"during runs" is too general.  Runs over 16 or 17 miles use up most of your glycogen stores.  Consuming simple carbs slows this depletion.  Under 15 miles, I doubt supplementation is anything more than psychological help.

Some protein metabolism is unavoidable.  But you want to minimize it.

Pete Pfitzinger wrote an article on "depletion" runs in Running Times some time ago.  They are runs >= to 17 miles purposely done on low carb reserves.  The idea is to  push the body to manage fat/glycogen consumption more efficiently.  I've experimented with them and believe them useful.  As a result of the article, I generally no longer usually supplement during my long runs except for Gatorade.  But I could have never completed my long runs in my first first 3 years of marathon training.  

I believe your body's metabolism continues to adapt if you keep up with the long runs all year long.

I've read that roughly 10% of the calories consumed running come from amino acids.  If that's the case, some protein replacement is in order.  I try to stick with independent studies, rather than one's you see in advertisements for products.  In that case, I've not seen any on the benefits of mixing protein in with your carb and electrolyte replacement supplements.  But I've not really investigated the topic. 

A good study on carb replacement: Jason Carp, A Matter of Survival - Training to Combat Fatigue, Running Times, 12/2007, citing his work published in the International Journal of Sport Nutrition and Exercise Metabolism in 2006: to maximize glycogen replenishment after an LSD or LT/LSD workout, consume 0.7 gm of simple carbohydrates per lb of body weight within 30 minutes of running. Continue to consume 0.7gm/lb every 2 hours for 4 to 6 hours afterwards.

He doesn't mention protein.

LSD is a long slow distance run

I actually have no idea....sorry!

Good luck though!

Lactate Threshold.  See http://www.mcmillanrunning.com/training2.htm under "Stamina Training" for  a good description. 

The carb replacement study I mentioned above is meant for after the run, not during.