Negative Effects of Sugar on the Brain

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The brain uses more energy than any other organ in the human body and glucose is its primary source of fuel. But what happens when the brain is exposed to an excessive amount of sugars in the standard American diet? In this case, more is definitely not better.

The effects of sugar on the brain can include:

  • Impaired cognitive skills and decreased self-control: For many people, having a little sugar stimulates a craving for more.
  • Drug-like effects in the reward center of the brain: Scientists have proposed that sweet foods—along with salty and fatty foods—can produce addiction-like effects in the human brain, driving the loss of self-control, overeating, and subsequent weight gain.

In early humans, this stimulus helped lead them to calorie-rich foods, which aided survival when food was scarce. But now, this primitive drive contributes to our epidemics of obesity and diabetes. The behavioral and neurobiochemical characteristics of substance abuse and overeating are quite similar, and the idea of food addiction is gaining ground among scientists.

This article discusses the effects that sugar has on the brain, including its impact on the reward response. It also covers how it affects memory, mood, and cognition.

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Sugar Impacts the Brain's Reward Response

Reward Response:

The reward response occurs when certain structures in the brain are activated in response to a reward, such as food, sex, or addictive drugs. Activating this pathway creates a connection between the activity and the feelings of pleasure, which increases the likelihood that the behavior will occur again.

In humans, high-glycemic foods have been found to activate regions of the brain associated with the reward response and provoke more intense feelings of hunger than low-glycemic foods. Foods that cause a higher elevation in blood glucose produce a greater addictive drive in the brain.

The glycemic index is a way of classifying carbohydrate-containing foods to estimate how quickly they are digested and their potential for increasing blood sugar levels. The various types of carbohydrates are processed differently in the body, some causing rapid spikes and dips in blood sugar and others leading to slower, more gradual increases and declines.

High-Glycemic Foods

High-glycemic foods are those with a high value on the glycemic index. They are digested quickly and cause a rapid increase in blood glucose levels.

Examples of high-glycemic foods include:

  • Processed foods
  • High sugar foods
  • Cereals, doughnuts, and white bread
  • Potatoes

Low-Glycemic Foods

Low-glycemic foods are those that have a low value on the glycemic index. Such food can help people control blood sugar levels and body weight and reduce the risk for health conditions such as heart disease and type 2 diabetes.

Examples of low-glycemic foods include:

  • Vegetables
  • Fruits
  • Dairy 
  • Nuts
  • Legumes

Research published in the American Journal of Clinical Nutrition used the glycemic index (GI)—a measure of how certain foods convert to sugar in the body—to test this process and found eating a high-GI meal elicited greater brain activity in regions involved in eating behavior, reward, and craving.

Sugar Causes Addiction-Like Responses

Additional studies on brain activity have provided evidence supporting the idea that overeating alters our brain’s reward system, which then further drives overeating. This same process is thought to underlie the tolerance associated with addiction.

Over time, greater amounts of the substance are required to reach the same level of reward. Studies imply that overeating results in a diminished reward response and a progressively worsening addiction to low-nutrient foods rich in sugar, salt, and fat.

A study published PLoS One found that sweet foods can be more addictive than cocaine. Though the research was performed on animals, investigators found that intense sweetness can surpass cocaine reward, even in drug-sensitized and -addicted individuals. 

Sugar Has Effects on Memory

In addition to sugar's negative effects on the brain, it also harms the entire body. Even a single instance of elevated glucose in the bloodstream can be harmful to the brain, resulting in:

Inflammation in the brain can contribute to further memory difficulties. A 2016 study published in Behavioral Brain Research found inflammatory markers in the hippocampus of rats fed a high sugar diet, but not in those fed a standard diet.

The good news, however, is this inflammatory damage from sugar may not be permanent.

A 2017 study in the journal Appetite found that the memory damage caused by sugar consumption can be reversed by following a low-sugar, low-GI diet.

In addition, research published in the journal Nutrients in 2015 found reducing sugar consumption and supplementing with omega-3 fatty acids and curcumin improves working memory.

Sugar Has Effects on Mood

Another serious effect of sugar on the brain its its impact on mood. Such effects may include:

  • Compromised emotional processing: In healthy young people, the ability to process emotion is compromised with elevated blood glucose, according to a brain imaging study.
  • Increased anxiety: Another study published in Diabetes Care found that people with type 2 diabetes reported increased sadness and anxiety during acute hyperglycemia (elevated blood sugar).
  • Higher risk for depression: One of the largest studies to link sugar with depression—an analysis of dietary consumption and mood of 23,245 individuals enrolled in the Whitehall II study—found higher rates of sugar consumption were associated with a greater incidence of depression.

The study, published in 2017 in the journal Scientific Reports, found those with the highest level of sugar consumption were a 23% more likely to be diagnosed with a mental disorder than those with the lowest sugar intakes.

Sugar Intake Hinders Mental Capacity

Elevated blood glucose harms blood vessels. Blood vessel damage is the major cause of the vascular complications of diabetes, leading to other problems, such as damage to blood vessels in the brain and eyes, causing retinopathy.

Studies of long-term diabetics show progressive brain damage leading to deficits in:

  • Learning
  • Memory
  • Motor speed
  • Other cognitive functions.

Frequent exposure to high glucose levels diminishes mental capacity, as higher HbA1c levels have been associated with a greater degree of brain shrinkage.

Even in those without diabetes, higher sugar consumption is associated with lower scores on tests of cognitive function. These effects are thought to be due to a combination of hyperglycemia, hypertension, insulin resistance, and elevated cholesterol.

Additional research shows that a diet high in added sugar reduces the production of brain-derived neurotrophic factor (BDNF), a brain chemical essential for new memory formation and learning. Lower levels of BDNF are also linked to dementia and Alzheimer's disease, according to a study published in the journal Diabetologia.

A Word From Verywell

As the research shows, any sugar added in our food is dangerous. We can avoid these dangers by satisfying our sweet tooth with fresh fruit in place of refined sugars.

Eating fresh fruit provides the satisfying sweetness of sugar-laden treats with the added bonus of the fruit’s fiber, antioxidants, and phytochemicals that curtail the surge of sugar in the bloodstream and block its negative effects.

12 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Joel Fuhrman, MD
Joel Fuhrman, MD, is a board-certified physician focused on nutrition and natural healing. He's a New York Times best-selling author and TEDx speaker.