Correspondence
Low-Carbohydrate Diets as Compared with Low-Fat Diets
N Engl J Med 2003; 349:1000-1002September 4, 2003
- Article
To the Editor:
The studies by Samaha et al.1 and Foster et al.2 (May 22 issue) are intended to expand our knowledge about low-carbohydrate diets. One potential long-term concern about the low-carbohydrate diet is its relatively high protein load and the effect this has on kidneys. This issue is especially important in persons with diabetes, who are more likely than others to have an underlying nephropathy. As a matter of fact, the population studied by Samaha et al.1 consisted of obese patients and among whom the prevalence of diabetes was high. For this reason, we are very interested in the data on the serum creatinine level at the conclusion of the study. Unfortunately, the study had a high dropout rate; nevertheless, data on renal function from the subjects who completed the study might shed light on this important issue. In addition, the death of one subject with diabetes in the low-carbohydrate group (whose death was thought to be due to poor compliance with drug therapy) should be kept in mind when the results of this study are interpreted.
2 ReferencesMurali K. Duggirala, M.D.
William C. Mundell, M.D.
Mayo Clinic, Rochester, MN 55905
duggirala.murali@mayo. edu Prasamsi Mikkilineni, M.D.
St. Elizabeth Hospital, Youngstown, OH 445011
Samaha FF ,Iqbal N ,Seshadri P , et al. A low-carbohydrate as compared with a low-fat diet in severe obesity. N Engl J Med 2003;348:2074-2081
Full Text | Web of Science | Medline2
Foster GD ,Wyatt HR ,Hill JO , et al. A randomized trial of a low-carbohydrate diet for obesity. N Engl J Med 2003;348:2082-2090
Full Text | Web of Science | Medline
To the Editor:
I do not agree with the conclusions of Samaha et al. and Foster et al. that a low-carbohydrate diet was more effective than a low-fat diet. This may be true if we simply rely on statistics, but both studies failed to achieve even a 10 percent reduction in weight with either diet. So the only conclusion that can be inferred from these reports is that neither diet was effective. Likewise, in both studies there was a very high dropout rate, making interpretation of the results difficult, as Ware points out in his accompanying editorial.1
1 ReferencesImran Aziz, M.B., B.S.
West Suffolk Hospital, Bury St. Edmunds IP33 2QZ, United Kingdom
imran.aziz@wsh. nhs. uk 1
Ware JH . Interpreting incomplete data in studies of diet and weight loss. N Engl J Med 2003;348:2136-2137
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To the Editor:
Samaha et al. do not report the proportions of different fatty acids in the dietary intake of subjects in their low-carbohydrate group. It is known that intake of monounsaturated fat increases the concentration of high-density lipoprotein (HDL) cholesterol1,2 and reduces the glucose concentration1 and the degree of insulin resistance, at least in patients with diabetes mellitus.3 Replacing dietary carbohydrate with polyunsaturated or monounsaturated fat decreases the risk of coronary heart disease, as predicted by favorable changes in the concentrations of triglyceride and HDL cholesterol.4 Therefore, information on the kind of dietary fat that subjects in the low-carbohydrate group consumed to replace carbohydrate intake would be important for explaining the lipid profile and insulin-sensitivity results.
