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Demystifying Fat
Demystifying Fat!
Assunta Aversano discusses the different types of fat we eat, which foods they are found in and how our modern diet often lacks the right balance of these different fats
Rarely is fat cast in a positive light. Excess body fat has been linked to numerous health problems, including obesity, cardiovascular disease and various types of cancer. However, it is a myth that we should avoid all fats in our diet, as some fat is essential for health. Fat provides a concentrated source of energy, and contains essential fatty acids and fat soluble vitamins such as vitamins A, D, E and K.
It is essential to choose the right type of fat in our diet
There are different types of fat, and knowing which we should eat more or less of can be confusing. All fats consist of fatty acids, made up of carbon and hydrogen atoms. Subtle changes in their chemical structure give rise to the different types of fat.
Saturated fats are solid at room temperature. They are commonly labelled ‘bad’ fats, as they can have detrimental effects on our health, and need to be limited in the diet. A high intake of saturated fat is associated with increased amounts of harmful LDL cholesterol (low density lipoprotein cholesterol) in the blood (22, 27). This may cause a person’s arteries to clog and narrow in a process known as atherosclerosis, which increases their risk of having a heart attack or a stroke.
Unsaturated fats are generally liquid at room temperature. They are considered healthier than saturated fats because scientists believe that they are able to lower levels of harmful LDL cholesterol in the blood. This is because some unsaturated fats are thought to maintain levels of HDL cholesterol (high density lipoprotein cholesterol) in the blood. This may protect against heart disease and strokes by removing harmful LDL cholesterol from the arteries.
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Sources of saturated fats
Saturated fats are mainly found in animal products such as fatty meat, butter, margarines (especially hydrogenated margarines), lard, dripping, suet, ghee, cheese, cream, full-fat milk and full-fat yoghurt (24). Saturated fats are also found in a few vegetable products, such as coconut oil, palm oil and cocoa (24, 3) |
| Sources of unsaturated fats
Unsaturated fats are mainly found in vegetable foods and the oils derived from them. Rich sources include olive, sunflower, safflower, rapeseed (also known as canola), soya, avocado, nuts and seeds, green leafy vegetables and oily fish such as salmon, sardines and mackerel (3, 24, 30) |
There are two types of unsaturated fat – monounsaturated and polyunsaturated.
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Rich sources of monounsaturated fat include: Olive oil and olives, rapeseed oil (or canola oil), peanut oil and peanuts, hazelnuts, almonds, sesame seeds and sesame seed oil, avocado and cod liver oil (3, 30). |
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Rich sources of polyunsaturated fat include: Safflower oil, sunflower oil and sunflower seeds, corn oil, soya oil, sesame seed oil and sesame seeds, flaxseeds (also known as linseed), walnuts and walnut oil, rapeseed oil, grapeseed oil and oily fish such as mackerel, sardines, pilchards, salmon, kippers, trout, herring, eel, anchovies, carp, sprats and fresh tuna (3, 24, 30). |
There are two essential polyunsaturated fats which cannot be produced by the body, called alpha linolenic and linoleic fatty acids. Our body uses them to make omega-3 and omega-6 fatty acids.
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Sources of alpha linolenic acid and omega-3 Alpha linolenic acid is used to form omega-3 fatty acids. Rich sources include flaxseed oil and flaxseeds (or linseed), walnuts and walnut oil. It is also found in rapeseed oil (canola), soya and soya oil and green leafy vegetables (3, 30). Omega-3 fats are also found in oily fish (3, 30) |
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Sources of linoleic acid and omega-6 Linoleic acid is used to make omega-6 fatty acids. Rich sources include walnuts and walnut oil, sunflower oil and sunflower seeds, sesame seed oil and sesame seeds, safflower oil, corn oil, soya oil and soya products, evening primrose oil and vegetable oils (3, 30). Omega-6 fats are also found in meat and dairy foods (30) |
Omega-3 and omega-6 fats have a wide range of functions in the body. For example they are used to form cell walls, make hormones, and are found in the nervous system, especially the brain. They are also important for lubricating joints, blood clotting and wound healing. There is also evidence that they can boost concentration in children with learning difficulties and improve memory in the elderly (3, 19, 22, 23).
It is important that the ratio of omega-3 to omega-6 is balanced in our diet as well. The WHO recommend a balance of between 5:1–10:1 of omega-6 to omega-3 (31). This is because there is evidence that people who have much more omega-6 compared to omega-3 than this have an increased risk of many health problems.
Fat propaganda! – The detrimental effects of modern day food processing
A relatively new food processing technique called hydrogenation or partial hydrogenation is used to transform a liquid fat (derived from either vegetable or fish) to a hard fat, such as margarine and low fat spreads. This involves changing the chemical structure of the liquid fat by adding hydrogen molecules to it, which produces trans fatty acids or trans fats. Food manufacturers favour the use of hydrogenated fats since they can improve the texture of processed foods, and can extend a product’s shelf life.
However, trans fats are thought to be even more harmful to the body than saturated fat. This is because they increase levels of harmful LDL cholesterol and may also lower the beneficial HDL cholesterol. There is growing evidence to suggest that high intakes of trans fats are associated with an increased risk of heart disease. Scientists agree that a person’s intake of trans fats should be limited due to their detrimental effects on our health. It is also recommended that people reduce their intake of foods high in saturated and hydrogenated fats, which will reduce their intake of trans fats at the same time.
