The National Institutes of Health announced study results showing that diet and exercise can lower the risk of diabetes by 58 percent for 10 million Americans on the cusp of developing this common but deadly illness. The results were so impressive that federal officials halted the study a year early. We know you have questions about what this means for you and your family. Some answers follow.

Oh, boy, more people telling me to lose weight and get up off the couch. What’s the big deal this time?

This study is one of the best demonstrations that a few simple changes in lifestyle can have a powerful impact on preventing disease in high-risk people. In this research, people on the brink of developing diabetes followed a lower-fat diet, walked or did some other form of moderate exercise about 30 minutes a day five days a week and lost around 10 to 15 pounds. These changes reduced their chances of getting type 2 diabetes by almost 60 percent. Even better, this program worked in men and women, in young adults and seniors, and in all races. And the lifestyle changes were nearly twice as effective as the expensive medication to which it was compared.

Hey, wait, I know statistics can exaggerate the importance of a study. What were the chances of these people getting diabetes without any treatment? What were their chances if they made the changes?

Wow, you’re good. Each year, 10 percent of the people in this study who got no treatment developed diabetes. Do the math over a period of years and you can see this group is at very high risk indeed. About 5 percent of those who followed the moderate diet and exercise program developed the disease each year. That’s an impressive drop in risk — but it’s not a perfect record. The lifestyle program does not appear to prevent the disease in everybody who is at risk, but it improves their odds significantly.

Why are we so worried about diabetes all of a sudden? I thought heart disease and high blood pressure were the real killers.

Type 2 diabetes has reached epidemic proportions, and the number of people at risk for developing it increases every year. Some 16 million people have the disease and an estimated 800,000 Americans will be diagnosed this year. Type 2 diabetes is a chronic degenerative disease characterized by elevated blood sugar levels; it’s the leading cause of kidney disease, limb amputations and acquired blindness in adults. It also increases the risk of heart disease and stroke. (Many deaths blamed on heart attack and stroke are associated with diabetes.) Rates of type 2 diabetes have tripled in the last 30 years because of the rise in obesity and sedentary living. Worse, type 2 diabetes is being diagnosed in people at increasingly younger ages — even in kids. So diabetes is one of the most pervasive and deadly results of the American lifestyle.

How do I know if I’m enough like the people in this study to benefit from the lifestyle changes?

Most people in this study were overweight and sedentary adults. To be eligible, they also had to have “impaired glucose tolerance” — a pre-diabetic condition in which the body fails to process glucose efficiently, elevating blood sugar levels. (Over time, high blood sugar damages organs and blood vessels throughout the body, leading to kidney failure, blindness, amputations and heart disease.) An estimated 10 million Americans have this pre-diabetic condition, and most have lifestyles that put them at risk for developing it. Strictly speaking, the benefits demonstrated in the study apply only to those who already have impaired glucose intolerance — but researchers believe that similar interventions can reduce risk for others.

How do I know if I’m “overweight”?

If your friends won’t tell you, we will. You can start with body mass index — a figure that considers height and weight. If you have a BMI of 30 or above — technically the cutoff for “obesity” — you’re in the diabetes danger zone. At 5 feet 10 inches tall, that’s 209 pounds; at 5-4, it’s 174 pounds. (To compute your BMI on the Web, go to www.nhlbisupport.com/bmi/ You’ll also find a link there to a BMI chart.)

A BMI above 25 (128 for a five-footer, 164 for someone 5-8, 184 for a six-footer) is considered “overweight” and is also associated with an increased risk for impaired glucose tolerance.

Every time you guys write about the body mass index, people write in and say it’s inaccurate, deeming even those who have muscular physiques “fat.”

If you have a muscular physique and low body fat like the professional athletes cited by those letter writers, chances are you’re not at risk for diabetes. We’ll be politic and say that if your BMI is 30 or over, chances are pretty good that you are at increased risk. If you prefer, measure your body fat instead — but it’s hard to do accurately without professional help. Healthy ranges vary by age and sex, but if you’re a woman with a body fat number above 35 percent or a man whose number is over 24 percent, you should be worried. (Log on to www.shapeup.org/bodylab/ frmst.htm for more information on body fat.)

