More support for dietary patterns involving high-fiber, high-complex carbohydrates

University of California, Los Angeles
Division of Cancer Prevention and Control Research
Los Angeles, CA 90095-6900
E-mail: wmccarth{at}ucla.edu

Dear Sir:

The experimental design of Gerhard et al (1) was refreshingly respectful of normal patterns of eating by examining the effects of varying macronutrient composition on serum lipids under ad libitum eating conditions and by varying the content of dietary fiber proportional to the amount of carbohydrate in each diet. In keeping with what one would expect from a dietary pattern similar to the high-fiber, low-fat diets consumed for millennia by Mediterranean and Asiatic peoples, the results of adopting a high-carbohydrate (65% of energy) diet yielded more desirable glucose and triacylglycerol concentrations. These findings appeared to be in contrast with previous studies in which the effects of adopting a high-carbohydrate diet were examined only under isocaloric eating conditions and were found to yield less desirable serum glucose and triacylglycerol concentrations.

The authors might not have been as surprised by their results had they cited a couple of pertinent studies. One of these studies reported the clinical experience of 652 diabetic inpatients consuming a complex carbohydrate (70–75% of energy), low-fat diet ad libitum continuously for 3 wk. Barnard et al (2) reported a 33% decrease in serum triacylglycerol concentrations with this diet. A second, less obviously pertinent, study (3) was conducted, ironically, by the authors of one of the isocaloric macronutrient comparisons tested in diabetic patients. Garg et al (4) contrasted a high-carbohydrate (55% of energy) diet with a high-monounsaturated-fat diet (40% of energy from carbohydrate) under isocaloric conditions and purported to show that diabetic patients who adopted a high-carbohydrate diet experienced an undesirable 24% increase in serum triacylglycerol concentrations. A critique of this study (5) pointed out that the observed rise in serum triacylglycerol concentrations with their high-carbohydrate diet could have been an artifact of the isocaloric design of the study and a consequence of the authors failing to increase the dietary fiber intake commensurate with the increase in carbohydrate intake. In a study designed to test this critique, Chandalia et al (3) reported that the adoption by diabetics of a diet providing 50 g fiber/d (and 55% of energy from carbohydrate) for 6 wk was associated with a desirable 10.2% decrease in plasma triacylglycerol concentrations.

Despite these supportive studies validating the results of Gerhard et al, readers might still wonder about the long-term clinical applicability of their 6-wk findings to community-living diabetics. Fortuitously, Esposito et al (6) recently reported that Europeans diagnosed with the metabolic syndrome and randomly assigned to a high-carbohydrate (50–60% of energy), Mediterranean-style diet were able to adhere to it for 2 y, with salubrious consequences for markers of vascular function, a 12% decrease in serum triacylglycerol concentrations, and a 5.4% decrease in body weight. The consumption of complex carbohydrates with high contents of intact fiber and water, as is characteristic of classic Mediterranean and Asian diets, appears to yield salubrious benefits with respect to serum triacylglycerol concentrations and long-term weight control that appear to be sustainable long-term by adults at risk of diabetes.

ACKNOWLEDGMENTS

The author consults occasionally for the Pritikin Longevity Center, a residential lifestyle change rehabilitation center that features a high-carbohydrate, low-fat diet.

REFERENCES

1. Gerhard GT, Ahmann A, Meeuws K, McMurry MP, Duell PB, Connor WE. Effects of a low-fat diet compared with those of a high–monounsaturated fat diet on body weight, plasma lipids and lipoproteins, and glycemic control in type 2 diabetes. Am J Clin Nutr 2004;80:668–73.
2. Barnard RJ, Jung T, Inkeles SB. Diet and exercise in the treatment of NIDDM—the need for early emphasis. Diabetes Care 1994;17:1469–72.
3. Chandalia M, Garg A, Lutjohann D, von Bergmann K, Grundy SM, Brinkley LJ. Beneficial effects of high dietary fiber intake in patients with type 2 diabetes mellitus. N Engl J Med 2000;342:1392–8.
4. Garg A, Bantle JP, Henry RR, et al. Effects of varying carbohydrate content of diet in patients with non-insulin dependent diabetes mellitus. JAMA 1994;271:1421–8.
5. McCarthy WJ, Inkeles S. Varying carbohydrate intake in NIDDM. JAMA 1994;272(23):1817–8.
6. Esposito K, Marfella R, Ciotola M, et al. Effect of a Mediterranean-style diet on endothelial dysfunction and markers of vascular inflammation in the metabolic syndrome—a randomized trial. JAMA 2004;292:1440–6.