If one were to exchange unhealthy refined fats, oils/fats and sugars, including those unhealthily added to refined, processed foods, for unrefined, healthy fats/oils, sugars and salts, the bulk of their diet, most likely at least 80% of it, would be changed for the better, forever.
That IS the starting point. No one can go wrong by making those initial changes, and will see benefit, perhaps much benefit, over time.