Strangely, I ate on the typical bagels-pasta-pizza-powerbars runner diet for a long time and thought it was just normal to have "cow patty" bathroom visits, although I was always quite lean on that diet too. And almost always had to plan runs around available bathrooms. I think gluten was to blame.
My wife, on the other hand, is clearly one of those people with a poor insulin response (both parents diabetic and obese) who isn't designed to do well on the high carb diet and has lost weight and run better on a much lower carb diet and feels more awake and alert.
My staple foods:
Sweet potatoes, Yellow yams, fruit of all kinds (strawberries, grapes, oranges, apples, bananas), almond milk, coconut milk (sugar free), egg protein powder, eggs, grass-fed meat, fish, avacadoes, cashews, almonds, walnuts, coffee, almond butter, low sugar dark chocolate (90% cocoa), some vegetables, salsa, hot sauce, walnut and olive oil. The carb concessions I make to being an endurance athlete needing more carbs include white rice sometimes and brown rice syrup. I drink a soda with sugar maybe twice a week only immediately post run - usually half regular, half diet. I don't have a regular intake of any refined sugar - sugar is like beer - I'll have some a few times a week as a treat, not a staple. I haven't had any dairy at all apart from a drop of half and half in my morning coffee and very little wheat (apart from maybe a single cookie or something at a work function here and there and whatever is in an IPA) in 2012.
I almost completely avoid legumes, dairy, soy , peanuts, and wheat or other gluten-containing grains (apart from an occasional beer - you can pry that treat from my cold dead hands).