I suspect everybody's metabolism is a bit different, It is a matter of finding what works best for you. YMMV and all that. So we should all take any recommendations (especially my out of the mainstream regimen) with some grains of salt.
I begin every morning (hiking or not) by drinking enough water to reestablish my normal hydration and prepare for the expected toll of the day. For me that is anywhere from 20 to 48 ounces of water before I eat anything. But I would not recommend approaching that upper range if you are not used to it, nor should one drink too much too rapidly. I don't drink any other fluids at breakfast (coffee, milk, juices) as I find they are too dehydrating for me.
I was told the protein you eat today will work for you tomorrow. The carbs you eat today will work for you today. I think the fats are somewhere in the middle.
Back in Winter School, we were taught that carbs were digested in about an hour, proteins in 3-4 hrs, and fats ~7 hrs. A quick search of my reference books gives carbs 1-2 hrs and fats 7-8 hrs (FOTH, pg 448, 3rd ed, 1974*)--didn't find a number for proteins.
A network source gives a range of 3-10 hrs for digestion of different proteins.
http://www.bodyrecomposition.com/nu...ces-of-protein-speed-of-digestion-part-2.html
Carbs and fats are your primary sources for energy. Proteins are necessary for maintenance (the requirement is pretty independent of the amount of exercise), but excess can be used for energy.
I am in agreement with all of this. I would add that the carbs you ate the prior day (at least from the evening meal) will also work for you today. That is why distance athletes carbo load the night prior to a competition. Contrary to the popular adage that breakfast is the most important meal of the day -- Dinner is without doubt the most important meal for the next day of hiking or any other endurance activity.
I would think eating protein in the morning will help late in the day.
I also agree with this. At the very least I believe it keeps me from feeling hungry during the late stages of a hike.
If I am eating breakfast at home I have 1-2 scrambled eggs and 2-3 small pancakes. The drive to the trailhead allows some time for digestion of the protein and carbs before starting the hike. That will supply me for most day hikes. Although I am mostly relying on the carbo load from dinner the night before (which also includes some protein and fats).
I generally don't eat anything during a hike unless it is a very long and strenuous hike - then I will have some easy to digest snacks - raisins, fruit, or carrots to munch on. I will always graze on whatever berries I find along the trail -- whether I need them or not.
In general anything you eat will require the body to burn some calories to digest. So eating hard to digest foods during a hike might be somewhat counterproductive. The easy to digest, natural sugars seem to supply me with the most energy more quickly than anything else. I suppose it may also help that I only eat two meals on non-hiking days (skipping lunch). So I feel no psychological compulsion to eat lunch while hiking. I also work odd and constantly changing hours so I doubt that I am subject to the normal diurnal biorhythms any more.
If I am eating breakfast in the mountains after a backpacking bivouac, I eat a whole wheat and jelly sandwich for breakfast. I am usually on the trail within a few minutes after eating, so there is no time to digest proteins.