Mounting evidence indicates that prediabetes increases the likelihood of eventually developing not only diabetes but also heart attack, stroke, and possibly cognitive decline and certain cancers.

Fortunately, most cases of prediabetes and diabetes are preventable, since they stem mainly from eating too much and exercising too little. Further, spotting the problem early, when treatment works best, can help even in cases caused by genetic susceptibility alone. But people hoping to evade, detect, or control these disorders face several obstacles:

• Public-health experts and even government agencies disagree on who should be screened for prediabetes and diabetes.
• It's still unclear how best to treat prediabetes. Some doctors recommend lifestyle changes only, while others advise medication as well.
• Although aggressive drug treatment of diabetes clearly saves lives and prevents complications, many people fail to control the disease adequately. One reason: It's hard for doctors and patients to manage the multiple medications often required. That task will now get even harder, because experts are increasingly recommending insulin—which requires daily injections and frequent blood-sugar checks—at an earlier stage.
• Losing weight permanently is hard. And the current low-carb craze has obscured crucial facts about how to achieve that goal as well as control blood sugar.

This report will provide the best available advice on how to stave off prediabetes and diabetes, who should get their blood sugar tested, and what to do if those sugar readings are on the rise.

Your digestive organs break down all carbohydrates in food—mainly grains, fruits, vegetables, and dairy products—into the simple sugar glucose. The hormone insulin normally escorts glucose from the blood into the muscle and fat cells, where it's burned up or stored for energy. But in the many people with at least some genetic susceptibility to diabetes—especially those who are overweight or inactive—the cells may start to resist insulin's actions. To compensate, the pancreas pumps out extra insulin, but the overworked organ eventually starts to fail, insulin output declines, and the blood-sugar level rises.

People with a modestly elevated glucose level—between 100 and 125 milligrams per deciliter (mg/dl)—have prediabetes. Those with a level greater than 125 mg/dl have type 2 diabetes, the most common kind. (Five to 10 percent of people with diabetes have type 1, an autoimmune disorder that causes sudden pancreatic failure.) Both types of diabetes increase the risk of cardiovascular disease, and possibly cognitive decline and certain cancers, even more than prediabetes does; moreover, they sharply raise the risk of infection, kidney disease, limb loss, and blindness.

A diet high in refined carbohydrates (such as white bread, white rice, regular pasta, sodas, and sweets) and starchy vegetables (notably potatoes) may speed the onset of prediabetes and type 2 diabetes in two ways. Because those foods are rapidly digested, they force the pancreas to produce lots of insulin quickly; those repeated surges may contribute to the organ's failure. Moreover, the insulin spikes can cause blood sugar to plummet several hours after meals. Some research suggests that such crashes can stimulate appetite and, in turn, provoke overeating and weight gain, which worsens the insulin resistance.

Recommendation: Regular exercise can help maintain a healthy blood-sugar level by increasing the cells' sensitivity to insulin and controlling weight.

As for carbohydrates, the message is subtler than shunning them entirely. Minimizing your intake of refined-grain products, sugar, and potatoes can help regulate blood sugar and possibly weight. But consuming plenty of healthful carbs—from whole grains, legumes, fruits, and most vegetables—may actually promote the same goals: They don't cause blood sugar to rise so quickly, so they curb hunger. Yet regardless of carbs, you won't lose weight unless you restrict your calorie intake from all sources.

At least a third of people with diabetes don't know they have it, apparently because their blood sugar hasn't been checked. That may stem partly from controversy over who should be tested.

The American Diabetes Association and the government's National Diabetes Education Program recommend screening the people most likely to have prediabetes or diabetes: everyone over 45, because insulin resistance tends to increase with age, and younger people who have other risk factors (see below).

In contrast, the U.S. Preventive Services Task Force, which advises the government on health policy, recommends testing only the people who'd be most harmed by an elevated sugar level: those with hypertension or a high level of the "bad" LDL cholesterol. The panel cites clear evidence that aggressively attacking those problems in people with diabetes reduces their risk of heart attack, stroke, and premature death.