4 ReferencesJuan Antonio Garrido, M.D.
Hospital A. Marcide, 15405 Ferrol–La Coruña, Spain
ja_garrido@terra.es 1
Mata P ,Garrido JA ,Ordovas JM , et al. Effect of dietary monounsaturated fatty acids on plasma lipoproteins and apolipoproteins in women. Am J Clin Nutr 1992;56:77-83
Web of Science | Medline2
Mensink RP ,Katan MB . Effect of dietary fatty acids on serum lipids and lipoproteins: a meta-analysis of 27 trials. Arterioscler Thromb 1992;12:911-919
CrossRef | Medline3
Garg A . High-monounsaturated-fat diets for patients with diabetes mellitus: a meta-analysis. Am J Clin Nutr 1998;67:Suppl:577S-582S
Web of Science | Medline4
Hu FB ,Stampfer MJ ,Manson JE , et al. Dietary fat intake and the risk of coronary heart disease in women. N Engl J Med 1997;337:1491-1499
Full Text | Web of Science | Medline
To the Editor:
The difference in weight loss between the two diets described by Samaha et al. reflects the greater energy deficit with the low-carbohydrate diet (approximately 34,000 kcal over a six-month period) than with the low-fat diet. Data on body composition are not provided, but such data are critical for documenting the components of weight loss (body fat, body water, glycogen stores, and muscle tissue). The low-carbohydrate diet varied only slightly from the base-line diet in macronutrient distribution (37 percent carbohydrates, 41 percent fats, and 22 percent proteins vs. 49 percent carbohydrates, 33 percent fats, and 17 percent proteins, respectively) and contained less fat than the base-line diet (74 g vs. 76 g) and an equal amount of protein (89 g). The absence of a true low-carbohydrate diet explains the absence of change in the uric acid concentration1; data on ketosis are not presented. The comparison of these diets is futile because the low-carbohydrate diet (which included approximately 150 g of carbohydrate per day) was not representative of the usual low-carbohydrate diet.2 The low-fat diet was not low in fat (33 percent of total calories) and included the same percentage of fat as the base-line diet.
2 ReferencesChristian K. Roberts, Ph.D.
Charles R. Drew University, Los Angeles, CA 90059
croberts@ucla.edu R. James Barnard, Ph.D.
University of California, Los Angeles, Los Angeles, CA 900951
Reddy ST ,Wang CY ,Sakhaee K ,Brinkley L ,Pak CY . Effect of low-carbohydrate high-protein diets on acid-base balance, stone-forming propensity, and calcium metabolism. Am J Kidney Dis 2002;40:265-274
CrossRef | Web of Science | Medline2
Atkins RC. Dr. Atkins' new diet revolution. Rev. ed. New York: Avon Books, 1998.
Author/Editor Response
Dr. Duggirala and colleagues raise an important question about protein intake and renal function in the subjects in our study. Protein restriction has been shown to have a small, long-term protective effect on renal function in persons with overt renal dysfunction at base line.1 This effect may be greatest with nondairy animal protein.2 In our study, we found no significant changes in the serum creatinine concentration from base line to six months in either diet group (from 1.00 to 0.99 mg per deciliter in the low-fat group and from 1.03 to 1.03 mg per deciliter in the low-carbohydrate group). However, assessment of more sensitive measures of renal function, such as the glomerular filtration rate, would be important for future studies of carbohydrate-restricted diets. Interestingly, a recent study found that patients with diabetes have regression of microalbuminuria in association with improvements in glycosylated hemoglobin and triglyceride concentrations3 — two factors that improved in the subjects on a carbohydrate-restricted diet in our study.
In response to Dr. Aziz's comments, we would like to clarify that we concluded that subjects on a low-carbohydrate diet lost more weight and had greater improvements in the triglyceride concentration and insulin sensitivity than those on a low-fat diet. These metabolic benefits were clinically meaningful and occurred independently of weight loss. We agree that a 10 percent reduction in weight by six months is an appropriate target. Nevertheless, achieving and maintaining this target have proved to be elusive, even in carefully controlled clinical trials.4,5 Those studies also demonstrated clinically important improvements in metabolic risk factors with lifestyle modification, despite weight loss of only 5 to 6 percent of base-line weight.4,5
Dr. Garrido inquires about the types of fats consumed by the subjects in our study. Subjects in both diet groups reported consuming roughly equal proportions of saturated fat at base line and at six months (29 percent of total fat at base line and 28 percent of total fat at six months).
