Carbohydrates and Brain Energy
Your brain is a hungry organ. Even though it makes up only about 2 percent of your body weight, it uses roughly 20 percent of all the energy your body needs. This energy comes primarily from glucose, which is a simple sugar that your body breaks down from the carbohydrates you eat.
When you consume carbohydrates like bread, rice, fruits, vegetables, or pasta, your digestive system converts them into glucose. This glucose enters your bloodstream and travels to your brain, where it fuels everything from basic thinking to complex problem-solving. Without adequate glucose, your brain cannot concentrate or focus properly. This is why skipping meals or eating too little can leave you feeling foggy and unable to think clearly.
The brain’s dependence on glucose is so fundamental that it has special systems to ensure it gets a steady supply. The blood-brain barrier acts as a gatekeeper, carefully controlling what enters the brain from the bloodstream. It prioritizes glucose delivery because the brain has almost no way to store energy on its own. Unlike muscles, which can store glucose as glycogen for later use, your brain needs a continuous stream of fuel from your blood.
However, glucose is not the only fuel your brain can use. Your brain can also run on ketones and lactate, which are alternative energy sources. Lactate provides about 8 percent of your brain’s energy under normal conditions, but this increases to 60 percent during intense exercise. Ketones become important when you eat very few carbohydrates or during fasting. During brain development, ketones can supply 30 to 70 percent of the brain’s energy needs. In adults, when carbohydrates are restricted, the body produces ketones that the brain can use as fuel.
The quality of carbohydrates matters significantly for brain health. Not all carbohydrates affect your brain the same way. Foods with a low glycemic index, such as whole grains, legumes, and most fruits, cause a slower, more gradual rise in blood sugar. Research shows that diets with low to moderate glycemic index foods are associated with a 16 percent reduction in the risk of developing Alzheimer’s disease. In contrast, diets with high glycemic index values are associated with a 14 percent increase in risk. This means that choosing whole grain bread instead of white bread, or eating an apple instead of drinking sugary soda, can have real effects on your long-term brain health.
Beyond providing energy, carbohydrates play another important role in brain chemistry. When you eat carbohydrate-rich foods, your body produces more serotonin, a chemical messenger in the brain that improves mood and how you feel. This is one reason why people often reach for carbohydrate-rich comfort foods when they are stressed or sad. The carbohydrates help your brain produce more of this mood-boosting chemical.
There is an important distinction to make about sugar and brain function. While your brain needs glucose to work properly, eating extra sugar beyond what your body needs does not boost your brain power further. Once your blood glucose is within the normal range, consuming additional sugary drinks or snacks will not improve your concentration or thinking ability. In fact, excessive sugar consumption may harm brain health over time by disrupting insulin signaling and contributing to conditions like cerebral glucose hypometabolism, where the brain cannot use glucose efficiently.
Some research suggests that very low carbohydrate diets, particularly ketogenic diets that are high in healthy fats, may benefit brain health in certain situations. Clinical trials have shown that ketogenic diets can improve cognitive function in people with Alzheimer’s disease and memory loss. The theory is that when the brain loses its ability to metabolize glucose efficiently, as happens in Alzheimer’s, ketones provide a cleaner and more efficient alternative fuel source. These ketone bodies can restore the brain’s energy supply and boost mitochondrial function, which are the energy factories inside cells.
The bottom line is that your brain needs carbohydrates for energy and optimal function. The type and amount of carbohydrates you choose matters for both immediate brain performance and long-term brain health. Choosing whole grains, fruits, vegetables, and legumes over refined sugars and processed foods supports better concentration today and may help protect your brain from cognitive decline in the future.
Sources
https://www.bda.uk.com/resource/food-facts-food-and-mood.html
https://pmc.ncbi.nlm.nih.gov/articles/PMC12753350/
https://medicalxpress.com/news/2025-12-quality-carbohydrates-diet-play-key.html
https://lifestylemedicine.stanford.edu/brain-food-connection/
https://es.uchealth.org/today/foods-to-fuel-good-mental-health/
https://www.mindbodygreen.com/articles/doctors-guide-eating-cognitive-longevity
