Fats: Food sources, Functions, Chemical Nature, Digestion, Absorption and Utilization
Fats, like carbohydrates, are compounds of carbon, hydrogen and oxygen. However, they differ from carbohydrates in structure and properties. The term fat include fats and oils which are greasy in feel and insoluble in water. In addition to fat and oils there are certain fat-like substances such as cholesterol which are important in the body.
Chemical Nature of Fats and Oils
The major constituent of all fats and oils are fatty acids and glycerol. The fatty acids are composed of a chain of carbon atoms with other elements like hydrogen and oxygen. Some of the common fatty acids are palmitic, stearic, oleic and linoleic acids. The fatty acids can be classified in three categories on the basis of chain length:
Shorter chain fatty acids (10 or fewer carbon atoms),
Long chain fatty acids (12 to 20 carbon atoms) and
Very long chain fatty acids (20 or more carbon atoms).
Whenever we talk about fats and oils we come across terms like saturated fatty acids, unsaturated fatty acids and essential fatty acids. What do we mean by these terms?
A fatty acid chain of specified chain length (in terms of number of carbon atoms) has a fixed maximum number of hydrogen atoms. Certain fatty acids have as many hydrogen atoms as the carbon chain can hold. They are called Saturated fatty acids. On the other hand, unsaturated fatty acids have the capacity to accommodate more hydrogen atoms i.e. some hydrogen atoms are missing from the carbon chain. Now let us learn about the essential fatty acids. There are two fatty acids which cannot be synthesized in the body. These fatty acids have to be provided in the diet and are referred to as essential fatty acids. These are linolenic and linoleic acids. Both these fatty acids are unsaturated in nature.
You may recall that fats and oils are made up of glycerol and fatty acid. In fact a molecule of fat or oil has three fatty acids and a molecule of glycerol. This is called a triglyceride. Fats and oils are composed of many triglycerides or fat molecules.
Let us now see what is the difference between fats and oils. Both fats and oils are triglycerides but fats are solid at room temperature and have a higher proportion of saturated fatty acids e.g. ghee and butter. Oils, on the other hand have more unsaturated fatty acids and are liquid at room temperature e.g, mustard oil. groundnut oil. Usualiy, the term fat is used for both fats and oils.
Food sources of fats and oils include all common fats and oils like ghee,,vanaspati, mustard oil, groundnut oil, Soya oil, coconut oil. They are almost 100 percent fat.
The presence of fat is also evident in other foodstuffs like milk and milk products (curd, paneer, khoa), nuts and oilseeds (almond, groundnut, coconut, mustard seeds)* eggs and flesh foods. These are known as fat rich fods. They have 13 to 50 percent fat as shown in the table.
|Fat Rich Foods|
|Food Stuff||Fat content(g)|
You may be surprised to know that fat is present in very minute quantities in almost all foodstuffs. Even foods like cereals, pulses, fruits have fats in them in minute quantities (invisible form). These foods contribute a substantial amount of fat to Indian diets by virtue of being consumed in large quantities.
The term fat may be associated in your mind with a substance which is harmful for health You may consider fats as substances which would make you overweight and may endanger your life by causing disease like heart attack. This is a negative view about fats. Fats as macronutrients play a crucial role in the body. Problems come up only if you take fats in excess amounts i.e. more than the requirement of the body. You would realize how important fats are for your body as you go through the following important functions:
Source of energy: Fat is a concentrated source of energy. Each gram of fat provides approximately 9 Kcal. This is more than double the amount of energy supplied by a gram of carbohydrate or protein. Usually only a small amount of fat is used to meet the energy needs of the body. Most of the excess fat is stored in the body in specific tissues called adipose tissue. Adipose tissue is present under the skin, and in the abdominal region among others.
Satiety Value: What happens when you consume fat-rich diets? Do you feel hungry sooner or later? In fact, as you would have noticed, you feel full and do not feel hungry for a long time. This is because fats remain longer in the stomach and take more time to digest. Hence, like fibre, fats also give satiety value.
Insulation and padding: You have read that fat is stored in the body in adipose tissues at specific places. Layers of stored fat under the skin act as an insulator and keep the body warm. A layer of fat is also present around the vital organs of the body Like the kidney and the heart. This serves as a padding and protects them against injury.
Source of essential fatty acids: Fats serve as sources of essential fatty acids which have important functions in our body.
Carrier of fat soluble vitamins: You may know a category of micronutrients called vitamins. Some of the vitamins are soluble in fats and are termed as fat-soluble vitamins. Fats serve as carriers of these fat-soluble vitamins in the body and also aid in their absorption.
Digestion, Absorption and Utilization
In the process of digestion fats are broken down to their constituent components i.e. glycerol and fatty acids. The two enzymes which aid in the digestion of fats are gastric. lipase present in gastric juice and pancreatic lipase poured into the small intestine from the pancreas. For enzyme action fats need to be dispersed or mixed in water. You know fats are insoluble in water. A secretion from the liver called bile helps in fat digestion by breaking fat into small droplets. These fat droplets are then dispersed in the liquid digestive juice and are easily acted upon by enzymes. Since bile is not present in the stomach, the action of gastric lipase is not very significant. This is the reason why fats are chiefly digested in the small intestine where pancreatic lipase breaks them into glycerol and fatty acids aided by the action of bile.
The end products of fat digestion i.e. glycerol and fatty acids present in the intestine move into the intestinal cells. The fatty acids cannot enter intestinal cells as such. Bile salts play an important role in fat absorption by dispersing the fatty acids into small tiny water soluble units called micelles which can easily move into the intestinal cells.
Fatty acids and glycerol then get transported from the intestinal cells to blood circulation. They do not travel directly into the bloodstream but first enter the network of vessels (present in the villi of the small intestine) called lymph vessels. Then fatty acids from the lymph vessels enter the heart and from there move into the blood. Blood then carries them either to the adipose tissues where they are stored as concentrated sources of energy or to cells where they are broken down to provide energy (in a similar fashion as glucose and amino acids).
Cholesterol and its relationship to health and disease is a hot topic of discussion. You would probably have encountered this term in conversation, advertisements, newspaper columns, magazines and books. What is cholesterol? Cholesterol is a fat-like substance present in foods. It is different in structure from triglycerides i.e. fats and oils. Animal foods like milk, egg, organ meats, ghee, butter, cream are all rich sources of cholesterol. Plant foods like vegetable oils (mustard oil, groundnut oil, soya oil), nuts and oilseeds do not contain cholesterol. Some manufacturers of vegetable oils try to mislead the general public by making claims that their products do not contain cholesterol. You know that this claim has no basis. None of the vegetable oils contain Colour screen cholesterol.
Cholesterol plays many important roles in the body:
However, extra cholesterol over and above the body needs can be harmful.
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