What would happen if I ate solely apples and drank apple juice or water for a week?

I need to do an experiment for a college Anatomy and Physiology course, that's solely independent, and has to do with the body. The only thing I can think of is to test out the saying, 'An apple a day keeps the doctor away.' I've taken a nutrition course before, and can guess some of the more harmful effects of only consuming apples, such as little to no protein or fat intake, as well as very few calories (though I'm hoping to remedy this with the amount of apples I consume). I'm not concerned with things like how much sugar will accumulate in my teeth (brushing is one of those things that's a given), but I'm worried about the repercussions for my digestive tract, and overall state of mind. Could you guys help me out with some guesstimation?