All fat has nine calories per gram, twice as many calories as carbohydrates and protein. However, not all fats are ‘bad’. We need a moderate amount of unsaturated so-called ‘good’ fats in the diet. These types of fat are essential for cell membranes, eyes, the brain and metabolic functions. These healthy fats are plentiful in plant foods such as nuts, seeds and their oils, avocados and soya foods. Green leafy vegetables contain them too, but not much as they are a very low-fat food.
We have no dietary requirement for saturated fat. Found widely in meat, dairy, eggs, processed foods and fish, this unhealthy type of fat contributes to the risk of CVD by raising blood cholesterol levels. When you eat saturated fat it is converted into cholesterol by the liver. Saturated fat also slows down how quickly cholesterol is removed from the blood. Cutting down on saturated fat in the diet and replacing it with unsaturated fats is an effective way of reducing cholesterol and therefore lowering the risk of CVD.
Trans fats are an unhealthy type of fat naturally found in low levels in meat and commonly produced industrially from vegetable fats used in processed foods, fried ‘fast foods’ and margarine (although not so much now). Trans fats have been shown to increase blood cholesterol levels and thus the risk of CVD.
The Department of Health recommends that saturated fat should contribute no more than 11 per cent of the total energy that we get from food (Department of Health, 1991). They say:
- The average man should eat no more than 30g of saturated fat a day.
- The average woman should eat no more than 20g of saturated fat a day.
Most people in the UK eat too much saturated fat: about 20 per cent more than the recommended maximum (British Dietetic Association, 2014). Most saturated fat in the average UK diet comes from: fatty cuts of meat, poultry skin, meat products such as sausages and pies, whole milk and full fat dairy products such as cheese and cream, butter, ghee and lard, coconut oil and palm oil, pastry, cakes and biscuits, sweets and chocolate.
The saturated fat content of meat varies widely depending on the species and breed of animal, the way the animal was raised, what the animal was fed, the part of the body from which the meat was taken and the method of cooking. Wild animals such as deer tend to be leaner than farmed animals. However, the fact remains that all meat contains significant amounts of saturated fat that we have no dietary requirement for.
Figure 4. Fatty acid composition of different foods shown as a percentage of the total fat content.
Source: FSA, 2002.
Figure 4.0 shows that meat, nuts, avocados and seeds vary widely in the proportion of ‘good’ and ‘bad’ fats they contain. For example, a roast leg of lamb contains 14.2g of fat per 100g, 5.7g of which is saturated and just 0.8g of which is polyunsaturated. Walnuts on the other hand contain 68.5g of fat per 100g (which is a lot of walnuts), 5.6g of which is saturated and a whopping 47.5g is polyunsaturated.
Most health organisations (including the WHO) recommend eating less food rich in saturated fat and more foods containing unsaturated fats such as avocados, nuts, seeds, plant-based oils and spreads. Other rich sources of healthy essential fats include walnuts, flaxseeds, hempseeds, rapeseeds and their oils and oils produced from some species of algae (which contain the omega-3 essential fatty acids EPA and DHA used in our eyes and brains).