Drs. Roberts and Barnard raise an important issue regarding changes in body composition, which we did not measure in our study. We suspect that our subjects did not lose only body water or muscle mass, given the clinically significant improvements in metabolic variables such as insulin sensitivity and triglyceride concentrations. With regard to dietary adherence, we acknowledge that neither group reported achieving their study-specified diet goals. Nevertheless, the subjects in the low-carbohydrate group did substantially reduce their carbohydrate intake, whereas those in the low-fat group followed fairly closely the National Heart, Lung, and Blood Institute Obesity Education Initiative guidelines for macronutrient composition, with a reduced intake of total calories and a slightly reduced intake of total fat (mean decrease, 4 g per day).
5 ReferencesFrederick F. Samaha, M.D.
Linda Stern, M.D.
Nayyar Iqbal, M.D.
Philadelphia Veterans Affairs Medical Center, Philadelphia, PA 19104
rick.samaha@med. va. gov 1
Klahr S ,Levey AS ,Beck GJ , et al. The effects of dietary protein restriction and blood-pressure control on the progression of chronic renal disease. N Engl J Med 1994;330:877-884
Full Text | Web of Science | Medline2
Knight EL ,Stampfer MJ ,Hankinson SE ,Spiegelman D ,Curhan GC . The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Ann Intern Med 2003;138:460-467
Web of Science | Medline3
Perkins BA ,Ficociello LH ,Silva KH ,Finkelstein DM ,Warram JH ,Krolewski AS . Regression of microalbuminuria in type 1 diabetes. N Engl J Med 2003;348:2285-2293
Full Text | Web of Science | Medline4
Tuomilehto J ,Lindstrom J ,Eriksson JG , et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med 2001;344:1343-1350
Full Text | Web of Science | Medline5
Diabetes Prevention Program Research Group
Full Text | Web of Science | Medline
Author/Editor Response
We agree with Dr. Aziz that it is important to distinguish between statistically significant and clinically significant differences in clinical trials. However, previous studies have shown that a weight loss of as little as 5 percent in obese persons — a weight loss similar to that observed in our low-carbohydrate diet group — is associated with considerable clinical benefits.1
The fact that the low-carbohydrate and high-carbohydrate (conventional-diet) groups had lost similar amounts of weight at one year allowed us to assess more precisely the relative clinical importance of the two approaches. Our data revealed no significant differences between the groups in total or low-density lipoprotein cholesterol concentrations but significantly greater increases in HDL cholesterol and significantly greater decreases in triglycerides in the low-carbohydrate group than in the high-carbohydrate group.
We agree that there are limitations in interpreting data from studies that have a high attrition rate. The attrition rate (approximately 40 percent at one year) was higher than we typically observe in clinic-based treatments2 but remarkably low, given the self-help approach used in our study. As Dr. Ware notes in his editorial, the similar pattern of results between analyses in which the base-line value is carried forward and “completers” analyses provides some reassurance that our results were not unduly biased by attrition. Nonetheless, larger studies of longer duration and with less attrition are needed to evaluate fully the efficacy and safety of low-carbohydrate diets as a potential therapy for obesity.
2 ReferencesGary D. Foster, Ph.D.
University of Pennsylvania School of Medicine, Philadelphia, PA 19104-3309
fosterg@mail.med. upenn. edu James O. Hill, Ph.D.
University of Colorado Health Sciences Center, Denver, CO 80262Samuel Klein, M.D.
Washington University School of Medicine, St. Louis, MO 631101
Klein S ,Wadden T ,Sugerman HJ . AGA technical review on obesity. Gastroenterology 2002;123:882-932
CrossRef | Web of Science | Medline2
Wadden TA ,Foster GD . Behavioral treatment of obesity. Med Clin North Am 2000;84:441-461
CrossRef | Web of Science | Medline
- Citing Articles (2)
Citing Articles
1
Jennifer L Miller, Janet H Silverstein. (2007) Management approaches for pediatric obesity. Nature Clinical Practice Endocrinology & Metabolism 3:12, 810-818
CrossRef2
Kathy McManus, Kris M. Mogensen. 2006. The Roles of Dietary Fats in Reducing Weight and Cardiovascular Risk Factors in Overweight and Obese Individuals. , 257-280.
CrossRef
