American Journal of Clinical Nutrition, Vol. 84, No. 6, 1550-1551,
December 2006
© 2006 American Society for Nutrition
Saturated fat does not affect blood cholesterol
Uffe Ravnskov
Magle Stora Kyrkogata 9
S-22350 Lund
Sweden
E-mail: ravnskov{at}tele2.se
Dear Sir:
The most striking observation from the study by Krauss et al (1) is the finding that a diet rich in saturated fatty acids (SFAs) results in a lower or a steady state concentration of total and LDL cholesterol and an increase in the concentration of HDL cholesterol, regardless of whether the diet has a reduced energy content. Similar effects on blood lipids have been observed in 4 weight-reducing trials with high intakes of SFAs (2-5) (Table 1
) and in many similar trials with unrestricted intakes of SFAs.
View this table:
[in this window]
[in a new window]
|
TABLE 1. Changes in blood lipids in 4 trials of calorie restriction in which a conventional diet was substituted for a low-carbohydrate diet rich in saturated fatty acids (SFAs)1
|
|
In 1973, Reiser (6) questioned the effects of SFA intake on serum cholesterol. In a thorough review of the relevant experiments, he noted several methodologic and interpretational errors. The most important errors are probably the attribution of differences between SFAs and polyunsaturated fatty acids to the former, when the effect could have been due to the latter, and the use of vegetable oils saturated by hydrogenation instead of natural SFAs.
A possible reason why the effects were more pronounced before weight reduction than after weight reduction in the study by Krauss et al was the difference in metabolism between the normal-weight and overweight subjects. Cornier et al (7) recently found that total and LDL-cholesterol concentrations decreased more with a low-carbohydrate than with a low-fat, calorie-restricted diet. Interestingly, the overweight subjects with reduced insulin sensitivity, but not those with normal insulin sensitivity, had an increase in cholesterol with the low-fat diet but a decrease with the low-carbohydrate diet. In both groups, the changes in lipids were more beneficial with a low-carbohydrate diet than with a low-fat diet. Therefore, the different lipid responses before and after weight reduction in the study by Krauss et al may have been because the loss of weight may have improved the participants’ insulin sensitivity and thus their lipid response.
Because the main reason for restricting the intake of SFAs in all official guidelines is to change blood lipids, demonizing these nutrients seems inappropriate. In his editorial, Katan (8) claims that high intakes of unsaturated fatty acids reduce the risk of heart attacks, but his evidence is based on a meta-analysis that had ignored 4 unsuccessful trials (9). Two meta-analyses of all controlled clinical trials in which the only intervention was a change in dietary fats found no effect on coronary or total mortality (10).
ACKNOWLEDGMENTS
The author had no vested interest in the subject of this letter.
REFERENCES
- Krauss RM, Blanche PJ, Rawlings RS, Fernstrom HS, Williams PT. Separate effects of reduced carbohydrate intake and weight loss on atherogenic dyslipidemia. Am J Clin Nutr 2006;83:1025–31.[Abstract/Free Full Text]
- Sondike SB, Copperman N, Jacobson MS. Effects of a low-carbohydrate diet on weight loss and cardiovascular risk factor in overweight adolescents. J Pediatr 2003;142:253–8.[Medline]
- Hays JH, DiSabatino A, Gorman RT, Vincent S, Stillabower ME. Effect of a high saturated fat and no-starch diet on serum lipid subfractions in patients with documented atherosclerotic cardiovascular disease. Mayo Clin Proc 2003;78:1331–6.[Abstract/Free Full Text]
- Meckling KA, O’Sullivan C, Saari D. Comparison of a low-fat diet to a low-carbohydrate diet on weight loss, body composition, and risk factors for diabetes and cardiovascular disease in free-living, overweight men and women. J Clin Endocrinol Metab 2004;89:2717–23.[Abstract/Free Full Text]
- Sharman MJ, Gomez AL, Kraemer WJ, Volek JS. Very low-carbohydrate and low-fat diets affect fasting lipids and postprandial lipemia differently in overweight men. J Nutr 2004;134:880–5.[Abstract/Free Full Text]
- Reiser R. Saturated fat in the diet and serum cholesterol concentration: a critical examination of the literature. Am J Clin Nutr 1973;26:524–55.[Medline]
- Cornier MA, Donahoo WT, Pereira R, et al. Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women. Obes Res 2005;13:703–9.[Medline]
- Katan MB. Alternatives to low-fat diets. Am J Clin Nutr 2006;83:989–90.[Free Full Text]
- Ravnskov U. The diet-heart idea is kept alive by selective citation. Rapid response. BMJ 8. December 2003. Internet: http://bmj.bmjjournals.com/cgi/eletters/327/7427/1348-c.
- Ravnskov U. Diet-heart disease hypothesis is wishful thinking. BMJ 2002;324:238.[Free Full Text]
