us an advantage in surviving in the wild. Unfortunately, the discovery of how to extract the sugar from plants and use it in all sorts of unnatural ways has meant that we cannot trust our ancient instincts to keep us safe any more.



Overeating, poor memory formation, learning disorders, depression – all have been linked in recent research to the over-consumption of sugar. A diet high in sugar reduces the production of a brain chemical known as brain-derived neurotrophic factor (BDNF). Without BDNF, our brains can’t form new memories and we can’t learn (or remember) much of anything. Low BDNF levels seem to promote several brain disorders including low mood and depression, obsessive-compulsive disorder, Alzheimer’s disease and other dementias.


Due to a combination of genes and environment, some of us are more likely to suffer from addiction to sugar (or other addictive substances/behaviours).

  • Be aware of your sensitivity to sugar/carbs

  • Adjust your way of eating so that most of the time your sugar/carb intake stays below the trigger level

  • Take immediate action when you notice your intake is increasing

  • For some people, only complete abstinence will be the answer; others can handle low levels of sugar

  • Be careful not to replace a sugar addiction with a different addiction. If you have the unfortunate biology to be vulnerable to addiction, replacing sugar with a glass of wine could be equally problematic.

  • If you know you will be eating sugar, for example a birthday party or other occasion, then make sure you have some favourite healthy foods available the next day just in case cravings strike

    – Caroline Rees PhD, Nutritionist at The Fold