April 19th 2018
A Healthy Curiosity
Has cholesterol had an unfair rap?
September 6th 2017 / 0 comment
For years cholesterol has been a dietary pariah and foods containing it - such as eggs and shellfish - have been on nutrition’s naughty step. But the tide has turned. Peta Bee investigates the latest thinking on cholesterol, food, fat and heart disease
With a worse reputation even than sugar and salt, cholesterol was for years the biggest nutritional baddie, a fast route to ill-health and potential heart disease. How things have changed. Science has now confirmed that much of what we thought we knew about cholesterol - and fat in general - has been riskily wrong. Far from being a killer, dietary cholesterol is now considered essential for life and foods containing it - cheese, butter, red meat and shellfish - have been given the green light for healthy consumption. Even eggs, once demonised in the diet and strictly rationed by government guidelines to a recommended upper limit of three per week, have now been given the go-ahead by experts.
What is cholesterol?
Cholesterol is a waxy substance found in your bloodstream (where it is attached to proteins called lipoproteins) but also in every cell in your body. It is essential for life and helps to produce cell membranes, hormones, vitamin D and bile acids that aid the digestion of fat. “Humans would die out without this vital substance,” says nutrition researcher and cholesterol campaigner, Zoe Harcombe. “We need it for every bodily function.”
But as it is one of the substances that causes furring of the arteries, too much is a bad thing. But the big question is - how do we arrive at too much cholesterol in the blood? For years it was assumed that consuming cholesterol-containing foods had a direct impact on blood cholesterol levels. Saturated fats, found predominantly in animal foods, were also cast aside as dietary demons because of their purported effect in raising blood cholesterol levels and as a result, clogging up our arteries.
However, recent studies have categorically proven that neither cholesterol from food nor saturated fats are responsible for raised blood cholesterol. And many scientists are now convinced that raised blood cholesterol levels are not as much of a marker for heart disease as was once thought.
What about ‘good’ and ‘bad’ cholesterol?
Cholesterol is carried in your blood by two types of lipoprotein - high-density lipoprotein (HDL) which carries cholesterol away from the cells and back to the liver, where it's either broken down or passed out of the body as a waste product; for this reason, HDL cholesterol is referred to as ‘good cholesterol’. Then there’s low-density lipoprotein (LDL), which carries cholesterol to the cells that need it, but if there's too much for the cells to use, it can build up in the artery walls, leading to disease of the arteries; for this reason, LDL cholesterol is known as ‘bad cholesterol’.
But now even the ‘good’ and ‘bad’ tags are disputed. A study from Cambridge University, published in the journal Science this year found that some people with high levels of HDL cholesterol have genetic differences that mean they are also at an increased risk of heart disease, contradicting what many thought to be true. To add to the confusion, a controversial review of research involving almost 70,000 people that was published in the BMJ Open journal this month reported that 92 percent of older people with a high LDL cholesterol level lived longer. “What we found in our detailed systematic review was that older people with high LDL levels, the so-called ‘bad’ cholesterol, lived longer and had less heart disease,” exclaimed Dr Malcolm Kendrick a GP and one of the authors of the paper, compiled by an international group of medical experts. Some academics have criticised the research as less than robust, but it has certainly opened the floodgates for discussion.
How did cholesterol get its bad reputation?
Much of the bad rap surrounding dietary cholesterol and saturated fat stems from misinterpreted studies that were carried out between the 1950s and 1970s, mostly by the American physiologist Ancel Keys. Findings associated rates of heart disease to raised blood cholesterol levels and connected this to a high intake of saturated animal fats. Other research implicated cholesterol in food and, before long, both saturated fats and cholesterol-containing foods were outlawed as risky to health. As a result, medical bodies around the world pushed out dietary guidelines that are still heavily promoted today: in short, cut down on saturated animal fats and dietary cholesterol for the sake of your heart.
However, critics say no association was ever proven and even Keys himself stated that “there’s no connection whatsoever between cholesterol in food and cholesterol in the blood”. In one of his landmark studies, for instance, Keys looked at animal fat consumption in seven countries. Although he found a high intake was a strongly linked to heart disease, the data wasn't rock solid, and in three of the countries studied there was no clear link.
