Our cells depend on a single simple sugar, glucose, for most of their energy needs. That's why the body has intricate mechanisms in place to make sure glucose levels in the bloodstream don't go too low or soar too high.

When you eat, most digestible carbohydrates are converted into glucose and rapidly absorbed into the bloodstream. Any rise in blood sugar signals the pancreas to make and release insulin. This hormone instructs cells to sponge up glucose. Without it, glucose floats around the bloodstream, unable to slip inside the cells that need it.

Diabetes occurs when the body can't make enough insulin or can't properly use the insulin it makes.

One form of diabetes occurs when the immune system attacks and permanently disables the insulin-making cells in the pancreas. This is type 1 diabetes, once called juvenile-onset or insulin-dependent diabetes. It affects about one million Americans.

The other form tends to creep up on people, taking years to develop into full-blown diabetes. It begins when muscle and other cells stop responding to insulin's open-up-for-glucose signal. The body responds by making more and more insulin, essentially trying to ram blood sugar into cells. Eventually, the insulin-making cells get exhausted and begin to fail. This is type 2 diabetes.

In addition to the 18 million adults with diabetes, another 41 million have "pre-diabetes." (1) This early warning sign is characterized by high blood sugar levels on a glucose tolerance test or a fasting glucose test. Whether pre-diabetes expands into full-blown type 2 diabetes is largely up to the individual-making changes in weight, exercise, and diet can not only prevent pre-diabetes from becoming diabetes, but can also return blood glucose levels to the normal range.

Although the genes you inherit may influence the development of type 2 diabetes, they take a back seat to behavioral and lifestyle factors. Data from the Nurses' Health Study suggest that 90% of type 2 diabetes in women can be attributed to five such factors: excess weight, lack of exercise, a less-than-healthy diet, smoking, and abstaining from alcohol.

Among 85,000 married female nurses, 3,300 developed type 2 diabetes over a 16-year period. Women in the low-risk group were 90% less likely to have developed diabetes than the rest of the women. Low-risk meant a healthy weight (body-mass index [BMI] less than 25), a healthy diet, 30 minutes or more of exercise daily, no smoking, and having about three alcoholic drinks per week.

Similar factors are at work in men. Data from the Health Professionals Follow-up Study indicate that a "western" diet combined with lack of physical activity and excess weight dramatically increases the risk of type 2 diabetes in men.

Information from several clinical trials strongly support the idea that type 2 diabetes is preventable. The Diabetes Prevention Program examined the effect of weight loss and increased exercise on the development of type 2 diabetes among men and women with high blood sugar readings that hadn't yet crossed the line to diabetes. In the group assigned to weight loss and exercise, there were 58% fewer cases of diabetes after almost three years than in the group assigned to usual care. Similar results were seen in a Finnish study of weight loss, exercise, and dietary change.

Learn more at: http://www.hsph.harvard.edu/nutritionsource/diabetes.html