The basic theory regarding altitude training is simple: when exposing an athlete to an environment that is low in oxygen the body will slowly adapt to the stress by getting more efficient at transporting and utilizing oxygen (Higher red blood cell count, and a stronger respiratory system). Lots have been written regarding this but what about nutrition and hydration when training at higher elevations?
Extra fluid intake is essential. Training at altitude means that breathing is shallower and more frequent meaning fluid loss through increased ventilation is higher. Additionally, sweat evaporates quickly due to dryer air so you are less inclined to drink adequately.
Your appetite can become suppressed by hypoxia so make certain you keep up with your calorie intake. There also seems to be a shift in calorie utilization with the reliance on carbs as opposed to fat stores. Carbs also attract water so increase your carb intake slightly over what you would do at sea level.
Iron is required to build hemoglobin so make sure you have sufficient ferritin levels prior to altitude training (ferritin is a protein used to store iron, it's concentration level gives a baseline of the bodies iron stores). Increasing your protein intake is essential in getting the iron that's required to manufacture hemoglobin as well as preventing illness and infections. Any Iron deficiency will negatively affect any altitude training.
It's important to be patient when beginning altitude training, pay attention to your body and don’t expect to feel great in the first few days and possibly up to two weeks.