Written by Dr. Nicole Avena
Dr. Avena is a professor, research neuroscientist, and author on food & addiction. She has done extensive research on sugar and the effects it can have on health. She is the author of Sugarless: A 7 Step Plan to Uncover Hidden Sugars, Curb Your Cravings and Conquer Your Addiction.
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As more and more research focuses on the negative implications of excess sugar intake, new questions arise on how sugar impacts the brain. While our food environment has changed over the past few centuries through the influx of ultra-processed food—that is often filled with added sugar—our brains, on the other hand, have not changed. So as much as our world has progressed and evolved, our brains are still the same as they were when humans were hunters and gatherers, back before ultra-processed foods ever existed.
The Brain Needs Sugar, But Not Added Sugar
You may have heard that our brains need sugar to function, and while that is technically true, there is a bit more to it: When our body breaks down and digests foods that are rich in carbohydrates, it forms glucose, a form of sugar that is the primary fuel source for the brain. In fact, half of all the glucose (aka sugar) within the body is used by our brains[1]. Despite the brain requiring glucose as an energy source for optimal functioning, too much of it can pose detrimental effects. The bottom line is that we don’t technically need any added sugar in order for our brain to get its fuel—our bodies can make it from other carbohydrates or even fats, if needed!
The Primitive Part of the Brain
We have an evolutionary drive to consume sugar. This can be traced all the way back to our hunter-and-gatherer ancestors, who used to seek out sweet fruits because they were safe to eat. Also, the first foods we are exposed to, breastmilk and baby formula, are naturally sweet! This is why the desire to consume sugar lies in the most primitive parts of our brain, which are instinctually tasked with ensuring our survival. The parts of our brain that are the most evolved belong to the outer area—this is where our primitive urges are halted. The rational part of our brain allows us to respond with judgment to situations—such as saying “no” when something might be too risky or dangerous, even though we may get pleasure out of it. In regard to limiting sugar intake, it becomes difficult for the rational part of the brain to do its job because the primitive parts of our brain take control and overpower the rational parts.
Sugar Dependence
In addition to our natural craving for sugar, research studies that have looked at the impact of sugar on the brain have found that sugar exhibits similar addictive properties as substances like drugs and alcohol. In addiction, whenever someone first uses a substance, they feel a “high,” which is the reward from it. Following this, they tend to experience a “low.” We see a similar situation with sugar. Think back to the first time you ate a candy bar—it probably felt so indulgent and amazing!
The pleasure we experience from consuming sugar happens because it causes the brain to release dopamine, our “feel good” neurotransmitter. In instances of frequent overindulgence like we see in the standard American diet (according to the American Heart Association, the average American consumes 2-3x the recommended amount for men and women), the brain’s reward system can go awry. In situations of addiction, the dopamine response in the brain is altered, which produces very intense feelings of reward[2]. Whenever an individual is trapped in the cycle of addiction, they may become hooked on capturing that feeling of reward again, but they are never quite able to. This can result in overindulgence and a strong desire to obtain a substance—in this instance: sugar..
Sugar and Brain Fog
A negative way that sugar can impact your brain is by contributing to how well you can easily remember or recall things. Sugar consumption, especially in large quantities, has been linked to the experience of brain fog, a state characterized by confusion, forgetfulness, and a lack of focus and mental clarity. When consumed, sugar causes a rapid spike in blood glucose levels, which can lead to an initial burst of energy. However, this is often followed by a sharp decline in blood sugar, leading to a crash that can impair cognitive function. Research suggests that high sugar intake can negatively affect the hippocampus, a brain region critical for memory formation, and may contribute to inflammation, which is associated with cognitive decline and brain fog[3]. Moreover, diets high in refined sugars have been shown to impair memory and slow cognitive function[4], further contributing to the sensation of mental cloudiness often described as brain fog.
Sugar and Hyperactivity
In addition to making us foggy, too much added sugar can also impair our ability to pay attention and to focus, in part, because of hyperactivity. The idea that sugar consumption causes hyperactivity, particularly in children, has been a topic of debate, but some research suggests a link between high sugar intake and increased levels of hyperactive behavior. Excessive sugar can lead to rapid spikes in blood glucose levels, which might temporarily elevate energy levels and cause restlessness. For instance, researchers conducted a meta-analysis of controlled studies and found that while sugar's impact on hyperactivity is not universally supported, certain individuals, particularly children who are sensitive to sugar, may exhibit increased hyperactivity after consuming large amounts of sugar[5]. Additionally, another study showed that parents often perceive their children as being more hyperactive after consuming sugar, possibly due to expectation bias, but also noted that sugar might exacerbate hyperactive behaviors in some children[6]. Although the overall evidence is mixed, the potential for sugar to contribute to hyperactivity in susceptible individuals should not be dismissed entirely.
Sugar and Attention
Along with potentially contributing to hyperactivity, high intake of added sugars can lead to rapid fluctuations in blood glucose levels, resulting in a "sugar crash" that diminishes mental clarity and focus. Sugar consumption can dysregulate dopamine levels, a neurotransmitter critical for attention and reward processing, leading to reduced cognitive function and focus. Additionally, diets rich in refined sugars can impair hippocampal function, which is crucial for memory and learning, further contributing to attention deficits. The cumulative effect of these metabolic and neurochemical disruptions can manifest as difficulty concentrating, shorter attention spans, and impaired cognitive performance. The bottom line is that too much added sugar can impair your ability to pay attention, and this can happen through multiple ways in the brain.
Fueling a Healthier Brain
Understanding the impact of sugar on your brain is a crucial step toward taking control of your health. It may take time, but each effort you make to reduce sugar can lead to clearer thinking, better focus, and a more balanced life. Stay encouraged—small steps can lead to big changes.
References
1. Harvard Medical School. Sugar and the Brain. Hms.harvard.edu. https://hms.harvard.edu/news-events/publications-archive/brain/sugar-brain. Published Spring 2016. Accessed July 19, 2024.
2. Avena, N. M., Rada, P., & Hoebel, B. G. (2008). "Evidence for sugar addiction: Behavioral and neurochemical effects of intermittent, excessive sugar intake." Neuroscience & Biobehavioral Reviews, 32(1), 20-39.
3. Noble, E. E., & Kanoski, S. E. (2016). "Dietary Sugars, Obesity and the Hippocampus: Emerging Roles for Dietary Sugar in Hippocampal Function and Cognitive Deficits." Frontiers in Behavioral Neuroscience, 10, 64.
4. Ye, X., Wang, R., Zhu, H., & Lei, X. (2021). "Sugar Consumption and its Impact on Memory and Cognitive Function in Middle-Aged and Elderly People." Nutrients, 13(4), 1344.
5. Wolraich, M. L., Wilson, D. B., & White, J. W. (1995). "The effect of sugar on behavior or cognition in children: A meta-analysis." JAMA, 274(20), 1617-1621.
6. Hoover, D. W., & Milich, R. (1994). "Effects of sugar ingestion expectancies on mother-child interactions." Journal of Abnormal Child Psychology, 22(4), 501-515.