After answering the above five questions, your brain will have burned two calories—around the same amount of calories found in a small sugar candy. In fact, if you take a standard college test, your brain alone will burn the same number of calories as you would burn while riding a stationary bike for six minutes.
Like all parts of the body, your brain needs energy to function. And the brain is one of the most metabolically active organs of the human body. One-fifth of the blood your heart pumps goes to the brain to supply its voracious appetite for nutrients.
But the brain has very special needs. Your other body parts can burn fat instead of sugar (carbohydrates) if blood sugar levels go down. The brain, however, cannot do this—it can only utilize sugar. This makes the brain very sensitive to fluctuations in blood sugar levels. Both high and low levels of blood sugar can affect your brain function.
Running low on fuel
The condition where your blood sugar level goes way below normal is called hypoglycemia. Among healthy adults, hypoglycemia is rare since the body’s “sugar thermostat” can trigger hunger, inducing you to eat, as well as stimulate the liver and muscles to release sugar from their stores. Only after prolonged starvation, usually aggravated by exercise, do healthy adults develop hypoglycemia. Ill individuals, however, can easily get hypoglycemia, as a result of loss of appetite, and the body’s increased demand of nutrients in an effort to recuperate.
Aside from the physical symptoms—weakness, tremors, palpitations, cold sweats, paleness, hunger, nausea and vomiting—hypoglycemia manifests through mental changes, such as anxiety, nervousness, poor concentration and judgment, confusion, moodiness, depression, irritability and poor memory. In extreme cases, paralysis, seizures and coma can ensue. All of these are a result of the brain lacking nutrients required for it to function.
Hyperglycemia is the opposite of hypoglycemia: It’s when blood sugar levels shoot way beyond normal levels. It’s more difficult for a healthy person to develop hyperglycemia than hypoglycemia, because the pancreas can quickly secrete insulin, which forces the liver, muscles and fat tissues to absorb excess sugar from the blood.
Temporary hyperglycemia, such as what happens immediately after a meal, doesn’t have symptoms and is quickly corrected. When hyperglycemia extends over days to months, symptoms such as frequent thirst, frequent urination, dry mouth, itchy skin, tingling of the feet, and recurrent infections can occur. It can cause adverse effects to the brain, such as sleepiness, stupor—seizures and coma can occur. These symptoms are usually caused by the brain reacting to changes in the blood’s chemistry as a result of the excess sugars.
Diabetes: double whammy
Unlike healthy individuals, patients with diabetes are at constant risk of both hyperglycemia and hypoglycemia, together with their effects on the brain. By definition, diabetes is a prolonged state of hyperglycemia. However, diabetics are also at risk of developing hypoglycemia because they’re prescribed drugs that forcibly lower the amount of sugar in the blood.
Recent studies show that specific parts of the brain are particularly sensitive to hypoglycemia. These parts include the cingulate gyrus, the thalamus, and the hypothalamus. The cingulate gyrus is a part of the brain that helps control emotions, learning and memory. The thalamus helps control consciousness, sleep and alertness. The hypothalamus helps controls body temperature, hunger, thirst, fatigue and sleep.
Put together, these studies suggest that the brain first tries to cope with short periods of hypoglycemia by working harder, but later on is unable to cope. Eventually, neurons begin to fail. You become less alert, less able to concentrate, and develop a depressed mood.
On the other hand, hyperglycemia due to diabetes can affect the brain by damaging the brain’s blood vessels, as well as excessively depositing certain kinds of proteins in brain cells, altering their function.