Concept about Lipid / Fat | CHAPTER 17 | Basic Science

Concept about Lipid/Fat – Introduction to fundamental concepts of Biological Science including the organization and common characteristics of living matters, cell structures and functions, food production by photosynthesis, harvesting energy, mechanism of cells reproduction, genetics, evolutions, and Human Biology. Introduction to general chemistry including basic concepts about matter, atomic structure, chemical bonds, gases, liquid, and solids, solutions, chemical reactions, acid, bases, and salt;

organic and biochemistry including hydrocarbons and their derivatives, carbohydrates, lipids, proteins, enzymes, vitamins, and minerals, nucleic acids; principles of physics and applications to nursing including gravity and mechanics, pressure, heat and electricity; nuclear chemistry and nuclear physics, effects of radiation on human beings, and protection and disposal. The aim of the course is to acquire knowledge and skills in general biological science, general chemistry and physics.

Concept about Lipid / Fat

Fat is one of the three main macronutrients, along with carbohydrate and protein. Fats, also known as triglycerides, are esters of three fatty acid chains and the alcohol glycerol. The terms “oil”, “fat”, and “lipid” are often confused. “Oil” normally refers to a fat with short or unsaturated fatty acid chains that is liquid at room temperature, Fat is an essential part of our diet and nutrition, and we cannot live without it.

Our bodies require small amounts of ‘good fat’ to function and help prevent disease. However, a lot of modern diets contain far more fat than the body needs. Too much fat, especially too much of the wrong type of fat, can cause serious health complaints including obesity, higher blood pressure and cholesterol levels, which in turn lead to a greater risk of heart disease. Dietary fats make food tasty they often improve the texture of food as well as flavor and smell they make food more appealing.

Definition of Lipid/Fat:

Lipids more commonly known as fats and oil, are integral part of our food. They are insoluble in water but soluble in organic solvents. They occur in both plant and animals. Lipids are a concentrated source of energy.

OTHER DEFINITIONS – NICE TO KNOW

• Fats are also known as lipids. Fat supplies main energy to the body. Fats are organic compounds composed of carbon, hydrogen and oxygen. Fats are insoluble in water and soluble in organic solvents like ether, benzene or chloroform. Smaller unit of fat is called as fatty acids.
• Fats or lipids are made of fatty acids (saturated, polyunsaturated, monounsaturated), triglycerides, phospholipids, glycolipid etc. Fats are solid at 20 degree; they are called ‘oil if they are liquid at that temperature.
• Fat is a major source of energy in the diet. Dietary fat contains nine calories per gram, which is more than twice the number provided by, carbohydrates or protein. Due to its high caloric content, the chance of becoming obese increases with a high intake of fat.
• Fat is an organic substance which composed of the elements carbon, hydrogen, oxygen. They formed by the combination of glycerol and fatty acid.

Classification of Fat/Lipid:

Lipids are classified into simple, compound and derived lipids whic are further subdivided as follows.

1. Simple lipids

• Fats and Oils are included in this type. At room temperature, oils are liquids and fats are solids. Fats and oils contain esters of fatty acid and glycerol, a form in which lipids are present in food.

2. Compound lipids

• They are esters of fatty acids containing phosphorous carbohydrate or protein. Phospholipids contain a phosphoric acid in addition to the alcohol and fatty acids.
• Glycolipids contain a fatty acid, carbohydrate and a nitrogenous base. Phospholipids and glycolipids form part of the cell membrane and the nervous system.
• Lipoproteins are macromolecular complex of lipids with proteins.

3. Derived lipids

• These are substances liberated during hydrolysis of simple and compound lipids which still retain the properties of lipids. The important members of this group are sterols, fatty acids and alcohol.
• Sterols

✓ Sterols are solid alcohols and form esters with fatty acids. In nature they occur in the Free State in the form of esters.
✓ Based on their origin sterols are classified as cholesterol (animal origin) and phytosterol (in plants),
✓ Cholesterol is a complex type of lipid that is regularly synthesised by and stored in the liver. It is present in all animal products.

(Ref: Joshi’s Nutrition and Dietetics/3rd/68)

Fatty acids:

Fatty acids are the main building blocks of fat. They have a methyl group (CH3) at one end and a carboxyl group (COOH) at the other end with a chain of carbon and hydrogen atom in the middle. They have a basic formula CH3 (CH2) n COOH. Where ‘n denotes the number of carbon atoms which may vary from 2 to 21.

Classification of Fatty Acids:

Fatty acids can be classified into Saturated Fatty Acids (SFA) & Unsaturated Fatty Acids (UFA)

1. Saturated Fatty Acids

• Saturated fatty acids are those that are unable to absorb more hydrogen. They are usually stiff and hard fats. Eg. Ghee, Butter.

