Tacking regular exercise on to a diet program for obese kids
and teens typically doesn't help them lose any more weight, a new review of
past data suggests.
"Changing diet, improving diet, reducing kilojoules is
enormously important for weight loss both in kids and adults," said Gary
Bennett, who studies obesity prevention at Duke University in Durham, North
Carolina. "Exercise is important too, but I think we sometimes
overemphasise how important exercise is," Bennett, who wasn't involved in
the new study, told Reuters Health.
Researchers analysed results from 14 earlier trials that
assigned overweight and obese youths to a diet and exercise program or a
diet-only intervention. Those programs lasted anywhere from six weeks to six
months. Most studies found kids tended to have a lower body mass index (BMI) --
a ratio of weight in relation to height -- and a smaller percentage of body fat
after completing either type of intervention.
Adding aerobic exercise such as jogging or dance to a restricted kilojoule
diet had little effect on weight loss. However, kids who did resistance
training lost more body fat than those who didn't exercise, according to the
Strength training for an hour or less each week was tied to
an extra half a percent drop in body fat and a greater increase in
muscle."Exercise does not just burn off kilojoules, more importantly it
helps to build muscle mass, which is beneficial for long-term weight loss and/or
weight maintenance," lead author Mandy Ho, from the University of Sydney,
Australia, told Reuters Health in an email.
"This is particularly important for the growing kids
because over restricting dietary intake may cause adverse effects on normal
growth and development." Ho and her colleagues found some measures of cholesterol
and blood sugar, including insulin and HDL ("good") cholesterol,
improved with the addition of regular exercise.
But changes in other levels, such as LDL ("bad")
cholesterol, were greater with a diet plan alone. In many of the studies, kids
gained back the weight -- and any cholesterol or blood sugar benefits went away
-- once the programs were over, the study team wrote in JAMA Pediatrics. Helping
young people lose weight, and especially keep it off, has proven a difficult
One recent study, for
example, found little evidence that at-home weight loss programs can affect
kids' BMI. According to Bennett, programs that can change both diet and exercise habits
probably are most effective. But for parents who are struggling with a heavy
child, "diet is absolutely critical", he said."That's really
where I would tell parents to focus their time."