What would increase a vegetarian's risk of atherosclerosis?

Different things: High calory diet especially using saturated fatty acids even in vegetarians can increase risk of atherosclerosis , also family history of premature or early coronary artery diseases especially when associated with familial high cholesterol or hyperhomocysteinemia can also lead to atherosclerosis , finally smoking of course.

Smoking, canned food: Fresh vegetables are healthy, but too many canned veggies are not healthy. Processed foods do not have the fiber, flavonoids, and non-oxidized mono and poly unsaturated fatty acids found in fresh fruits and vegetables essential for health. Eating processed vegetable derived foods like bread, bagels, cookies, cakes, pizzas, pastas, and sugar are "high" glycemic and must be limited. Don't smoke.