Low-Carb Craze Unwarranted
Low-carbohydrate diets have developed into a multimillion-dollar industry. They promise healthy, rapid, and indulgent weight loss for relentless dieters. This is especially remarkable, since no randomized, controlled clinical trials evaluated its efficacy until 2003.
Foster et al. (2003) conducted a one-year, multi-center study among 63 obese men and women with a body mass index (BMI) greater than 30. The results demonstrated greater weight loss on the low-carbohydrate diet within the first six months than on a conventional diet of 1,200–1,800 kcal/day, but this apparent difference did not continue through the remainder of the study period.
Of particular interest is that the frequently observed dyslipidemia (elevated cholesterol, depressed HDL, increased LDL) associated with moderate overweight was not resolved between the study groups, and the post-prandial glucose and insulin levels did not differ. These results were also confounded with poor compliance and high attrition.
A review of the literature from January 1966 through February 2003 (Bravata et al., 2003) indicates that there is not a clear consensus as to what amount of carbohydrates consumed daily constitutes a low-carbohydrate diet; and that there is insufficient evidence to make recommendations for use of low-carbohydrate diets, especially among subjects older than 50 years of age or for more than 90 days. Among the reviewed studies, participant weight loss while using low-carbohydrate diets was principally associated with decreased caloric intake and diet duration but not with reduced carbohydrate content.
While clinical and scientific impression is that any diet that ensures caloric restriction—e.g., limits food choices—will promote weight loss, the overwhelming popular trend continues to emphasize regimens organized around high-fat, high-protein content. Popularity of this dietary strategy persists despite available evidence suggesting that long-term safety and improved compliance are strongly associated with moderate fat balance and variety in a diet regimen (Freedman et al., 2001).
In discussing variety, it is worth noting the popular impression that the prevalence of refined sugar and fast-food is causally linked to obesity. Epidemiological data refute this assertion dramatically. World Health Organization data (DeOnis and Blössner, 2000) demonstrate that some of the highest rates of childhood obesity occur in developing countries and Eastern Europe, where access to refined sugar and processed food is virtually nonexistent.
Thus, calories do count, the source of those calories may not require conformation to some extreme ideal, and most diet algorithms that effectively reduce caloric intake do result in weight loss. Achieving and maintaining a healthy weight over a meaningful duration is another matter. Medically supervised, safe and effective weight reduction is not an acute event, but a chronic process that includes simultaneous caloric restriction (through a diet that truly facilitates compliance) and regular physical activity (Freedman et al., 2001).
Never before in history have we enjoyed such quality, quantity, and variety of food, but we have a growing responsibility to develop and market foods that reduce the risk of acute and chronic disease. We’ve gone beyond basic nutrition and are responding to consumer demands for rapid adjuncts to health. In the face of these unprecedented market pressures, it is essential that food industry innovation be scientifically based and medically well founded. The evidence demands critical examination and rational decisions rather than implicit promotion of fads and crazes.
Obesity prevention and health improvement are everyone’s responsibilities. These include “model” eating habits and moderate exercise. In conjunction with evidence-based, clinically validated dietary regimens, what seems essential are partnerships among academic institutions, food industry members, regulatory agencies, and popular media that promote healthy diets and appropriate levels of physical activity.
This is the first of a continuing series of articles that will provide medical and scientific perspectives on the relationship of food, medicine, and public health.
by ROGER CLEMENS, Dr. P.H.
Director, Analytical Research & Services
Molecular Pharmacology & Toxicology
USC School of Pharmacy, Los Angeles, Calif
by PETER PRESSMAN, M.D.
Assistant Professor of Clinical Medicine
USC Keck School of Medicine, Los Angeles, Calif.
Bravata, D.M., Sanders, L., Huang, J., Krumholz, H.M., Olkin, I., Gardner, C.D., and Bravata,D.M. 2003. Efficacy and safety of low-carbohydrate diets: A systematic review. J.Am. Med. Assn. 289: 1837-1850.
deOnis, M. and Blössner, M. 2000. Prevalence and trends of overweight among preschool children in developing countries. Am. J. Clin. Nutr. 72: 1032-9.
Foster, G.D., Wyatt, H.R., Hill, J.O, McGuckin, B.G., Brill, C., Mohammed, S., Szapary, P.O., Rader, D.J., Edman, J.S., and Klein, S. 2003. A randomized trial of a low-carbohydrate diet for obesity. New Eng. J. Med. 348: 2082-2090.
Freedman, M.R., King, J., and Kennedy, E. 2001. Popular diets: A scientific review. Obes. Res. 9(Suppl. 1): 1S-40S.