Jury Still Out on Low-Carbohydrate Diets
Scientific Evidence Lacking on High-Protein, Low-Carb Diets
April 8, 2003 (New York) - Despite the popularity of
high-protein, low-carbohydrate diets such as the Atkins diet, a new study shows
there still isn't enough research to prove whether the diets really work at
promoting long-term weight loss.
Researchers say there simply isn't enough scientific evidence
to make a recommendation for or against these low-carbohydrate diets for people
trying to lose weight, and very little is known about their long-term
"Despite all the hype, the published literature suggests
that calories are what's important for weight loss," says researcher Dena
M. Bravata, MD, MS, of Stanford University.
Bravata presented the findings, which appear in the April 9
issue of The Journal of the American Medical Association, at a briefing
on obesity today in New York.
For the study, Bravata and colleagues reviewed 107 studies on
high-protein, low-carbohydrate diets published between Jan. 1, 1966 and Feb.
15, 2003. They compared how the 94 different diets described affected the more
than 3,200 participants in terms of weight loss as well as health factors, such
as cholesterol levels, blood sugar and insulin levels (indicators of diabetes
risk), and blood pressure.
Advocates of low-carbohydrate diets, such as best-selling
author and cardiologist Robert Atkins, MD, say they produce rapid weight loss
by stimulating the body to burn fat rather than dietary carbohydrates without
any significant long-term problems.
But many health organizations, including the American Dietetic
Association and the American Heart Association, have cautioned against
low-carbohydrate diets. They say there are concerns the diets lead to abnormal
metabolic functioning in the body that could have serious medical consequences,
particularly among people with heart disease or heart-disease risk factors such
as type 2 diabetes, high cholesterol, or high blood pressure.
After reviewing the studies performed on the low-carbohydrate
diets to date, researchers found at least three major gaps in the research:
- No study has evaluated a diet containing 60 grams or less of carbohydrates
(a common level recommended by many of the lower-carbohydrate diets) among
people over an average age of 53.
- Only five of the studies evaluated low-carbohydrate diets for more than 90
days, and none of those studies were randomized or had comparison groups to
ensure scientific validity.
- Some of the most popular lowest-carbohydrate diets that recommend less than
20 grams per day of carbohydrates have been studied in only 71 people.
Bravata says those findings show that much more research is
needed to evaluate the long-term safety of lower-carbohydrate and very
low-carbohydrate diets as well as their effect on older people who may have
other health issues aside from obesity.
Researchers found that among obese people who participated in
the studies, successful weight loss was linked to limiting calorie intake and
longer diet duration, but not with limiting the amount of carbohydrates they