Eating too much fat is bad for us. This is logical. Fatty food intake causes a build-up of fat in our arteries, which clog up and give us heart attacks; and the same fat also builds up in our body and makes us fat. Cholesterol is traditionally seen as the villain here. It was the first measure of fat in the blood that could be assessed by doctors, so it has become synonymous with the risk of heart disease. This was an easy and clear story that doctors have told their patients since the 1980s – and they still are. Unfortunately, it is just a story: cholesterol has been wrongly framed as the arch-criminal it never was. Some fats in our diet are not only good for us, but essential.
Fat makes up around a third of our body weight and we can’t survive without it. But the word and its use are very confusing. As well as being another common word for ‘obese’ or ‘wide’, and for the contents of a beer belly, it has a more scientific use. It is a term applied to any substance made of fatty acids, which take many different forms, most of which are essential building blocks for our cells and our life. The groups of fatty acids that together form fat are called lipids, a more precise term, and they are what I’m referring to when I use the term ‘fat’ in relation to diet or the blood. Fats are not soluble in water or blood; they are mainly produced and packaged in the liver, and are transported around the body joined to proteins via the blood. Fats come in a variety of shapes and sizes to replenish the cells and provide energy for useful organs like the brain. We couldn’t exist long without fat, and when deprived of it in the diet our livers will do whatever it takes to make some.
When lipids are joined to proteins they are called lipoproteins, and are much more useful and interesting than total cholesterol. They can now be measured accurately in the blood as high-density or low-density lipoproteins, called HDL and LDL respectively, and they transport cholesterol around. The low-density lipoproteins are the bad guys, allowing small drops of lipids to get caught in the blood vessel walls, which leads to a build-up of a plaque and heart disease or stroke. If your liver produces a lot of HDL, the good guys, most of your lipids are transported safely to their target and disposed of without any collateral damage. When lipids are made up of short chains of fatty acids they are generally liquid (oils), and when in longer chains they are solid at room temperature (fats).
Cholesterol – a big fat mistake
The reason cholesterol is fairly useless as a medical marker (with a few exceptions) is because it’s a mixture of both good and bad lipids, and this mixture varies between people. A high level of total cholesterol is usually a problem, as on average it contains more bad lipids than good. However, it is even less useful as a marker in women than in men, and in the elderly a high total cholesterol is strangely protective against heart disease. Increasingly, the ratio of two transporters of cholesterol around the body, HDL and LDL, is used as a marker of risk, although we cannot yet measure LDL directly. A much better marker of the amount of high-risk lipids in your system is another small cholesterol transporter protein called ApoB, which deposits cholesterol in the wrong places and opens channels in the vessels allowing the lipid to form the plaque that causes the damage. It is not, as previously believed, the total amount of circulating cholesterol that is important but where the cholesterol localises, and this varies widely. Most cardiologists use this more accurate blood test to assess risk, but it is more expensive to test and underused because of our obsession with total cholesterol.1
Fat is a key macronutrient in our diet and comes in many forms. Total fat is often the first thing you read on a food label, but it is pretty unhelpful as it could be either very good or very bad for you, depending on the type. Most foods contain a mixture of many different types of fats: the commonest are saturated fats, mono-unsaturated fats, polyunsaturated fats and trans fats. Within each of these categories there are many subtypes – for example, there are at least twenty-four types of saturated fat, usually lumped together on the label. Scientists have long thought we knew which combination of fats was good and which was bad for us, but the fact is that we don’t really.
Moving in a gradient from what is traditionally considered good to what is probably bad for our health, omega 3 fats, a type of polyunsaturated fat, traditionally come top. They are known as essential fatty acids and derive from our diet – mainly from fatty wild fish and from some plants like linseed (flaxseed) – and are probably beneficial for the heart in reducing lipids and inflammation (dampening down the body’s reaction to threats of infection). They have also been widely promoted as good for most diseases known to man, including dementia, attention disorders and arthritis.
Confusingly, another very similar omega fat (6) is also a polyunsaturated fat found in most vegetable oils and nuts and can also come from fatty meat and some farmed fish fed on soy and corn. By contrast with its squeaky-clean omega 3 cousin it has developed a bad name where our hearts are concerned. Having a high omega 3 to omega 6 fat ratio in your diet was believed to be beneficial – a verdict based on reasonable, but mainly weak, observational evidence.2 However, when supplements are given in randomised trials to alter our ratios, no clear benefits are seen. This lack of effect is confirmed by careful meta-analysis of observational studies, which also shows no definite or beneficial effect.3 In fact in a large multi-country study of blood levels, high omega 6 fat levels were actually much more beneficial for the heart than omega 3.4 So the hype over omega 3 supplements and the determination to foist fish oils onto us to the detriment of omega 6 is way over the top.
A 2015 study from New Zealand of thirty-two products from thirty-two countries found that fewer than 10 per cent had as much omega 3 as claimed, and most of the products had much less.5 This mirrored earlier surveys conducted by the US, UK, Canada and South Africa.6 7 You should also be wary of relying on these products as the majority of tested fish oil supplements don’t contain the ingredients they claim to. Nevertheless, both these fats are likely to be good for us – at least as foods.
