Hens fed animal fat died more often, had more cholesterol in their blood and arteries, but surprisingly had less visible artery damage than hens fed no extra fat — meaning more fat in the arteries doesn’t always mean worse damage.

As chickens get older, their blood cholesterol goes up — but that doesn’t tell you how bad their artery damage is. You need to watch them for years to really understand how diet affects their arteries.

In chickens, the lower part of the main artery has more cholesterol and more damage than the upper part — and how bad the damage is in each bird is linked to how much cholesterol is in that specific spot, not how much cholesterol is in the whole body.

Feeding hens corn oil for three years seemed to reduce artery damage more than feeding them no extra fat, even though their blood cholesterol didn’t change much — maybe the type of fat matters more than how much cholesterol is in the blood.

Adding fat to the chickens’ diet didn’t change their blood pressure — so high blood pressure probably isn’t why their arteries got damaged.

Corn oil made the chickens’ blood and arteries richer in certain healthy fats, while animal fat made them poorer in those fats — but this had nothing to do with how much cholesterol was in their blood.