Conflicting evidence on the influence of dietary factors on health make it difficult to know what's good and what's bad. Haydn Shaughnessy presents the case for and against in the battle of the fats
Imagine. The main course is over and you turn to a full-fat aromatic cheese, perhaps an aged Durrus, lying next to a slice of soda bread lavishly treated to a thick coating of slightly salted, cholesterol-loaded butter. This, doctors have advised patients for 50 years, is a heart attack on a plate. Cheese, milk, butter and meat are saturated fats and bad for you because of their high cholesterol content. Cholesterol causes heart problems. Unsaturated fats (from olive oil to Omega fatty acids), on the other hand, are an unassailable good.
Not true, says a growing band of full-fat advocates. Pack the margarine and vegetable oils away. Get out the butter and the cheese. Saturated fats are health-enhancing. Now we really are confused.
The advocates of this apparently perverse dietary advice go one step further. Cholesterol, they argue, does not cause health problems at all. Not of any kind. Though medics labelled it the health bogey half a century ago, there is, according to Swedish researcher Uffe Ravnskov, no association between cholesterol intake and illness. The body creates 20 times more cholesterol than we feed into it.
Even advocates of low-fat diets - such as the Harvard School of Public Health, which has drawn up a radically changed food pyramid with a new emphasis on polyunsaturated fats - concede that the cholesterol found in meat, milk and cheese is not strongly connected with the cholesterol circulating in the blood.
Radical nutritionists, led by Mary Enig, author of Know Your Fats and an expert and campaigner on fat issues, claim that polyunsaturated fats are bad for you in the form most people consume them - in vegetable oils and spreads. This sounds like the kind of advice to further confuse and torment the health-conscious consumer, but there's more. The father of the low-fat/low-cholesterol/healthier living connection, David Kritchevsky, a senior researcher at the Wistar Institute in Pennsylvania and formerly a member of the Dietary Guidelines Advisory Committee at the US Department of Agriculture, said recently: "I collated the available literature [back in 1954] and found that saturated fat was without effect when added to a commercial diet." According to the experts from Harvard "... the total amount of fat in the diet, whether high or low, has no real link with disease."
One of the many benefits of a newly-affluent country is the capacity for indulgence, which many of us embrace eagerly. Still, a large slice of the dietarily conscious Irish population would think twice before swallowing Enig's and Ravnskov's message on fats and cholesterol, despite the growing body of opinion that natural sources of saturated fat are at least neutral in the health wars.
Doctors would no doubt be horrified, even though Ravnskov has published his findings in prestigious medical publications such as the British Medical Journal. According to Ravnskov and Enig, saturated fats play a vital role in immune response. Enig points out that arteriosclerosis is increasingly seen as a problem with viral origins, a point that Kritchevksy endorsed in a recent study. "Newer players on the heart disease stage are homocysteinemia [a metabolic deficiency], chlamydia infection and cytomegala-virus [a germ related to fibro-myalgia]," he wrote. Kritchevsky also now blames high cholesterol deposits on inflammation creating lesions in the artery, which the body then tries to patch-up by laying down a course of fat. In other words, high cholesterol deposits are a response to disease.
More disconcerting for doctors, who use cholesterol as a marker for clinical intervention and drug prescribing, Ravnskov claims that although people need a healthier balance of fats, for many reasons, "this has nothing to do with the cholesterol content in the blood."
The link between food and heart disease is central to health-care planning and intervention in Ireland. Irish men and women have the highest rate of premature death from coronary heart disease in the European Union. With an ageing population, the numbers exposed to cardiovascular risk will increase substantially over the next 15 years.
According to the Irish Heart Foundation, "high levels of cholesterol, which lead to hardening and narrowing of the arteries, are influenced by a diet high in saturated fat." The problem, though, is that attempts to address cardiovascular illnesses through diet may have been counter-productive and misguided.
