By Serena Gordon
People who lost weight while taking metformin maintained a loss of about 6% of their body weight for six to 15 years. People who lost weight through lifestyle changes -- eating healthily and exercising regularly -- managed to keep off just under 4% of their initial body weight for the same period, the study found.
Metformin doesn't seem to be particularly helpful for shedding pounds in the first place, though. In fact, an earlier phase of the study found that people were much more likely to lose 5% or more of their body weight through lifestyle changes -- healthy eating and exercising -- than by using metformin.
"Although lifestyle changes were superior for inducing weight loss early on, metformin was better for long-term weight maintenance," said senior study author Dr. Kishore Gadde. He's a professor in heart disease prevention at the Pennington Biomedical Research Center in Baton Rouge, La.
Not everyone is convinced that metformin can keep you slim, however. After reviewing the findings, Dr. Joel Zonszein, director of the Clinical Diabetes Center at Montefiore Medical Center in New York City, said, "This study was very well done, but it doesn't show metformin is effective for everyone. The ones on metformin who did lose weight only regained a little less weight."
An effective intervention for losing weight and maintaining that loss is clearly needed. Nearly three-quarters of the American population is overweight or obese -- a major risk factor for type 2 diabetes, according to the U.S. Centers for Disease Control and Prevention.
Losing a significant amount of weight -- more than 5% of your body weight -- seems to help prevent pre-diabetes from turning into type 2 diabetes, and can help delay the progression of type 2 diabetes.
The latest study was a continuation of the three-year diabetes prevention clinical trial that compared three different groups of people with pre-diabetes to see what type of intervention would help prevent type 2 diabetes from developing. One group was given metformin, another was coached on intensive lifestyle changes, and the third group was given a placebo.
This study found that lifestyle changes led to the greatest initial weight loss, followed by the metformin group, according to Gadde.
From the original study group -- more than 3,000 people -- just over 1,000 lost more than 5% of their body weight.
The researchers followed this group for as long as 15 years to see who maintained their weight loss.
People taking metformin had the greatest weight loss from years six to 15, according to the study. The study also found that being older and losing a greater amount of weight in the first year were consistent predictors of lasting weight loss, the study authors said.
Gadde said it's not exactly clear why the metformin group was better at maintaining weight loss. "Metformin does reduce food intake a little bit, but it's not a dramatic effect. And, from what we know, it doesn't significantly alter energy expenditure."
He said other recent research suggests that metformin may alter the body's microbiome (the healthy bacteria in your gut). It also seems that metformin may have some effects on muscle function. But Gadde said, more research is necessary to know for sure.
This study only looked at people with pre-diabetes, so how the drug might affect people without the condition isn't clear from this study.
The findings were published April 22 in the Annals of Internal Medicine.