I have no first hand experience with this, and you don't give your starting weight or desired finished weight
but nothing ever stopped me shooting my mouth off, even when I don't have the facts.

Bike fit, within reason, is based on your skeleton, which doesn't change during weight loss.
So, loosing 20 to 30 lbs isn't going to affect bicycle fit. However, a 400 lb person has difficulty reaching the drops on a racing bike, but if they loose 200 lbs, they can, and their ideal bike fit will be different than their fit when they were 400 lbs.