Avoid high fat grain fed meats and farmed fish. High protein foods may be 'chewy' and 'dry'. An easy way to guesstimate fat content is by texture. Fat gives a creamy or juicy texture. Proteins are naturally dry and chewy when cooked by methods other than boiling or slow roasting.
Fats become more liquid with heat.
Proteins become drier and tougher. Use moisture to keep low fat protein foods palatable. Using proteins in soups and stews, steaming and slow cooking keep proteins moist and tender, making them more digestible. Do not overcook proteins. Bacon, hot dogs, 'lunch meats' and such would not be considered good sources of protein.