No matter how old you get, your mother may think she should has a say over your life. She probably means well, and of course she’s lived longer than you and has probably learned a thing or two along the way. Don’t reject mom’s advice out of hand just because it comes from her! If you feel she’s overstepping her bounds and need to tell her to back off, though, do so in a polite and assertive manner.
Start by thanking mom for her concern. In most cases, mothers have good intentions, even if they are overbearing, pushy or critical or otherwise drive their children nuts. Give mom the benefit of the doubt: assume she loves you and wants to help, and acknowledge that.
Let her know you’ve got this situation covered. Say something like, “Mom, I appreciate your concern for my health, but I’m following the diet and exercise plan recommended by my doctor.”
Keep the focus on yourself and use “I" statements. That means saying “Mom, I feel frustrated when you tell me what to eat” instead of “Mom, you drive you crazy, always telling me what to eat!”
Stick to the issue at hand. Avoid statements like “You always criticize me for everything!” Resist the impulse to point out that she does the same thing with other people, as well. Don’t bring up something mom did last week or last month or last year that you felt angry about. Focus on the present and talk about the specific thing that’s bothering you. Don’t make vague complaints.
Let her know you don’t want to discuss the issue any further. Say something like “Mom, I don’t want to talk about my weight any longer.” If necessary, be firm with her. Then change the subject. Ask her about a topic she enjoys discussing and steer the conversation away from yourself.
End the conversation if mom refuses to let the issue drop. Say something like “Mom, I can’t talk about this anymore right now. I’ve got to run. I’ll see you later.”