2. Unsaturated fatty acids

• Unsaturated fatty acids have one or more double bond in their molecule and are thus not saturated with hydrogen. They are liquid at room temperature. Eg. Sunflower oil.

Sources of Fat:

1. Animal fat:

Animal fat containing mainly saturated fatty acid and glycerol.
E.g. –

• Milk and milk product,
• Eggs meat,
• Fish,
• Cord liver oil.
• Halibut liver oil,
• Sea fish etc.

2. . Sea fish:

• Salmon fish.
• Trout.
• Mackerel.

3. Vegetable sources:

It containing mainly unsaturated fatty acids and glycerol.

E.g. –

• Seeds of grounds,
• Mustard oil,
• Sesame,
• Coconut oil,
• Pum oil, dulta, corn oil, coconut oil.

Lipids perform several important functions:

Effects of Fat Deficiency:

1. Dryness of the skin.
2. Swelling of the foot and leg.
3. Eczema of the children
4. Toad skin or phrenoderma.
5. Indigestion.
6. Constipation.
7. Acidosis.
8. Coma e.g. Diabetic coma
9. Gall bladder, urinary bladder (stone).

Demerits of Taking Excess Fat in Diet:

• Obesity.
• Coronary heart disease.
• Cancer of colon
• Cancer of breast.
• Others-Skin lesion

Essential Fatty Acids:
Essential fatty acids are those that cannot synthesize by human, they can be derived only from food.

Name and sources of essential fatty acids

Fig: Structure of essential fatty acids

Functions of essential fatty acids:

1. Maintenance of the function and integrity of cellular and subcellular membrane.
2. Regulation of cholesterol metabolism by transporting it between the blood and body tissues
3. Acts as precursor of hormone like – prostaglandin which aid in regulating vascular function and help relieving pain and inflammation.
4. Delays blood clotting time.

Digestion, Absorption and Metabolism of Fat:

Digestion

1. In the mouth:

• Fat digestion starts in the mouth with hard fats beginning to melt when they reach body temperature
• The salivary glands at the base of the tongue release a lipase enzyme which digest fat to a less extent in adults.

2. In the stomach:

• In the stomach fat floats as a layer above the others components of swallowed food. As a result little fat digestion takes place.

3. In the small Intestine:

• When fat enters the small intestine, the hormone cholescystokinin signals the gall bladder to release bile.
• Bile emulsifies fat and also provides an alkaline medium for the action of pancreatic lipase and intestinal lipase.
• The triglycerides are acted upon by these lipases and hydrolyzed to monolycerides and fatty acids.
• The cholesterol esters are hydrolyzed to give cholesterol and fatty acids.

Triglycerides —————–> Monoglyceride + fatty acids

Cholesterol esters —————–> Cholesterol + fatty acids

Absorption and metabolism:

1. Small molecules of digested triglycerides (glycerol, short & medium chain fatty acids) can diffuse into intestinal cells and are absorbed directly into the blood stream.

2. Larger molecules (Monoglycerides, long chain fatty acids) merge into spherical complexes known as miscelles. The lipid contents of the miscelles diffuse into the intestinal cells. Once inside the monoglycerides and long chain fatty acids are reassembled to new triglycerides.

3. Within the intestinal cells the new triglycerides and larger lipids like cholesterol and phospholipids are placed into transport vehicle called chylomicrons.

4. The intestinal cells then release chylomicrons into the lymphatic system. The lymph circulation empties into the thoracic duct which inturn enter the subclavian vein and subsequently into the blood stream.

5. The blood transport lipids to the rest of the body and cells absorb them and utilize for energy. This breakdown of fat to yield energy is called lipolysis.

6. Majority of lipids enter via the lymph to the liver where the protein and lipid (cholesterol, triglycerides) are bound together to form lipoproteins.

Briefly discuss about visible and invisible fat.

Foods in general contain two types of fat namely “visible fats” and “invisible” or “hidden” fats.

Visible Fats

Visible fats are fats extracted from the natural sources.

• Oil seeds: coconut, corn, corn seed, groundnut, mustard, palm, rice bran, safflower, seasame, soyabean, sunflower and hydrogenated vegetable oils (vanaspathi).
• Animal fats: Butter and Ghee.
• Fish oils: Shark and cod liver oils.

Invisible Or Hidden Fats:

Invisible or hidden fats are those which form an integral part of foods and are therefore not visible. It includes the fats present in the cells and cell walls and cell membranes of both plant and animal tissues.
Almost everything we eat as listed below carries some invisible fats.

• Plant food – Cereals, millets, vegetables, spices, nuts and oil seeds, coconut, avacado.
• Animal food – Milk and milk products (curd, cream, cheese), flesh foods, (mutton, beef, pork, chicken) organ meats (brain, liver, kidney), fish, shrimp, prawn.

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