A title claimed by many have-been hollywood types, wannabe doctors, and your regular garden variety hollywood "fitness" guru. There is no legal definition therefore allowing any charlatan to use it. Normally used to imply that the person has some knowledge on the science of biochemical reactions which occur in energy expenditure and metabolism as an organism converts food into usable energy-but notice they never use R.D. after their name, as they would be prosecuted for impersonating real scientists.
"No, I'm a Registered Dietitian"
"what does that mean?"
"I have a degree in biochem and clinical training in the field in addition I don't wear spandex on TV"