In a head-to-head comparison with a traditional diet, people who stuck to a
diet of portion-controlled packaged foods lost almost twice as much weight as
those who only got advice on how to trim calories, according to a new study.
Dr Michael Dansinger, a nutrition expert at Tufts Medical Center, said having
less freedom in choosing meals seems to help people meet their dieting
"When there's less structure, then participants are making more decisions,
and I think too often they're making decisions that undermine their goal to
stick to a calorie target," said Dansinger, who was not part of the study.
The diet the researchers studied was the Medifast 5 & 1 Plan. It consists
of five pre-packaged meals each day, along with one meal of vegetables and
protein prepared by the dieter.
Dieters can pick from 70 different packaged foods to create five meals
totaling about 1,000 calories a day.People on the plan can also purchase
different levels of support along with the meals, such as access to dieticians
and recipes. Typically, the plan costs about $300 a month.
To see how effective the Medifast diet is in helping people lose weight and
keep it off, the researchers asked 60 people to join the plan for free.
They compared these dieters to another 60 people who were given advice on how
to meet a 1 000 calorie-per-day target, but who continued to buy and prepare
their own food.
How the study was done
For everyone in the study, the goal for the first 26 weeks was to lose
weight, and during the second half of the study the goal was to maintain
All of the participants were obese, having a body mass index (BMI) - a
measure of body size relative to height - between 35 and 50.
A BMI of 35 represents, for example, a person who is 5-feet 8-inches tall and
230 pounds. By the end of the study, 15 people dropped out of the regular-food
group and 10 dropped out of the Medifast group.
After six months, those who stuck with either dieting approach lost weight.
People in the Medifast group shed an average of 16.5 pounds, or 6.7 percent of
their starting weight.
Dansinger said such a reduction in weight is modest, but it can have a
meaningful impact on people's health.
"That's been demonstrated in numerous studies to be effective for improving
blood sugar in people with diabetes or delaying the progression from
pre-diabetes to type 2 diabetes and to reduce other heart disease risk factors,
including blood pressure, cholesterol and inflammation," he said.
The regular-food group lost an average of 8.4 pounds, or 3.4% of their body
weight. The Medifast dieters also had greater reductions in body fat, waist
circumference and cholesterol than the other group.
Of the average 16.5 pounds Medifast dieters lost, 14 were fat mass.
Regular-food dieters lost an average of 8.14 pounds of fat. The study did not
examine the diets' effects on bone and muscle mass.
Medifast users lost an average 2.24 inches around their waists and their
total cholesterol dropped an average 8.4 milligrams, compared to 1.46 inches and
1.1 milligrams, respectively, in the regular diet group.
Over time, though, the dieters in both groups tended to rebound somewhat
toward their original weights.
After one year in the study, the Medifast group ended up about 10 pounds, or
4.2%, lighter than when they started, while the other group was about four
pounds, or 1.7%, lighter.
James Shikany, the lead author of the study, said the results show that
sticking to the Medifast diet makes it harder for dieters to eat more calories
than they should.
"It's more of a regimented type of diet, and some people find that's what
they need in order to limit their portion intake," said Shikany, who is a
professor at the University of Alabama at Birmingham Division of Preventive
Dansinger said the weight loss results from the Medifast diet appear to fall
in the middle of the pack of other weight loss interventions.
Some approaches, such as weight loss surgery or more extreme diets can have
more dramatic results.
But in terms of dietary interventions or FDA-approved weight loss pills, the
effect is roughly comparable, he said.
Lisa Davis, the vice president of science and clinical affairs at Medifast,
said earlier studies of the diet actually found greater weight reductions.
One explanation she offered is that the current study participants'
demographics, such as race, appeared to be different in Shikany's study than in
In particular, Shikany's study included a majority of African Americans
whereas other studies had mostly caucasians, Davis said."I think that's worth
investigating in the future," she said.
Medifast funded the current study, and one of the researchers has been a
consultant to Medifast.
Dansinger said that based on this and other studies, he would recommend
meal-replacement diets."In my opinion, for patients who have had repeated
failures with other attempts at sustaining weight loss, the Medifast plan or
other similar plans appear to be a good option," he said.
Shikany agreed, but said it's unclear whether cost could be a factor in the
diet's appeal."If you take (cost) out of the equation, I think it would be a
good option for some people, especially for people who need that extra
assistance in weight loss efforts as far as determining portions," he said.