A documentary by celebrity chef Pete Evans — which depicts a high-fat, low-carb diet as a treatment for autism, asthma and even cancer — is back in the spotlight this month after Netflix was urged to pull the film from its streaming service.

The Magic Pill, a 2017 documentary narrated and produced by Evans, advocates for "the paleo way" of living. It follows people suffering different chronic illnesses who adopt a high-fat, low-carb diet and are shown to drastically reduce their symptoms.

In one case study, a woman claims her breast cancer tumour shrank as a result of transforming her diet. In another, a four-year-old girl with autism who is non-verbal is able to speak for the first time after avoiding processed foods and carbohydrates for 10 weeks.

But earlier this month, the Australian Medical Association called for the film to be removed, saying "the risk of misinformation is too great".

So, what is it about the documentary that has public health experts so concerned? And what is the evidence for adopting a high-fat, low-carb "ketogenic" diet to alleviate a host of health conditions?

I watched The Magic Pill and took some of its claims to health, nutrition, and medical experts.

Paleo is the way … or is it?

The film begins in north-east Arnhem Land, where it explains that the plague of chronic disease and poor health affecting the Yolngu people (and other Indigenous communities in Australia) is a result of a modern, western-style diet.

We hear from "nutritional therapist" Nora Gedgaudas, who works closely with Evans on his paleo programs and products, who says the introduction of agriculture about 10,000 years ago has led us to "suddenly eating a carbohydrate-based diet" which "has just gone down a slippery slope".

This is the philosophy behind the paleo diet: the idea that our bodies have not evolved to cope with our modern diet, so we must eat the way our hunter-gatherer paleolithic ancestors ate more than 10,000 years ago.

This means focusing on fresh vegetables, fruit, lean meat and healthy fats, and excluding highly processed foods — and more controversially — legumes, dairy and grain products.

But Amanda Lee, a nutrition and public health expert from The Sax Institute, says it is "nonsense" to suggest traditional diets were low in carbohydrates. She says there is a mismatch between "the rhetoric of a restrictive paleo diet" and "what people ate traditionally".

She adds that although the connection between health and diet is indisputable, there are many complex factors that contribute to health outcomes in Indigenous communities.

"There are contemporary socio-economic challenges in Aboriginal communities that make it very hard for people to eat a healthy diet," she says.

Manny Noakes, research director of the Nutrition and Health program at CSIRO, says although there are some positive elements to the paleo diet, the evolutionary argument" is not "a particularly valid one".

"To say that our bodies haven't adapted over time shows there is a lack of understanding of how our bodies do adapt — not only through our genes, but what we call the epigenome, which is very responsive to our environment," she says.

Grains aren't the enemy — junk food is

According to Evans, "there is nothing you can get in a grain that you can't get anywhere else".

But Professor Lee says that's not true.

"There's something protective about having wholegrains in our diet that reduces our risk of cardiovascular disease, that can help us control our weight gain, and that can help control diabetes," she says.

She says the paleo diet's exclusion of key food groups — namely grains, legumes, and dairy — is not supported by modern nutrition science.

"The most important thing is that we eat a variety of healthy foods, and that we have adequate intake of protective foods," she says.

"The problem we have at the moment is that most of the foods that are available, affordable, accessible and advertised in our food environment are not those healthy foods — it's the junk foods."

As for embracing "healthy fats" — a key focus of the paleo diet — Professor Lee says Australian Dietary Guidelines already support a moderate intake of good fats.

"If you eat all the healthy fats and oils that are recommended — olive oils, seeds and nuts, oily fish, avocado — there's plenty of good fat sources," she says.

However, Professor Noakes says unlike in the film, it isn't necessary to mainline animal fats (such as butter and lard), nor are vegetable oils "toxic" (as is claimed in the film).

It's also worth noting that the use of coconut oil, which has lucrative reputation as a "superfood" and is promoted widely through the film, has previously been discouraged because of its high saturated fat content.

High-fat 'keto' diets are a drastic measure

The documentary sees a series of people with varying medical conditions, including asthma, diabetes and autism, adopt an extremely low-carb, high-fat "ketogenic diet" in a bid to alleviate or entirely eradicate medical conditions.

The idea behind the ketogenic diet is to change the way your body turns food into energy, by replacing the body's typical go-to energy source, carbohydrates — which get converted to blood glucose during digestion and metabolism — with fats.

