Glucose is a sugar that comes from the breakdown of all carbohydrates in the diet. Among other functions, glucose is a vital part of brain function as it is the only fuel that your brain can use. If you are consuming a low-carbohydrate diet, you may not be getting enough glucose for your brain to function properly. Because your brain ultimately controls all other functions within your body, giving your brain too little glucose can be dangerous to your overall health.
Glucose Requirements
According to Iowa State University Extension, the Recommended Dietary Allowance of carbohydrate is 130 grams daily. It is important to note that this is the amount that is needed to support only the function of the brain and other central nervous system activities that depend only on glucose as fuel. If you plan to do any physical activity, more carbohydrate is needed. It is recommended to consume 40 to 50 percent of your daily calories from carbohydrate.
Glycogenolysis
If you are following a low-carbohydrate diet, or if you are in a period of starvation, your brain will likely not get enough glucose to function properly. Under normal circumstances, excess glucose is stored in your liver and muscle in the form of glycogen. Only a limited amount of glycogen can be stored. Under starvation conditions, your liver will release glycogen as glucose to help raise blood sugar and feed the brain. Enough glycogen is stored to last you approximately one day under starvation conditions. .
Gluconeogenesis
Once glycogen stores are depleted, your body will resort to gluconeogenesis to produce glucose. Gluconeogenesis is a process that creates glucose from non-carbohydrate sources such as fats and proteins. Most of the glucose formed from gluconeogensis comes from the amino acids of proteins. Any non-glucose products of this breakdown will fuel tissues in the body that do not depend on glucose, leaving all glucose produced for the brain. Long-term reliance on gluconeogenesis can be harmful, because you are forcing your body to use nutrients for functions other than what is normal. For example, by breaking down protein to produce glucose, you are leaving little protein to build and fuel your muscles.
Ketosis
When the body can no longer produce adequate glucose, your body goes into a state of ketosis, or a switch from using primarily carbohydrates for energy to using primarily fat for energy. Instead of relying on glucose alone, the brain will use a small amount of glucose along with ketone bodies. Ketone bodies are formed by the breakdown of fatty acids in the liver. Long-term ketosis is undesirable in most people, as it can cause dizziness, nausea, bad breath and liver or kidney problems.
References
- Iowa State University Extension: Carbohydrates
- McGraw Hill Higher Education: Starvation
- "Basic Neurochemistry: Molecular, Cellular and Medical Aspects, 6th edition"; George J Siegel, MD, et. al; 1999
