Lowering Dietary Saturated Fat and Total Fat Reduces the Oxidative Susceptibility of LDL in Healthy Men and Women

The present study examined the effects of reducing dietary total fat and saturated fat (SFA) on LDL oxidative susceptibility in 27 healthy men and women (age 24–65 y). Each subject consumed each of three diets for 8 wk: an average American diet (AAD, 34% energy from fat, 15% from SFA), a Step-1 diet (29% fat, 9% SFA) and a very low SFA diet (Low-Sat, 25% fat, 6% SFA). In vitro LDL oxidation was assessed by copper-mediated oxidation, as measured by the kinetics of conjugated diene formation and lipid peroxide formation. Compared with the AAD, plasma LDL-cholesterol (LDL-C) and HDL cholesterol levels were 8% lower (P = 0.16 and P = 0.11, respectively), in subjects when they consumed the Step-1 diet and 11% (P < 0.03) and 14% (P < 0.057) lower, respectively, when they consumed the Low-Sat diet. Conjugated diene production and oxidation rate were 7% (P < 0.05) and 9% (P < 0.05) lower, respectively. The reduction of lipid peroxide formation was 9% (P < 0.05) in subjects when they consumed the Low-Sat diet vs. the AAD. In addition, lipid peroxide and conjugated diene formation were positively correlated with plasma total and LDL-C and apolipoprotein B (apo B) levels (r = 0.5–0.6, P < 0.001), suggesting that quantity of LDL is an important determinant of oxidative modification. Furthermore, at the same level of apo B or LDL-C, LDL from subjects when they consumed either Step-1 or Low-Sat diets was less susceptible (P < 0.05) to oxidation than those when they consumed the AAD, suggesting that qualitative changes also affect LDL oxidative susceptibility. Therefore, the benefits of lowering dietary SFA may extend beyond decreasing LDL-C levels and include favorable qualitative changes in LDL that further decrease risk of coronary heart disease.