The debate over saturated fat stretches back 50 years. Today, there is one substantial difference forcing a rethink, even among mainstream scientists. As cardiovascular risk declines, obesity is fast becoming the number-one cause of morbidity. A reappraisal of diet is overdue.
Stephen Hulley is an epidemiologist at the University of California and has spent a lifetime studying diet and disease. "Studies showed dietary fat has only a modest effect on cholesterol. Even so, this led to the dietary recommendations we've lived with ever since. But there are two problems. First, the "modest effect". Second, when you reduce fat intake you change other things. We don't know if these changes are healthy or not. Some people argue that reducing dietary fat has contributed to obesity, because the higher carbohydrate diet is conducive to weight gain."
So is food advice confusing or potentially distorted? Links between cholesterol and heart disease had been investigated in Europe at the begining of the 20th century, but it was in the 1950s that heart disease became the number one killer in the United States and gave a new impetus to diet-disease research.
By the mid-1950s the level of cholesterol in the blood was identified by scientists as a possible health risk, though not with any degree of certainty. This was established through animal experiments. Many of those experiments were conducted by feeding cholesterol to rabbits, even though rabbits are herbivores. Scientists observed that the rabbits, fed the fats that we derive from animal products, developed arterial lesions apparently in response to the cholesterol.
A young researcher at the time, David Kritchevsky, now one of the most prominent nutritional experts in the world, began experimenting with saturated and polyunsaturated fats (animal fats and vegetable oils). Kritchesvky's findings appeared to support the suggestion that polyunsaturated fats (found in vegetable oils, which at that time were relatively new to the market) helped lower blood cholesterol levels. The low-fat diet was born with these simple experiments and for 50 years food production companies have sought variations on the cholesterol-lowering theme.
The majority of us accept the need for dietary fat reductions and look to new products like Benecol, produced by pharmaceutical companies who play an increasingly important role in food innovation, that seem to make cholesterol lowering easier, and whose benefits are marketed through medical practitioners.
Stephen Hulley cautions, "we have a tendency to make recommendations like - switch from butter to margarine - and then find out we got it wrong. I tend to the view that reducing dietary fat is not the most important thing. It just doesn't make sense to focus on diet in relation to heart disease and we haven't much evidence that diet is causing cancers. We just don't know."
"It is wrong," says Kritchevsky now, "to jump on any one factor. I didn't push my results one way or another. That was the oil companies. More recently, we've begun to see other factors enter the heart disease equation."
Stephen Hulley agrees: "The medical profession takes a view on healthy or unhealthy diet versus disease, but disease takes decades to develop so it is difficult to study. It is difficult to hold the variables steady and isolate any one cause. It is difficult to know."
No part of human nutrition is less understood and more controversial than fat. Over the past 20 years in most advanced countries the consumption of dietary fat has fallen by as much as 30 per cent. As fat consumption has declined, people have become obese at an alarming rate.
An argument that the food pyramid has dangerously skewed energy consumption away from fats towards carbohydrates is gaining ground. There is another view, arising out of molecular genetics, that the body deals intelligently with fats, but becomes something of a dummy when faced with carbohydrates. Given the right balance of fats, which means saturates, mono-unsaturates and a small quantity of polyunsaturates, the body seems to know how to partition these energy sources, directing them to productive use.
Steve Clarke, formerly at the University of Texas, has demonstrated that the body is artful in partitioning fats into those it needs and will use for cellular construction, those that it needs for energy, and those it has no use for and which it needs to dispose of.
The guiding lights in this process are the Omega 3 polyunsaturated fatty acids (found in oily fish and green vegetables), which seem to act as the body's chief scout. Kritchevsky cautions that even apparently healthy polyunsaturates found in vegetable oils are potentially damaging in the absence of Omega 3 fatty acids.
When confronted with carbohydrates as opposed to fats, the body seems less gifted. Whereas it can rid itself of natural fats, it tends to be super-efficient at storing fats converted from carbohydrate. If there is no need to use the carbohydrate, the body stores it as fat and keeps it as the body's ultimate backstop, only to be drawn on when all other energy sources fail. Carbohydrates seem to signal to the body that either a potential shortfall of food or high energy expenditure lies ahead.
