22.18: Diabetes is caused by the body’s inability to regulate blood sugar effectively.

When it functions properly, the human body can resemble a finely tuned, responsive machine. Nowhere is this more evident than in the processing of food. After you digest and absorb food, there’s an increase in the amount of glucose circulating in your bloodstream. This triggers the release of insulin by your pancreas. Insulin is a storage-stimulating hormone that causes your body’s cells, especially muscle cells and fat cells, to pull the glucose in. They can then either use it for energy or convert it to glycogen or fat for storage until the energy is needed some other time. This leads to a reduction in glucose in the bloodstream and brings your blood sugar level back down to normal.

Foods differ in the extent to which they cause a surge in blood sugar and subsequent release of insulin. Foods that cause a rapid and large surge—such as orange juice, honey, and white potatoes—are classified as having a high glycemic index and are less desirable in the diet. More desirable are foods that cause only a slow, moderate increase, having a low glycemic index. These include whole grains and beans. With a reduced insulin response comes a more efficient utilization of the sugar and lipids in the bloodstream and a reduction in fat storage. Insulin surges can also be reduced by eating smaller meals or, if you consume foods that have a high glycemic index, eating them with other foods as part of a meal.

Even finely tuned machines can malfunction. More than 10 million Americans (and 100 million people worldwide) have problems with their insulin-response systems, referred to as diabetes. These problems are chiefly of two types (FIGURE 22-36): either (1) the pancreas doesn’t secrete enough insulin in response to an increase in blood sugar, or (2) the pancreas secretes plenty of insulin, but the cells of the body don’t respond to it, usually due to a deficiency in glucose receptors on their cell membranes. In both cases, blood sugar remains high, and a host of problems can result from such persistence of glucose in the bloodstream.

The first type of diabetes (called type 1) is believed to be an autoimmune disease and is most often diagnosed in children or young adults. Generally, people with type 1 diabetes have a pancreas that doesn’t secrete enough insulin, and thus they can be treated by insulin injections (FIGURE 22-37). (Unfortunately, because insulin is a protein, it is digested by stomach acids and the enzymes of the small intestine, so insulin must be injected in order to get it into the bloodstream intact.) The second type of diabetes (type 2) is about 10 times more common. It generally develops after the age of 40, and in about 90% of cases it is a consequence of obesity. It appears that chronic and excessive amounts of sugar in the diet (and, later, in the bloodstream) reduce the sensitivity and/or number of cellular insulin receptors that help control blood sugar. This causes even greater releases of insulin, which can, ultimately, wear out the insulin-producing cells of the pancreas. Type 2 diabetes is treated by minimizing the glucose fluctuations in the bloodstream. Weight loss is also encouraged, as it reduces insulin resistance.

Because chronically high levels of blood sugar affect nearly all the cells of the body, the health effects can be far-reaching and severe. Cells in the eye lens can become deformed, causing blurry vision; blood vessels can be damaged, causing circulatory system and kidney malfunction; and nerves can also be damaged. Taken together, the varied problems resulting from diabetes make it the sixth leading cause of death in the United States.