5.5: Summary

We require a daily minimum of about 200 calories worth of carbohydrate (50 grams) for normal metabolism. But much more than this is recommended for good health, mainly as a diet rich in whole grains, vegetables, and fruits.

The carbohydrates in our diet are all broken down by digestion into single sugars, mostly glucose, before being absorbed into our bloodstream. The level of glucose in our blood is kept within a normal range by the pancreatic hormones insulin and glucagon: insulin lowers blood glucose, and glucagon raises it.

When blood glucose is abnormally high, the most common cause is diabetes. Normally, insulin allows cells to take in glucose from the blood, thereby lowering blood levels. In diabetes, body cells can’t take in glucose normally from the blood because of a lack of insulin (type 1 diabetes) or a resistance to insulin action (type 2 diabetes). Diabetes is very common in the U.S. Diabetics have a much higher risk of heart disease, stroke, kidney disease, and nerve damage as compared to those of the same age without diabetes.

Most diabetics in this country have type 2 diabetes. This form of diabetes increases as adults get older, mostly from a combination of obesity and genetic predisposition. Type 2 diabetes has become more common in young adults and children as obesity has become more common.

About 5-10% of diabetics in this country have type 1 diabetes. They require an outside source of insulin because the pancreatic cells that make insulin have been destroyed. This diabetes isn’t related to obesity and is typically diagnosed in children and young adults.

Abnormally low blood sugar (hypoglycemia) occurs when there’s excess insulin. The most common cause of severe hypoglycemia is excess insulin taken by a diabetic.

Reactive hypoglycemia is a mild form of low blood sugar that some people experience when they ingest a large amount of carbohydrate after hours of not eating. The pancreas temporarily overshoots its secretion of insulin in response to the surge in blood glucose.

Sugar can cause tooth decay by providing food for mouth bacteria. The bacteria make acid, which erodes tooth enamel and allows bacteria to infect the tooth. Otherwise, the problem of too much sugar is that sweets tend to displace more healthful foods in the diet.

Sugar doesn’t cause hyperactivity in children. In fact, sugar appears to have a calming effect. In animal studies, a high-carbohydrate dose causes a rise in insulin, which in turn, increases the amount of serotonin in the brain. Serotonin is a brain chemical that has a calming effect.

Fiber adds bulk to the diet, bulk and softness to the stool, and plays other roles within the digestive tract, including affecting the microbial population. These attributes of fiber are thought to reduce the risk of constipation, diverticulosis, hemorrhoids, and possibly colon cancer.

In endurance events, depletion of muscle glycogen results in muscle fatigue. To delay this depletion during competition, endurance athletes often use a carbohydrate-loading regimen to achieve a higher-than-normal deposition of glycogen in the relevant muscles at the start of the event. Also, carbohydrate-containing drinks are successfully used in competitions lasting more than 90 minutes.