DECREASING DIETARY LAURIC AND MYRISTIC ACIDS IMPROVES PLASMA-LIPIDS MORE FAVORABLY THAN DECREASING DIETARY PALMITIC ACID IN RHESUS-MONKEYS FED AHA STEP-1 TYPE DIETS

Current dietary recommendations advocate reductions in saturated fatty acids (SFA) and cholesterol (C) as a primary intervention for achievi ng a more desirable plasma lipid profile, To ascertain whether it is m ore efficacious to decrease dietary lauric and myristic acids (12:0 +/ - 14:0) or dietary palmitic acid (16:0) in conjunction with a reductio n in dietary C, 11 rhesus monkeys (8 males, 3 females) were initially fed a control diet rich in SFA + C for 14 wk [dietary fat similar to 3 8% of energy (%en), SFA 16%en and C at 180 mg/1000 kcal], Plasma lipid s were measured between the 9th and 13th wk, and LDL metabolism was as sessed after 13 wk. Monkeys were then split into two groups and fed on e of two American Heart Association (AHA) Step 1 diets (similar to 30% en fat, 10%en SFA, 75 mg cholesterol/1000 kcal) for an additional 14 w k, and plasma lipids and LDL metabolism were reevaluated. Group 1 rece ived a 16:0-rich diet in which most 12:0 + 14:0 were deleted (similar to 8.6%en from 16:0 and similar to 0.3%en from 12:0 + 14:0), whereas G roup 2 received a diet rich in 12:0 + 14:0 from which 16:0 was selecti vely removed (2.6%en from 16:0 and similar to 6.3%en 12:0 + 14:0). In all three diets, oleic and linoleic acid were held relatively constant so that only SFA, the level of total fat and cholesterol were manipul ated. Only the Step 1 diet that selectively removed 12:0 + 14:0 (the 1 6:0-rich diet) significantly reduced ail lipid fractions, including to tal cholesterol (TC), HDL-C, LDL-C, apolipoprotein B (apoB) and the LD L pool size. Plasma triglyceride (TG) and the ratio of TC/HDL-C were n ot altered by either Step I diet. The smaller LDL pool size following the 16:0-rich diet in Group 1 was attributable to a significantly high er fractional catabolic rate (FCR) of LDL because the transport rate o f LDL apoB was unaffected. Although the FCR was increased with the 12: 0 + 14:0-rich diet, the LDL apoB pool was not affected because the tra nsport rate of LDL tended to increase as well. The data suggest that a Step 1 diet that reduces total fat by decreasing 12:0 + 14:0 in conju nction with dietary C, improves plasma lipids more favorably than a si milar diet that selectively removes 16:0 and C. Previous data would im ply that the benefit resulted from removal of 12:0 + 14:0 per se, but the possibility is not eliminated that removal of C (independent of 12 :0 + 14:0) muted the potential interaction between C and palmitic acid that tends to raise TC.