Summary
This 24-week crossover study followed 26 healthy Yeshiva students to compare how diets rich in monounsaturated fats (MUFA) versus polyunsaturated fats (PUFA) influence cholesterol levels and the vulnerability of LDL to oxidative stress. Each participant followed both diets—each for 12 weeks—with identical amounts of carbs, fat, and protein, allowing a direct comparison of how the type of fat affects the body.
Both diets improved cholesterol numbers, but in different ways and with different trade-offs:
Total cholesterol dropped by about 10% on the MUFA diet and about 16% on the PUFA diet.
LDL cholesterol decreased on both diets, with a slightly stronger reduction during one of the periods, but without major differences attributable to the type of fat alone.
HDL (“good” cholesterol) stayed the same, no matter which diet participants were on.
Tests looking at LDL-receptor activity, LDL composition, and how LDL particles interacted with cells showed no meaningful differences between MUFA and PUFA diets.
But the key finding came from oxidation testing. When participants were on the PUFA-rich diet, their LDL particles showed a significantly higher tendency toward oxidation, reflected by increased formation of thiobarbituric acid–reactive substances—a standard marker of lipid peroxidation.
This matters because oxidized LDL is a major driver of atherosclerosis, more so than LDL cholesterol levels alone.
In simple terms:
PUFA lowers total and LDL cholesterol a bit more, but
MUFA makes LDL much more resistant to oxidative damage—meaning it may be safer for long-term cardiovascular health.
This study adds to growing evidence that the quality of dietary fat matters just as much as the amount, and that diets richer in monounsaturated fats (like those found in olive oil and avocados) may reduce cardiovascular risk by producing LDL particles that are less likely to oxidize and form plaque.
PMID: 2008870
DOI: 10.1093/ajcn/53.4.899
Abstract
Twenty-six Yeshiva students were randomly assigned to a 24-wk crossover study of monounsaturated fatty acid (MUFA) vs polyunsaturated fatty acid (PUFA) diets (50% carbohydrate, 32% fat, 18% protein) fed alternately during two 12-wk periods. Total plasma cholesterol (TC) decreased significantly by ∼ 10% and ∼16% on the MUFA and PUFA diets, respectively. Plasma triglyceride response was variable. Low-density-lipoprotein cholesterol (LDL-C) decreased in both groups with an additional significant effect between periods. Concentrations of high-density-lipoprotein cholesterol did not change significantly. LDL-receptor status in fresh monocytes, affinity of LDL towards the LDL receptor in cultured fibroblasts, zonal-centrifugation profiles, and lipoprotein composition were not significantly different between the diets. There was a significantly higher tendency toward lipid peroxidation on the PUFA diet, as ascertained by more thiobarbituric acid-reactive-substances formation on that diet. Dietary PUFA results in somewhat lower TC and LDL-C concentrations whereas with MUFA the susceptibility of LDL to oxidative stress is lower.
Berry EM, Eisenberg S, Haratz D, Friedlander Y, Norman Y, Kaufmann NA, Stein Y. Effects of diets rich in monounsaturated fatty acids on plasma lipoproteins--the Jerusalem Nutrition Study: high MUFAs vs high PUFAs. Am J Clin Nutr. 1991 Apr;53(4):899-907. doi: 10.1093/ajcn/53.4.899. PMID: 2008870.