Journal Name:
J. Nutr.
Article Title:
Varying dietary fat type of reduced-fat diets has little effect on the susceptibility of LDL to oxidative modification in moderately hypercholesterolemic subjects.
Date Written:
1998
Volume:
128
Number:
10
Page:
1703
Author(s):
Schwab, U.S.; Vogel, S.; Lammi-Keefe, C.J.; Ordovas, J.M.; Schaefer, E.J.; Li, Z.G.; Ausman, L.M.; Gualtieri, L.; Goldin, B.R.; Furr, H.C.; Lichtenstein, A.H.
Article:
The fatty acid composition of the diet has been reported to affect the in vitro susceptibility of low density lipoprotein (LDL) to oxidation. This may be due to a number of factors including the fatty acid composition of the particle, the particle size, the antioxidant concentration in the particle itself or as yet unidentified factors. LDL particles formed during the consumption of a diet high in polyunsaturated fatty acids (PUFA) appear to be more susceptible to oxidation than after consumption of a diet high in saturated or monounsaturated fatty acids (MUFA). The aim of this study was to examine the effect of reduced-fat diets varying in fatty acid composition resulting from the substitution of one predominant fat source for another on the in vitro susceptibility of LDL to oxidation in middle-aged and elderly subjects with moderately elevated plasma LDL cholesterol levels. These data were related to plasma fatty acid patterns, LDL particle size and the antioxidant content of the LDL particle.
Fourteen moderately hypercholesterolemic (LDL of 3.36 mmol/L) postmenopausal female and male subjects (age 44–78 y) consumed each of five reduced-fat diets [30 energy percent (E%) fat, 17 E% protein and 53 E% carbohydrate] enriched in beef tallow, canola oil, corn oil, olive oil or rice bran oil (20 E%) for 32 day periods. Diets fed were consistent with Step 2 guidelines (30% fat and 7% saturated fatty acids) with the only difference among the experimental diets being the predominant fat source. In vitro oxidation of LDL was assessed by incubating LDL with hemin and hydrogen peroxide, and measuring the time required for the reaction to reach maximum velocity (lag time). There were no significant differences in LDL particle score among the diet periods and no correlation between resistance of LDL to oxidation and LDL particle size. LDL lag times were 93.2+/-25.8, 95.9 +/- 26.4, 104.2 +/-32.7, 108.0+/- 26.6 and 113.1+/- 24.0 min for corn oil, beef tallow, rice bran oil, canola oil and olive oil periods, respectively. When the data from all dietary phases were pooled, LDL alpha-tocopherol level and plasma MUFA/linoleic ratio were positively related to resistance of LDL to oxidation.
Within the context of these diets, the results of this study suggest that LDL particle size was not sufficiently changed to have an effect on the in vitro oxidation of LDL. Previous investigations reported an association between dietary fatty acid composition on in vitro oxidation of LDL. Increased LDL oxidative degradation has been noted after subjects consumed high fat diets with relatively high levels of PUFA. The amounts of alpha-tocopherol in the diets may have protected LDL as these compounds are the most powerful antioxidant in the LDL particle. In this study, there was a positive significant relationship of LDL alpha-tocopherol concentration and resistance of LDL to oxidation when the data from all of the diet phases were combined.
This study showed that in middle-aged and elderly moderately hypercholesterolemic subjects, the consumption of reduced-fat diets enriched in animal fat or vegetable oils with a relatively wide range of fatty acid profiles did not alter the in vitro susceptibility of LDL to oxidation. The advantages of reducing the saturated fat content of the diet were reflected in lower total and LDL cholesterol levels.
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