The human brain needs over 20%Trusted Source of the body’s energy to function, and it gets this from metabolizing either glucose or ketone bodies.

Hypometabolism occurs when brain cells cannot use glucose as an energy source.

The brain is vulnerable to changes in metabolism.

People with Alzheimer’s disease often experience a severe dropTrusted Source in the brain’s glucose metabolic rate, and the extent of this reduction is associated with the severity of their illness.
Carbohydrate metabolism is the whole of the biochemical processes responsible for the metabolic formation, breakdown, and interconversion of carbohydrates in living organisms.

Carbohydrates are central to many essential metabolic pathways. Plants synthesize carbohydrates from carbon dioxide and water through photosynthesis, allowing them to store energy absorbed from the sunlight internally. When animals and fungi consume plants, they use cellular respiration to break down these stored carbohydrates to make energy available to cells. Both animals and plants temporarily store the released energy in the form of high-energy molecules, such as ATP, for use in various cellular processes.

Humans can consume a variety of carbohydrates, digestion breaks down complex carbohydrates into a few simple monomers (monosaccharides) for metabolism: glucose, fructose, mannose and galactose. Glucose is distributed to cells in the tissues, where it is broken down or stored as glycogen. In aerobic respiration, glucose and oxygen are metabolized to release energy, with carbon dioxide and water as endproducts. Most of the fructose and galactose travel to the liver, where they can be converted to glucose and fat.

Some simple carbohydrates have their own enzymatic oxidation pathways, as do only a few of the more complex carbohydrates. The disaccharide lactose, for instance, requires the enzyme lactase to be broken into its monosaccharide components, glucose and galactose.