The Brain on Sugar

*Disclaimer: The following information is for educational purposes only and should not be taken as medical advice. This information should not be read to recommend or endorse any specific products. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease.

When you indulge in a sugary treat, be it a pint of ice cream, a powdery cream-filled confection, or a handful of bite-sized candy, your brain goes through a rollercoaster of neurochemical reactions. Sugar engages some of the brain's most complex reward systems.

Below, we explore how sugar impacts the brain, why we crave it so much, and ways to find balance after your next sugar crash.

Despite what you may tell yourself as you reach for a post-lunch sweet treat, a sugar rush—the sudden burst of energy and hyperactivity after eating sugar—isn’t grounded in science. In fact, the opposite is true: In a study from Neuroscience & Biobehavioral Reviews, compared to a placebo, carbohydrates were associated with higher levels of fatigue and less alertness within the first hour post-ingestion, and had no beneficial impact on any aspect of mood in healthy participants.¹ Sugar rush? More like sugar crash.

Let’s say you snack on a chocolate chip cookie or two: When your body consumes sugar, it quickly converts it into glucose. This influx triggers a cascade of normal effects, most notably a spike in blood sugar (especially when enjoyed without fiber or protein, which would help slow the glucose absorption). After eating sugar, there’s an immediate availability of glucose in the bloodstream, raising blood sugar levels. But, what goes up must come down: When blood sugar levels subsequently fall, it can lead to a “crash”—leaving us feeling tired, irritable, and with concentration difficulties.¹

That’s not to say to avoid carbohydrates—they’re essential! Our bodies need the glucose that carbohydrates convert into energy. The issue lies in what types of carbohydrates we’re putting on our plates. It takes your body longer to break down complex carbs (like fruits, starchy vegetables, and brown rice), so they are less likely to cause blood sugar spikes. Plus, complex carbs are more likely to contain beneficial vitamins, minerals, and fiber.

We’re not here to villainize sugar either: An occasional sweet treat won't cause lasting harm. Persistently consuming high amounts of sugar can disrupt your brain function by altering your brain’s rewarding signaling pathways (neurotransmission signaling).² A diet high in sugar has also been linked to an increased risk of developing cognitive issues, like negative neuroplasticity.³

Along with increased glucose in the bloodstream, a sweet treat also releases a quick hit of dopamine, a neurotransmitter responsible for pleasure and motivation. As part of the brain’s reward system, dopamine’s release encourages you to seek out more and more of those sugary foods.⁴ Over time, the  brain's dopamine receptors can become less responsive, leading to tolerance—where more and more sugar is needed to achieve the same pleasure. (This is why it can sometimes feel impossible to eat just one piece of candy. They’re scientifically engineered to make you want more.)

For example, sugar activates dopamine-containing neurons in areas of the brain that process behavior reinforcement, meaning you’ll go back to it time and time again, even if it's harming your health.⁵⁻⁶ High fructose corn syrup, in particular, has been shown to alter hormonal and brain responses similarly to addictive substances.⁷ 

Fructose is a natural sugar, found in foods like apples, pears, honey, sweet corn, and beets. Unfortunately, fructose gets a bad rap thanks to high-fructose corn syrup (HFCS): A processed derivative of fructose that’s become a major player in the American diet, found in everything from crackers to salad dressings.

Compared to glucose, you’re more likely to overeat foods high in fructose as it activates brain regions involved in attention and reward processing.⁸ Fructose triggers stronger brain responses to food cues, leading to greater hunger and a higher tendency to seek immediate food rewards.⁹ In this study, there was a greater willingness amongst participants that consumed fructose to give up long-term monetary rewards to obtain immediate high-calorie foods in comparison to the participants that consumed glucose.⁹

Fructose is also metabolized differently than glucose: It goes directly to the liver for processing.¹⁰ This can lead to the production of uric acid, which can accumulate (with an excess of foods made with HFCS) and contribute to oxidative stress in the body, which can negatively impact cognitive health, function, mood, and more.¹¹

Fructose (in the form of table sugar and high-fructose corn syrup) and uric acid have also been researched as drivers of a hyperactive foraging response, increasing the potential risk for behavioral issues.¹² Sugar overconsumption can also affect mood, causing compulsivity and impulsivity repetitive behaviors, reminding us of the importance of diet in the health and function of the brain.¹³ 

There’s no need to avoid an occasional sweet treat, but why not avoid the crash that follows?

Before your next sweet treat, eat a meal rich in fiber, protein, and healthy fats to help stabilize blood sugar response. (Foods like nuts, seeds, and fish are especially great additions as they help promote stable energy levels by combining fiber, protein, and healthy fats.)

