Immune cells kill using peroxides, superoxides and other free radicals. Anyone with an over-active immune system that's triggered easily — allergies, chronic stress, sub-optimal sleep, genetics, exposure to pollutants, metal ions etc¹ — you're better off reducing immune system activity.
So yes, eat less fat but also focus on the immune system. A study found 29% of Japanese babies less than 1 year old had fatty streaks and they were not spending the first 11 months chugging slurpies and McDs.⁴
TL;DR: Dietary fat and adipose tissue/adipocytes involved in AS are two different things⁵, and try not to get oxidized to death by a glitchy immune system while busy chasing fats or the latest fad diet. Fats are just one piece of the puzzle.
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¹Mechanisms of LDL oxidation: http://sci-hub.tw/10.1016/j.cca.2010.08.038
²This means sleeping better, reducing stress, taking anti-oxidants, reduce insulin triggers i.e., reduce food with IF/ADF/CR³ and reduce carbs
³Intermittent Fasting/Alternate-Day Fasting/Calorie Restriction. This study finds ADF to be superior to CR; if you can stick to it, that is: Differential Effects of Alternate-Day Fasting Versus Daily Calorie Restriction on Insulin Resistance — http://sci-hub.tw/10.1002/oby.22564
⁴https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2812791/ - conjecture is the mothers were smokers, see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2644569/ for more info. Pollution should be focused more strongly when it comes to heart health, the evidence is clear.
⁵Any excess energy gets stored as fat, so reduce fat intake but increase protein or carb intake to compensate? No dice, the body will generate fat for you in the form of adipose tissue which will lead to AS in the presence of an unregulated immune system.