Urging people to follow low fat diets and to lower their cholesterol is having "disastrous health consequences", a health charity has warned.
In a damning report that accuses major public health bodies of colluding with the food industry, the National Obesity Forum and the Public Health Collaboration call for a "major overhaul" of current dietary guidelines.
They say the focus on low fat diets is failing to address Britain's obesity crisis, while snacking between meals is making people fat.
Instead, they call for a return to "whole foods" such as meat, fish and dairy, as well as high fat healthy foods including avocados, arguing that "eating fat does not make you fat".
The report - which has caused a huge backlash amongst the scientific community - also argues that saturated fat does not cause heart disease while full fat diary - including milk, yoghurt and cheese - can actually protect the heart.
Processed foods labelled "low fat", "lite", "low cholesterol" or "proven to lower cholesterol" should be avoided at all costs and people with Type 2 diabetes should eat a fat-rich diet rather than one based on carbohydrates.
The report also said sugar should be avoided, people should stop counting calories and the idea that exercise can help you "outrun a bad diet" is a myth.
Instead, a diet low in refined carbohydrates but high in healthy fats is "an effective and safe approach for preventing weight gain and aiding weight loss", and cuts the risk of heart disease.
The report added: "Eating a diet rich in full fat dairy - such as cheese, milk and yoghurt - can actually lower the chance of obesity.
"The most natural and nutritious foods available – meat, fish, eggs, dairy products, nuts, seeds, olive, avocados – all contain saturated fat. The continued demonisation of omnipresent natural fat drives people away from highly nourishing, wholesome and health promoting foods."
The authors of the report also argue that the science of food has also been "corrupted by commercial influences".
Just as big tobacco companies bought the "loyalty of scientists" when a link was made between smoking and lung cancer, the influence of the food industry represents a "significant threat to public health", they argued.
They said the recent Eatwell Guide from Public Health England (PHE) was produced with a large number of people from the food and drink industry.
Professor David Haslam, chairman of the National Obesity Forum, said: "As a clinician, treating patients all day every day, I quickly realised that guidelines from on high, suggesting high carbohydrate, low fat diets were the universal panacea, were deeply flawed.
"Current efforts have failed - the proof being that obesity levels are higher than they have ever been, and show no chance of reducing despite the best efforts of Government and scientists."
Dr Aseem Malhotra, consultant cardiologist and founding member of the Public Health Collaboration, a group of medics, said dietary guidelines promoting low fat foods "is perhaps the biggest mistake in modern medical history resulting in devastating consequences for public health.
"Sadly this unhelpful advice continues to be perpetuated. The current Eatwell guide from Public Health England is in my view more like a metabolic timebomb than a dietary pattern conducive for good health. 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. It's now truly time to bring back the fat."
Professor Iain Broom, from Robert Gordon University in Aberdeen, said: "The continuation of a food policy recommending high carbohydrate, low fat, low calorie intakes as 'healthy eating' is fatally flawed.
"Our populations for almost 40 years, have been subjected to an uncontrolled global experiment that has gone drastically wrong."
But Professor John Wass, the Royal College of Physicians' special adviser on obesity, said there was "good evidence that saturated fat increases cholesterol".
He added: "What is needed is a balanced diet, regular physical activity and a normal healthy weight. To quote selective studies risks misleading the public."
Professor Simon Capewell, from the Faculty of Public Health, said: "We fully support Public Health England's new guidance on a healthy diet. Their advice reflects evidence-based science that we can all trust. It was not influenced by industry.
"By contrast, the report from the National Obesity Forum is not peer reviewed. Furthermore, it does not it indicate who wrote it or how is was funded. That is worrying."
Dr Mike Knapton, associate medical director at the British Heart Foundation (BHF), said: "This report is full of ideas and opinion, however it does not offer the robust and comprehensive review of evidence that would be required for the BHF, as the UK's largest heart research charity, to take it seriously.
"This country's obesity epidemic is not caused by poor dietary guidelines; it is that we are not meeting them."
Dr Alison Tedstone, chief nutritionist at PHE, said: "In the face of all the evidence, calling for people to eat more fat, cut out carbs and ignore calories is irresponsible. Unlike this opinion piece, our independent experts review all the available evidence - often thousands of scientific papers - run full-scale consultations and go to great lengths to ensure no bias."
Professor Naveed Sattar, from the University of Glasgow, said the report's "main headline - simply to eat more fat - is highly contentious and could have adverse public health consequences."