Could eating too much margarine be bad for your critical faculties? The "experts" who so confidently advised us to replace saturated fats, such as butter, with polyunsaturated spreads, people who presumably practise what they preach, have suddenly come over all uncertain and seem to be struggling through a mental fog to reformulate their script.

Last week it fell to a floundering professor, Jeremy Pearson, from the British Heart Foundation to explain why it still adheres to the nutrition establishment's anti-saturated fat doctrine when evidence is stacking up to refute it. After examining 72 academic studies involving more than 600,000 participants, the study, funded by the foundation, found that saturated fat consumption was not associated with coronary disease risk. This assessment echoed a review in 2010 that concluded "there is no convincing evidence that saturated fat causes heart disease".

Neither could the foundation's research team find any evidence for the familiar assertion that trips off the tongue of margarine manufacturers and apostles of government health advice, that eating polyunsaturated fat offers heart protection. In fact, lead researcher Dr Rajiv Chowdhury spoke of the need for an urgent health check on the standard healthy eating script. "These are interesting results that potentially stimulate new lines of scientific inquiry and encourage careful reappraisal of our current nutritional guidelines," he said.

Chowdhury went on to warn that replacing saturated fats with excess carbohydrates – such as white bread, white rice and potatoes – or with refined sugar and salts in processed foods, should be discouraged. Current healthy eating advice is to "base your meals on starchy foods", so if you have been diligently following that dietetic gospel, then the professor's advice is troubling.

Confused? Even borderline frustrated and beginning to run out of patience? So was the BBC presenter tasked with getting clarity from the British Heart Foundation. Yes, Pearson conceded, "there is not enough evidence to be firm about [healthy eating] guidelines", but no, the findings "did not change the advice that eating too much fat is harmful for the heart". Saturated fat reduction, he said, was just one factor we should consider as part of a balanced diet and a healthy lifestyle. Can you hear a drip, drip in the background as officially endorsed diet advice goes into meltdown?

Of course, we have already had a bitter taste of how hopelessly misleading nutritional orthodoxy can be. It wasn't so long ago that we were spoon-fed the unimpeachable "fact" that we should eat no more than two eggs a week because they contained heart-stopping cholesterol, but that gem of nutritional wisdom had to be quietly erased from history when research showing that cholesterol in eggs had almost no effect on blood cholesterol became too glaringly obvious to ignore.

The consequences of this egg restriction nostrum were wholly negative: egg producers went out of business and the population missed out on an affordable, natural, nutrient-packed food as it mounded up its breakfast bowl with industrially processed cereals sold in cardboard boxes. But this damage was certainly less grave than that caused by the guidance to abandon saturated fats such as butter, dripping and lard, and choose instead spreads and highly refined liquid oils.

Despite repeated challenges from health advocacy groups, it wasn't until 2010, when US dietary guidelines were amended, that public health advisers on both sides of the Atlantic acknowledged that the chemical process for hardening polyunsaturated oils in margarines and spreads created artery-clogging trans-fats.

Manufacturers have now reformulated their spreads, hardening them by chemical methods which they assure us are more benign. But throughout the 20th century, as we were breezily encouraged to embrace supposedly heart-healthy spreads, the prescription was killing us. Those who dutifully swallowed the bitter pill, reluctantly replacing delicious butter with dreary marge, have yet to hear the nutrition establishment recanting. Government evangelists of duff diet advice aren't keen on eating humble pie.

But what lesson can we draw from the cautionary tales of eggs and trans fats? We would surely be slow learners if we didn't approach other well-established, oft-repeated, endlessly recycled nuggets of nutritional correctness with a rather jaundiced eye. Let's start with calories. After all, we've been told that counting them is the foundation for dietetic rectitude, but it's beginning to look like a monumental waste of time. Slowly but surely, nutrition researchers are shifting their focus to the concept of "satiety", that is, how well certain foods satisfy our appetites. In this regard, protein and fat are emerging as the two most useful macronutrients. The penny has dropped that starving yourself on a calorie-restricted diet of crackers and crudités isn't any answer to the obesity epidemic.

As protein and fat bask in the glow of their recovering nutritional reputation, carbohydrates – the soft, distended belly of government eating advice – are looking decidedly peaky. Carbs are the largest bulk ingredient featured on the NHS's visual depiction of its recommended diet, the Eat Well Plate. Zoë Harcombe, an independent nutrition expert, has pithily renamed it the Eat Badly Plate – and you can see why. After all, we feed starchy crops to animals to fatten them, so why won't they have the same effect on us? This less favourable perception of carbohydrates is being fed by trials which show that low carb diets are more effective than low fat and low protein diets in maintaining a healthy body weight.

When fat was the nutrition establishment's Wicker Man, the health-wrecking effects of sugar on the nation's health sneaked in under the radar. Stick "low fat" on the label and you can sell people any old rubbish. Low fat religion spawned legions of processed foods, products with ramped up levels of sugar, and equally dubious sweet substitutes, to compensate for the inevitable loss of taste when fat is removed. The anti-saturated fat dogma gave manufacturers the perfect excuse to wean us off real foods that had sustained us for centuries, now portrayed as natural born killers, on to more lucrative, nutrient-light processed products, stiff with additives and cheap fillers.

In line with the contention that foods containing animal fats are harmful, we have also been instructed to restrict our intake of red meat. But crucial facts have been lost in this simplistic red-hazed debate. The weak epidemiological evidence that appears to implicate red meat does not separate well-reared, unprocessed meat from the factory farmed, heavily processed equivalent that contains a cocktail of chemical additives, preservatives and so on. Meanwhile, no government authority has bothered to tell us that lamb, beef and game from free-range, grass-fed animals is a top source of conjugated linoleic acid, the micronutrient that reduces our risk of cancer, obesity and diabetes.

Government diet gurus and health charities have long been engaged on a salt reduction crusade, but what has been missing from this noble effort is the awareness that excessive salt is a problem of processed food. High salt is essential to that larger-than-life processed food taste. Without salt, and a sub-set of assorted chemical flavour enhancers, processed foods would be exposed for what they are: products that have lost their natural savour and nutritional integrity. Salt-free cornflakes, for instance, would be well nigh inedible. No one would want to buy them because they would see that they are a heap of nutritional uselessness. But where is the evidence that salt added as normal seasoning to home cooked food constitutes a health risk?

With salt, as with sugar, the public health establishment is too cowardly to take on the powerful processed food companies and their lobbyists by drawing a distinction between home-prepared food cooked from scratch and industrial convenience food.

The crucial phrase "avoid processed food" appears nowhere in government nutritional guidelines, yet this is the most concise way to sum up in practical terms what is wholesome and healthy to eat. Until this awareness shapes dietetic advice, all government dietary guidance should come with a tobacco-style caution: Following this advice could seriously damage your health.

Joanna Blythman is the author of Bad Food Britain and What to Eat

This article originally appeared on guardian.co.uk



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