Sources of trans fats
Trans fats are found in shop-bought processed foods, for example hydrogenated and partially hydrogenated margarine and other spreads, cakes, biscuits, pastries and deep fried foods. Trans fats are also naturally found in dairy products, beef and lamb because they are formed during bacterial fermentation in the digestive systems of cattle and sheep. However, the main source of trans fats in the modern diet are those produced artificially by the food industry (1, 3, 6). Small amounts of trans fats have also been introduced into our diets through animal feeds which contain hydrogenated fat, so are found in poultry and pork, for example (1). Commercial oils may also contain trans fats (1).
The upshot of our modern-day existence
Our modern-day diet and sedentary existence unfortunately has many associated undesirable health implications. Societies are consuming far too much fat overall, and often the wrong types of fat. A modern diet contains much more hydrogenated and saturated fats and a higher proportion of omega-6 to omega-3 fats. Our healthier ancient diet consisted of more unsaturated fats and omega-3 fats, less saturated fat and certainly no hydrogenated fats or refined oils!
So How Much Fat Should I Eat?
The consumption of fat in moderation as part of a healthy diet and opting for ‘healthier’ types of fat are the initial steps to maintaining a healthier body and mind. In addition the Food Standards Agency recommends that we should consume at least 2 portions of oily fish per week (a portion is about 140g) (24). There is also evidence to suggest that people with coronary heart disease may benefit from eating 2 – 4 portions of oily fish per week (28, 29).
The daily recommendations for men and women are listed below and are a rough guide to the amounts of calories and nutrients a person should have in their daily diet.
Daily Energy and Nutrient Recommendations
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Daily Nutrient Recommended Amounts |
Men | Women |
| Energy (Kcals) | 2500 | 2000 |
| Carbohydrate (as sugars) (g) | 70 | 50 |
| Total Fat (g) | 95 | 70 |
| of which Saturated Fat (g) | 30 | 20 |
| Fibre (g) | 20 | 16 |
| Sodium (g) | 2.5 | 2 |
| or Salt (g) | 6 | 6 |
Scientific Advisory Committee on Nutrition, 2006 (13)
References
1. Department of Health, Dietary References Values for Food Energy and Nutrients for the United Kingdom. Committee on Medical Aspects of Food Policy, Report on Health and Social Subjects No 41,1991 HMSO, London.
2. B Holland et al. McCance and Widdowson’s The Composition of foods, 5th edition. (1991) The Royal Society of Chemistry and Ministry Agriculture, Fisheries and Food.
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13. Scientific Advisory Committee on Nutrition. Paper for information: development of guideline daily amounts 2006; SACN/06/28.
14. Grundy M S. The optimal ratio of fat-to-carbohydrate in the diet. Annu Rev Nutr 1999;19:325-41.
15. Wijendran V and Hayes KC. Dietary n-6 and n-3 fatty acid balance and cardiovascular health. Ann Rev Nutr 2004;24:597-615.
16. Fleith M and Clandinin MT. Dietary PUFA for preterm and term infants: review of clinical studies. Crit Rev Food Sci Nutr 2005;45(3):205-29.
17. Auestad N et al. Visual, cognitive, and language assessments at 39 months: a follow-up study of children fed formulas containing long-chain polyunsaturated fatty acids to 1 year of age. Pediatrics 2003;112 (no.3):e177-e183
18. Boehm G et al. Docosahexaenoic and arachidonic acid content of serum and red blood cell membrane phospholipids of preterm infants fed breast milk, standard formula of formula supplemented with n-3 fatty and n-6 long chain polyunsaturated fatty acids. Eur J Pediatr 1996;155: 410-416.
19. Stevens LJ et al. Essential fatty metabolism in boys with attention-deficit hyperactivity disorder. Amer J Clin Nutr 1995;62:761-8.
20. O’Connor et al. Growth and development in preterm infant fed long chain polyunsaturated fatty acids :a prospective, randomized controlled trail. Pediatrics 2001;108 (2): 359-71.
21. Innis S M. Trans fatty intakes during pregnancy, infancy and early childhood. Atherosclerosis 2006 (Suppl 7) 17-20.
22. Mahan LK and Escott-Stump S. Krause’s food, nutrition and diet therapy, 10th edition; 2000 W.B Saunders Company.
23. Seddon JM et al. Dietary fat and risk for advanced age-related macular degeneration. Arch ophthalmol 2001;119 1911-1199.
24. Food Standards Agency website, accessed 08/05/2007; http://www.eatwell.gov.uk
25. Stampfer MJ et al. Primary prevention of coronary heart disease in women through diet and lifestyle. The New Engl J of Med 2000; 343 no.1: 16-22.
26. Pedersen JI et al. Adipose tissue fatty acids and risk of myocardial infarction-a case control study. Euro J Clin Nutr 2000; 54:618-625.
27. British Nutrition Foundation website, accessed 12/05/2007. http://www.nutrition.org.uk
28. British Heart Foundation website, accessed 12/05/2007. http://www.bhf.org.uk
29. National Institute for Health and Clinical Excellence website, accessed 04/05/2007. http://www.nice.org.uk
30. Manual of dietetics practice 2nd edition; edited by Thomas B for The British Dietetic Association; 1994 Blackwell Science Ltd.
31. ISSFAL (International Society for the Study of Fatty Acids & Lipids); 1994 international recommendations on dietary polyunsaturated intake: http://www.issfal.org.uk
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