Only when I substitute any whole wheat into my sandwich bread recipes, the slices of bread fall apart very easily; almost crumble to the touch.
My 100% white flour breads do not have this issue.
I used this KA recipe http://www.kingarthurflour.com/recipes/classic-sandwich-bread-recipe
I used KA white flour and in the recipe you will notice that it calls for 3 cups. I only substituted 1/2 cup (one half cup) of freshly grounded whole wheat berries (Red)