No longer.

These days no food restriction regime is worth its salt unless it belongs to a movement, with the potential to change the world as well as your inner gut health.

Each tribe has its warriors and (disputed) by-laws.

At one end is the fruitarian, described in the 1999 film Notting Hill: "We believe that fruits and vegetables have feelings so we think cooking is cruel. We only eat things that have actually fallen off a tree or bush - that are, in fact, already dead."

Thereafter marches a parade of food tribes, from pescetarians (vegetables and fish only) to vegetarians (no meat, animal products OK), and from freegans (only food retrieved from dumpsters) to vegans (no meat or animal products).

Doctors and mainstream nutritionists are suspect about any strict diet that has the ultimate aim of weight loss.

Medical doctor Rick Kausman says the research shows two-thirds of people that go on weight loss diets end up heavier than before they started. He is also concerned that a broader obsession with weight loss in society encourages discrimination against certain body types.

"In the early days people were pretty much traditionally dieting, cutting calories, weighing and measuring their food and there were a few variations on that, but it does seem particularly in the last few years or so marketers have latched on to these as a terrific idea [to promote] something new on a regular basis."

Dietitian Joanna McMillan says the phenomenon is aided by the enthusiasm that can be generated on social media.

"I feel like people are picking their tribe, joining it, and perhaps not even understanding what it is. Everyone's joining a community and it's all a bit silly."

Here are some of the big ones.

Paleo:

The poor old paleo movement has not had much good press of late, with celebrity chef Pete Evans' new cookbook pulped by publishers amid concerns that the recipes would kill babies.

But it has had an avid following since the 2002 publication of Loren Cordain's book The Paleo Diet, which promotes the food that was consumed by our paleolithic ancestors.

Meat, fish, fruit, vegetables, eggs, nuts and seeds are good. Grains, legumes, dairy, processed food, refined sugar and salt are bad.

But accredited practising dietitian Julie Viney warns that its followers can miss out on essential nutrients.

"Helping people choose more natural food is not a bad thing but it can be taken to the extreme," she says.

"A lot of the tribes or approaches start off with a real element of truth … and the original germ of an idea gets completely exploited. I see paleo now as a marketing tool."

Anti-sugar:

Life is more exciting in the tribe when there is an enemy.

Popularised by Sarah Wilson, whose bestselling cookbook I Quit Sugar sold more than 96,000 copies last year, the anti-sugar movement claims that eliminating sugar from the diet is good for your health, skin and energy levels.

Melbourne nutritionist Arabella Forge says refined sugar contains no essential nutrients and just adds kilojoules to the diet, but warns against versions of the diet that recommend cutting out all fruit and vegetables and grains that contain sugar.

"There is no evidence to support avoiding these foods because of their natural sugar content."

Vegan:

Vegans abstain from meat and any animal product.

It's one of the mysteries of the nutrition world that people who follow such a gentle food philosophy have gained a reputation as militant. Or maybe not. "How can you spot a vegan?" goes the joke. "Oh, they'll tell you."

The advantages of the diet is that it leads to a high intake of fruit and vegetables.

But Forge recommends that people only embark on the diet under the guidance of a health professional.

"Nutrient deficiencies on vegan diets can be common, in particular the nutrients obtained from animal products such as iron, B vitamins, zinc and calcium."

It is particularly risky for children, who have different nutritional requirements and need amino acids in their diet.

Gluten-free:

This is one food tribe which most of its members would prefer not to belong to.

Celiac disease is an autoimmune condition that affects the small intestine. Those who have been diagnosed by a professional need to avoid gluten, a protein found in wheat and related grains like barley and rye, because it stops them absorbing nutrients.

These people can easily be spotted at restaurants that serve banquet food, dolefully spooning from their personal serving bowls, while the rest of their party tucks into noodles and rice.

Viney says she often sees clients who are gluten-free by choice because they believe that they will lose weight.

"But there's no research to prove that at all," she says.

Flexitarian:

Cheating vegetarians to some, meat eaters with a conscience to others.

The diet is mainly vegetarian, with occasional meat, which also makes it difficult to break the rules.

Forge describes it as a "one size fits all approach". The imperative is moral and environmental, rather than nutritional.

It picked up speed in Britain after 2009, when Paul, Mary and Stella McCartney initiated the Meat Free Mondays climate change initiative.

Viney classifies it as a philosophy of living, rather than a diet per se, with no nutritional consequences.