Paul Lewandowski​ does not mince his words when it comes to the myths we swallow alongside our kale and blueberry smoothies.

But while the Associate Professor at Deakin University's School of Medicine urges caution when it comes to fad foods, his words come at a time when more of us than ever are approaching foods as a way to treat serious illness and disease.

"There used to be a fixation on diet for weight loss, but there is a subtle shift in diet being considered for other conditions instead of obesity," says the expert in nutrition in the treatment of disease, who in part credits TV cooking shows with putting food at front of mind for people. It is, however, the internet that has given a platform to a cacophony of fantastical claims made by some of the squeakiest wheels in the food-as-medicine camp.

Step forward, Belle Gibson, an Australian who wrote a book about curing her brain cancer by shunning conventional medicine and opting for a dairy, gluten, and caffeine free diet. She was later exposed as a compulsive liar with no illness besides. And Vani Hari, aka the Food Babe, implores her massive following to shun "toxic foods" on the back of claims like this: "The enzymes released from kale go in to your liver and trigger cancer fighting chemicals that literally dissolve unhealthy cells throughout your body."

Even before she was outed as a pathological liar, Gibson's claims were so spurious that Dr Joanna McMillan, dietitian and registered nutritionist, calls them "frightening".

"Nutrition has a very key role in preventive medicine," she says. "Diet is intricately involved in the development of these diseases but that's a whole different thing to using food as a cure to treat disease.

"It's dangerous if people start to think that food is more powerful than it really is."

This weekend's Mindd International Forum 2015 at The Australian Turf Club takes on chronic illnesses through a gamut of nutritional and natural therapies, including theorising that diet can help treat autism. Its marketing material features mothers whose autistic children have been transformed by integrative healthcare, but scientific studies have so far failed to prove some of the claims.

"The problem with the Mindd group is that it is a mess of sensible ideas, along with ideas that are exaggerated, some that are distorted, and some that are just plain nonsense," says Professor Ian Musgrave, a toxicologist at Adelaide University.

The same can disappointingly be said of diet-based treatments for autism. Dr Andrew Whitehouse, head of autism research at Telethon Kids Institute, says there has long been a strong link between gut problems and autism, but that there is not a single study that supports gluten-free and/or casein-free diets in the treatment of autism.

"Unless you have hard evidence backing up what you are selling, you are doing damage by taking up the emotional and financial resources of people whose resources are already stretched," he says of "well-meaning" diet-related autism claims and individual anecdotes that are not proven at group level.

Studying foods is a hugely complex area of research. Comparing component parts and isolated nutrients is simply not the same as analysing a varied, individual diet. Foods that show a causative relationship with certain illnesses, such as Coeliac disease or extreme allergies, are very limited and most research focuses on the associative links between foods and disease, such as studies that show the effects of omega-3 fats on inflammation.

Especially positive in this regard are the leaps that have been made by the likes of the CSIRO, which has identified a set of foods which have very real, and potentially radical, implications for combating disease on a vast scale. Step forward the hungry microbiome and the millions upon millions of bacteria which call our guts home.

"We used to think that gut microbiota were bad for you. People used to clean themselves out," says David Topping, a chief research scientist at CSIRO Food and Nutrition Flagship. "But now, we've realised that the bacterial population is integral to health."

Thanks to our quest for cleaner, fresher and processed foods, we are no longer eating enough of the types of fibre and starch that feed the bacteria whose product, short chain fatty acids, have been shown in humans to have a positive effect on colo-rectal cancer and in animal studies, diminished risk of autoimmune diseases, arthritis, asthma and even Parkinson's and Alzheimer's. There are also implications for obesity.

"These bacteria can help you prevent and control serious disease," says Topping, who points to evidence linking the gut to Alzheimer's and the the gut-brain connection. "The claims are not fanciful, they need to be substantiated but they are not outlandish."

These fermentable fibres, high in the "resistant starch" that feeds the microbiome, are found in legumes, chickpeas, beans, brown rice, wholegrain bread, cooked and cooled potatoes and unripe bananas. The CSIRO has developed strains of barley and maize in an attempt to address the amount of resistant starch that the population needs – over a million tonnes a year for Australians alone.

For the most part, though, the message is unchanged when it comes to eating foods to combat illness.

"The true diet is the unsexy diet," says accredited practicing dietitian Kate Di Prima. "Eat a variety of foods, limit sugars, limit processed, refined foods, cook at home and sit down and enjoy food."

The Mindd Foundation could not be reached for comment.