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Fats in our diet are a valuable source of energy (1 g is equivalent to 9 kcal), and they are essential in a healthy balanced diet. While some fats are beneficial, others, if consumed in excessive amounts, have detrimental effects on health. Fats are classified by their chemical structure, falling into several groups including saturated fats, mono-/polyunsaturated fats and trans fats. The fatty acid chains in saturated fats consist of only single bonds, indicating that there are no bonds available for further binding. Foods that contain high levels of saturated fat include whole milk, butter, cheese, lard, palm oil, coconut oil, “fatty” meat and meat products, fried food, and some cakes, biscuits and pastries. All of the above should be eaten in small amounts as saturated fats have a proven association with increased cholesterol levels, which can progress to clogged arteries and increased risk of heart disease and stroke. There have been numerous studies confirming the benefits of reducing saturated fats in our diets. For example, replacing saturated fats with unsaturated fats reduces cholesterol levels, thus decreasing the risks of heart disease and stroke.,  Both epidemiological and randomised clinical trials have consistently evidenced that replacing saturated fat with unsaturated fat, is beneficial in coronary heart disease. The fatty acid chains in unsaturated fats contain either one double bond (monounsaturated fat) or more than one double bond (polyunsaturated fat). Foods rich in these types of fats include vegetable oils such as olive, rapeseed or sunflower oils, avocados, nuts and seeds. It has been demonstrated these fats help decrease the risk of heart disease.,  Omega-3 fatty acids are a group of polyunsaturated fats found mainly in oily fish such as mackerel, salmon or sardines. Omega-3 fatty acids have many health benefits, and are associated with good heart health as they reduce the risk of blood clots and assist in the regulation of heart rhythm.,  They are also important during pregnancy and breastfeeding, supporting infant development.,  Trans-fats are the most harmful to our bodies. This group of fats are manufactured by partially hydrogenating vegetable oils, resulting in a firmer, better tasting fat with an increased shelf life. They are found in most processed and ‘fast’ foods, that are already very high in saturated fats. Manufactured trans-fats have been shown to have an even more adverse impact on cholesterol levels than saturated fats, which in turn is associated with diabetes and cardiovascular disease.,  Whilst knowing which fats are more healthy than others can certainly help in reducing the risks associated with fat consumption, some fats can actually become more harmful during cooking, depending on the processes involved. Vegetable oil, for example can accumulate by-products known to pose a significant risk of cardiovascular disease when heated repeatedly. Cooking can also change the ratio of healthier unsaturated fatty acids to unhealthy saturated fats and trans fats. Reducing fat in the diet is advisable to prevent obesity and its related complications, such as type 2 diabetes. Even beneficial mono-/polyunsaturated fats should be consumed in moderation, as they still have a high calorific value. In fact studies on mice have shown that a high fat diet induces greater weight gain than a low fat diet, even if their calorific intake is the same. A reduction of saturated and trans-fats in the diet can be achieved by avoiding processed and ‘fast’ foods as much as possible and choosing food prepared at home from fresh, low fat ingredients. Lean sources of protein, low fat dairy foods, legumes, fresh fruit and vegetables are a healthier choice than foods high in fat, although beneficial oils such as olive, canola and sunflower oil can be used for cooking and salad dressings.  Nelson, D & Cox, M. (2008). Lehninger principles of biochemistry. (5 ed.)  Jakopsen, M.U. (2009). Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. The American Journal of Clinical Nutrition. 85(5). 1425-1432  Mozaffarian, D. et al. (2010). Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLos Med. 7(3). e1000252  Siri-tarino, P.W. et al. (2010). Saturated fatty acids and risk of coronary heart disease: modulation by replacement nutrients. Current atherosclerosis reports. 12(6). 384-390  Covas, M.I. (2007). Olive oil and the cardiovascular system. 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