Urging people to follow low fat diets and lower their cholesterol is having "disastrous health consequences", according to a health charity.
In a growing debate between food health experts, major public health bodies were accused of colluding with the food industry.
The National Obesity Forum and the Public Health Collaboration have now called for a "major overhaul" of current dietary guidelines, claiming that the focus on low fat diets is failing to address Britain's obesity crisis.
In reality, snacking between meals is a major cause of weight gain, the report cites.
In response, the organisations have called for a return to "whole foods" such as meat, fish and dairy, as well as high fat foods including avocados, arguing that "eating fat does not make you fat".
But other experts have labelled the report's advice to eat more fat as "irresponsible".
Full fat dairy can "protect the heart"
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 dairy - 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.
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.
Call for people to eat more fat "irresponsible"
Dr Aseem Malhotra, a founding member of the Public Health Collaboration said dietary guidelines promoting low fat foods "is perhaps the biggest mistake in modern medical history resulting in devastating consequences for public health".
He added: "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".
But 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".