Yep I've fed apples a few times. We have apple trees at home and you have to pick up the apples before you mow so instead of throwing them out in the field and going to no use I bag them up and take them out to the woods and put them out in front of my trail cam. the deer love apples. Now about the fat question. Apples don't have fat in them but they do provide large quantities of sugar to the deer which they would not normally have in their system so the buildup of sugar in their system could lead to an increase in caloric intake and therefore an increase in fat. Although if you have corn in your area I could see a larger increase in fat due to intake of corn over intake of apples because corn is higher in lipids (fat). and yes corn fed deer taste better than deer that live in a pine forest at least from the deer I've tasted I can vouch for this.