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1.
A person who contantly provides their opinions on dieting, exercise, and weight loss in an arrogant and pushy manner. They constantly criticize and suppress' others opinions, no matter how factual they may be.
"That stupid Health Nazi lectured me for an hour on why the Atkins diet doesn't work after I told her I've been on it"
by James1234 August 21, 2005
 
2.
A person who forces his or her healthy lifestyle on others through supporting legal bans of anything unhealthy. As well as being an all around A-hole to anyone who isn't like them. Such people generally have a "holier-than-thou" attitude all around, are only looking for yet another reason to look down on people who don't live up to their perceived view of the world.
Don't be such a health Nazi!
by Salemcripple December 17, 2010
 
3.
A weight-loss "expert", usually weighing excess of 300 pounds, that tries to mentally scar skinny kids by telling them how drugs, McDonald's, and themselves are killing people.
I went to the health nazi yesterday. She told me I will have a heart attack at age 17.
by Lock and Chain June 23, 2004