Small study from the 1990s. Effects of two diets were compared:
- Diet 1: relatively high monounsaturated fatty acid content (MUFA; oleic acid)
- Diet 2: high polyunsaturated fatty acid content (Ω-6 PUFA; linoleic acid).
Linoleic acid is the dominant fatty acid in MOST seed oils, like soybean oil; oleic acid tends to predominant in fruit oils, like olive oil.
A notable exception to this rule is canola oil, a seed-derived oil that has a more olive oil-like profile, with more MUFA and less Ω-6 PUFA (linoleic acid) than most other seed oils.
In the study below, MUFA:PUFA varied, while total calories, total fat, saturated fat, carbs, protein, and cholesterol were held constant (Image 2).
What did they see?
BOTH diets lowered the following (Image 3):
- Total cholesterol
- Triglycerides
- LDL
- vLDL
What differed between high MUFA:PUFA and low MUFA:PUFA diets?
Peroxidation rate of LDL. There was a strong, significant association between MUFA:PUFA ratio and peroxidation rate (Image 4).
Higher linoleic acid (Ω-6 PUFA) lower oleic acid (MUFA) --> more LDL peroxidation.
This result makes perfect sense if you already understand the basic underlying biology: PUFAs like linoleic acid are very susceptible to oxidation, whereas MUFAs like oleic acid are resistant.
This is far from the only study to show such an effect.
Oxidized LDL (oxLDL) is bad news.
OxLDL particles are filled with rancid fats from oxidized PUFAs, which immune cells (macrophages) want to gobble up for disposal, because they're toxic.
In fact, it's possible to increase the PUFA content of diets, seeing an overall decrease in LDL but an increase in oxLDL rate.