This is surprisingly easy. Unless you have some medical condition, in which case it may be impossible. ~2 years ago I was 110 kilos, 185cm. Borderline obese. Now I'm in the upper 60's. The 6(8 turns out in my case) packs became a thing only as a consequence of the wfh, and subsequently boredom and eventually "let's see if it's possible". Realistically it took me about a month. And while exercise played a role, most of it came from food. Without starving at all either.