Moderate intake of myristic acid in sn-2 position has beneficial lipidic effects and enhances DHA of cholesteryl esters in an interventional study

Abstract

Among the saturated fatty acids (SFA), myristic acid is known to be one of the most atherogenic when consumed at high levels. Our purpose was to compare the effects of two moderate intakes of myristic acid on plasma lipids in an interventional study. Twenty-five male monks without dyslipidemia were given two isocaloric diets for 5 weeks each. In diet 1, 30% of the calories came from fat (8% SFA, 0.6% myristic acid) and provided 200 mg cholesterol/day. Calories of diet 2 were 34% fat (11% SFA, 1.2% myristic acid) with the same levels of oleate, linoleate, α-linolenate and cholesterol. A baseline diet was provided before each diet.

In comparison with baseline, diets 1 and 2 induced a decrease in total cholesterol, LDL-cholesterol and triglycerides (P<.001); HDL-cholesterol was not modified and the apo A-I/apo B ratio increased (P<.001). Plasma triglycerides were lower after diet 2 than after diet 1 whereas HDL-cholesterol was higher (P<.05). In phospholipids, myristic acid, oleic acid, linoleic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) increased after diet 2 vs. baseline (P<.01) and diet 1 (P<.05). Both diets were associated with an increase in α-linolenate of cholesteryl esters (P<.05), but only diet 2 was associated with an increase in DHA of cholesteryl esters (P<.05). In diet 2, myristic acid intake was positively correlated with myristic acid of phospholipids, and α-linolenic acid intake was correlated with α-linolenic acid of cholesteryl esters.

Moderate intake (1.2% of total calories) of myristic acid has beneficial lipidic effects and enhances DHA of cholesteryl esters.

Introduction

Many epidemiologic studies have documented an association between fatty acid intake and the risk of coronary heart disease (CHD) [1], [2], [3], [4]. In general, long-chain saturated fatty acids (SFA) (12–16 carbon atoms) tend to increase the risk of CHD, whereas monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) tend to decrease this risk, mainly α-linolenic acid [5], [6]. These effects may be mediated in part by fatty acid-induced changes in serum lipid levels, especially LDL-cholesterol but also VLDL- and IDL-cholesterol (grouped together under the term non-HDL-cholesterol), oxidative status, hemostasis and blood pressure. The results of these studies were used to make specific dietary recommendations for the prevention and treatment of CHD which have led to a change in eating habits [7], [8], [9].

Recent feeding studies [10], [11], [12], [13], [14], [15], [16] have shown that individual SFA may affect the cholesterolemic response with different potencies. Myristic acid (C14:0) is more potent than lauric (C12:0) or palmitic (C16:0) acids in inducing increase in total cholesterol and LDL-cholesterol. In the Nurses' Health Study, Hu et al. [17] demonstrated that intake of stearic acid at 4.1% of total energy was associated with a 1.30 risk (P=.009) for CHD. Intakes of C12:0+C14:0 in five quintiles from 0.98% to 2.14% of total calories were associated with a U-shaped curve, with a lower CHD risk at 0.96 for an intake of 1.45%.

In many experimental diets myristic acid has been given in relatively high concentrations up to 3.4–4% of total energy (level in mother's milk where it is also in sn-2 position). Consequently, results have been obtained in a nonpertinent manner for utilization of myristic acid in medicine: 52% of total energy in Spady et al. [18], 17% in Tholstrup et al. [19], 11.3% in Zock et al. [20] or 10% in Temme et al. study [21]. Myristic acid came from trimyristine (a product of synthesis), or from coconut oil where it is usually in the external position of the triglyceride, and is associated with lauric acid in a ratio C12:0/C14:0 greater than 1.

Furthermore, Gillman et al. [22] have recently shown in the Framingham Heart Study that intakes of fat, saturated fat, and monounsaturated fat, but not polyunsaturated fat, were surprisingly associated with reduced risk of ischemic stroke in men. In addition, the initial results of the EVA Study [23] point out the lower risk of cognitive decline in the elderly (26% reduction) with a 1% increase in n-3 PUFA level, whereas a 1% increase in n-6 levels was associated with a higher risk (twofold greater). Intake of SFA increased this risk to a lesser extent.

The aim of our study was to test the effects of pertinent moderate intake of myristic acid (1.2% of total energy) on plasma lipids, lipoproteins and fatty acids of phospholipids and cholesteryl esters compared to a diet containing only half the amount of myristic acid but with ‘physiological’ intakes of oleic, linoleic and α-linolenic acids, at identical levels in both diets to avoid any bias.