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Why do some people experience negative side effects when they quit sugar?

The reasons are poorly understood but it’s worth sticking with the change, writes James Brown

Tuesday 24 August 2021 00:01 BST
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<p>Sugar makes the brain release the pleasure chemical dopamine </p>

Sugar makes the brain release the pleasure chemical dopamine

It might surprise you to learn that sugar consumption has been steadily decreasing since 2008. This could be happening for any number of reasons, including a shift in tastes and lifestyles, with the popularity of low-carbohydrate diets, like keto, increasing in the past decade. A greater understanding of the dangers of eating excess sugar on our health may also be driving this drop.

Reducing sugar intake has clear health benefits, including reduced calorie intake, which can help with weight loss, and improved dental health. But people sometimes report experiencing negative side effects when they try eating less sugar – including headaches, fatigue or mood changes, which are usually temporary. The reason for these side effects is currently poorly understood. But it’s likely these symptoms relate to how the brain reacts when exposed to sugary foods – and the biology of “reward”.

Carbohydrates come in several forms – including as sugars, which can naturally occur in many foods, such as fructose in fruits and lactose in milk. Table sugar, known as sucrose, is found in sugar cane and sugar beet, maple syrup and even honey.

As mass production of food has become the norm, sucrose and other sugars are now added to foods to make them more palatable. Beyond the improved taste and “mouthfeel” of foods with high sugar content, sugar has profound biological effects in the brain. These effects are so significant it’s even led to a debate as to whether you can be “addicted” to sugar, though this is still being studied.

Sucrose activates sweet taste receptors in the mouth which ultimately leads to the release of a chemical called dopamine in the brain. Dopamine is a neurotransmitter, meaning it passes messages between nerves in the brain. When we’re exposed to certain stimuli, the brain responds by releasing dopamine, which is often called the “reward” chemical.

Its effects are largely seen in the part of the brain involved in pleasure and reward. Reward governs our behaviour – meaning we’re driven to repeat the behaviours that caused dopamine to be released. So dopamine can often drive us to seek food (such as junk food).

A change in the brain’s chemical balance is almost certainly behind the symptoms reported in humans who remove or reduce dietary sugar

Experiments in both animals and people have shown how profoundly sugar activates these reward pathways. Intense sweetness surpasses even cocaine in terms of the internal reward it triggers. Interestingly, sugar is able to activate these reward pathways in the brain whether it’s tasted in the mouth or injected into the bloodstream, as shown in studies on mice. This means its effects are independent of the sweet taste.

In rats, there’s strong evidence to suggest that sucrose consumption can actually change the structures in the brain that dopamine activates, as well as altering emotional processing and modifying behaviour in both animals and humans.

Quitting sugar

It’s obvious that sugar can have a powerful effect on us, so it’s not surprising to see negative effects when we cut down on it or remove it from our diet completely. It’s during this early “sugar withdrawal” stage that both mental and physical symptoms have been reported – including depression, anxiety, brain fog and cravings, alongside headaches, fatigue and dizziness. This means giving up sugar can feel unpleasant, both mentally and physically, which may make it difficult for some to stick with the diet change.

The basis for these symptoms has not been extensively studied, but it’s likely they’re also linked to the reward pathways in the brain. Although the idea of “sugar addiction” is controversial, evidence in rats has shown that like other addictive substances, sugar is able to induce bingeing, craving and withdrawal anxiety. Other research in animals has demonstrated that the effects of sugar addiction, withdrawal and relapse are similar to those of drugs. But most research on this has been on animals, and it’s currently difficult to say whether it’s the same for humans.

Sugar’s effect on the brain may drive people to crave more junk food

The reward pathways in the human brain have remained unchanged by evolution – and it’s likely many other organisms have similar reward pathways in their brains. This means that the biological impacts of sugar withdrawal seen in animals are likely to occur to some degree in humans too because our brains have similar reward pathways.

A change in the brain’s chemical balance is almost certainly behind the symptoms reported in humans who remove or reduce dietary sugar. As well as being involved in reward, dopamine also regulates hormonal control, nausea and vomiting and anxiety. As sugar is removed from the diet, the rapid reduction in dopamine’s effects in the brain are likely to interfere in the normal functioning of many different brain pathways, explaining why people report these symptoms. Although research on sugar withdrawal in humans is limited, one study has provided evidence of withdrawal symptoms and increased sugar cravings after sugar was removed from the diets of overweight and obese adolescents.

As with any dietary change, sticking to it is key. So if you want to reduce sugar from your diet long-term, being able to get through the first few difficult weeks is crucial. It’s important to also acknowledge however, that sugar isn’t “bad” per se, but that it should be eaten in moderation as part of a healthy diet and alongside exercise.

James Brown is an associate professor in biology and biomedical science at Aston University. This article first appeared on The Conversation.

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