Mono-unsaturated fats come mainly from olive oil and canola oil, derived from rapeseed. Although predominantly beneficial, the evidence is of variable quality, being much better for olive oil. Polyunsaturated fats (sometimes called PUFA) come from natural vegetable oils and are fairly neutral or protective, but the claims that margarines containing them are heart-protective are exaggerated and not backed up by hard evidence.
Saturated fats come from animal meats and dairy products and are the traditional villains, depending on their origin. A subgroup of saturated fats is medium-chain triglycerides, which come from palm oil and coconut oil. These have been used extensively in countries like Sri Lanka and Samoa, who at over 25 per cent of total calories have the highest saturated-fat intakes in the world.8 There is still a lack of good evidence for or against coconut oil’s effects on health, notwithstanding its increasing hype and commercial promotion. This is mainly because it is unclear whether this particular type of saturated fat, medium-chain triglycerides, is beneficial or harmful. Many of the promotional websites claim there is a wealth of research on coconut, but most that I found were unscientific and some were plainly bogus.
Trans fats (also called hydrogenated fats) are the worst kind, and as they are totally artificial come only from processed or fried foods. They were initially hailed as the healthy alternative to butter (we discuss them in detail later).
Cholesterol is singled out on food labels in the US and many other countries – below the other fats so that you can avoid it and its ‘deadly’ effects. But highlighting its content in foods is crazy, as proportionally there is nearly three times as much of the lipid cholesterol in ‘healthy’ foods like lobster, crab meat or fish oil as in ‘unhealthy’ lard, beef or pork. Eggs are packed with cholesterol, and many people stopped eating them decades ago because of erroneous advice to avoid cholesterol at any cost. Cholesterol is a complex lipid that is part of virtually every cell in our bodies: 80 per cent of it is synthesised naturally inside us and only around 20 per cent is eaten as food. As well as providing the protective and nourishing lining to the walls of our cells, cholesterol is a key ingredient of many vitamins and important hormones. It is only thanks to the unfortunate combination of there being an easy blood test for it and a rotten PR campaign that cholesterol has acquired such an ill-deserved reputation.
When did fat get a bad name?
The anti-fat campaign has its origins in many places and events, but it really began in America. One reason was the very public spectacle of the heart attack suffered by President Eisenhower in 1955 and his subsequent attempts at a healthy low-cholesterol diet. This diet failed to reduce his blood cholesterol or his heart attacks, which he later died from. The driving force of the anti-fat campaign was a Minnesotan epidemiologist called Ancel Keys who was famous for inventing the ‘K-rations’ for US troops in the Second World War. He spent a sabbatical in the UK and was unimpressed by the fattiness of the English diet at the time, which in his view largely consisted of greasy fish and chips wrapped in newspaper, bangers and mash, and eggs and bacon. He noticed that wealthier English men, like their US counterparts, who could afford the most food were starting to die from heart attacks, which had previously been quite rare. He returned to the US determined to get the funds to prove his hypothesis.
The key to his theory was the famous Seven Countries study which associated rates of heart disease in seven countries with different dietary fat intakes. The countries ranged from Japan, with virtually no heart disease, to England and the US, with plenty. Keys’s correlations were very convincing and his conclusions clear: dietary fat levels equated to heart attack risk. He actually looked at twenty-two countries and the correlations were not all as convincing (or as well publicised). But no matter – diet was not easy to measure. The studies had a major impact on the press and on medical and public opinion. Policy was altered to reduce fat intakes.
Other observational studies confirmed the opinions of the anti-fat movement. A large population project, later named ‘the China Study’, amassed a huge amount of dietary data from sixty-five counties and 120 villages in rural China in the 1970s when it was still a poor country and bicycles were the main means of transport. They compared in detail the diets of each county collected a few years before with the current rates of over fifty diseases as well as a number of blood markers.9 Dietary fat levels and blood cholesterol were half those of the US, and the most common diseases seen in the West such as heart disease, diabetes and cancer were virtually non-existent.
Colin Campbell and his team at Cornell University running the China Study believed that the lack of both animal proteins and dairy products packed with fat, plus the large amount of vegetables consumed, were the reason for the amazing absence of cancers or heart disease. The conclusion was that we should eat vegetables and give up meat and dairy completely. This gave vital evidential support to the growing vegan and vegetarian movements while comprehensively contradicting the Atkins high-protein movement. Campbell’s book The China Study became a worldwide bestseller.10 Bill Clinton is reported to have lost 20 lb on the diet after reading the book following his heart problems.
Early lipid researchers uncovered some rare families who on testing were found to have blood cholesterols at over twice the normal levels, and they often died of heart disease in young or middle age. These families were later revealed to suffer from a group of genetic diseases known as hypercholesterolaemia (more simply, high cholesterol in the blood) caused by faulty genes, and they were put on strict fat-free diets. These rare patients showed a clear correlation between their blood cholesterol and disease. If you lowered their cholesterol to normal levels via diet or drugs, their risk of dying decreased significantly. In the remaining 99 per cent of the population a high-saturated fat diet would slightly increase total cholesterol levels, and it was assumed this would also increase the risk of heart disease. Thus the image of cholesterol as universally bad was further cemented.
As the simple message, ‘Fat is deadly’, spread around the developed world our diets changed for the worse. As well as reducing the diversity of our food it deprived us of many nutrients. But as we have seen, food fats come in many shapes and forms, some good, some bad and some ugly. So before you routinely reach for the zero-fat labelled items on the shelf it would be a good idea to find out more about them.