Let’s say we are looking for a 5hr bottle as a stand alone nutrition source and getting hydration from the course.
That 5hr bottle should have
Maltodextrin at ~1g/kg/hr
Dextrose at ???
i’ve read research suggesting benefits of small anounts of protein and AA. How much?
What about electrolytes? I understand the major manufactures have an electrolyte blend that is predominately Na, some K, and trickles down with a few small amounts of other goodies. Any idea what amount to start on?
Dextrose is the short-chain version of maltodextrose, ie, plain glucose. The research I’ve seen has compared straight maltodextrin to fructose/maltodextrin mixtures as regards to maximal carbohydrate oxidation. A quick survey of articles (http://www.ncbi.nlm.nih.gov/pubmed/15741841, http://www.ncbi.nlm.nih.gov/pubmed/21071509 and http://www.ncbi.nlm.nih.gov/pubmed/18369092) have between 0.5-0.8 (g fructose:g maltodextrin) as the ratio that produces the most CHO oxidation with the least stomach upset. Fructose in high concentrations is no fun in your stomach.
The last thing I read from Alex Patterson at sweatscience was that the evidence for consuming protein with your carbohydrates during exercise is not very compelling (http://sweatscience.com/protein-during-exercise-good-for-strength-not-endurance-training/), but eat it after, certainly. It’s much better in your recovery drink.
There is a very long, but detailed, article at the Science of Sport site (http://www.sportsscientists.com/2007/11/sports-drinks-sweat-and-electrolytes.html) about electrolytes and sports drinks and the conclusion is that electrolytes in sports drinks make a very tiny difference in your plasma sodium. Anecdotal evidence being what it is, I know a certain world champion on here swears by lots and lots of salt during races, so I don’t think you’re going to go much more wrong than putting some extra money in Salt Stick’s pockets (hedge your bets, salt your food more heavily leading up to a long race/training run:)
If you’re looking for a place to start with a 5hr bottle,
- 1g maltodextrin/kg/hr
- 0.25g fructose/kg/hr (this may be over the top sweet when you’re exercising, test it out on a small scale first, I also wouldn’t run too far from a toilet if you’re sensitive to fructose, or don’t know if you’re sensitive to fructose)
- whatever flavouring you find palatable
If you tolerate that much fructose, try again with 0.5g/kg/hr (test some race pace efforts, of course). Make sure to take a couple good mouthfuls of water each time you take a swig off that 5hr bottle. You’re going to be trying to dilute it down to something that your gut can process without too much work and avoid fructose-inspired issues. It’s probably going to have the consistency of cough syrup 
I’ve started to make my own gels instead of taking up a water bottle (1/2 cup malto, 1/4 cup boiling water, couple drops vanilla, stir forever, then pour into a flask and let sit in the fridge overnight).