Too much carb cutting affects your brain
What nutrient is praised by athletes, craved by many, cursed by dieters and sometimes blamed for the blues? If you answered "carbohydrate," then you win the prize. But how can carbohydrate have such a mixed reputation?
Question: What is carbohydrate?
Answer: Carbohydrate in foods is present in the forms of starch, sugar and fiber. Starch, found in foods like rice, bread, pasta and potatoes, is essentially just sugar molecules bound together in long strands. Starch molecules are broken down to their sugar components by digestion in the intestine. These sugars, along with sugars from fruits and sweets, end up in our blood as glucose, or "blood sugar."
Dietary fiber contains carbohydrate in a form we cannot digest.
Q: Does the body need carbohydrate?
A: The brain requires glucose for energy and uses about 400 calories of glucose each day. Red blood cells and a few other parts of the body also require glucose, but most of the body can use fat and protein as energy sources.
Q: What happens if a person consumes too little carbohydrate to meet the body's glucose needs?
A: Glucose is an essential energy source for certain body cells, and the liver can make glucose by converting the amino acid components of protein into glucose. However, if glucose production is too slow, people can find themselves feeling tired, unable to do vigorous physical activity and not thinking clearly.
Q: Why do athletes like carbohydrate?
A: During exercise, working muscles get most of their energy from a mixture of carbohydrate and fat. As exercise intensity increases, the use of carbohydrate for energy greatly increases. At maximal exercise intensity, the fuel mix is virtually all carbohydrate.
Carbohydrate is like high-octane fuel for athletes' muscles. Athletes cannot maintain high-intensity efforts when they run low on carbohydrate. In stop-and-go, quick-reaction sports like basketball and soccer, normal levels of blood glucose also help to support the mental part of the game.
Q: Can carbohydrates sabotage weight loss?
A: Both too little and too much carbohydrate can complicate weight loss. Too little can cause muscle to break down to provide needed glucose. Excess carbohydrate, ingested at the expense of required protein, also can cause muscle breakdown. Eating a moderately low-calorie diet with adequate carbohydrate and protein promotes fat loss, inhibits lean tissue loss and will help to lower weight over time.
, Ph.D., C.N.S. and Joannie Dobbs
, Ph.D., C.N.S. are
nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, UH-Manoa. Dr. Dobbs also works with the University Health Services and prepares the nutritional analyses marked with an asterisk in this section. See also: Health Events