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 a low-carbohydrate 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. 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. Five years later, much of
that benefit had been retained. Studies of whether weight
loss from low-carbohydrate diets is maintained for more than one
year have not been performed.
In a one-year clinical trial reported in JAMA in 2005,
researchers randomly assigned 160 overweight individuals to one
of four popular diets. Participants assigned to the Atkins diet
lost 2.1 kilograms, while Weight Watchers dieters lost 3.0 kilograms, Zone
dieters lost 3.2 kilograms, and dieters following the Ornish program
lost 3.3 kilograms.
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. 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.
A review on the safety of low-carbohydrate diets notes
that Atkins-type diets are at a greater risk for being nutritionally
inadequate and raise the issue of potential long-term health
effects.
