Erin,

Not only the amount of food that you've eaten in the last week, or lack there of, is important to consider, but how much fiber was in it as well. Things that are primarily animal sourced proteins like meat, fish, poultry and dairy products, as well as refined starches like bread, pasta, white rice - all have very little fiber in them and so, tend to leave little residue.

On the other hand, if you have eaten a fair amount of vegetables, complex carbohydrates like oats and whole grains, and fruit, you should expect some substance to remain after digestion.

Hope that this helps and that things back on track for you.
Good luck with the PT for your shoulder.

With love, Erika