Low fat marinades that still work
If you google fat free marinade, you will find a myriad of recipes from many sources.

As a more general principal, you have many options:


For chicken and pork, brining (which seasons, but despite the myth does not add flavor)
Some marinades have soy, water, or citrus as their main base with little or no fat
Dry rub the meat with herbs and spices, which is probably the most effective method of adding flavor
Use a sauce or mop (as the barbecue folks say) during the cooking to add flavor; these tend to be low fat.