Optimal fruit intake for weight loss is probably 0. My random out of the blue assumption is that 1-2 small pieces of fruit won't stall your weightloss. A small melon, half a pineapple, that kind of thing is probably what I would call excessive for weightloss purposes. I personally ate one piece of fruit to break my fast when I was dieting, and that worked well for me. For some more scientific numbers, I believe the fructose limit is somewhere around 20-30g for how much it takes to replete liver glycogen, and where further consumption will become adipose tissue.