Any time is a good time to lose weight if your body mass index is over 25. So I'm surprised to learn that there is a best time.

A large study that the professional journal Diabetes Care will publish in its October issue indicates that if you have diabetes, the best time to lose weight is right after your diagnosis. Even if you gain back that weight, by taking off the pounds then you have a better chance of keeping your blood glucose and blood pressure levels under reasonably good control.

The study comes from Kaiser Permanente in Oregon and Washington, one of the country's largest health maintenance organizations with about 480,000 members. Its Center for Health Research in Portland, Oregon, has taken the lead in analyzing the electronic health records of its members. This is one HMO that knows how the improved health of its members can improve the organization's bottom line at the same time -- and acts on that knowledge.

For four years between 1997 and 2002 Kaiser Permanente followed 2,574 of its HMO members with type 2 diabetes. Their scientists followed the weight gain and loss patterns of these people for three years. And then in the fourth year they compared their blood glucose control tests and blood pressure readings.

This is the first study to show that benefits of weight loss remain even when people with diabetes regain their weight. Those who lost weight within an average of 18 months after their diagnosis were up to twice as likely to achieve their blood pressure and blood glucose targets as those who didn't lose weight. I think we all know which serious complications that achieving these targets can forestall.

The targets were moderate: An A1C level of 7.0 percent or less and blood pressure of 130/8 mmHg or less. While even lower levels will reduce chances of complications even further, these are the de facto standards of much of the American medical profession.

Most of the people in the study remained at about the same weight during the first three years. But a small group of 314 people lost an average of 23 pounds. This group was more likely to meet blood pressure and glucose targets during the fourth year. The kicker is that they nevertheless regained the weight that they lost.

Last week Kaiser Permanente kindly sent me an advance copy of the study with my agreement that I wouldn't publish the results before Diabetes Care put the study online. The journal evidently thinks that this study, "Weight Change in Diabetes and Glycemic and Blood Pressure Control," was important enough to make the full-text available yesterday, well ahead of publication.

"It appears there may be a critical window of opportunity following diagnosis in which some lasting gains can be achieved if people are willing to take immediate steps toward lifestyle changes," says Dr. Adrianne Feldstein, MD, MS. She is the study's lead author, a practicing physician, and an investigator at Kaiser Permanente's Center for Health Research.

The question, of course, is why it would help to lose weight right after diagnosis only to regain it. "We don't know if the initial weight loss increased the body's sensitivity to insulin or if the sustained lifestyle changes were the reason for the long-term health benefits," says Gregory A. Nichols, Ph.D. He is a co-author of the study and a Center for Health Research scientist.