Dieting Basics 2: Fats – mono, poly, trans – which are good?

by Ali on May 29, 2008


(This is the second post in the Dieting Basics series.)

What are fats?

Fats, like carbohydrates, provide energy – in fact, they’re an even more concentrated source of energy (containing 9 calories per gram.) They’re made up of fatty acids (chains of carbon and hydrogen atoms), and just as with carbohydrates, the length of the chain varies between different types of fats.

We need fats in our diet – they’re an essential nutrient for our bodies to keep functioning. There are small amounts of fat in most foods, even fruits and vegetables.

Different types of fat

Most of the fats in the food we eat are triglycerides. These consist of three fatty acid molecules attached to a glycerol molecule and are used as a source of energy or stored as body fat. These fatty acid molecules can be saturated (with no double-bonds between carbon atoms) or unsaturated (one or more double-bonds in the carbon chain.)

The types of fatty acids in the triglycerides determine the physical state of the fats. Those with saturated fatty acids, like meat, are solid at room temperature, whereas those with unsaturated fatty acids, like vegetable oils, are liquid at room temperature.

Unsaturated fats are further divided into monounsaturated and polyunsaturated.

Monounsaturated fats are liquid at room temperature, but turn solid when refrigerated. They’re often found within other foods, though: olive oil contains oleic acid, which is one monounsaturated fat. There are also some monounsaturated fats in foods like peanuts and avocados.

Polyunsaturated fats are liquid when at room temperature and when refrigerated: these generally come from plant sources (nuts, seeds and vegetable oils).

Why are saturated fats bad and unsaturated fats good?

Saturated fats raise your cholesterol levels, and high cholesterol can lead to heart problems.

But we do need some fat to keep our body functioning. In particular, there are two fatty acids that our body can’t make on its own – so we need to get these from our food. These are called linoleic acid (omega-6s) and linolenic acid (omega-3s). Both are polyunsaturated fats, found in plant foods, and oily fish is also rich in omega-3.

If you don’t get enough omega-6 and omega-3, you risk health problems such as inflammation and heart disease. These fatty acids also help to keep your cholestoral levels low. Dry skin and dry hair can be symptoms that you’re lacking in these essential fatty acids.

What are trans fats and why are they so bad?

Most trans fats are created by an artificial process; hydrogenation (this is why they are also known as partially hydrogenated fats). Hydrogen atoms are forced onto the molecules in polyunsaturated vegetable fats, to turn the oil into a solid rather than liquid substance, and prolong the shelf-life of the food. This means that the double bonds between carbon atoms in the unsaturated fat become single bonds.

If a vegetable oil is fully hydrogenated, it’s not a trans fat, but it becomes firm and. difficult to use in cooking. So oils are partially hydrogenated instead, creating a soft product used in baking and processing foods such as margarine and partially hydrogenated frying oils. Trans fats are commonly found in cakes, doughnuts cookies and any processed foods – though the consumer backlash against them has led many manufacturers to produce products that don’t use trans fats.

Trans fats have been linked to cardiovascular disease, as they raise levels of “bad” cholesterol and reduce levels of “good” cholesterol. There are also concerns that consumption of trans fats may lead to increased risk of diabetes, obesity, liver dysfunction and infertility.

Small amounts of natural trans fats occur in milk and beef, but these are not associated with the same health risks as artificially produced fats.

What foods are sources of “good” fats?

Keep an eye on your overall calorie intake (it’s particularly important to weigh out portions of high-fat foods) but try to include a few of these in your diet:

  • Avocados
  • Olive oil (in cooking and on salads)
  • Oily fish: salmon, mackerel, tuna and sardines
  • Seeds and most nuts
  • Polyunsaturated margarines

If you missed part one of the Dieting Basics series, find it here: Carbohydrate confusion – are they good or bad? … and make sure you get the rest of the series by subscribing to The Office Diet in your feed reader.(Image above by 96dpi)

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