Professor Cheryl Dissanayake, director of the Olga Tennison Autism Research Centre at La Trobe University in Melbourne, says there is no evidence to support Evans' claim in a 2100-word Facebook post that a diet based on current Australian healthy eating guidelines is behind a rise in autism.
Nor is there proof a caveman-style Paleo diet - of which Evans is a fervent proponent - can reverse or cure autism.
"There is absolutely no evidence that diet is the cause of autism," says Prof Dissanayake, who has been studying and researching autism for 30 years. "Throwaway lines can be damaging because parents will try anything to help their children."
The Paleo diet is a low-carbohydrate plan based around meat, eggs, fat and vegetables but bans all types of grain, dairy and legumes.
Evans is ambassador of the Mind Foundation, which suggests autism is reversible through "nutritional medicine", including a change in diet and adding extra supplements.
Current scientific understanding is that autism develops in the womb and is a complex spectrum of disorders caused by multiple factors. About 300 genes are implicated in its development.
While it may not become obvious or be diagnosed until later in early childhood, says Prof Dissanayake, the brains of kids with autism appear different from very early in life.
Some parents do report improvements in children with autism after changing their diet – but this is thought to be because they may be predisposed to stomach problems.
"A number of children with autism do have gastrointestinal issues so diet may improve that and then, because they are no longer in pain, their behaviour may improve," says Prof Dissanayake.
In his post, Evans refers to an increase in rates of autism to one in 50 - autism organisations say the current figure is one in 100.
Some of the increase in prevalence is attributed to better awareness and diagnosis, a broadening of criteria for autism spectrum disorder, epigenetic changes and the rise in the age of parents having babies, meaning there are more likely to be flaws in the DNA of sperm and eggs.
In his post, Evans said, "Why is Australia fast becoming the most obese and unhealthy nations on earth? Is this because we are a nation of self-obsessed, weak-minded people with no self-control? No. Is it because we are a nation that for far too long has been told to steer clear of foods naturally high in fat, which naturally trigger our fullness hormone, and instead told to eat 6 - 8 servings of processed carbohydrate a day, and wonder why we are still hungry after eating 3 cups of rice or 6 slices of bread?
"Why has our rate of autism jumped from 1 in 10000 children in 1974, to 1 in 50 in 2014, where do you think it will be in another 40 years if it is escalating at this rate? This has grown rapidly since the guidelines have been in place!"