Fats and oils are compounds of fatty acids and glycerol and consist of carbon, hydrogen and oxygen, but in different proportions from those of carbohydrates. Fats and oils differ only in their physical states. When exposed to high temperatures, fat will melt and become oil; similarly, when oils are exposed to low temperatures, they solidify and become fats. Fats are found in plant and animal foods, but generally, oils are obtained from plants and fats from animals. Fats are broken down into fatty acids after digestion. There are several fatty acids, each with its own characteristics; some are known as essential fatty acids as they cannot be synthesised in the body.
Functions of fats and oils
1. The main function of fats and oils is to provide energy and heat. They are more concentrated energy foods than carbohydrates; thus, there are as many joules in a tablespoon of oil as in three slices of bread. If we depended solely on carbohydrates for energy, we would have to eat enormous amounts of food.
2. They serve as packing material in the body and help to support the kidneys, the eyes and most internal organs. They also help to round off the bones and give shape to the body.
3. They are necessary for the transportation of fat-soluble vitamins.
4. They are essential for the formation of nerve sheaths.
5. They are needed for the secretion of bile and sebum.
6. They act as a lubricant in the intestine and facilitate the passage of food along the digestive tract.
7. They add flavour to food when used in cooking.
However, if meals are too oily or contain too much fat, digestion will be upset. Fats and oils should form 12% of a person’s diet.
Digestion and absorption of fats
Chemical digestion of fats begins in the stomach, where the enzyme lipase, which occurs in the gastric juice, changes emulsified fats into fatty acids. In the duodenum, bile emulsifies the remaining fats, and lipase in the pancreatic juice converts the fats into fatty acids and glycerol. The digestion of fats is completed by the lipase in the intestinal juice. Fats take much longer to digest than carbohydrates, and for this reason one feels hungry sooner after a meal of carbohydrates than after one containing a large amount of fats.
The lacteals in the villi of the small intestine form part of the lymphatic system and are responsible for the absorption of fatty acids and glycerol.The lacteals convey these and products of fat digestion via the cisterna chyli and the thoracic duct to the left subclavian vein, where they join the blood circulation
During fat metabolism, fatty acids and glycerol combine with oxygen in the tissue cells to produce energy and heat. As a result of this reaction, carbon dioxide and water are produced and the body gets rid of this as waste.
Excess fats are stored in fat depots under the skin and help to keep the body warm. Some fats may be deposited around organs such as the kidneys, eyes and heart. However, too much fat around the heart will affect its efficiency and may result in heart disease. On the other hand, deficiency of fats in the body may be brought about by a condition known as malabsorption syndrome. In this disease, the body cannot absorb fats, and the person becomes ill.