By drastically lowering your carbohydrate intake, your body is pushed into a metabolic state known as ketosis, whereby ketone bodies (or ketones) are produced by the liver from fat, and used as fuel source to produce energy for the body.

In the film, neurologist David Perlmutter says "being in a mild state of ketosis is really the place to be".

But Professor Noakes says the ketogenic diet should only be used to treat specific medical conditions, and should always be done under the supervision of a health professional.

"It is very, very limited in what you can eat, and it's not impossible to become malnourished from such an eating plan if it's not done properly."

Diet is protective but not a magic pill

So, what about the documentary's depiction of the ketogenic diet as a treatment for diabetes, autism and even cancer?

"In the scientific literature, the ketogenic diet is used therapeutically in some conditions, but a very limited number," Professor Noakes says.

The diet was first developed as a treatment for epilepsy in the 1920s, and has been shown to be effective in reducing the frequency and severity of seizures in patients with severe epilepsy.

As for whether it can be used in the treatment of autism spectrum disorder, Professor Noakes says the question remains "speculative".

"It's not clear precisely whether there is or is not a benefit there," she says.

"There is some encouraging laboratory data on ketogenic diets and autism, but it's really only one clinical study and it's not enough to show that there is universal benefit."

When it comes to diabetes, Professor Noakes says a healthy diet can make "profound differences" to the condition, as it can with "a lot of illnesses".

"A low-carb diet can be incredibly effective with diabetes. But it doesn't have to be a ketogenic diet," she says.

"You could equally go on a healthy eating plan, lose weight, and that would be incredibly powerful for type 2 diabetes as well."

Cutting sugar won't 'starve' your cancer

Perhaps more controversial is the film's depiction of a woman named Sara, who says her breast cancer tumour "started shrinking" after she began eating a strict ketogenic diet.

Sara claims cancer cells need sugar and refined carbohydrates to proliferate: "If you don't want them to reproduce, stop feeding them," she says.

But Darren Saunders, a cancer biologist and associate professor of medicine at the University of New South Wales, says the way the film presents Sara's case study is "kind of devious".

"We can't argue with that woman's story — we have to take on face value that fact that she says this is what happened.

"But there's no evidence that I'm aware of that just having a ketogenic diet on its own will cure any form of cancer."

Dr Saunders says the notion that tumour cells rely on sugar is overly simplistic and not entirely correct.

"Some tumour cells rely on sugar, some tumour cells rely on fat, some rely on amino acids, and they're very adaptable in the way they use their metabolic fuel," he says.

"This simplistic notion that you can just stop putting sugar into somebody and that it will starve their cancer is completely facile and wrong."

Dr Saunders says there is research currently underway into the use of ketogenic diets as an additional (or adjuvant) therapy in the treatment of cancer. But he says the documentary doesn't make this distinction clear.

"The takeaway message that most people get from watching this movie is that you can use diet to cure your cancer, and you don't need to have chemotherapy and other things," he says.

"The truth is you can modify your risk of getting cancer by modifying your diet, but that's not the same thing as trying to treat cancer by modifying your diet."

Dr Saunders adds that Evans is "putting a lot of very questionable information out there".

Evans at loggerheads with AMA — again

AMA president Tony Bartone told Fairfax Media that Netflix "should do the responsible thing" by not screening the documentary.

"All forms of media have to take a responsible attitude when trying to spread a message of wellness," he said.

Dr Bartone isn't the first high-profile member of the medical community calling for the documentary to be scrapped.

Last year when the film was released, the AMA's then-president Michael Gannon tweeted that The Magic Pill should be nominated for an award for the film "least likely to contribute to public health".

Evans, who is no stranger to controversy, hit back at the AMA, suggesting the peak medical body had an interest in keeping Australians unhealthy.

"Does the head of the AMA believe that eating vegetables and fruit with a side of well sourced meat/seafood/eggs to be a dangerous way of life? Perhaps the bigger question to ask would be, 'Is the head of the AMA fearful of people in Australia becoming healthy? What would this mean to their industry?'"

In a statement to the ABC, Evans added:

"We say in the film to always consult with your health professional."

The film also begins with a disclaimer that tells viewers, apart from food, "exercise, sleep, sunlight, meditation and other lifestyle factors" also play an important role in achieving better health.

"While we emphasise the science behind dietary advice, the personal stories in this film are anecdotal, and we make no claims that these experiences are typical," it says.

The disclaimer is immediately followed by a quote attributed to ancient Greek physician Hippocrates that "nature is the healer of disease".