What it is
Egg yolk, oil and acid whipped into an emulsion — a whole-food sauce at heart. The catch is the oil: nearly every jar uses refined soybean oil.
Why your biology objects
The structure is fine — egg, lemon or vinegar, fat — but the bulk is usually soybean or canola oil, so it carries that oil's linoleic-acid load. The score follows the oil: a soybean-oil mayo is a seed-oil delivery vehicle; an avocado- or olive-oil mayo is genuinely green.