The British Dietetic Association [BDA] has released a list of detailing what it describes as 'celebrity diets to avoid'.
Topping the list is raw veganism - a lifestyle which involves not consuming any food that is refined, chemically processed, tinned, or heated above 48C.
According to raw foodists, heating food destroys natural enzymes. They claim this means the body has to work harder to digest it.
But the BDA believes a raw vegan diet can actually harm you if followed longterm.
Sian Porter from the BDA said: "If something sounds too good to be true, it probably is."
According to the organization: "The human body can digest and be nourished by both raw and cooked foods so there's no reason to believe raw is inherently better.
"Raw food can be time-consuming to prepare, hard to find when eating out, and is not suitable for certain groups like children or pregnant women so family meals could be a challenge and you could miss hot food."
Also, heat can enhance the nutrients in some foods - like tomatoes.
In addition, Porter spoke about veganism.
She said: "People think that vegan is shorthand for healthy, but it requires careful planning to make sure you don't miss out on important nutrients
"A carefully planned vegan diet with the necessary supplements like vitamin B12 and vitamin D can be healthy, but it is not a guarantee of losing weight.
"A vegan cake is still a cake, [and] vegan foods often contain the same calories as non-vegan foods.
The BDA supports plant-based diets in principle: it has previously said a well-planned vegan diet can 'support healthy living in people of all ages'.
Earlier this year, the organization renewed its memorandum of understanding with The Vegan Society to state that a balanced vegan diet can be enjoyed by children and adults, including during pregnancy and breastfeeding, if the nutritional intake is well-planned.
Andy Burman, BDA Chief Executive, said: "We are pleased to have renewed this memorandum with The Vegan Society, so that we can continue our positive working relationship.
"It is important that people choosing to eat a vegan diet can get the right advice from the right sources, and know to visit a dietitian for advice on tailoring their nutrition and diet. The BDA will continue to work with The Vegan Society to promote this message."