A diabetic patient fills a syringe as she prepares to give herself an injection of insulin. (Reed Saxon/AP)

Losing a small amount of weight doesn’t appear to lower the risk of heart attacks and strokes in people with diabetes who are already getting good medical care, according to a long and expensive clinical experiment whose results were announced Friday.

While modest weight loss has benefits in how overweight diabetics feel, sleep and move, whatever benefit it may confer in preventing cardiovascular disease — which is what most diabetics die from — is too small to measure, the study found.

“We were hoping that a weight-loss program would help reduce cardiovascular disease, but now we have the answer that it doesn’t,” said Mary E. Evans, a physician at the National Institute of Health’s National Institute of Diabetes and Digestive and Kidney Diseases, which paid for the study.

The results will probably surprise many physicians and patients but are not likely to change the advice they give and get.

“We feel that there are many reasons why people with Type 2 diabetes should control their weight,” said Rena R. Wing, the researcher at Brown University’s Miriam Hospital in Providence, R.I., who headed the experiment. But she added: “I think the patients in the intensive weight-loss group are very disappointed. They’d worked hard to make these changes.”

The study, which began in 2001, was scheduled to last two more years. In mid-September, however, an independent monitoring board advised NIH that it be stopped in its current form because the weight-loss “intervention” wasn’t having its hoped-for effect.

The Look AHEAD (Action for Health in Diabetes) trial involved hundreds of doctors, nurses, dieticians and exercise therapists at 16 medical centers. It cost about $20 million a year, or about $220 million over its 11-year-life.

The researchers recruited 5,145 people with Type 2 diabetes, which is the form that generally comes on in adulthood and is strongly associated with being overweight. Type 1 diabetes, an auto-immune disease, is the opposite. It comes on in childhood, and its sufferers are usually thin.

About 60 percent of the volunteers were women and slightly more than one-third were minorities. The average age was 58.

Half of the people were randomly assigned to get intensive dietary counseling on how to limit their calories. They were provided meal substitutes such as Slimfast drink. They were also urged to exercise more and instructed how to do so safely. They met weekly in support groups and once a month with a counselor, although that amount of attention was eventually reduced to a monthly visit and a monthly phone call.

The other half of the participants got less intensive diet and exercise advice, at first four times a year and later just once a year. Everyone was treated by her or his own doctor, who got an annual summary of the patient’s progress.

In the first year, the people with the intensive counseling lost 8 percent of their weight. They gained some back, but over the decade of the study maintained an average 5 percent reduction from their starting weight — about 10 pounds. The people in the less-intensive “arm” of the study lost, on average, about 1 percent of their body weight.

By the end of 11 years, there was no difference between the two groups in the rate of heart attack or stroke.

The study illustrates the difficulty of doing research on how to treat a disease at a time when treatment is changing rapidly.

There is currently a big push to have diabetics lower their cardiovascular “risk factors” even if they have no evidence of heart disease. Many physicians urge much lower blood pressure and cholesterol goals than was common a decade ago. That more aggressive treatment appears to be having an effect.

Nationwide, death rates from heart attack and stroke in diabetics fell 40 percent between 1997 and 2006. The difference between diabetics and non-diabetics in the risk of dying of cardiovascular disease was cut by more than half. This was a period during which obesity rates rose for both diabetics and non-diabetics. Overall, this trend was evidence that, for whatever reason, diabetes was less deadly than it used to be.

The downward trend in heart attack and stroke was experienced by the people in the Look AHEAD study,too. The entire group suffered only half the heart attacks and strokes that the researchers had predicted when they designed the study. Four years into the study, the group getting the less-intense counseling actually had a slightly more favorable cholesterol profile than those in the intensive weight-loss group.

How the risk profile of the two groups changed over the last seven years of the study isn’t known at this point. The information exists and will be analyzed over the next few months.

It may turn out that because of changing norms of medical practice, along with the attention of being in the study, the people in Look AHEAD reduced their risk so much that the benefit of modest weight loss — if it exists — was too small to see.