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Little Evidence to Support Low-Carbohydrate Diets CME
News Author: Laurie Barclay, MD
Clinical Reviewer: Gary Vogin, MD
CME Editor: Bernard M. Sklar, MD, MS
Complete author affiliations and disclosures, and other CME information, are available at the end of this activity.
Release Date: April 8, 2003; Valid for credit through April 8, 2004
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April 8, 2003 — Low-carbohydrate diets have been all the rage lately, but a systematic review published in the April 9 issue of The Journal of the American Medical Association reveals insufficient evidence to support or refute the concept thus far. The bottom line appears to be that a calorie is a calorie. The editorialist reviews the issue of adult weight loss.
"Recently, low-carbohydrate diets have resurged in popularity as a means of rapid weight loss, yet their long-term efficacy and safety remain poorly understood," write Dena M. Bravata, MD, MS, from the Center for Primary Care and Outcomes Research in Stamford, California, and colleagues. "Our results demonstrated the marked discordance between the knowledge needed to guide dietary choices and the information that is available in the medical literature."
Although millions of copies of three books on low-carbohydrate diets have sold in the U.S. over the past five years, the American Dietetic Association, the American Heart Association, and other professional organizations have warned the public against potentially serious medical consequences of these diets.
The investigators searched the literature for studies of low-carbohydrate diets published between 1966 and February 2003. They identified 107 articles reporting data on 3,268 participants, of whom 663 patients received lower-carbohydrate diets (60 grams of carbohydrates per day [g/d] or less), and 71 patients received the lowest-carbohydrate diets containing 20 g/d or less of carbohydrates, which is the recommended threshold for some of the most popular diets.
None of the studies evaluated diets of 60 g/d or less of carbohydrates in subjects with a mean age older than 53 years, and only five studies evaluated these diets for more than 90 days. Weight loss in obese patients was associated with longer diet duration (P = .002) and restriction of calorie intake (P = .03), but not with reduced carbohydrate content. Low-carbohydrate diets had no significant adverse effects on serum lipid levels, fasting serum glucose levels, fasting serum insulin levels, or blood pressure.
"Our quantitative synthesis...on the efficacy and safety of low-carbohydrate diets suggests that there is insufficient evidence to make recommendations for or against the use of these diets," the authors write. "We found insufficient evidence to conclude that lower-carbohydrate content is independently associated with greater weight loss compared with higher-carbohydrate content.... Given the limited evidence in this review, when lower-carbohydrate diets result in weight loss, it also is likely due to the restriction of calorie intake and longer duration rather than carbohydrate intake."
The investigators recommend additional research evaluating the long-term effects and consequences of low-carbohydrate diets in both older and younger subjects with and without diabetes, high cholesterol, and hypertension.
None of the authors has financial or other conflicts of interest concerning low-carbohydrate diets or diet projects. No manufacturer or vendor of dietary goods or services funded this study.
In an accompanying editorial, George A. Bray, MD, from Louisiana State University in Baton Rouge, notes that the worldwide epidemic of obesity will be followed by a worldwide epidemic of diabetes.
"The broader issue of whether a unique diet exists that will produce long-term weight loss has yet to be evaluated," he writes. "Although the truth of 'a calorie is a calorie' has been reaffirmed by [this review], the question of whether patients can adhere more easily to one type of diet or another remains to be answered."
JAMA. 2003;289:1837-1850, 1853-1855
Learning Objectives
Upon completion of this activity, participants will be able to:
Discuss the systematic review of low-carbohydrate diets and the conclusions that were drawn.
Describe the potential complications that can be a result of low-carbohydrate diets.
Clinical Context
The prevalence of obesity among American adults is now estimated to be about 30%. About 325,000 deaths and about 5% of direct health costs are attributed to obesity annually. A 1998 survey showed that roughly one third of U.S. adults were trying to lose weight and another third were trying to maintain weight.
