Glucose is a primary fuel for the brain. Your brain uses about 100 to 150 grams of glucose each day—roughly half to three-quarters of a cup. This probably sounds like good news to people who love sweets, but it’s not quite what it seems.
Your brain gets glucose from naturally occurring carbohydrates, not the highly refined sugars of today. The body can also produce glucose when carbohydrate intake is low, and the brain can use ketones as an alternative fuel.
Understanding how the brain responds to sugar is the first step in recognizing whether you might be experiencing the consequences of a disrupted metabolism and a sugar-drunk brain.
Why Is Sugar Hard to Resist?
When a sweet treat melts on the tongue, the pleasure can be almost intoxicating. Sweet-taste receptors on the tongue send signals to the brain, triggering the release of dopamine and endogenous opioids—substances that reduce pain and make you happy. This is the body’s way of telling us to keep eating these energy-rich foods, a signal that now can go awry and turn sugar into something akin to a drug.
“Sugar addiction is like alcohol or drug addiction,” Kenneth Blum, a neuropsychopharmacologist and professor at Western University Health Sciences, told The Epoch Times.
The pleasure is short-lived and intense. That’s why some people feel hooked. When processed sugar and refined carbs that rapidly turn into sugar in the blood repeatedly stimulate the brain over time, dopamine receptors may decrease, making the brain less sensitive to dopamine. As a result, you may need a higher “dose” to produce the same sense of pleasure. Foods with natural sweetness can begin to seem less appealing. The reduced dopamine sensitivity may also lead to low mood and difficulty concentrating.
Some sugars also blur the sense of fullness—the very signal that tells us when to stop.
A hormone called leptin signals the brain when you are full. It’s produced mainly by fat cells, with a small amount also secreted by the stomach lining. Greater body fat and energy stores are generally associated with higher leptin levels. Unfortunately, ultra-processed foods often contain high levels of fructose, a sugar that can disrupt those signals.
Fructose is a very sweet sugar—roughly twice as sweet as glucose—and inexpensive to produce, which is why it is widely added to processed foods. High-fructose corn syrup is one of the best-known examples of this inexpensive added sugar.
The Sugar Roller Coaster
While natural, whole foods have their sugars bound up with fiber and other compounds that slow absorption, ultra-processed foods have sugars and refined carbs that hit the bloodstream like a freight train.
These “sugar spikes” are a real problem, Dr. Daniel Amen, a double board-certified psychiatrist and founder and CEO of Amen Clinics, told The Epoch Times.
After a meal, your body releases insulin to move glucose from the bloodstream into cells, where it can be used or stored for energy. However, high-sugar foods trigger the body to release a surge of insulin to get the high levels of blood sugar under control. In some people, this can lower blood sugar enough to cause reactive hypoglycemia—low blood sugar.
Low blood sugar then triggers a counterresponse, with the body releasing hormones such as adrenaline, glucagon, and cortisol to raise blood glucose again.
These fluctuations can contribute to fatigue and even brain fog. This is why a lunch high in refined carbs can leave some people feeling sleepy afterward.
However, brain fog may only be the beginning. This blood sugar roller coaster can quickly take your metabolism off the rails.
The Starved Brain Cells
To handle repeated surges in blood sugar, the body must repeatedly release insulin. After prolonged excessive stimulation, cells can gradually reduce their insulin sensitivity.
One way to picture this is a house with doors on every side. If too many people keep knocking at the same time, the homeowner may eventually stop answering the door.
Of course, this is just one part of a larger, complex mechanism. And when that happens, insulin signaling and glucose metabolism in the brain may also be affected. In healthy people, the brain can use sugar well; but when glucose metabolism is affected, brain cells may struggle to use energy efficiently.
As a result, neurons can face an energy shortfall even when blood glucose is high. This can lead to slower thinking and memory problems.
“Many cases of Alzheimer’s [disease] develop because of diabetes or insulin resistance,” Dr. Joshua Helman, chief medical officer of both Alzheimer’s Treatment Centers of America and BrainPower Clinics, told The Epoch Times. “In fact, people have referred to Alzheimer’s [disease] as type three diabetes.”
The Gummed-Up Blood Vessels
“Too much sugar is like giving a Ferrari cheap gasoline—it gums up the engine,” Amen said.
Sugar molecules in the bloodstream can attach to proteins, fats, and other substances. Over time, this process produces compounds known as advanced glycation end products (AGEs).
