Experts estimate that almost two-thirds of U.S. adults are overweight (BMI over 25), and approximately half of overweight adults are obese (BMI over 30).
Overweight and obesity are known risk factors for diabetes, coronary heart disease, high blood pressure, stroke, hypertension, degenerative joint disease of the knees and hips, and some forms of cancer, among other conditions.
Typical methods for treating and preventing obesity as a rule advocate both dietary and lifestyle changes but the effect of dietary counseling for weight loss had not until now been evaluated.
The new study has found that the effect of dietary counseling for weight loss on average, resulted in weight loss of approximately 6 percent of initial body weight after one year, compared with people not involved in formal weight loss programs.
Dr. Michael Dansinger of the Tufts-New England Medical Center in Boston and colleagues analyzed 46 trials that included 6,386 people who were participating in dietary counseling-based weight loss programs and 5,467 people not involved in formal weight loss programs.
They found that programs with more frequent meetings and greater calorie restrictions tended to produce greater weight losses over time but while around half the weight loss remained at three years, almost none of the weight loss remained at five years.
Those who are searching for the perfect diet can expect to be disappointed as the researchers say all diets have just about the same result, and none of them are brilliant.
A typical diet helps people lose an average of 6 percent of their weight, 10 to 15 pounds (5 to 7 kg), with most people piling it all back on after five years.
Dr. Dansinger says weight loss drugs too are similarly ineffective in the long run, which is disappointing but he says even a small, temporary weight loss can benefit health and delay the onset of diabetes.
Programs that made people eat fewer calories worked better, along with those that involved more frequent visits to either diet groups or to a counselor's office.
The only commercial program included in the study was Weight Watchers and no studies that involved commercially prepared food or shakes were included because they did not include a non-dieting group for comparison.
Dansinger says the results were essentially the same, around a 6 percent weight loss after one year but that weight loss gradually disappears and almost all the weight was back on within five years, similar to what has been found with weight loss medications.
Dansinger says though some of the studies included exercise, his analysis was not designed to tell whether exercise helped weight loss last longer.
The research is published in the Annals of Internal Medicine.