Is there a way to stop parents from controlling my diet?

I am a 17 year old boy. I used to be obese weighing 250 lbs. Then I lost weight and got to 165. My parents think I am too thin now and are trying to make me eat more than I wish to and to eat unhealthier foods. I do not see the rationale behind their plan. I do not wish to be overweight ever again and now I am back to 180 after a couple of months. When I refrain from eating fried foods or other foods with high fat content they say they worry about me and now schedule appointments to the doctor. What can I do to get this to stop?