After your treat, go for a quick walk to help your body use up the excess glucose and maintain healthy blood sugar levels. Also, be sure to hydrate. Dehydration can worsen the symptoms associated with consuming too much sugar.¹⁴

¹Mantantzis, K., Schlaghecken, F., Sünram-Lea, S. I., & Maylor, E. A. (2019). Sugar rush or sugar crash? A meta-analysis of carbohydrate effects on mood. Neuroscience & Biobehavioral Reviews, 101, 45-67. https://doi.org/10.1016/j.neubiorev.2019.03.016

²Witek, K., Wydra, K., & Filip, M. (2022). A High-Sugar Diet Consumption, Metabolism and Health Impacts with a Focus on the Development of Substance Use Disorder: A Narrative Review. Nutrients, 14(14), 2940. https://doi.org/10.3390/nu14142940

³Jacques, A., Chaaya, N., Beecher, K., Aoun Ali, S., Belmer, A., & Bartlett, S. (2019). The impact of sugar consumption on stress-driven, emotional, and addictive behaviors. Neuroscience & Biobehavioral Reviews, 103, 178-199. https://doi.org/10.1016/j.neubiorev.2019.05.021

⁴Hernandez, L., & Hoebel, B. G. (1988). Food reward and cocaine increase extracellular dopamine in the nucleus accumbens as measured by microdialysis. Life Sciences, 42(18), 1705-1712. https://doi.org/10.1016/0024-3205(88)90036-7

⁵Ahmed, S. H., Guillem, K., & Vandaele, Y. (2013). Sugar addiction: pushing the drug-sugar analogy to the limit. Current opinion in clinical nutrition and metabolic care, 16(4), 434–439. https://doi.org/10.1097/MCO.0b013e328361c8b8

⁶Avena, N. M., Rada, P., & Hoebel, B. G. (2008). Evidence for sugar addiction: behavioral and neurochemical effects of intermittent, excessive sugar intake. Neuroscience and biobehavioral reviews, 32(1), 20–39. https://doi.org/10.1016/j.neubiorev.2007.04.019

⁷Meyers, A. M., Mourra, D., & Beeler, J. A. (2017). High fructose corn syrup induces metabolic dysregulation and altered dopamine signaling in the absence of obesity. PLoS ONE, 12(12), e0190206. https://doi.org/10.1371/journal.pone.0190206

⁸Page, K. A., & Melrose, A. J. (2016). Brain, hormone and appetite responses to glucose versus fructose. Current Opinion in Behavioral Sciences, 9, 111-117. https://doi.org/10.1016/j.cobeha.2016.03.002

⁹Luo, S., Monterosso, J. R., Sarpelleh, K., & Page, K. A. (2015). Differential effects of fructose versus glucose on brain and appetitive responses to food cues and decisions for food rewards. Proceedings of the National Academy of Sciences of the United States of America, 112(20), 6509-6514. https://doi.org/10.1073/pnas.1503358112

¹⁰Malik, V. S., & Hu, F. B. (2015). Fructose and Cardiometabolic Health. Journal of the American College of Cardiology. https://www.sciencedirect.com/topics/medicine-and-dentistry/fructose-metabolism#:~:text=%2C%202015-,Fructose%20Metabolism,is%20metabolized%20without%20requiring%20insulin%20secretion%20and%20without%20increasing%20plasma%20glucose.,-Sign%20in%20to

¹¹Bernardes, N., Ayyappan, P., De Angelis, K., Bagchi, A., Akolkar, G., da Silva Dias, D., Belló-Klein, A., & Singal, P. K. (2017). Excessive consumption of fructose causes cardiometabolic dysfunctions through oxidative stress and inflammation. Canadian Journal of Physiology and Pharmacology, 95(10), 1078-1090. https://doi.org/10.1139/cjpp-2016-0663

¹²Johnson, R. J., Wilson, W. L., Bland, S. T., & Lanaspa, M. A. (2021). Fructose and uric acid as drivers of a hyperactive foraging response: A clue to behavioral disorders associated with impulsivity or mania? Evolution and Human Behavior, 42(3), 194-203. https://doi.org/10.1016/j.evolhumbehav.2020.09.006

¹³Witek, K., Wydra, K., & Filip, M. (2022). A high-sugar diet consumption, metabolism and health impacts with a focus on the development of substance use disorder: A narrative review. Nutrients, 14(14), 2940. https://doi.org/10.3390/nu14142940

¹⁴Zaplatosch, M. E., & Adams, W. M. (2020). The Effect of Acute Hypohydration on Indicators of Glycemic Regulation, Appetite, Metabolism and Stress: A Systematic Review and Meta-Analysis. Nutrients, 12(9), 2526. https://doi.org/10.3390/nu12092526