Nutritionist

... "dietician" [as a term] is like "dentist", and "nutritionist" is like "toothiologist". A nutritionist is a person interested in nutrition, but most likely is a person interested in selling their ideas about nutrition. They often give out diet advice which is a mix of sensible suggestions, product placement, and outright woo.

What it isn't
It is important to realise that the term generally does not refer to people who give sensible, common-sense dietary advice. No one could argue with "eat lots of fruits and vegetables, and take it easy on fatty and sugary foods"; however, while well-known nutritionists' advice (paid for of course) may indirectly lead to such eating habits, they often go further and make magical claims about certain foodstuffs which often outright contradict reality.

Meaningless term
"Nutritionist" as a term is meaningless. Notably, it requires very little formal training to become a "nutritionist". Guardian columnist and writer Ben Goldacre once got his cat (which had died a few years previously) registered as a certified member of the American Association of Nutritional Consultants, the same organisation that gave a "qualification" to Dr Gillian McKeith PhD.

There are various permutations such as Nutritional Therapist, Clinical Nutritionist, and Diet Expert, which are all equally meaningless.

Protected terms
Protected terms do exist for people who give out diet advice. You can't go around calling yourself any of these terms unless you're certified by the appropriate agency, in much the same way that you can't call yourself a Medical Doctor (MD) or a police officer without official and recognized authority, training and qualification. Here are some of the more meaningful protected terms:

Dietitian
Dietitians – also called Registered Dietitians – are certified by the Academy of Nutrition and Dietetics (formerly called the American Dietetic Association) in the US. The advice they offer about food, nutrition, and medical diets is backed by science, and there are standards in place for the things they advise.

Recently, and somewhat confusingly, the Academy of Nutrition and Dietetics has added the protected term "Registered Dietitian Nutritionist" (RDN) to the short list of titles it grants.

In the UK, dietitian is the only protected title in the field of nutrition and is regulated by the Health & Care Professions Council. The Association for Nutrition is a reputable body which controls the UK Voluntary Register of Nutritionists, listing Associate Nutritionists and Registered Nutritionists who have relevant training and experience, but these are not (yet) protected titles. In the UK, only registered dietitians can work in clinical contexts with ill people, while registered nutritionists largely focus on preventing disease in healthy people (or work under dietitians' direction).

Physician Nutrition Specialist&reg;
The title "Physician Nutrition Specialist" (PNS) is a registered service mark of the American Board of Physician Nutrition Specialists (ABPNS) reserved exclusively for physicians who specialize in nutrition. Extra course work and supervised practice is required to obtain the certification. Such physicians generally do not hawk their nutrition advice directly to patients, however; they tend to serve as nutrition coordinators at hospitals or clinics, work with specialized cases that require more knowledge than what a registered dietician might have at hand, or work on studies, trying to better understand the body's needs under various physical conditions, illnesses, or stresses.

Certified Nutrition SpecialistSM
The title "Certified Nutrition Specialist" (CNS) is a service mark belonging to the Certification Board for Nutritional Specialists. Until 2010, this organization had a pretty decent reputation for standards: It offered the CNS credential only to professionals with an accredited master's or doctoral degree who had clinical experience and passed an examination. However, since that time they've removed their clinical experience requirement and added "Naturopath" to the degrees they'll accept for their CNS credential. They still require the applicant to pass an exam, but their certification requirements are less substantial than those of ABPNS.

Some questionable credentials
The following are technically "protected terms," in the sense that some organization has registered them as service marks. However, that doesn't mean said organizations have a certification program any more complex than "click on the 'print certificate' button":


 * Certified Clinical Nutritionist (CCN), given out by the Clinical Nutrition Certification Board (CNCB) of the International and American Association of Clinical Nutritionists
 * Certified Nutritionist (CN), given out by American Health Science University
 * Certified Nutritional Consultant (CNC), given out by the American Association of Nutritional Consultants

Possible dangers
One of the things about "nutritionists" is that they often mix in good advice (which doesn't change, and is free) with quite bad advice. This bad advice is usually their own specific piece of woo that they like to trot out to make money – to make it seem like they're doing some actual original thinking or possibly even research. At best, this wrong advice is harmless and causes people to just waste money buying exotic fruit for its purported anti-cancer properties. At worst it can be risky, or outright dangerous. Nutritionists may suggest cutting out entire food groups which can seriously and adversely affect someone's mood or they can suggest procedures such as colonic cleansing/irrigation that can be quite dangerous and somewhat uncomfortable.

In Portugal
Portugal, curiously, is one of the countries which recognises both nutritionists and dietitians as legitimate professions.

In fact, they are both regulated by the same body, the Ordem dos Nutricionistas ("Nutritionists' Order"), which plans to abolish distinctions between both by abolishing "dietitians" and bring them both under the "nutritionist" title.