Recommendation: Our medical consultants advise merging those guidelines. Have your blood sugar measured at least once every three years starting at age 45. Start younger or get tested more often if you have any of these factors:

• A systolic blood pressure above 130 millimeters of mercury (mm Hg), a diastolic pressure higher than 85 mm Hg, or use of an antihypertensive drug.
• A high level of "bad" lipids—LDL cholesterol of 130 milligrams per deciliter (mg/dl) or above, or triglycerides of 250 mg/dl or more—or a low level of "good" HDL cholesterol (35 mg/dl or less in men, 45 mg/dl or less in women).
• Excess weight, indicated by a body mass index above 25. (To figure your BMI, go to the CDC's Web site, at www.cdc.gov/nccdphp/dnpa/ bmi/calc-bmi.htm.)
• A parent or sibling with diabetes.
• Race other than Caucasian.
• Gestational diabetes (diabetes during pregnancy) or delivery of a baby weighing 9 pounds or more.
• Polycystic-ovary syndrome, featuring irregular periods, excessive hair growth, and sometimes multiple ovarian cysts.

The same lifestyle changes that help prevent blood-sugar disorders are also the single best way to treat prediabetes. One study, published in 2002, found that such changes reduced progression to diabetes by 58 percent, compared with 31 percent in those who took metformin (Glucophage), which decreases insulin resistance. Whether combining the two approaches yields even greater benefits or helps those who don't improve with nondrug measures alone is not known.

Recommendation: People with prediabetes should have their blood-glucose level tested at least annually and make rigorous lifestyle changes. If the changes fail to normalize their glucose level, they and their doctor could consider whether the benefits of adding metformin outweigh the risks. They should also talk with their doctor about taking aggressive steps to reduce their cardiovascular risk. That includes probably taking a daily low-dose aspirin to thin their blood (since insulin resistance increases the risk of blood clots) and possibly starting medication for hypertension or high cholesterol levels sooner than other people would.

Prolonged failure to control blood glucose is so destructive that medication should be started promptly if nondrug measures alone don't bring blood sugar down to normal within three months or if the initial readings are very high.

For the past decade or so, doctors typically started drug therapy with oral medication rather than injectable insulin. That was more convenient for patients and allowed doctors to combat the disease from the optimal angle or, if necessary, from multiple angles. But doctors are now returning to early treatment with insulin because new formulations are easier and safer to use and because recent research shows that taking insulin plus oral drugs soon after diagnosis can substantially improve glucose control and may preserve pancreatic function.

But selecting and managing those drugs is complex. Doctors must choose based on a person's metabolic needs and overall health. And patients must monitor their blood-glucose level at home, often several times a day, and have their doctor analyze the results frequently. Surveys show that patients and doctors often fail to follow those steps.

Recommendation: Scrupulous use of a home blood-glucose monitor is essential. Devices that require pricking a fingertip are more reliable than those that use blood from other sites, according to a December 2003 analysis by The Medical Letter on Drugs and Therapeutics. When Consumer Reports tested monitors in 2001, most users preferred devices that require touching the test strip to the blood droplet rather than placing the droplet onto the strip.

In addition, patients should encourage their primary-care doctor to build and oversee a team of experts—including an endocrinologist, an ophthalmologist, and a podiatrist—to manage the disease and its complications, plus a dietitian and diabetes educator to facilitate lifestyle changes. And they should make sure their doctor measures their level of a protein called HbA1c—the best index of long-term glucose control—three to four times a year, and checks their feet, blood pressure, and weight at every visit.

Finally, patients need to treat cardiovascular risk factors even more aggressively than people with prediabetes do. In particular, they should try to get their LDL level below 100 mg/dl, usually by taking a statin drug, such as atorvastatin (Lipitor) or lovastatin (generic, Mevacor); if their LDL is already under 100, they should ask their doctor if it's worth trying to get it lower still. They should also try to get their blood pressure below 130/85 mm Hg, usually by taking an ACE inhibitor such as captopril (generic, Capoten) or enalapril (generic, Vasotec), which not only lowers blood pressure but also protects the kidneys from diabetes-related damage.