Fats are an essential part of the human diet as it has many functions including :
- being a source of energy
- absorption of fat-soluble vitamins
- components of vital structures within the body such as cell membranes and nerve linings
- providing cushioning for vital organs
- insulation for the body
Whilst the human body can synthesize many forms of fatty acids itself there are certain fats that need to be sourced from food. These are called essential fats.
Fat enhances the taste and flavor of food and slows the rate at which stomach contents are emptied (gastric emptying) thereby leading to the feeling of satiety after a fat laden meal. In order to be absorbed, fat must be emulsified by bile released from the gall bladder and then broken down by digestive enzymes like pancreatic lipase. Overall, the process of fat digestion and absorption is very efficient – up to 95% of the fat from the diet is absorbed into the body.
While fats are an essential part of a healthy diet, it can also cause a host of diseases. Fat provides more energy ounce for ounce than carbohydrates or proteins. If this energy supply is not needed, it will be stored in the adipose tissue thereby leading to obesity. In developed countries, obesity is the leading cause of death as it has a host of health consequences especially due to its role in heart disease and diabetes mellitus (sugar diabetes).
There are three types of fats that should be taken note of in terms of the dietary management of hypercholesterolemia and hypertriglyceridemia.
- Saturated Fats
- Unsaturated Fats
- Trans Fats
These days, the quantity of different types of fats are clearly indicated on food packaging.
What are Saturated Fats?
A fat is made up of long chains of hydrogen and carbon. Between carbon atoms there may be double or single bonds. If there are no double bonds the fat is completely saturated with hydrogen, and therefore a saturated fat. Although the exact mechanisms between dietary elements and health consequences are unclear, it appears that saturated and unsaturated fats have different effects on the cholesterol levels.
Excess saturated fat raises LDL cholesterol, the “bad cholesterol”, thereby contributing to build up of fatty deposits in the arteries (atherosclerosis), with heart and vascular disease as the consequence. Sources of saturated fats include :
- dairy products – butter, cheese, milk, ice cream, cream
- certain oils – coconut, palm and palm kernel oil.
What are Unsaturated Fats?
If there is a double bond between the two carbon molecules in fatty acids, then it is termed unsaturated fats, as less hydrogen can be present in the molecule. Unsaturated fats may be monounsaturates, with one double bond or polyunsaturates with more than one double bond.
Monounsaturates and polyunsaturates appear to increase HDL cholesterol (the good cholesterol), which assists in the removal of triglycerides from the bloodstream.
Sources of polyunsaturated fats include :
- certain oils – sunflower, corn and soybean oils
Sources of monounsaturated fats include :
- olive oil
- canola oil
In monounsaturated fats there are two types of molecules, depending on the arrangement of the carbon chains on either side of a double bond. Where the two carbon chains appear on the same side of the double bond (the molecule winds back on itself) this is called cis-fatty acid. Where the carbon chains appear on separate sides of the double bond (the molecule appears as a straight line) and this is called a trans-fatty acid or trans fats.
What are Trans-Fats?
Trans fat has a similar effect to saturated fat in the body. It increases LDL cholesterol (bad cholesterol) and lowers HDL cholesterol (good cholesterol).
Trans fats tend to be found when vegetable oils harden or hydrogenate, therefore any food reported to contain hydrogenated or partially hydrogenated fat should be avoided. Trans fats are typically found in :
- fried food
- baked goods such as cakes and pastries
- processed foods