Negative Impact of Sugar on the Brain
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.
In the brain, excess sugar impairs both our cognitive skills and our self-control. For many people, having a little sugar stimulates a craving for more. Sugar has 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.
Sugar's Reward Response
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 compared to low-glycemic foods. Foods that cause a higher elevation in blood glucose produce a greater addictive drive in the brain.
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 Addiction
Additional studies on brain activity have provided evidence supporting the idea that overeating alters our brain’s reward system, which then further drives overeating.2 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.3 Though the research was performed on animals, investigators found that intense sweetness can surpass cocaine reward, even in drug-sensitized and -addicted individuals.
How Sugar Impacts Memory
Throughout the body, excess sugar is harmful. Even a single instance of elevated glucose in the bloodstream can be harmful to the brain, resulting in slowed cognitive function and deficits in memory and attention.
Some research suggests high sugar consumption causes inflammation in the brain, leading to memory difficulties. A 2016 study published in Behavioral Brain Research found inflammatory markers were present 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
Sugar also affects mood. In healthy young people, the ability to process emotion is compromised with elevated blood glucose, according to a brain imaging study.
Another study published in Diabetes Care found that people with type 2 diabetes reported increased feelings of sadness and anxiety during acute hyperglycemia (elevated blood sugar).
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 was associated with a greater incidence of depression.8
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, and other cognitive functions.9 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 brain-derived neurotrophic factor (BDNF), a brain chemical essential for new memory formation and learning.10 Lower levels of BDNF are also linked to dementia and Alzheimer's disease, according to a study published in the journal Diabetologia.