What Is a Low-Carbohydrate Diet?
The theory behind low-carbohydrate diets is that if
dieters avoid foods containing carbohydrate—that
is, starches or sugars—they will shed pounds.
Such diets eliminate or dramatically restrict the intake
of fruit, fruit juice, starchy vegetables, beans, bread,
rice, cereals, pasta and other grain products, and all
other foods containing carbohydrate, leaving a limited
diet of foods that contain primarily fat and protein:
meat, cheese, nonstarchy vegetables, and very little
else. As the diet proceeds, the carbohydrate restriction
relaxes somewhat, but fatty, high-protein foods continue
to dominate the dieter’s plate.
Despite anecdotal accounts of seemingly dramatic weight
loss, the effect of low-carbohydrate diets on body weight
is similar to that of other weight-reduction diets.
In research studies at the University of Pennsylvania
and at the Philadelphia Veterans Affairs Medical Center,
the average participant lost weight during the first
six months on the diet, but regained some of this weight
during the next six months so that the net weight loss
after one year (15.8 pounds in the University of Pennsylvania
study and 11.2 pounds in the VA study) was not significantly
different from that seen with other diets used for comparison.5,6
This degree of weight loss is not greater than that
which occurs with programs using low-fat, vegetarian
diets.
In Dean Ornish’s program for reversing heart disease,
for example, a combination of a low-fat, vegetarian
diet and exercise led to an average weight loss of 22
pounds in the first year, along with dramatic reductions
in cholesterol levels and reversal of existing heart
disease.7 Five years later, much of that benefit had
been retained.8 Studies of whether weight loss from
low-carbohydrate diets is maintained for more than one
year have not been performed.
A review of 107 research studies on various low-carbohydrate,
high-protein weight-loss diets concluded that weight
loss on these diets is not due to any special effect
of restricting carbohydrate; rather, weight loss depended
on the extent to which the dieters’ caloric intake
fell and how long they continued with their regimens.9
Other reports have also found calorie reduction to be
the most important factor in weight loss, with no special
weight-loss advantage from the restriction of carbohydrates.10,11
Some low-carbohydrate diet books, such as those promoting
the Atkins diet, describe how a diet devoid of carbohydrate
forces the body to turn to other fuels for energy. That
means getting energy from fats and protein in the diet
or from body fat. When fats in the diet or in body fat
are used for energy, they produce compounds called ketones,
and low-carbohydrate dieters sometimes check for the
presence of ketones in their urine as a sign that they
have managed to eliminate carbohydrate. It turns out,
however, that, in controlled trials, the degree of ketosis
does not appear to influence weight-loss speed.
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