Advice to eat more fat is irresponsible and potentially deadly, Public Health England's chief nutritionist has said.
Dr Alison Tedstone was responding to a report by the National Obesity Forum, which had suggested eating fat could help cut obesity and type 2 diabetes.
The charity had said promoting low-fat food has had "disastrous health consequences" and should be reversed.
Other experts have also criticised the recommendation to eat more fat, saying the report cherry-picked evidence.
Dr Aseem Malhotra, a senior adviser to the National Obesity Forum, said: "The change in dietary advice to promote low fat foods is perhaps the biggest mistake in modern medical history.
"We must urgently change the message to the public to reverse obesity and type 2 diabetes. Eat fat to get slim, don't fear fat, fat is your friend."
Dr Tedstone responded by saying: "In the face of all the evidence, calling for people to eat more fat, cut out carbs and ignore calories is irresponsible."
She said thousands of scientific studies were considered as part of the official guidance adopted throughout the UK, whereas the National Obesity Forum quoted just 43 studies, some of which were comment pieces.
She added: "It's a risk to the nation's health when potentially influential voices suggest people should eat a high fat diet, especially saturated fat. Too much saturated fat in the diet increases the risk of raised cholesterol, a route to heart disease and possible death."
The report argues:
Eating fat does not make you fat
Saturated fat does not cause heart disease and full-fat dairy is probably protective
Processed foods labelled "low fat", "lite", "low cholesterol" or "proven to lower cholesterol" should be avoided
Starchy and refined carbohydrates should be limited to prevent and reverse type 2 diabetes
Optimum sugar consumption for health is zero
Industrial vegetable oils should be avoided
People should stop counting calories
You cannot outrun a bad diet
Snacking will make you fat
Evidence-based nutrition should be incorporated into education curricula for all healthcare professionals
The report also said humans had evolved to be a "healthy well-nourished species with a long life expectancy", but this had gone wrong in the past 30 years.
It said there was too much focus on calories when "it is highly irrelevant how many calories a portion of food on a plate contains" and it was "untrue" that excessive calories caused obesity.
Naveed Sattar, a professor of metabolic medicine at the University of Glasgow, said the report was "good, bad and ugly".
He backed calls to cut snacking, but said eating more fat as a cure for obesity and type 2 diabetes was "not warranted" by the evidence and would have "adverse" consequences.
He said the authors had been selective in their choice of evidence and had ignored "an abundant literature which goes against their conclusions".
The government's obesity adviser Prof Susan Jebb said the "current dietary advice is based on the best evidence we have".
She said the debate should be widened from a focus on fat. "We're eating too many calories — if we want to tackle obesity people do need to eat fewer calories [and] that means less fat and less sugar."