Sugar’s Impact on Brain Health
By Anne Danahy, MS, RDN
Chances are, if you ask clients which foods they take pleasure in eating the most, sugary fare may make the list. It’s well known that humans have an innate preference for sweets. Some people will go so far to say they’re addicted to sugar—but can sugar become an addiction? It turns out eating too much refined, added sugar indeed can have some negative effects on brain health.
Sugar, Cravings, and Neurotransmitters
Research suggests that, in some people, genes in part seem to regulate a strong desire for sugar. Variations in a specific chromosome are linked with a greater preference for sweets.1 This may explain why some people have a natural and lifelong affinity for sweet-tasting foods.
Other studies have found that a natural preference for sweets is present at birth. A newborn’s face relaxes when tasting a sweet solution. Infants also will consume a greater amount of a solution that tastes sweeter than a less sweet option.2 This isn’t surprising, as glucose fuels the brain and nearly every cell in the human body. According to several reviews, this innate preference for sweets may be an evolutionary mechanism for survival, ensuring a baby’s acceptance of its mother’s milk.
Additional research shows that a person’s diet when they’re young also plays a role in how much they like sweets as an adult. Some evidence suggests early exposure to sugar-sweetened foods leads to increased preference for sweets and an inclination for foods higher in sugar later on.2
The innate preference for sweets also may be associated with the fact that sweet taste receptors are located not just in the mouth but also throughout the body, including the gut and brain. Activating these sweet taste receptors triggers metabolic and behavioral reactions that help maintain energy stores.3
In addition, research shows that sugar and fat activate certain neurotransmitters in the brain, including dopamine, serotonin, gamma aminobutyric acid, endogenous opioids, and endocannabinoids. These neurotransmitters increase one’s sense of reward, pleasure, and happiness.3,4
Studies also suggest sugar has pain-relieving properties, possibly by releasing endogenous opioids. A sucrose solution (but not water) reduces the reaction to a pain or cold stimulus in both children and infants. Young children appear to have the strongest positive response to sugar. It tends to lessen with age, but, in most cases, it’s still present in adults.2
In some people, the rewards associated with sugar are powerful enough for them to consume it more frequently. With regular sugar consumption, the brain learns to associate the stimulus with the reward. What’s more, over time, higher amounts of sugar are needed to achieve the same level of reward or satisfaction.2,5,6
Still, there’s some debate over whether sugar can be addictive. Part of the controversy is that for some people, and not others, cutting their ties with sugar isn’t just a matter of willpower. Instead, it’s so difficult to live without it, that it’s like learning to manage an addiction. The American Psychiatric Association defines any type of addiction as “a brain disease manifested by compulsive substance use despite harmful consequence.” Note that a person has to meet only two of the following diagnostic criteria to receive an addiction diagnosis6:
- repeated attempts to quit or control use;
- using larger amounts and for longer than intended;
- social/interpersonal problems related to use;
- hazardous use;
- physical or psychological issues related to use;
- tolerance; and
- withdrawal symptoms.
The addictive effects of sugar have been clearly demonstrated in animal studies. When rats are offered sugar ad libitum, they progressively eat more, likely because they develop a tolerance. Then, when given an opioid antagonist medication to curb their sugar intake, they exhibit withdrawal symptoms including agitation, teeth-chattering, diarrhea, and writhing.5,6
Excess Sugar’s Health Effects
Dietitians are well aware of the metabolic effects of frequent excessive sugar intake. High sugar intake is associated with an increased risk of obesity, diabetes, and heart disease, and it may play a role in cancer and inflammatory conditions such as rheumatoid arthritis. High sugar intake also has significant impacts on brain health. Studies have found that diets high in sugar increase the risk of dementia, Alzheimer’s disease, stroke, impaired cognitive function, mood disorders and depression, and impulsivity and generalized anxiety disorders.7-10
There likely are many mechanisms at play. Excess sugar intake may replace healthful fats, vegetables, and other nutrient-dense foods in the diet, affecting the brain’s health. Sugar also promotes production of proinflammatory compounds that affect not only the body but also the brain. In addition, sugar promotes the production of advanced glycation end-products (AGEs).11
AGEs are toxic compounds formed when sugars react with lipids or proteins, such as in the Maillard reaction, which causes various foods to brown and/or caramelize during cooking. AGEs also are formed endogenously from a high-sugar diet. They can build up in the body and brain, and high levels appear to promote oxidative stress and inflammation. Animal studies suggest AGEs may interfere with several protein functions and activate proinflammatory signals. AGEs also have been implicated in metabolic diseases, Alzheimer’s disease, and cell damage throughout the body, including in the brain.11
Breaking the Sugar Habit
Nutrition professionals should recognize that sugar cravings are real and their effects impact not only physical health but also one’s mental and emotional health. It’s also important to understand that some people have a stronger preference for sweets than others. Telling someone who has a strong craving for sweets to “eat less sugar” probably won’t help them.
When developing strategies to help clients rein in sugar intake, help them identify when they’re most likely to crave sweets. Studies suggest cravings tend to be higher before a meal than after.2 Encouraging more nutrient-dense snacks in between meals may help. For those who insist on something sweet to end a meal, eating more slowly and including fruit as the last course may be helpful.
The bottom line is patients need to learn about the effects sugar has on brain health—not only long term, but also the way sugar functions to rewire the brain, making it harder to relinquish the habit of high sugar intake. Sugar-cravers will appreciate learning that their cravings aren’t all about lack of willpower. There are physiological factors at play, too.
— Anne Danahy, MS, RDN, is a Scottsdale, Arizona–based dietitian and freelance health and wellness writer. She’s the author of The Mediterranean Diet Cookbook for Two and owner of the food and nutrition website CravingSomethingHealthy.
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