Taking a daily pill called metformin also cut the risk of developing diabetes by almost a third not nearly as effective as a modest diet and exercise but far better than no treatment. It's the first time a medication for diabetes has proven protective.
So concludes the largest study ever performed on ways to prevent the most common form of diabetes, called Type 2 or adult-onset diabetes. The findings were so dramatic that the government announced Wednesday it was ending the clinical trial a year early.
Many doctors have long advised losing weight and getting active to fend off Type 2 diabetes. But they didn't have proof of how much weight loss and exercise is needed to make a difference nor are Americans heeding the advice. This deadly disease is growing at epidemic proportions even as Americans get steadily fatter and more sedentary.
The new findings show people don't need to run marathons or try starvation diets. Indeed, the study participants lost, on average, a mere 15 pounds (6.75 kilograms).
"For 30 minutes a day, five days a week, to go for a walk with your spouse doesn't seem to me to be asking the impossible," said lead researcher Dr. David Nathan of Massachusetts General Hospital.
"We're not saying to people you need to achieve ideal body weight. These are reasonable goals," added Rena Wing, a University of Pittsburgh psychiatrist who oversaw the study's lifestyle portion.
The big question now is how to identify those people who could benefit from the findings if only they knew they were at risk. Diabetes screening is not routine.
"We're going to need to rethink how we approach care and prevention," said Yale University's Dr. Robert Sherwin, past president of the American Diabetes Association. But if so, "it could have a significant impact."
"We're not doomed to seeing this epidemic go on forever if we have the will, collectively, to implement these modest changes," said Dr. Allen Spiegel, the National Institutes of Health's diabetes director.
Some 16 million Americans have diabetes, the vast majority Type 2, yet experts say at least a third don't know it is silently festering in their bodies. Diabetes is a leading cause of blindness, kidney failure, limb amputations and heart disease, and kills 180,000 Americans each year.
Type 1 diabetics cannot make insulin, a hormone crucial to converting glucose into energy, and need regular insulin injections to live.
Type 2 diabetics' bodies gradually lose the ability to use insulin properly. It is most common after age 40, and risk rises with increasing age, although overweight children are increasingly getting the disease, too. Also at high risk are blacks, Hispanics and American Indians; the overweight; people whose relatives have diabetes; women who had gestational diabetes during prgnancy.
The NIH study enrolled 3,234 Americans who were at very high risk of getting diabetes soon, because they had those risk factors and because an exam called the oral glucose tolerance test showed their bodies already weren't properly processing blood sugar. Almost half the study participants were minorities.
Some were advised to do moderate exercise for 150 minutes a week and to lose 5 to 7 percent of their body weight. Others tested metformin, a common Type 2 diabetes treatment. The rest were given dummy pills.
After three years, the diet-and-exercise group had cut their risk of getting diabetes by a staggering 58 percent, a benefit seen for every race and ethnicity. Interestingly, the oldest people those over age 60 cut their risk the most, by 71 percent.
How hard did they work for that benefit? Most patients' exercise was brisk walking. They lost about 15 pounds and kept most of it off, largely by cutting fat consumption to 25 percent of calories which many could do with small dietary changes such as eating baked chicken instead of fried and seasoning vegetables with lemon, not butter.
Metformin cut diabetes risk by 31 percent. In contrast, about 11 percent of the placebo patients developed full-blown diabetes during each year of the study.
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