Don't mess with my food!

I know I'm going to get chewed out for this but I think you should check your friends and other family members, but I was raised to give mothers the ultimate respect. We will never ever be able repay our mother's for just one contraction and I'm sure that there were plenty of times when they had their favorite foods in the house and we ate it. Sometimes we have to sit and think about the things our mothers sacrificed for us, then we can look at situations like these with a bit more understanding. How many groceries have your mom bought you? I'm not trying to come down on you but I just want you to look at the situation from another angle. Maybe eating like you is a way your mom feels is supporting you. Her intentions may not be bad. If you are really having money issues with paying for the food, just sit down and tell her that you are happy to see she wants to eat healthy foods along with you, but you are having difficulty paying for enough of those foods for you both and ask if she could help you buy the foods so that you both can continue to eat those particular foods. I lost my mom to breast cancer in 1993, and I wish I had her here today sneaking my protein shakes. 

Do you live with her or does she live with you? I assume it is her house. Honestly, if it is her house and she is paying all the bills, I believe she has a right to eat anything in her fridge. If you are paying rent and have an agreement as to how the household bills are split up, then I guess you have an issue. You could always get a small refrigerator for your room and say it is off limits or move out.