Hi Roth
One or two pieces of fruit a day is fine. The sugar in fruit is a monosacharide and breaks down quickly and easily in the digestive system. An apple is about 70-90g and only contains about 60-80kcals, so that's a lot of fibre and not much energy content. don't forget there's a lot of nutrients in fruit too: Anti-oxidant vitamins, and minerals.
I tend to eat one piece of fruit on non-training days and two on a training day, right after my workout. This elevates my blood sugar levels nicely and helps secrete insulin to shuttle carbohydrates to muscles after lifting. That's just one way of looking at it if you're worried about the sugar and kcals. And Headholio is bang on about it being a good and filling replacement compared to other snacks that are loaded with crap.
Craig