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American Journal of Clinical Nutrition, Vol. 84, No. 2, 461, August 2006
© 2006 American Society for Nutrition

LETTER TO THE EDITOR

The low fat paradox—do dietary carbohydrates increase circulating saturated fatty acids?

Stephen D Phinney

6108 Boothbay Court
Elk Grove, CA 95758
E-mail: sdphtb{at}comcast.net

Dear Sir:

King et al (1) present very intriguing fatty acid profiles from the serum lipids of subjects fed varying amounts of carbohydrate. One of the many points of interest is the elevation in myristic acid (14:0), palmitic acid (16:0), and total saturates in the phospholipids (PLs) and cholesteryl ester (CE) fractions in response to a low-fat (17% of energy), high-carbohydrate diet. Also of interest in this report is the lack of data quantitating the total serum triacylglycerol fraction and its fatty acid composition.

Given the great interest in the atherogenic properties of saturates, particularly palmitic acid (2), the composition of serum total and saturated fatty acids in response to a low-fat diet is important. This is especially true for the serum triacylglycerol fraction, which transports the greatest amount of fatty acids among the serum lipid fractions.

Ruderman et al (3) and Dreon et al (4) reported that the substitution of carbohydrate for fat during a eucaloric diet raises total serum triacylglycerol, which was confirmed by others (5, 6). If, as these prior reports have shown, the low-fat, high-carbohydrate diet raised fasting serum triacylglycerol in the current study by >50%, and assuming that the 14:0 and 16:0 contents in the triacylglycerol fraction increased by 10–20% (as King et al report for the PL and CE fractions), this translates to a near doubling of the circulating mass of 14:0 and 16:0, despite the total dietary fat being cut by 50% in these subjects.

Given the intensified discussion of the health effects of a low-fat diet because of the recent publication of the Women's Health Initiative results (7), it would be of considerable interest to see data from the current study for the serum total triacylglycerol and its saturated fatty acid composition with the transition to the 17%-fat diet in King et al's study. This apparent paradox of markedly increased 14:0 and 16:0 contents in the triacylglycerol fraction despite the dramatic reduction in dietary fat might help explain the lack of health benefits observed in the Women's Health Initiative diet study, despite the increase in dietary fruit and vegetables during the low-fat arm.

ACKNOWLEDGMENTS

The author had no personal or financial conflict of interest with respect to the study by King et al.

REFERENCES

  1. King IB, Lemaitre RN, Kestin M. Effect of a low-fat diet on fatty acid composition in red cells, plasma phospholipids, and cholesterol esters: investigation of a biomarker of total fat intake. Am J Clin Nutr 2006; 83: 227–36.[Abstract/Free Full Text]
  2. Dietschy JM. Dietary fatty acids and the regulation of plasma low density lipoprotein cholesterol concentrations. J Nutr 1998; 128(suppl): 444S–8S.
  3. Ruderman NB, Jones AL, Kraus RM, Shafrir E. A biochemical and morphologic study of very low density lipoproteins in carbohydrate-induced hypertriglyceridemia. J Clin Invest 1971; 50: 1355–68.[Medline]
  4. Dreon DM, Fernstrom HA, Miller B, Kraus RM. Low-density lipoprotein subclass patterns and lipoprotein response to a reduced fat diet in men. FASEB J 1994; 8: 121–6.[Abstract]
  5. Kasim-Karakas SE, Almario RU, Mueller WM, Peerson J. Changes in plasma lipoproteins during low fat, high carbohydrate diets: effects of energy intake. Am J Clin Nutr 2000; 71: 1439–47.[Abstract/Free Full Text]
  6. Parks EJ, Hellerstein MK. Carbohydrate-induced hypertriacylglycerolemia: historical perspective and review of biologic mechanisms. Am J Clin Nutr 2000; 71: 412–33.[Abstract/Free Full Text]
  7. Howard BV, Van Horn L, Hsia J, et al. Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative randomized controlled dietary modification trial. JAMA 2006; 295: 655–66.[Abstract/Free Full Text]




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