No one really knows which diets
work and which are a waste of time, with the possible exception
of Weight Watchers, U.S. researchers reported.
A review of 10 separate studies
of weight-loss programs showed there was very little hard
data to support any commercial or nonprofit diet approach,
the researchers found.
Only Weight Watchers had scientific
research to back up its simple approach of keeping a food
diary and focusing on low-calorie foods, especially vegetables
and whole grains, they wrote in the Annals of Internal Medicine.
"With the exception of one
trial of Weight Watchers, the evidence to support the use
of the major commercial and self-help weight-loss programs
is suboptimal," Dr. Adam Tsal and Thomas Wadden of the University
of Pennsylvania wrote.
The pair started out scanning
more than 1,500 diet studies, but rejected most because they
were done outside the United States, had fewer than 10 participants,
lasted only a few weeks or differed from the diet as offered
to the public.
They also looked for at least
one year of follow-up and did not include commercial self-help
programs based on books alone or meal replacement plans.
They ended up with 10 studies
that included Weight Watchers, Jenny Craig, eDiets.com and
the nonprofit Overeaters Anonymous group.
"Currently, the three largest
nonmedical commercial programs in the United States are Weight
Watchers, Jenny Craig and LA Weight Loss," Tsal and Wadden
wrote.
The largest trial showed dieters
using the Weight Watchers program lost and kept off 3.2 percent
of their weight after two years.
"Weight Watchers, at $12
per week, is moderately priced, whereas the weekly costs of
Jenny Craig's prepackaged meals ($70 to $100) make
it expensive," they noted.
"Controlled trials are needed
to determine the amount of weight lost and health benefits
associated with Jenny Craig and LA Weight Loss programs,"
the study said.
Some diets can be dangerous,
according to the researchers.
"Medifast offers both very-low-calorie
and low-calorie meal replacement plans, which participants
may purchase directly from the manufacturer," they wrote.
But it does not require medical supervision, as is advised
by government experts for very-low-calorie diets.
"Serious complications, including
death, have been reported in obese persons who consumed very-low-calorie
diets without medical supervision," they wrote.
Many Internet-based programs
are available, but there is little study to show whether they
work, the researchers said.