These changes may disrupt the glymphatic system, which helps clear waste from the brain during deep sleep. The rhythmic pulsing of blood vessels helps move fluid through this system, so damage to blood vessels and poor circulation may interfere with the process. When proteins such as beta-amyloid and tau are not cleared efficiently, they can accumulate in the brain.
The brain also contains enzymes that help break down beta-amyloid into smaller components, facilitating its clearance. When insulin levels remain chronically high, more of this enzymatic capacity may be directed toward breaking down insulin, leaving less available to break down beta-amyloid.
The Compromised Protective Barriers
Excess sugar may also affect two important protective barriers in the body: the gut barrier and the blood-brain barrier.
Helman said that zonulin, a protein known to regulate intestinal permeability, has also been implicated in blood-brain barrier function. “Basically, if you have a leaky gut, you also have a leaky brain. It’s the same pathway, unfortunately.”
More specifically, both the gut and brain barriers are formed by tightly connected cells, and zonulin can help regulate the permeability of these cellular seams. When the body detects potentially harmful substances in the gut, zonulin production can increase and loosen these seams.
This response helps the body expel harmful substances. However, substances that would not normally enter the bloodstream may also pass through these gaps.
Toxins and inflammatory substances circulating in the blood can then further weaken the blood-brain barrier. This may trigger chronic inflammation in the brain and interfere with neuronal signaling, leading to symptoms such as brain fog and memory problems.
“Inflammation specifically targets your immune system, which will then target blood vessels and do damage to the lining, which then promotes damage in the brain and other tissue,” Helman said.
Lipopolysaccharide (LPS) is one example of such a toxin. It’s a major component of the outer membrane of Gram-negative bacteria such as Escherichia coli (E. coli) and can be released when bacterial cells die or break down.
“Most of the people I see with dementia or Alzheimer’s disease actually have impaired blood-brain barrier function. The basement membrane that keeps toxins and other substances out of the brain has been damaged,” Helman said.
Less ‘Fertilizer’ for the Brain
The brain’s ability to learn new things and form new memories depends on neurons continually growing and forming connections. This process is supported and regulated in part by a protein called brain-derived neurotrophic factor (BDNF).
“BDNF is like fertilizer for the brain,” Dr. David Perlmutter, a board-certified neurologist and professor at the University of Miami Miller School of Medicine, told The Epoch Times.
“Refined sugar shrinks the hippocampus—your memory center,” Amen said, noting that this can impair memory function.
How the Brain Can Use Sugar Safely
There are, however, safer ways to provide the brain with fuel.
Refined carbs from heavily processed foods can act like an energy bomb, releasing large amounts of glucose in a short period. In contrast, whole grains, vegetables, and legumes release glucose more gradually, which can help maintain more stable blood sugar levels and provide the brain with a steadier supply of energy.
If you do eat sugar, walking afterward or doing other exercise can help your muscles absorb the circulating glucose and blunt the rise in blood sugar.
Linda Sparks, a naturopathic physician at Naturally Sue Wellness Clinic, recommends making a habit of walking after meals. “That’s pretty easy and cheap,” she told The Epoch Times.
The order in which you eat foods may also make a difference.
If a meal contains a substantial amount of sugar or carbs, Dr. Christina Miller, an integrative and functional medicine physician, recommends starting with vegetables and protein and leaving carbohydrate-rich foods until the end. “Then your blood sugar won’t spike at all the same way it would if you just sit down and eat a brownie,” she told The Epoch Times.
Miller stressed that people vary considerably in how their blood sugar responds to food. Some can eat sugar without experiencing a large glucose spike. She said that, for her, however, even a little sugar can lead to overeating, so she is particularly careful.
“For the people who are looking in general for brain health, the number one thing I would say is ask your doctor for a continuous glucose monitor,” Sparks said. A continuous glucose monitor can track glucose levels in real time, helping people identify foods and habits that affect their blood sugar and make adjustments accordingly.
Sugar Substitutes May Not Be the Answer
A wide range of sugar substitutes are now available, but replacing sugar with them does not necessarily make a diet healthier.
Perlmutter said that the primary mechanism is not direct toxicity—although erythritol may have direct toxic effects—but disruption of the gut microbiome, which plays an important role in brain health.
“We don’t need the artificial sweeteners,” Perlmutter said. “By and large, I think gravitating towards nonsweet is what the messaging needs to be.” For those who do need a sweetener, he suggested allulose and monk fruit as safer alternatives.
He encourages people to turn to whole foods.
