"I made your Favorite!"
If a family member (or co-worker) makes homemade cookies, brownies... whatever your tempted with - You Are NOT Obligated To Eat it!!!
Many cultures equate food with love (The way to the heart is through the stomach.) so you may feel lots of pressure to eat it. And it is okay to have a bit, if you think it is okay to eat that extra 300+ calories. Just remember to count them!!
Note: If you feel bad about saying no, see if you can pull off the trick we all learned at age 5 with Brussels Sprouts: Secretly transfer it to a napkin and throw it away.