Dietary fat
In the UK the average diet is far too high in fat and experts believe this is a major factor in the development of a number of important health problems. For example, heart disease, certain cancers and obesity have all been linked to diets rich in fat.
What is fat?
There are various types of fat, however, and they are not all bad. The three most important types are
- saturated fat
- polyunsaturated fat
- monounsaturated fat
Fats are classified by their "saturation" - a term that refers to the amount of hydrogen atoms attached to the molecules of fat. Many foods contain all three types in different proportions and, together, the three different types are known as "total fat". However, each type has a different effect on the body.
What is saturated fat?
Saturated fats are completely "saturated", in other words each fat molecule is covered in hydrogen atoms. Saturated fat is the "villain" of the three types of fat because it is known to increase health risks if too much is eaten over a long period of time. In particular, it has the effect of increasing blood cholesterol levels which, in turn, can lead to heart disease.
Where is it found?
Meat, meat products, dairy products and coconut oil contain the greatest amount of saturated fat. The easiest way to check whether a fat is saturated or not is to see how hard, soft or liquid it is at room temperature. It is easy to recognise saturated fat because it goes hard at room temperature. For example, the hard white substance that you can see in the pan after cooking foods such as roast beef, lamb, and bacon is the saturated fat that has melted out of the meat and then solidified. Hard cheese is the same. Many processed foods such as cakes, biscuits, pastries and crisps also contain saturated fats.
What is polyunsaturated fat?
Polyunsaturated fats are not "saturated" with hydrogen atoms. In other words there are a number of spaces around each fat molecule where hydrogen atoms could be attached. Polyunsaturated fat is beneficial to health. Particularly good are polyunsaturated fats from fish, known as omega-3 polyunsaturated fatty acids. These may help prevent heart disease by lowering blood cholesterol levels. Also they may help to reduce the symptoms of arthritis, other joint problems and certain skin diseases. Unlike saturated fat, they are liquid when at room temperature.
Where is it found?
Good sources of polyunsaturated fats are oily fish (for example mackerel, salmon, trout, herring and sardines) and soft polyunsaturated spreads. Other sources include cooking oils such as safflower, grapeseed, sunflower and corn.
What is monounsaturated fat?
Monounsaturated fats are also not "saturated" with hydrogen atoms. As their name suggests, each fat molecule has space for one more hydrogen atom only. Generally, monounsaturated fats have been thought to be neutral in terms of their effect on health. However, some experts now believe that they do have health benefits, for example, reducing heart disease risk. The so-called "Mediterranean diet" is rich in monounsaturated fat.
Where is it found?
Monounsaturated fats are found in olives, olive oil, groundnut oil, nuts, and avocados.
How much fat should we eat?
All types of fat are energy dense: 9 kcalories per gram. In fact fat (in all its forms) contains more kcalories than any other food source. Because of this it is easy to consume too many calories from fat and this, in turn, may contribute to weight problems.
The current recommendation is that we should take in no more than 33 percent of our total energy (kcalories) from total fat. Breaking this down further, saturated fat should account for no more than 10 percent of our total energy (calories) because of its harmful effects on health. The rest of the calories from fat should come from monounsaturated or polyunsaturated fats because these are more beneficial to health.
What does this mean in practical terms?
If you are eating 2,000 calories a day, 33 percent amounts to 73 grams of total fat. If your daily calorie intake is 1,500 calories, 33 percent amounts to 55 grams of total fat.
Fortunately, most food labels do contain information about the number of grams of fat in the product.
Some tips to help reduce the fat in your diet
- use semi-skimmed or skimmed milk instead of whole milk
- switch to a low-fat spread instead of butter or margarine
- eat more chicken and fish and less red or fatty meats
- choose lean cuts of meat and trim off all the excess fat
- grill, bake, steam or microwave food rather than frying it
- try low-fat varieties of dairy products such as cheese and yoghurt
- choose polyunsaturated cooking oil or monounsaturated olive oil
- avoid high-fat snacks such as crisps, biscuits, cakes and pastries
References
Department of Health. Nutritional Aspects of Cardiovascular Disease. HMSO. 1994
Department of Health. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. HMSO. 1991.
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