I was wrong - we should be feasting on FAT, says The Fast Diet author DR MICHAEL MOSLEY

Dr Mosley used to believe all saturated fats were bad for us

So he ditched beef, full fat milk and butter

They were thought to cause weight gain and heart attacks

But new studies have revealed this isn't the case

There's a stronger link between sugar consumption and heart disease

Eggs are a prime example of how we got it wrong on fats

People were advised to eat just one a week in the Eighties

But now regular consumption is encouraged as they are high in protein

Milk, cheese, butter, cream - in fact all saturated fats - are bad for you. Or so I believed ever since my days as a medical student nearly 30 years ago.

During that time I assured friends and family that saturated fat would clog their arteries as surely as lard down a drain. So, too, would it make them pile on the pounds.

Recently, however, I have been forced to do a U-turn. It is time to apologise for all that useless advice I've been dishing out about fat.

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Go ahead: New studies have found that saturated fats, found in butter, don't cause heart disease

New studies have not only failed to find a convincing link between saturated fat and heart disease, they have shattered other long-held anti-fat beliefs, too.

We now have compelling evidence that low-fat diets rarely work and that eating the right kind of fat is not only good for your heart but may also help you lose weight.

So why the sudden change? And what is making us fat?

The roots of our current confusion lie in a paper by an American scientist called Ancel Keys in 1953. It covered the increasingly common problem of clogged arteries.

Keys included a simple graph comparing fat consumption and deaths from heart disease in men from six different countries. Americans, who ate a lot of fat, were far more likely to have a heart attack than the Japanese, who ate little fat. Case solved. Or was it?

Other scientists began wondering why Keys chose to focus on just six countries when he had access to data for 22. If places like France and Germany were included the link between heart disease and fat consumption became much weaker. These were, after all, countries with high fat consumption, but relatively modest rates of heart disease.

Change of diet: Dr Mosley now eats more oily fish, Greek yoghurt and eggs

In fact, as a renowned British scientist called John Yudkin pointed out, there was actually a much stronger link between sugar consumption and heart disease.

Professor Yudkin argued that sugar was behind the rise in heart disease ravaging the West. He also pointed to another dangerous trend emerging in Fifties Britain: the close relationship between the number of televisions being bought and fatal heart attacks.

Buying a TV in the Fifties was a sign that you were affluent, but it also meant you'd spend a lot more time sitting down. This research was among the first to highlight the dangers of a sedentary lifestyle.

But Yudkin's warnings about sugar were denounced by a fellow scientist as 'nothing more than scientific fraud'. He was, as one of his colleagues colourfully put it, 'thrown under a bus'.

Meanwhile, the war on fat gradually gained momentum, to the extent that by the time I reached medical school in the Eighties, there was no mention of Yudkin's findings.

People were cutting down on dairy products and switching to sugary carbohydrates and vegetable oils.

This, it turns out, was a mistake. To turn vegetable oil into margarine, manufacturers used a process called hydrogenation (gas pumped through oil at high temperature), which produces trans fats. These are the Darth Vader of the fat world: good fats turned bad.

Unlike saturated fats, there is clear evidence that trans fats damage your heart. They were found in most shop-bought biscuits and cakes until they were removed in 2007.

Which was a bit late in the day for me. As a student I took the advice that saturated fats - not hydrogenated fats - were the enemy very seriously. I was slim and I did a lot of exercise, but I also ate butter and burgers. With a family history of heart disease, strokes and a father who'd just been diagnosed diabetic, I told myself it was time to act. I persuaded my father to go on a low-fat diet. He lost a little weight, but soon gave up.

Low-fat diets rarely succeed because people won't stick to them - they get too hungry ...

Reluctantly, I said goodbye to beef, switched to skimmed milk and avoided yoghurt with any hint of fat. It made for a much duller diet, but at least I was healthier. Or was I? Well, no. I kept this up for the next few decades - and the results? I put on over two stone, despite regular exercise. My cholesterol soared past the healthy range and two years ago I discovered I was borderline diabetic.

