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LETTER TO THE EDITOR |
Division of Nutrition and Chronic Disease
Pennington Biomedical Research Center
6400 Perkins Road
Baton Rouge, LA 70808-4124
E-mail: lefevrm{at}pbrc.edu
Dear Sir:
Giugliano and Esposito are correct in noting that in our study (1) HDL-cholesterol concentrations declined, whereas triacylglycerol concentrations increased, when participants were fed diets that were low in total fat and saturated fat and that these results differed from those observed by Vincent-Baudry et al (2), whose study compared a low-fat diet with a Mediterranean-type diet. The changes observed in our study are consistent with those observed in many other controlled feeding studies and agree with the changes predicted in a meta-analysis (3).
Giugliano and Esposito offered that the differences in weight loss between the studies may underlie the differences in the HDL-cholesterol and triacylglycerol responses. We do not disagree that weight change associated with low-fat diets may influence the resulting lipoprotein responses, as has been summarized by others (4). Indeed, we specifically chose for the participants to maintain a constant weight during the study so that we could examine the effects of genetic and nongenetic predictors of individual lipoprotein responses on diet without the confounding influence of varying degrees of weight loss.
It is worth noting, however, that other study design differences may have also played a role in defining the differences in the HDL-cholesterol and triacylglycerol responses. As mentioned, our study was shorter in length (6 wk compared with 3 mo). Additionally, our study examined only healthy men, whereas the study by Vincent-Baudry et al studied both men and women with at least one risk factor for cardiovascular disease. Importantly, our study was a controlled feeding trial in which all diets were chemically validated before the study and all foods were prepared and provided to the participants (with the exception of a weekend evening meal). Thus, in our study, there was a high degree of confidence that the diets consumed by our participants achieved the differences in total fat and saturated fat specified by the study design. This contrasts with the study by Vincent-Baudry et al, where diet change was achieved through counseling and validated by food records and 24-h dietary recalls. Differences associated with the interpretation and implementation of the dietary instructions, along with errors associated with diet reporting, provide less confidence that the designed differences in dietary fat intakes were, in fact, achieved or accurately reported in that study. The net effect is that the reported change in dietary fat intake in the persons who were counseled to consume a low-fat diet was approximately half that achieved in our controlled dietary study (–4.9% compared with –8.7% of calories on the Step I diet). Given the dependence of the changes in HDL cholesterol and triacylglycerols on changes in total fat intake, it is likely that the differences in achieved reductions in fat intake between our studies also contributed to the differences in outcomes.
The study conducted by Vincent-Baudry et al is immensely important in that they tested whether the benefits (or adverse effects) of a particular dietary approach, which are identified through controlled feeding studies such as ours, were realized under real-world conditions. However, because the goals and resulting experimental designs of the studies are often quite different, it can be difficult to precisely identify those factors that may be responsible for any apparent discrepancies in observed outcomes. This is best resolved through additional carefully designed and executed studies of both types.
ACKNOWLEDGMENTS
The authors had no conflicts of interest.
REFERENCES
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