The answer to the question of whether fruit can or will make you fat isn't as simple as yes OR no...because the answer is yes AND no.
Sound confusing? It's not so bad!
There have been studies done on fruit sugar (fructose) and how it's metabolized in the body and liver, which I'll get into in a bit, but I'm also going to talk about fruit from a practical standpoint.
First, here is why it WON'T make you fat...
Fruit is a fat-free (with rare exception, like avocados) and fairly low-calorie, high-fiber food. It's going to be hard to eat ENOUGH fruit to result in an excess of calories, resulting in noticeable fat gain...hard, but not impossible.
You would have to look long and hard to find somebody who ate a lot of fruit and had gained a lot of fat because of all the fruit they ate. Fruit roll-ups, fruit juice (with 10% real juice), Fruity Pebbles and Froot Loops...maybe not so hard, though I do have to say high fructose corn syrup is NOT a fruit just because it has the word "fructose" in it, so that doesn't count.
And I don't know about you, but I have yet to hear of somebody sitting down in front of the television and not realizing they ate an entire bag of apples or saying their doctor told them they need to lay off the bananas!
"Real" fruit actually contains a lot of water, nutrients, fiber, etc...healthy stuff...stuff your body NEEDS. It's generally when we start mucking around with fruit that we start to run into problems.
In the words of Homer Simpson..."This jelly donut has purple stuff in it. Purple is a fruit."
That being said, there ARE metabolic issues with fruit and fat.
Yes, it IS true that the body has certain limitations processing fructose (the type of sugar found in fruit).
Fructose can only be stored as glycogen (glycogen is the carbohydrate storage molecule in the body) in the liver, not in the muscles. Muscle cells lack the proper enzymes to convert fructose into this storage molecule.
So that leaves the liver for storage...
When liver glycogen levels are full and your body can't store any more carbs in the liver, fructose IS easier for the body to convert into fat than other carbs because of its molecular structure.
This fat is NOT immediately converted into bodyfat, however. It becomes free fatty acids circulating in the bloodstream. If they're not burned, they CAN be stored as bodyfat.
But the OTHER good stuff you find in fruit, notably the fiber and vitamins and minerals, outweigh the "dangers" of storing a little extra fat.
And here's the point that a lot of people miss, especially when they hear that fruit has the potential to work against fat loss when on a diet...
If you're dieting, you should be in a caloric deficit. This means that your liver glycogen levels should very RARELY be full. You're in a deficit after all!
1. The fructose should have little chance of being converted into fat.
2. If some excess fructose IS converted to fat, chances are good it'll be USED by the body soon after being converted to fat because you're in a caloric deficit.
Granted, just like ANY other carbohydrate, if you eat too much of it, it can be stored as fat. If you're a competitive bodybuilder peaking for a competition, you MAY have to watch your fruit intake to be sure you come in at your leanest.
But for the average person looking to drop bodyfat, fruit is not something I would be too worried about (unless you're on a low-carb diet, in which case you're watching ALL carbs anyway).
I would be FAR more concerned about a person drinking too much of that diet soda garbage while dieting before I'd even be slightly concerned about them eating an apple.
Bottom line, my stance is this...DO NOT feel guilty about eating fruit, even while dieting. Treat it as you would any other food with calories in it and simply be aware of your intake because ANY food has the potential to make you fat, especially if you eat it when your body doesn't need any more calories for that day.
If you want to minimize the impact of fruit on your fat-loss diet, eat it in the morning when liver glycogen levels are naturally at their lowest point. This will help ensure fructose won't be converted into fat.
Honestly, there are MUCH more important things to worry about when it comes to fat loss...your training and overall nutrition are much more important than worrying about eating too much fruit.