While I didn't look fat, I'd piled on the pounds in the worst place possible: tucked away in my abdomen, coating internal organs.

My response was to exercise more but it had little effect. I was eating less fat, but compensating with starchy pasta and potatoes. What I hadn't appreciated is the way these foods act on your body. A boiled potato will push your blood glucose up almost as fast as a tablespoon of sugar, since it is rapidly digested.

Ironically, we now know that if you eat that potato with butter, the fat will slow absorption and the blood sugar peak will be less extreme.

Rapid spikes in glucose force your pancreas to pump out insulin, which drives it back down, but can leave you hungry again a few hours later.

Carbohydrates are also less satiating than fat or protein. So you eat more and the weight creeps up.

Back on the menu: Eggs are now celebrated for their protein content while adding butter to potatoes can prevent a spike in blood sugar levels

Eggs are a prime example of how we got it wrong on fats. In the Eighties we were told they were cholesterol time bombs and were warned to eat no more than one a week. So I gave up eggs and tried to persuade my family to do likewise. What a mistake that was.

A study in the British Medical Journal in 2013 concluded: 'Higher consumption of eggs is not associated with increased risk of coronary heart disease or stroke.'

So eggs are back, and the protein means you'll feel fuller for longer.

So, is fat really fattening? It contains far more calories than carbohydrates or protein, and the easiest way to lose weight is obviously to cut it out. Yet low-fat diets rarely succeed because people won't stick to them - they get too hungry.

In the Fifties, Oxford professor Hugh Sinclair argued that we should be eating more fat, not less. He'd been to Canada and was intrigued to see that the Inuit had a high-fat diet yet low rates of heart disease. Was something in oily fish protecting them? He decided to find out by eating nothing but seal, oily fish, molluscs and crustaceans.

While making Medical Mavericks for the BBC, I decided to repeat his experiment. Thankfully, the seal we tried to import was impounded by customs, so I ate a diet mainly of fish. Sinclair stuck to his for three months, I managed a month.

While on his diet, Sinclair timed how long it took for his blood to clot by cutting himself once a week. It increased from three minutes to a terrifying 50. For me, it doubled.

Even though he'd taken it to dangerous extremes, Sinclair showed that fish oils reduce the stickiness of platelets in your blood and thus the risk of clot formation, which can lead to a heart attack or stroke.

A more recent example of how wrong we were about low-fat diets was the Look Ahead trial, which began in 2001. Over 5,000 overweight diabetics were put on a low-fat diet and encouraged to exercise.

SLIM PICKINGS The NHS says the average man should eat no more than 30g of saturated fat a day, and the average woman no more than 20g

After almost ten years the study was stopped. Those on the low-fat diet had lost little more than a control group, and there was no significant change in heart attacks or strokes.

A study last year put a further nail in the low-fat diet's coffin. A group of 7,500 men and women were randomly allocated a low-fat diet or a much higher-fat Mediterranean one. On this diet, along with fruit, vegetables, meat and fish, they were to eat oily nuts, olive oil and have a glass of wine with their meal.

Again, the trial was stopped early. But this time it was because those on the Mediterranean diet were doing so much better than those on the low-fat diet, with a 30 per cent drop in heart attacks and strokes.

So some fats are good for us, but surely saturated fats are bad?

Even this has been undermined by a study funded by the British Heart Foundation and published this year. Based on 72 previous studies the researchers found no evidence that saturated fats cause heart disease.

This isn't a licence to pour cream down your throat, because even if saturated fats don't directly harm the heart, too many calories will.

Personally, I try not to have biscuits and cakes in our house as I know I can't resist them. But I have gone back to butter, Greek yoghurt and semi-skimmed milk. I eat more oily fish, eggs and the odd burger.

After all those years believing them the enemy, saturated fats taste more delicious than ever.