Old-fashioned calorie-cutting and exercise really can keep the pounds off for the long haul, according to a review of dozens of clinical trials.

In an analysis of 80 weight-loss studies, researchers found that approaches that focused on trimming calories -- with or without exercise -- were most effective at keeping the pounds off over four years.

The results were not dramatic. On average, participants in these studies shed 11 to 19 pounds at most, then typically gained a little bit back over time.

However, the findings show that diet and exercise changes can work over the long haul, if people keep them up and have realistic expectations, the study authors report in the Journal of the American Dietetic Association.

"Although there is some regain of weight, weight loss can be maintained," write the researchers, led by Marion J. Franz, a registered dietitian and health consultant with Minneapolis-based Nutrition Concepts by Franz Inc.

The studies Franz and her colleagues analyzed ranged in their weight-loss tactics. In some, participants were given only general advice on cutting pounds. In others, they received exercise advice or actual help with boosting their physical activity levels, but no help with diet.

Among trials that focused on diet, some emphasized calorie reduction alone, and some used a combination of diet and exercise. In certain studies, participants were given meal replacements or weight-loss medications like orlistat (Xenical) to enhance their diet changes.

In general, Franz's team found, diet-focused trials were most successful. Advice-only and exercise-only studies produced "minimal" weight loss, the researchers write. This may be largely due to the types of exercise practiced and whether participants were actually as consistent as they reported.

In trials that used calorie-cutting alone and in those that added exercise, weight loss typically hit a plateau after six months, the analysis found. After that, participants gained a few pounds back, on average.

According to the researchers, the findings suggest that after six months, people should be prepared for their weight loss to taper off. Then the goal should be maintaining whatever success has been achieved.

Dieters often become "frustrated," Franz and her colleagues note, because they think that if they maintain their lower-calorie ways, the pounds should continue to fall off. "This appears not to happen," the researchers write, "even when weight-loss interventions are continued."

"However," they stress, "if weight-loss interventions are discontinued entirely, weight regain is likely to occur."

SOURCE: Journal of the American Dietetic Association, October 2007.