What Happens to Your Brain When You Eat Too Much Sugar

Your brain runs on sugar—literally. Glucose is the brain’s preferred energy source, providing the fuel it needs to remember everything from the words of your favorite song to the fastest way to drive home from work. 

Your brain is so hungry for glucose that it uses between 20% to 25% of your body’s glucose to keep functioning. That might make you assume more sugar is better, but that’s not the case, says Erin Person, M.S., RD. Yes, our brains need carbohydrates from healthy foods like fruit, whole grains and beans. “But too much sugar can have deleterious effects on our brain, overall health and body,” says Person. Between sweetened beverages, desserts and the surprising amount of sugar added to everyday foods like yogurt, bread and condiments, many of us eat far more sugar than recommended. And the side effects are far from sweet, adversely affecting focus, mood and even long-term cognition. 

How does it happen? Read on, and we’ll explain exactly what happens to your brain when you overdo it on sugar, and how to find a healthier balance.

How Sugar Affects Brain Health

It May Increase Your Risk of Dementia

The occasional cookie is unlikely to hurt you. Yet, chronically consuming too much sugar over the long haul can slowly chip away at your cognitive health. 

“Excess sugar can negatively affect the brain by impairing memory through mechanisms such as insulin resistance, which makes it harder for brain cells to obtain the glucose (fuel) they need to function, and through neuroinflammation,” says Juliana Vocca, M.S., RD. This disruption in glucose availability and energy metabolism can lead to a series of reactions that cause an increase in amyloid plaque production, which causes the signature neuronal death in Alzheimer’s dementia.

Large-scale research supports this connection. A recent study analyzing the diets of 172,000 participants found that higher intakes of total sugar and added sugars were associated with increased dementia risk, particularly in women.

It May Make You Moody

If you’ve ever felt irritable or crabby after coming down from a sugar high, you’re not imagining things. Eating too much sugar can adversely affect your mood, and it’s associated with a higher risk of depression.

“Excess sugar—especially frequent, high amounts—may trigger low-grade inflammation and metabolic stress, which can interfere with brain function and neurotransmitter balance, potentially harming mood regulation,” explains Karolin Saweres, M.S., RDN, LD. The impact is so profound that one study of more than 18,000 adults found that consuming 100 grams of sugar per day (roughly the amount in a 20-ounce bottle of soda plus 1 cup of ice cream) increased a person’s odds of depression by 28%.,

Then, there are the more immediate effects of blood sugar swings. “Consuming lots of sugar can lead to rapid blood sugar fluctuations, which may cause emotional instability—quick spikes and crashes that affect mood, energy and stress,” says Saweres. 

It May Mess with Your Brain’s Hunger Signals

Knowing when to stop eating isn’t about willpower. It’s controlled by a structure in your brain, called the hypothalamus, that regulates appetite and energy balance. This control center gets many of its hunger and fullness cues from hormones, like leptin and insulin. When you’ve had enough to eat, leptin and insulin rise, sending signals to your brain letting it know that your body doesn’t need additional food.,

Eating lots of sugar can disrupt this communication system. Over time, chronically eating too much sugar can lead to insulin resistance in the brain, making your hypothalamus less responsive to insulin. To complicate matters, insulin resistance may make your brain less sensitive to leptin. As a result, it takes longer for your brain to register fullness signals, so you’re more likely to continue eating past the point when you’ve actually had enough.

What Are the Sugar Recommendations?

Decades of research have established that too much sugar can be harmful to your health, increasing the risk of heart disease, type 2 diabetes and weight gain. But how much is too much? The Dietary Guidelines for Americans currently recommends that no more than 10% of your daily calories come from added sugars. To put that into perspective, that’s about 12 teaspoons (or 50 grams) of added sugars for someone who eats 2,000 calories a day. For many people, this leaves room for the occasional sweet while still supporting overall general health. 

However, if you’re focused on supporting your cognitive and cardiovascular health, the American Heart Association’s guidelines may be a better fit. The AHA recommends no more than 6 teaspoons (25 grams) of added sugars per day for women and no more than 9 teaspoons (36 grams) for men. 

Other Tips to Support Brain Health

While eating less sugar is a great way to support a healthy brain, it’s only a small part of the picture. “Daily exercise and movement, good restful sleep and maintaining social connections are equally as important as the foods we choose to consume,” says Corissa Keefner, D.P.T., RDN. 

For a holistic approach to brain health, keep these habits in mind as well: 

• Eat more fiber-rich carbohydrates: While too much added sugar may be problematic for your brain, there’s no need to worry about carbs from fruits, vegetables and whole grains. These foods are packed with brain-healthy nutrients. They are also rich in fiber, which feeds your good gut bacteria, helping them produce compounds called short-chain fatty acids that decrease inflammation in the brain, explains Person.
• Keep your social calendar booked: Staying socially connected can have big benefits for brain health. Research has repeatedly found that social connection is associated with slower cognitive decline, particularly as we age.
• Make exercise a habit: “Physical activity supports the brain by improving blood flow and growth of new brain cells,” says Vocca. While it sounds simple, the effects can impact every part of your life, from improved mood to enhanced focus and thinking. Regular movement may also protect against age-related cognitive decline and reduce the risk of some neurodegenerative diseases, such as Alzheimer’s disease.
• Make sleep a priority: Lack of sleep doesn’t just mess with your thinking, memory and mood. Chronic sleep deprivation and sleep disorders are linked to an increased risk of stroke and dementia. Create a relaxing and supportive evening sleep routine to help you get the seven to nine hours of sleep you need at night. If sleep still eludes you, talk to your health care provider, who can help determine the root cause of your sleep troubles. 

Our Expert Take

While your brain depends on glucose for fuel, too much added sugar can have serious consequences, both in the short term and over time. From impaired focus and mood to an increased risk of depression, dementia and metabolic disease, chronically high sugar intake affects nearly every aspect of brain health. The good news is, you don’t need to eliminate sugar entirely to support a healthy brain. Instead, focus on limiting added sugars, prioritizing whole, fiber-rich foods, staying physically active and socially connected, and sleeping soundly at night to provide your brain with the fuel, rest and recovery it needs.