By encouraging carbohydrate consumption, policy advisers have focused on the health benefits of fibre contained in complex carbohydrates and unwittingly contributed to substantial weight gain. Moving policy away from this undue emphasis will be politically sensitive.
As the argument drifts slowly in favour of reviving the reputation and use of saturated fats, the temptation to eat more and load the body with proteins is already evident in the success of the Atkins Diet.
If you are reading this over a breakfast of croissant and a full milk latte, all is not necessarily well. The only questions to ask at the counter of the supermarket, or at the butcher or in your local café, according to Mary Enig, are whether the cheese and the butter you are about to buy are made of raw or pasteurised milk and whether the red meat comes with its fat intact. Lean meat is bad.
The enzymes, minerals and vitamins in raw milk aid digestion and allow the body to direct the fats to perform their appropriate duties in the body, claims Sally Fallon, who leads the global campaign for raw milk.
The fats in red meat contain the tools to help the body deal with the potential adverse aspects of digesting so much protein. They enable the body to absorb the meat's nutrients.
The croissant, however, is more than likely to be made of what are called trans-fats, fats modified from a liquid form to become solid and stable. Trans-fats are polyunsaturates made to behave like saturates. This, argue an increasing number of researchers from America and Europe, is where the real problems in our diets begin.
The production of trans-fats involves altering polyunsaturated fat molecules to make them resemble the molecules in fats found in meat and cheese. The use of trans-fatty acids in a broad range of foods, including pizzas, wholemeal bread, biscuits, crackers, cakes, prepared foods (whether cheap or premium priced), invites us to take into our bodies a stealth weapon. Confronted with trans-fatty acids, the body's cells believe they are dealing with an everyday fat from a traditional diet and innocently incorporate it into the cellular structure. Once the chemicals start reacting though the cells the body finds it is dealing with something altogether alien. As yet, scientists are divided over what the effects might be.
Trans-fatty acids, though, are everywhere in our diets. So is the pro-saturated fat argument a license to pig out? Not so. Enig and Kritchevsky both advocate balance, and since science can't yet tell us what the appropriate balance might be, the best guide, according to Kritchevsky, is to reduce all fats. Stephen Hulley sees it differently. "I'm inclined to advise people to eat in moderation what appeals to them," he says. According to Enig, the best course of action is to revert to a traditional approach to food.
Given that Ireland's wealth is relatively recent, the path back to tradition might also be the best route to moderation.
THE FAT FILE
Fats are characterised by roughly how solid and stable they are. Saturated fats, solid at room temperature, are generally animal fats that are saturated with hydrogen and are very stable (have a relatively long shelf life). There are two types of unsaturated fats (mono and poly) that contain progressively less hydrogen than they are capable of holding. occupies the mid ground between saturated and polyunsaturated, and the most popular form is olive oil. Polyunsaturated fats are vegetable oils and fish oils. Essential polyunsaturated fats are the few fatty acids the body cannot create itself, the Omega 3 and 6 fatty acids that are highly unstable (go off quickly). Trans-fatty acids are hydrogenated and partially hydrogenated fats (hydrogen atoms added) so that a polyunsaturated fat acts like a saturated fat, i.e stable and solid. Typically they are found in cakes and biscuits, breakfast cereals, and prepared foods. Omega 3 fats are the new kings of beneficial fats. Doctors and nutritionists encourage people to eat them in the form of oily fish or supplements. Scientists investigating their benefits have produced a long and impressive list, ranging from heart protection to fat partitioning. But the Omega fatty acids are the least stable of all fats and their shelf life can be as short as 15 minutes once exposed to light and oxygen. They need specific proteins for the body to absorb them properly, proteins found in saturated fat products such as cheese, and in plants. Radical nutritionists warn against loading the body with these substances and advise relying instead on dietary sources, such as fish, flax seeds and green leafy vegetables.