Simply, unprocessed food and drinking plain water (not pure as in distilled but with sufficient electrolytes in it).

But the greatest impact would be lifestyle changes in general. You cannot just diet your way out of a heart disease.

Well, maybe this population [0] of subsistence farmers will give you a hint.

In the modern world it is an uphill battle. And there are some people with hypocholesterolemia [1] who will have arteries in near pristine condition despite living a modern (unhealthy) lifestyle.

There are two broad strategies here which can be combined:

(1) Adhering to (strict) rules which will consume your resource of willpower. A very effective one: Don't drink sugary drinks. An unconvenient one for most people: Don't eat out.

(2) Modifying your modern environment to such an extent that it resemble choices humans made before the modern lifestyle i.e. a lot of physical activity, offline times, no processed food, being outdoors (e.g. a garden). To reap the benefits from both a modern lifestyle and a lifestyle we are evolutionary adapted to, this of course will cost you money in a crowded city and (unpaid) time you would otherwise use for earning money.

[0]https://www.thelancet.com/journals/lancet/article/PIIS0140-6...

[1]https://www.sciencedirect.com/science/article/abs/pii/B97803...