Dear DanceWithin, sorry you are feeling shamed by your step-mom.
Is she one of those who believes there is no such thing as "too thin"? What is the objective truth here?

My heart goes to you because I hear your suffering. On the other hand it would be extremely irrsponsible to leave the army of obese american children alone because to suggest they eat less and exercise more may hurt their feelings. They do need help to deal with their feelings, for sure. They need love and compassion, not shaming, but they also need help to get healthy. They don't need to die of coronoary disease at 20 years of age, or lose their limbs to diabetes.

Are you one of those young ones? What is the truth of the situation? Is your step-mom a nut case, or is she exposing something you have been hiding from yourself, and would prefer never to face?

You don't need to tell me, but you, you have to know the truth for yourself. If you are at healthy weight, if your family doctor does not worry, then accept it. Grab it and hold onto it. Then use your step-mom's push to stabilize your self-image. Push back: "No step-mom. I am not fat. I am not out of control. I have a healthy lifestyle. I know I can eat this or that." You may not be able to change her mind or her behavior, and you may not even be able to SAY this to her too often, but if you do it in your own thoughts this inner resistance can help you regain a balanced and accepting view of yourself. Sometimes we need someone's unjust criticism to stop our own self-scathing thoughts.

But, if you have been fooling yourself and there in fact IS a problem, then you need to stop hiding from it. If your step mom lacks in empathy, perhaps you can get her satisified and off your back, by finding and joining some local group that helps youngsters develop healthy lifestyles with understanding and compassion.