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Apples, celery, cabbage, and etc. are considered "negative" calorie foods. While I understand that the "negative" portion of that statement is largely mythical in nature, as they are actually just lower calorie, high fiber foods[1], I'm wondering if they're a good source to renew energy or stave off that gnawing hungry feeling during or after a workout, such as a long run, and if they are a better, more "natural" alternative for energy as opposed to something along the lines of a Clif bar, energy packets like Hammer Nutrition, or something similar?

Granny Smith apple

A typical Granny Smith apple has 80 calories in it, with 17g of sugars, and 5g of fiber[2]. Approximately 10% of that should be burned off by the digestive process, leaving about 70 calories[1]. Eating one of these will give you a fairly satisfying "full" feeling, but doesn't contribute much to your daily caloric intake. The sugar contained in the apple is all raw fructose and glucose[3], and is combined with enough fiber to take car of the negative effects of eating the carbohydrates as far as a nutritional/dietary standpoint is concerned.

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It would be helpful for discussion if you cite or clarify some of your assertions. I believe fruits contain a variety of sugar types (i.e., fructose, glucose and many others), with the granny smith variety apple that you mentioned being relatively starchy as well. Also, what do you see as the "negative effects" of eating this, and how would fiber "take care of" those effects? –  J. Winchester Apr 27 '12 at 19:07
    
By "negative" this means that people think/assume that this item will take more calories to digest than the item itself contains. Thus resulting in a net loss of calories just from the consumption of that food. As for fiber, fiber is effective in reducing the bad parts of biological interactions from sugar (HDL/LDL cholesterol, fat storage, insulin spikes, etc.) –  Nathan Wheeler Apr 27 '12 at 19:22
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I doubt that one granny smith apple will affect your energy, although it might make you feel better, which might in turn improve performance. I don't think that it will be significant in terms of the bad effects associated with overconsumption of sugar. There are a number of implied sub-questions in your post so the answer is complicated:

Will eating an apple help athletic performance by providing calories? Probably not. During intense exercise, such a small amount of calories would be expended very quickly, so it's not likely to contribute much to fueling movement. In fact, eating during exercise can be counterproductive, as digestion diverts blood supply to the stomach instead of to the muscles. Generally commercial "athletic fuel" formulations are designed for quick digestion, made of liquid or gel with simple molecules like glucose and amino acids, and (I think) the more solid or fibrous the meal, the harder it is to digest. I believe these kind of fuels are only shown to be effective in long endurance events lasting multiple hours (e.g. longer than a half-marathon), where the body's glycogen is significantly reduced.

Will eating an apple help athletic performance by sating hunger? I doubt it. It's true that your feeling of hunger may be relieved by eating something, but in my experience that can be ignored while exercising and has no impact on athletic performance. I would much rather feel hungry while training than feel like food is sitting in my stomach.

Is there any way eating during exercise can improve athletic performance? Possibly. In spite of the above, there may be a psychological or morale benefit to eating something like this. If an athlete is in the habit of never allowing a feeling of hunger to exist without immediately eating, or if the athlete is convinced that lack of food is degrading performance (even if it's not true physiologically), it could be possible that eating even a few bites would enhance the ability to perform.

Is an apple more natural than commercial products? Yes! "Natural" is a vague term, but my impression from looking at the cliff bar label is that it's made out of a long list of seeds, sugar and chemicals just like most any candy bar. The apple is definitely more natural than anything in a package (of course that doesn't mean it's better for you - tobacco is natural too).

Is there anything I can consume that is natural and fills the stomach, which provides a feeling of energy without making me slow down? Yes. Water, tea, coffee are obvious ones. Pickle juice is one that is not so well-known but has lab research behind it (Phys Ed: Can Pickle Juice Stop Muscle Cramps? - NYTimes.com]1).

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