High cholesterol foods do not increase heart disease risk
In February 2016, the latest study to confirm that high cholesterol foods don’t raise risks of heart disease came in the form of a Finnish paper published in the American Journal of Clinical Nutrition. It followed 1,032 men aged 42 to 60 who were healthy at the point they embarked on the trial, although approximately one third of the subjects carried a gene that predisposed them to a raised risk of heart disease. Each man completed questionnaires and diet diaries detailing what they ate and drank over a period of 21 years.
By the end of the trial, around 230 of the men developed coronary artery disease. Yet their weekly cholesterol intake – which amounted to an average 2,800mg (one egg contains about 180 milligrams of cholesterol) – was found to have no impact, even on the subjects carrying the heart disease gene. What’s more, the high cholesterol consumers were no more likely to have thickened arteries than those who ate very little of the substance in food. “Moderate intake of cholesterol didn’t seem to increase the risk of heart disease, even among those people at higher risk,” said Jyrki Virtanen, a professor of epidemiology at the University of Eastern Finland and lead author of the study.
Cholesterol in food is (mostly) fine
The upshot of studies (such as that carried out by the Finnish scientists) is that experts are less concerned about cholesterol intake from food for most of the population. For around 250,000 people in the UK with familial hypocholesterolaemia (my mum is one of them), it’s a slightly different story - they have an inherited genetic condition, which means that their cholesterol levels are higher than normal from birth and their risk of heart disease is therefore more pronounced. Studies have shown that someone with FH can have the same heart attack risk at 40 as a non-affected person has aged 70 and, according to the British Heart Foundation, on average one person a day with FH has a heart attack. Because of this higher risk of heart disease, people with FH are encouraged to look at all lifestyle risk factors and to adopt a healthy diet that avoids obesity.
If it’s not by eating food such as eggs, saturated fat, red meat and prawns, what does cause raised cholesterol?
Nutrition expert Ian Marber explains that most (around 75 per cent) of the cholesterol in our bodies is naturally made by the liver - only 25 per cent comes from our diet. “And for most of us, eating foods that contain cholesterol means that the liver makes less of it to compensate,” says Marber. Studies have shown that the body auto-regulates its cholesterol levels – up to a point. But over-consumption of all fats or food in general - especially high amounts of refined processed foods is bad news, as it not only raises the risk of obesity but of the liver producing too much cholesterol. “It’s easy to forget that we need to consider our whole diet to reduce our overall risk of heart disease,” says Victoria Taylor, Senior Dietitian for the British Heart Foundation. “No single food or nutrient is solely responsible for the risk.”
Should we aim to lower?
For years, government guidelines have stated that our total blood cholesterol level should be maintained at 5mmol/litre for healthy adults or under 4mmol/litre or less for those ‘at high risk’ of heart disease. But government obsession with lowering total cholesterol levels has led to millions of people being over-prescribed cholesterol-lowering statins, wrote consultant cardiologist Aseem Malhotra, in the British Medical Journal in 2013. The real issue for heart disease is not cholesterol but other dietary issues such as chemically produced trans fats.
“Scientists universally accept that trans fats — found in many fast foods, bakery products and margarines — increase the risk of cardiovascular disease through inflammatory processes,” Malhotra said. And a damning report published last month further accused public health bodies of misleading people about fat and cholesterol, a move that was said to be having “distastrous health consequences”. According to the National Obesity Forum, which published the report, products labeled “low cholesterol” or “proven to lower cholesterol” should be avoided at all costs, adding that nutrition science has been “corrupted by commercial influences”.
NEED TO KNOW
1. Cholesterol in food has no direct link with elevated blood cholesterol levels. Eating cholesterol-rich foods such as eggs does not increase blood cholesterol.
2. Some saturated fatty acids in food have been found to protect against heart disease rather than cause it. Many foods high in saturated fat – red meat, butter, eggs and cheese – do not raise blood cholesterol levels.
3. Your liver produces 75 per cent of the cholesterol your body needs to function healthily. You need cholesterol in the body to stay alive.
4. A small proportion of people - those with Familial Hypercholesteraemia - are genetically susceptible to extremely high cholesterol levels.
5. A bad diet (especially trans fats), lifestyle (smoking, lack of exercise) and obesity remain major risk factors for heart disease.
6. A Mediterranean-style diet including healthy fats, wholegrains and fresh fruit and vegetables, has been shown to reduce the risk of heart disease.