Are there other things aside from body mass or body fat that put me in a high-risk group?

Having a family member with diabetes adds to your risk. African Americans, Hispanics and Native Americans also face much higher risk of diabetes. So do women who developed gestational diabetes while pregnant, about half of whom develop full-blown diabetes later in life. People in these groups may want to consider preventive lifestyle changes even if their BMIs are not near 30.

How can I find out if my glucose tolerance is impaired?

Ask your doctor for a fasting glucose tolerance blood test. You’ll have to go without food for 10 hours before the test. At the doctor’s office, you drink a sugary liquid and then have your blood drawn at regular intervals over the next two hours to see how your body metabolizes the sugar.

Sounds like fun. How much is this going to cost me?

It’s a bargain: about $15 to $35. It’s often covered by health insurance. It’s also the only way to definitively tell whether you are moving toward diabetes — or perhaps already have it.

What happens if I have an abnormal result?

Depends on how abnormal. If your fasting blood sugar — that’s the first sample they take — is between 95 and 125 milligrams, you have impaired glucose tolerance and are a candidate for treatment. The same goes for a two-hour blood sugar level — that’s the last one drawn in the test — of 140 to 199 milligrams. Treatment could be lifestyle changes or a prescription for metformin (Glucophage), a drug that is approved to treat diabetes.

If your fasting blood sugar is 126 milligrams or above, or if your two-hour blood sugar level is 200 milligrams or above — sorry, but you already have diabetes. You’ll need to consult your doctor for immediate treatment.

So what were these lifestyle changes, anyway?

Participants ate between 1,200 and 1,800 calories per day, with about 25 percent of total calories coming from fat — not a huge reduction below the 30 percent-from-fat maximum recommended by many health authorities, and not as strict as many low-fat weight loss diets. They also learned how to exercise daily. Most walked for 30 minutes a day at least five times a week. Those unable to walk because of arthritis — or disinclined to do so — did other activities including swimming, tennis and jogging that equaled the number of calories burned by walking.

I’ve tried these diets and programs a thousand times, but I always fail. How did the study manage to keep people with the program?

Participants got a lot of hand-holding and group support. While this aspect of the study has gotten little attention, it’s very important. Many people need help to sustain lifestyle changes.

The people in this study received intensive, one-on-one weekly diet counseling for nearly six months. They got personal coaching for workouts and attended small groups that taught low-fat cooking and emphasized healthful grocery shopping. They kept daily records of their diet and exercise.

You could duplicate the program a number of ways, some of them free, some costly. You can take a low-fat cooking class, join a walking group or gym, form a network of support, check out local hospitals or your insurance group for support services or hire a personal trainer or dietitian.

When lifestyle changes fail, it’s often because the pressures that trigger the condition in the first place — the constant rushing that leads to fast-food meals, the stress and exhaustion that leads to evenings in front of the TV, the lack of exercise in most daily activity patterns — undermine the best intentions to change. So creating a structured environment, ideally involving other people attempting the same changes, may be very useful. Enlisting the family may help, too.

If I can’t make the lifestyle changes, can’t I take a pill?

Maybe. If you don’t think you can make diet and exercise changes, taking metformin may be the choice for you — provided you don’t have liver or kidney disease or suffer from congestive heart failure. Therapy with Glucophage, the brand name for metformin, costs between $2 and $4 per day, but generic metformin is expected to hit the market in the fall, bringing prices way down.

Yes, participants in the study who took Glucophage lost a few pounds and reduced reduced their risk of diabetes significantly, although not nearly as much as the lifestyle group. But if you continue to live a sedentary life, take in more calories than you burn off, eat a high-fat diet with few fruits, vegetables and whole grains, experts believe that you won’t be as effective at lowering your risk of diabetes, heart disease, high blood pressure, arthritis, stroke and other equally entertaining conditions. It’s your choice. Really.