Replacing regular meals with shakes and prepackaged entrees boosts obese teens’ weight loss in the early stages of dieting, new research shows.

But these “meal replacements” were no better than a standard low-calorie diet for helping young people continue losing weight over the course of a year, Dr. Robert L. Berkowitz of the Children’s Hospital of Philadelphia and his colleagues found.

Swapping regular meals for shakes, bars or prepackaged entrees can be a useful weight loss strategy for adults, Berkowitz and his team note in the journal Obesity.

One reason that these meal replacements may work is that they take the guesswork out of dieting; people often sharply underestimate their calorie intake when they eat regular foods. Given that adolescents also underestimate how many calories they consume, the researchers sought to investigate whether meal replacements might be helpful for teens as well.

The researchers randomly assigned 113 obese teens and their families to one of three regimens: following a standard 1,300- to 1,500-calorie-a-day diet for a year; four months of meal replacements (three SlimFast shakes, one prepackaged entrée, and five servings of fruits and vegetables) followed by eight months on the low-cal diet; or an entire year of meal replacements.

At four months, patients in the meal replacement groups had reduced their body mass index (BMI) by about 6.3 percent on average, compared to 3.8 percent for teens in the low-calorie diet group. But during the second phase of the study, teens in each group gained weight.

By one year, average BMI reduction was 2.8 percent for the low-calorie diet group, 3.9 percent for the meal replacement plus low-calorie diet group, and 3.4 percent for the meal replacement-only group. In statistical terms, there was no significant difference in degree of weight loss among the three groups by the end of the study.

One-third of the patients dropped out of the study. Among those who stuck with it, adherence waned as time wore on. By the end of 12 months, the researchers note, the meal-replacement group reported using SlimFast only 1.6 days a week, compared with 5.6 days a week in month two.

“The potential benefit of (meal replacement) in maintaining weight loss was not supported,” the researchers conclude, and further study is needed to find ways of getting obese teens to start diets and stay on them.

SOURCE: Obesity, online December 9, 2010.