The winter of our dietary discontent? Saturated fats and health
Australia might have just had one of the warmest winters on record, but to many of us in the south-eastern part of the continent it’s felt pretty much like a normal winter. Quite dry, so not much use for umbrellas; frosty minimum temperatures that have given our coats, boots and beanies a solid airing.
Winter has its compensations, with one of the best being ‘comfort food’. Slow-cooked lamb shanks, pumpkin soup with crusty bread, lasagne, roast potatoes, osso bucco, cauliflower cheese, sticky date pudding with caramel sauce … many of us relish these cold-weather foods. And, of course, we use more energy to keep warm in winter, so we find it easy to justify eating hearty (and often hefty) meals.
Needing more energy in winter is one thing, but how you get it is another. Many traditional winter meals are high in fat, and much of it is saturated fat. We’ve been warned against eating too much saturated fat for decades, on the grounds that it’s a major contributor to heart disease, obesity and other chronic conditions. In this article, we look at the health effects of saturated fat in the diet.
What is fat?
Fat is a macronutrient that provides more energy per gram to the human body than carbohydrate and proteins. Dietary fat is a source of two ‘essential’ fatty acids (alpha-linolenic acid, an omega-3 fatty acid, and linoleic acid, an omega-6 fatty acid) – so-called because the human body cannot manufacture them.
Vitamins A, D, E and K are fat-soluble, which means they can only be digested, absorbed and transported in conjunction with fats. Fat helps us maintain healthy skin and hair, maintain body temperature, protect our body organs from trauma, and promotes cell function.
Dietary fat, cholesterol and heart disease
Fat in our diet is either saturated or unsaturated. Saturated fats contain a high number of hydrogen atoms and are solid at room temperature – think butter and lard – while unsaturated fats are liquid at room temperature, like olive oil. Saturated fatty acids come primarily from red meat and processed foods, but dairy products, coconut and palm oil also contain them.
Eating too much saturated fat raises blood cholesterol, in particular low-density lipoprotein (LDL) cholesterol, commonly called ‘bad’ cholesterol. The National Heart Foundation recommends that saturated fats should comprise only 7 per cent of our total energy intake – about 16 grams per day for an average adult. Australians currently eat about 28 grams of saturated fat per day, about 70 per cent more we need.
Cholesterol is a waxy substance found only in animal products; it’s an essential component of our bodies. However, if cholesterol production increases, it can accumulate on the walls of the coronary artery, restricting blood flow, causing inflammation and dramatically increasing the risk of heart attack or stroke.
Some highly processed foods contain trans fats, which are generated during the hydrogenation of (unsaturated) vegetable oils for margarine, commercial cooking and manufacturing. This process alters the structure of the fat, and the resulting ‘trans fatty acids’ are associated with increased risk of heart disease.
Research shows that high levels of cholesterol can cause arterial damage and this, in turn, can cause coronary heart disease. Consequently, populations that consume low amounts of trans and saturated fats have low rates of heart attack and stroke.
Writing for The Conversation (October 2013), Associate Professor David Richmond Sullivan (University of Sydney) stated that ‘rates of cardiovascular disease have fallen in countries where efforts have been made to reduce saturated fat intake, but have risen in developing countries where consumption has increased.’ Large, well-designed studies of people with Mediterranean-style diets demonstrate that replacing saturated fat with foods containing healthier unsaturated fat – nuts, extra virgin olive oil, polyunsaturated margarine – reduces the incidences of heart attack and premature death.
Saturated fat and diabetes
While the link between a high intake of saturated- fat and heart disease is well established, its effect on other chronic diseases is not yet clear. Recent research has revealed that not all saturated fats are associated with heightened risk of developing type 2 diabetes.
In a study of 340 234 adults across eight European countries, researchers measured the nine fatty acids found in the participants’ blood samples, and compared those who developed diabetes (12 403 participants) over the following 16 years with those who did not. They concluded that some foods high in saturated fats, such as dairy products, can actually lower the risk of diabetes.
Dietary fat and obesity
A recent editorial in the journal Open Heart urged a return to consumption of equal amounts of omega-6 and omega-3 polyunsaturated fatty acids as a strategy to help combat global obesity.
In traditional societies, humans consumed roughly similar amounts of omega-6 and omega-3 by eating diets rich in fish, plants and free grazing animals, and eggs from chickens that ate plants high in omega-3 fats. In many industrialised societies the ratio of omega-6 to omega-3 intake is closer to 16:1, and in Australia it is estimated at 8:1. High consumption of processed foods, fatty red meat and insufficient fish and vegetables mean too much saturated fat and too little omega-3 in the diet, promoting obesity and chronic disease.
There is now considerable high-quality evidence that a Mediterranean-style diet high in unsaturated fat from extra virgin olive oil is superior to a low-fat diet in preventing heart disease and reversing fatty liver, which is associated with risk of type 2 diabetes. Moreover, because fat is satiating, a high-fat Mediterranean diet is superior to a low-fat diet for losing weight and sustaining weight loss.
Advice on dietary fat consumption
Around the middle of the 20th century, research about fat and human health, particularly cardiovascular health, showed a statistical association between eating saturated fat and an increased risk of coronary heart disease. Early governmental dietary guidelines – including the first Australian Dietary Guidelines (1982) and those in the United States (1980) and the United Kingdom (1994) – advised people to minimise their total fat intake, avoid saturated and trans fat and moderate consumption of ‘healthier’ unsaturated fats.
Current Australian Dietary Guidelines (2013) are similar to the previous ones and mirror the advice given in many other countries: be careful of overall fat intake, due to its energy density and therefore its propensity to promote excess weight and obesity, and avoid or minimise saturated and trans fat intake because of their detrimental effects on cardiovascular health. The guidelines also recommend eating unsaturated fats in moderation for their health benefits. This means choosing:
- high-protein and dairy food such as lean meat, fish, some nuts and reduced-fat dairy
- eating foods high in unsaturated fat, such as nut butters and olive oil, in small amounts
- avoiding foods high in saturated fats and trans fats such as butter, coconut oil and processed foods like biscuits.
A 2015 Cochrane review of 15 randomised controlled trials with over 59 000 participants concluded that:
Replacing the energy from saturated fat with polyunsaturated fat appears to be a useful strategy. Lifestyle advice to all those at risk of cardiovascular disease and to lower-risk population groups should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturated fats.
The scientific literature suggests that our winter comfort foods, many of which contain high levels of saturated fat, should be eaten in moderation – and perhaps confined to the winter months when we can justify a few extra kilojoules. Considerable evidence supports the effectiveness of the Mediterranean diet – low in saturated fat, but high in unsaturated fat – in minimising rates of obesity, heart disease and diabetes. The Mediterranean diet is broadly in line with current Australian dietary guidelines.