It is so hard to keep up with research on diet and disease prevention, especially with so many conflicting reports in the media. To try to sort through this, some researchers looked comprehensively at all of the high quality research available about diet and prevention of heart disease. They put together this nice summary table showing which foods show evidence of harm, which show evidence of benefit, and which are inconclusive.
It is important to remember that this is addressing heart disease specifically, not general health or general disease prevention. And they limited their conclusions to the most thorough studies of heart disease outcomes. For example, I think a diet which is low in wheat-based carbohydrates can be very beneficial for maintaining weight and preventing long-term health complications.
If you, or a family member, suffers from chronic heart disease, this table is a good starting point for a discussion with your physician and other health providers about the optimal diet to prevent future heart issues.