Colorado has no law which limits the practice of nutrition, but does limit who may call themselves a dietitian.
No person may, orally or in writing, claim to be a “dietitian”, “dietician”, “certified dietitian”, or “certified dietician” or uses the abbreviation “C.D.” or “D.” to indicate that such person is a dietitian, unless such person has met certain educational and credentialing requirements under the law.
Source: Colorado Code 6-1-707(b)