Obese women who follow low-carbohydrate diets, such as the
Atkins diet, may lose more weight in a four-month period than those who
go on low-fat diets, new study findings show. The reason for the
greater weight loss, however, is not clear.
"The differential
weight loss is not explained by differences in resting energy
expenditure, thermic effect of food or physical activity," write study
author Dr. Bonnie J. Brehm, of the University of Cincinnati, Ohio and
her team.
In a previously published study, Brehm and her
colleagues compared the effects of a low-carbohydrate diet versus a
low-fat diet among obese women. They found that the women on the
low-carbohydrate diet lost more than twice as much weight as those in
the comparison group during a six-month study period.
The
researchers hypothesized that the greater weight loss among those on
the low-carbohydrate diet was due to the women’s greater energy
expenditure. "If it’s not calories in, it must be calories out," Brehm
told. Some advocates of low-carbohydrate diets say that such diets
promote increased energy expenditure, but this claim has not been
formally tested, until now.
To investigate, Brehm and her team
randomly assigned 50 moderately obese women to a low-carbohydrate diet
group or a low-fat diet group. Only the low-fat group was told to
restrict their caloric intake. Forty women completed the study.
By
the end of the four-month study, women in both groups had lost weight
and body fat, the researchers report in this month’s issue of the
Journal of Clinical Endocrinology and Metabolism. However, the
low-carbohydrate group lost more than 10 percent of their body weight,
while the low-fat group lost about 7 percent. Specifically, the
low-carbohydrate group lost 9.8 kilograms (21.6 pounds) of weight and
6.2 kilograms (13.7 pounds) of body fat, while the low-fat group lost
about 6.1 kilograms (13 pounds) of weight and 3.2 kilograms (7 pounds)
of body fat, the report indicates.
To estimate their level of
physical activity, women in both groups were fitted with pedometers,
which recorded the number of steps they took daily. At the start of the
study, both groups of women had similar pedometer readings, and by the
end of the study, there were no significant changes, according to Brehm
and her team. Resting energy expenditure was also similar between the
two groups at the start of the study and remained comparable four
months later.
The thermic effect of food (TEF), which comprises
up to 10 percent of the amount of energy consumed daily, includes the
energy expended during digestion. When the investigators obtained TEF
measurements after the women ate breakfasts containing a similar number
of calories, they found that those on the low-fat diet expended more
energy in a five-hour period.
This suggests that the low-fat
meal was absorbed more quickly than the low-carbohydrate meal, the
report indicates. Yet, even if the TEF of the low-carbohydrate meal had
been underestimated, the researchers "would not have approached the
amount of energy needed to account for the greater weight loss in this
group," they write.
"These results confirm that short-term
weight loss is greater in obese women on a low-carbohydrate diet than
in those on a low-fat diet even when reported food intake is similar,"
according to Brehm and her team. Weight loss by diet pills like acomplia is not a bad solution for treatment of obesity.
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