Paula Mee: The truth eludes researchers in the saturated fat wars

Saturated fat is often used as an umbrella term for different and individual saturated fatty acids. Early research suggested they all exerted similar biological effects and that it was a good idea to classify them together as the “bad fats”.

However, as research unfolded, it emerged that different saturated fatty acids (SFA) might give rise to different health outcomes. The SFA in milk, cheese and yogurt may have led some people to reduce or omit these foods completely for heart health, but there is no evidence that this strategy is either helpful or necessary. In fact, the opposite is probably true.

According to Dr Arne Astrup of the University of Copenhagen, the overall effect of a food cannot be assessed on its saturated-fat content alone. “Several observational studies suggest that cheese protects against cardiovascular disease and experimental studies show that cheese consumption does not produce the effects on blood lipids that would be expected from its saturated fatty acid content.”

Astrup says foods high in SFA that are also high in calcium don’t seem to raise harmful LDL cholesterol fractions. They may even positively increase healthy HDL cholesterol. A meta-analysis of prospective cohort studies also shows that certain dairy foods are associated with either neutral or beneficial health outcomes on the risk of stroke, ischaemic heart disease and type 2 diabetes.

Some of the protective effects of dairy foods may be due to a “food matrix” effect, meaning that other nutrients in these foods may work in combination with the SFAs to affect health outcomes.

Many of the studies are based on milk, although a matrix effect is also observed for cheese. A review by Dr Emma Feeney and Dr Anne Nugent of Food for Health Ireland at University College Dublin found that SFA from cheese did not appear to adversely affect blood lipids and that specific bioactive peptides and other nutrients found in cheese may be interacting with the SFA, preventing its absorption.

Irish data show that the mean daily intake of SFA as a percentage of total energy is 14 per cent for adults, 14.4 per cent for teenagers and 14.7 per cent for children; higher than the Department of Health recommended level of 10 per cent of our total calories.

There is a worldwide scientific focus and debate about SFA in the aftermath of a systematic review and meta-analysis of 72 published studies with 530,525 participants in total last March. This appeared in the Annals of Internal Medicine and suggested there was little evidence to support the recommendation to limit SFA.

However, Walter Willett, chairman of the department of nutrition at Harvard School of Public Health, warned that the conclusions were seriously misleading, as the analysis contained major errors and omissions. A corrected version of the publication was posted shortly after it appeared on the website of the Annals of Internal Medicine but Willett claims the study should be disregarded. As the fat war rages on, Willett asserts that if we replace SFA with poly- and monounsaturated fatty acids, found in oily fish, olive and rapeseed oils, and avocado, our risk of heart disease is reduced. However, if SFA is replaced with refined starch and sugar, the risk of heart disease stays the same.

Nutrients

Critically, the various sources of SFA in the Irish diet are worthy of consideration. Milk, cheese and yogurt certainly contribute to our SFA intake, yet they contain components and proprieties that could attenuate our risk of heart disease.

They are also very nutrient-rich, providing a source of vitamins and minerals, many of which are not eaten in enough quantities in Ireland. A 25g portion of cheddar cheese, for example, is a source of calcium, phosphorus, vitamin B12 and protein, according to the EU Nutrition and Health Claims Regulation. In addition, cheese is an important source of vitamin A and zinc.

On the other hand, cakes, biscuits and pastries contribute significant amounts of saturated fat to the Irish diet. They often contain refined carbohydrates, such as sugar and white flour, and few essential nutrients. These are and should continue to be the primary target for reduction in order to improve heart health and general health.

Fats help us to absorb fat-soluble vitamins A, D and E from the food we eat. We need healthy fats to produce healthy cell membranes and prostaglandins or hormone-like substances. However 1g of fat, no matter what type of fat it is, contains twice the calories of 1g of protein or 1g of carbohydrate. Reducing your total fat intake, and choosing healthier types of fat, can help lower your calorie intake and improve your balance of fats. We should avoid trans fats altogether.

Not all SFAs have an adverse effect on blood cholesterol. We can continue to eat low-fat milk, cheese and yogurt daily, but we should try to reduce highly refined sources of SFA, sugar and starch found in confectionary such as cakes, biscuits and so on.

So the advice is to enjoy moderate amounts of olive oil, rapeseed oil, avocados, nuts and seeds which are higher in mono- and polyunsaturates than SFA. Oily fish, walnuts and walnut oils, linseed, dark green leafy vegetables also contain healthy omega-3 fats and these are good for us, too. They contain other vital nutrients such as vitamin D and selenium, unlike processed fatty foods which are usually a combination of saturated fat, trans fat and sugar.

Paula Mee is a dietitian and a member of the Irish Nutrition and Dietetic Institute. Email paula@paulamee.com; @paula_mee

What to avoid and what to choose

BAD FATS TO AVOID

Trans-fatty acids Avoid all trans fats. They increase the “bad” LDL cholesterol and lower the “good” HDL cholesterol; an overall negative effect. You will often find trans-fatty acids in hard margarines and spreads, biscuits, crackers, frozen pizzas and frozen meals.

Saturates These are solid fats, mainly animal fats. In excess, certain but not all saturated fats have adverse effects on heart health. Limit them, especially when combined with refined sugar and starch in biscuits, cakes and so on. They are found in butter, cream, milk, cheese, yogurt and in visible fat. BETTER FATS TO CHOOSE

Omega-3 fatty acids These polyunsaturated fatty acids help reduce triglycerides and the risk of thrombosis (blood clots), heart attacks and strokes. You will find omega 3 fatty acids in oily fish, walnuts and walnut oils, linseed and dark green leafy vegetables.

Polyunsaturated omega-6 fatty acids These reduce “bad” LDL cholesterol but, at very high intakes, can also reduce “good” HDL cholesterol. Therefore, a good balance of omega 3, 6 and 9 is recommended. You will find polyunsaturated omega-6 fatty acids in vegetable oils, polyunsaturated margarine and in foods made with these oils.

Monounsaturated omega-9 fatty acids These are liquid at room temperature but solidify when chilled. They can reduce “bad” LDL cholesterol but maintain “good” HDL cholesterol and can reduce the free-radical damage associated with heart disease. You will find monounsaturated fatty acids in olive oil, rapeseed oil, peanut oil, avocados, nuts and seeds.