I am probably silly to lose sleep over this, but I don't want to have the same problems as my ancestors. How can I prevent atherosclerosis?

Healthy lifestyle. There are no guarantees, but you may decrease risk of atherosclerosis by eating a plant-based diet or one with small amounts of lean meat and fish. Look into the mediterranean diet, which includes olive oil, nuts, fruit, veggies & fish. Whole grains have been shown to decrease risk. Aerobic exercise to keep your cardiovascular system tuned. If you tend to have a lot of anger, consider counseling.
Avoid Risk Factors. Atherosclerosis occurs when substances called plaque begin to build up in the walls of the arteries. Stop smoking; control your diabetes, high blood pressure and cholesterol by controlling your diet and exercising regularly, monitor your blood sugar levels and visit your doctor regularly. See a vascular surgeon for a vascular screening to assess your risks.