Does fat make you fat? Peta Bee investigates whether we should be swallowing the advice to eat low-fat food

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If there is a dietary rule that has been largely unchallenged for the last 40 years, it is that fat is bad - for the waistline, for the heart and for overall health. Fat will make us fat, has been the message we’ve been fed, and we eat too much of it at our peril. But is this accepted wisdom a big fat lie? Mounting evidence from scientists suggests that the argument against dietary fat is waning, and some experts even suggest we could benefit from eating more of it - not less.

Sweden recently became the first nation to make a U-turn on conventional dietary advice and recommend that people consume more fat and fewer refined carbohydrates for the good of their health. The move followed findings published in the highly reputable New England Journal of Medicine, in which researchers compared the benefits of a conventional low-fat diet with two types of Mediterranean diet, containing significantly higher amounts of fat in the form of olive oil and other types.

Although they expected to uncover major differences, the researchers were not fully prepared for the outcome. In fact, the study had to be aborted because the risk of heart attack and stroke rate among those on the low fat diet was so much higher than that of patients in other groups.

And the low fat backlash is gaining pace. An online debate in the British Medical Journal last month saw one leading cardiologist highlight the fact that the low fat mantra has had little effect on weight problems since it became stock advice in the 1970s. Current UK recommendations are that people should reduce fat intake to 70 grams daily, about one third of total energy intake, and to cut saturated fat intake to 20 grams. But Dr Aseem Malhotra, interventional cardiology specialist registrar at Croydon University Hospital, London, claims such measures have had little effect here or in the US where obesity has ‘rocketed’ despite a big drop in calories consumed from fat.

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So if fat is not making us fat, what is? Emerging evidence suggests that obesity is more closely linked to carbohydrate foods, sugars in particular, than previously thought. “A lot of work has looked at the impact of foods on hormones, especially insulin which is crucial for controlling fat stores in the body,” says Louise Sutton, a dietician at Leeds Metropolitan University. Too many carbs cause a rapid rise in the amount of glucose circulating in the bloodstream, triggering the body to respond by producing more insulin. “When you produce more of this hormone, more fat gets laid down,” Sutton explains. Since a reduced sugar diet limits this effect, it stands to reason that weight loss becomes easier as less fat is likely to be stored.

Add to this the fact that researchers have slammed the food industry for misleading consumers about how foods labelled ‘low fat’ can help with weight loss and the low fat message becomes increasingly hard to swallow. According to research by Consumer Reports published last month, many foods that claim to be 'reduced fat', often make up for it with an excess of sugar. They cited the example of a Reduced Fat Creamy Peanut Butter Spread, which contains four grams of sugar while the full fat version has just three grams, and a Ranch dressing that is 'fat free', but it does have three grams of sugar per serving, which is an incredible three times the amount of sugar found in the full-fat version. “It’s often the case that when you cut fat, you gain sugar,” Sutton says. “Your best bet is to go for unprocessed, unpackaged food.”

Critics of the low-fat hypothesis, including nutritionist and researcher Zoe Harcombe, have always been concerned that simply lowering fat intakes could have a range of other unforeseen effects. “Fat is important in the diet,” Harcombe says. “It is a major component of cell membranes and important for all sorts of processes, from immune responses to hormone levels.”

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Others agree, suggesting that even the previously outlawed saturated fat from animal sources is far from harmful. In her controversial book ‘Fat: An Appreciation of a Misunderstood Ingredient’, Jennifer McLagan, a leading Canadian chef and nutrition expert, not only questions the scientific evidence of the low fat diet, but argues that many of our other health woes have arisen from our attempts in recent years to cut down on butter, lard, suet and other saturated animal fats. “You can’t live without fat,” she says. “It gives us energy and boosts the immune system. Some fats have antimicrobial properties, others lower bad cholesterol. Your brain is made of fat and cholesterol, as are the membranes of your cells.”

There is a growing sense among nutrition scientists that much of the bad rap surrounding saturated fat stems from studies that were carried out in the 1950s, 60s and 70s and that are now known to be flawed. In the recent BMJ debate, Dr Malhotra pointed out that there is no confirmed link between saturated fat intake and risk of cardiovascular disease, with saturated fat actually found to be protective. “There are different forms of saturated fat and many are now known not to be linked to heart disease,” Sutton says. The British Nutrition Foundation (BNF) published a major 77-page report that challenged conventional wisdom about the effects of saturated fat in red meat. In the document, Dr Carrie Ruxton, an independent dietitian, confirmed there is “no conclusive link” between cardiovascular disease and red meat which contains some fatty acids, like stearic acid, that actually protect the heart.

What, then, are we to make of the new fat rules? Sutton says to shop with vigilance, “and avoid foods that are highly processed and carry ‘low fat’ claims as they are likely to be high in sugar and refined carbohydrate” which won’t help with weight issues. And while the new findings are not a green light to gorge on fat, they do suggest we can adjust our preconceptions. Harcombe is an advocate of wholesome, ‘real’ food. And that includes some meat, butter and cheese in moderation. “Nature puts saturated, monounsaturated and polyunsaturated fats in foods in the ‘right’ measure,” she says. “Real food that is not high in sugar is not going to kill us or make us fat.”