There has been a recent resurgence in popularity of low-carbohydrate diets as a means of rapid weight loss. These diets have been popularized without detailed evidence of their efficacy or safety.
The most popular text on low-carbohydrate diets is by cardiologist Robert Atkins. Dr. Atkins and other proponents of low-carbohydrate diets claim that diets higher in protein and lower in carbohydrates promote the metabolism of adipose tissue and result in rapid weight loss without significant long-term adverse events.
But many have cautioned against low-carbohydrate diets. There has been concern that low-carbohydrate diets can cause accumulation of ketones and can result in abnormal metabolism of insulin and impaired liver and kidney function. Such diets could also lead to salt and water depletion causing postural hypotension, fatigue, constipation, and kidney stones; excessive consumption of animal proteins and fats leading to hyperlipidemia; and higher dietary protein loads could impair renal function.
These potential complications of low-carbohydrate diets would be especially important for dieters with cardiovascular disease, type 2 diabetes mellitus, dyslipidemia, or hypertension.
The objective of this systematic review was to evaluate changes in weight, serum lipid levels, fasting serum glucose levels, fasting serum insulin levels, and blood pressure among adults using low-carbohydrate diets in the outpatient setting.
Study Highlights
The investigators performed MEDLINE and bibliographic searches for English-language studies of low-carbohydrate diets published between 1966 and February 2003. They searched for key words such as low-carbohydrate, ketogenic, and diet.
They identified 107 articles meeting the required criteria. These articles reported data on 3,268 participants. Of those, 663 patients received lower-carbohydrate diets (60 g/d or less of carbohydrates); 71 patients received the lowest-carbohydrate diets containing 20 g/d or less of carbohydrates.
Study variables (number of participants, design of dietary evaluation), participant variables (age, sex, baseline weight, fasting serum glucose level), and diet variables (carbohydrate content, caloric content, duration) were abstracted from each study.
Weight loss in obese patients was associated with longer diet duration and restriction of calorie intake, but not with reduced carbohydrate content. Low-carbohydrate diets had no significant adverse effects on serum lipid levels, fasting serum glucose levels, fasting serum insulin levels, or blood pressure.
Pearls for Practice
This study found no evidence that lower-carbohydrate diets are associated with greater weight loss compared with higher-carbohydrate diets.
This study also found no evidence that low-carbohydrate diets have significant adverse effects on serum lipid levels, fasting serum glucose levels, fasting serum insulin levels, or blood pressure.
When lower-carbohydrate diets result in weight loss, the weight loss is probably due to the restriction of calorie intake and longer duration rather than carbohydrate intake.
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This activity is intended for primary care physicians, internists, endocrinologists, bariatricians, and other specialists working with obese patients.
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Authors and Disclosures
News Author
Laurie Barclay, MD
Writer for Medscape Medical News
Disclosure: Dr. Barclay has reported no significant financial interests.
This article may discuss investigational products or unapproved uses of products regulated by the U.S. Food and Drug Administration.
Clinical Reviewer
Gary Vogin, MD
Senior Medical Editor, Medscape
Disclosure: Dr. Vogin has reported no significant financial interests.
CME Editor
Bernard M. Sklar, MD, MS
Writer for Medscape Medical News
Disclosure: Dr. Sklar has disclosed that he has served as a consultant for Schering-Plough.
News CME Staff
Elliott Silverman
News CME Manager
Elliott Silverman has reported no significant financial interests.
Deborah Flapan
Medscape Medical News Coordinator
Deborah Flapan has reported no significant financial interests.
About News CME
News CME is designed to keep physicians abreast of current research and related clinical developments that are likely to affect practice, as reported by the Medscape Medical News group. Medscape Medical News Coordinator is Deborah Flapan. Clinical review is provided by Gary Vogin, MD. News CME is managed by Elliott Silverman. Send comments or questions about this program to
cmenews@webmd.net.
Medscape Medical News 2003. © 2003 Medscape
lo carbing....a study ...... 
ok...here goes... 
