Authors: Apurva Sharma, Syama M. A., Chitra Gupta and Sumit Arora
ICAR-National Dairy Research Institute
Functions of lipids on human health
- Lipids as a source of energy: Fats are primary source of energy and has a high calorific value than carbohydrate and protein. Thus it is good fuel for energy production. Fats supply 9.0 Kcal/g energy whereas, proteins provide 4.0 Kcal/g and carbohydrates supply around 3.8 Kcal/g. Therefore, fats supply two times more energy per unit weight as supplied by proteins and sugars. Being a concentrated form of energy, fats are particularly useful for the infants and children to meet their energy requirement. It increases the energy density and decrease the bulk of diet. High calorific value of fat is of special significance because the fat stored in the body is available as source of energy during food shortage. Saturated fatty acids containing more than 18 carbons are less digested and the efficiency of digestion decreases as the chain length of fatty acids increases. Therefore, fats which have high proportion of very long chain saturated fatty acids have low digestibility compared with fats which contain shorter and more unsaturated fatty acids.
- Lipids as supplier of structural components: Dietary fats supply structural components (i.e. the lipids used in the cell formation) in the form of fatty acids or cholesterol.
- Lipids as supplier of essential fatty acids: Certain poly unsaturated fatty acids are needed for various body functions but it cannot be synthesized by body. Therefore, these kinds of fats are called essential fatty acids. It is one of the most important constituents of lipids which contribute towards human health and nutrition. The most important essential fatty acids are linoleic, linolenic and arachidonic acid. These poly unsaturated fatty acids perform two vital functions. Firstly, it play a role in stability of biological membranes by creating desirable physical properties and secondly, it acts as a precursor in the biosynthesis of a range of oxygenated compounds like prostaglandins, thromboxanes, leukotrienes, hydroxyl fatty acids etc. which perform number of physiological activities. Deficiency of essential fatty acids results dermatosis which affects growth and reproduction.
- Lipids as supplier of fat soluble vitamins: Dietary fats provide several fat soluble vitamins (like vitamin A, D, E and K).
- Vitamin A: It is found as such in animal fats. However, green vegetables and veg oils contain precursor called carotenoids such as ß carotene which gets converted into vitamin A in the body. It helps to initiate vision from light energy, essential for growth and maintenance of epithelial tissue. Deficiency of vitamin A causes night blindness, inflammation of cornea, retardation of normal growth, defects in teeth and disturbance in bone growth.
- Vitamin D: There are two forms of vitamin D i.e. D3 (cholecalciferol) from animal origin and D2 (Ergocalciferol) from plant origin. It helps in the absorption, retention and better utilization of calcium and phosphate in the body which essential for bone formation and teeth formation. It also regulates the levels of calcium and phosphorous in blood. Its deficiency leads to rickets in children and osteomalacia in older people. Both these diseases are characterized by soft bones and twisting of bones or deformed bones.
- Vitamin E: This vitamin is wide spread in foods. It store in the body so that deficiency states are rarely seen. It is a powerful antioxidant which prevents peroxidation of unsaturated fatty acids and membrane fatty acids. Its deficiency results sterility in males and missed abortion in females therefore, vitamin E is called as anti-sterility factor.
- Vitamin K: There are two forms of vitamin K i.e. Vitamin K1 (phytyl menaquinones) from plant origin and vitamin K2 (prenyl menaquinones) from animal and bacterial origin. Human intestinal bacteria are capable of producing our entire needs. This vitamin is necessary for normal clotting of blood. Deficiency of vitamin K causes hemorrhagic problem.
- Contribution of lipids to palatability of food: The presence of fat particularly milk fat contributes substantially to the palatability of food. Mainly low molecular weight volatile fatty acids contribute to flavour. Short chain fatty acids have a more intense taste and smell than longer chain fatty acids. Chemical changes of lipids may give rise to alcohols, esters, carbonyl compounds and lactones which contribute to the unique flavour to different fat containing products. Lipids also contribute towards body and texture of product which are concerned parameter for consumer.
- Toxicity of lipids: Toxicity of lipids can be due to the presence of following:
- Cyclopropene fatty acids: Cyclopropene fatty acids i.e. malvalic acid (18:1) and sterculic acid (19:1) which present in cottonseed oil can cause toxicity effects like inhibition of desaturation of stearic acid to oleic acid. Thereby altering the permeability of membrane.
- Branched chain fatty acids: Some branched chain fatty acids e.g. phytanic acid (3, 7, 11, 15-tetra methyl hexadecanoic acid) are present in ruminant tissue and also in some dairy products. Due to some specific disorders some people cannot utilize branched fatty acids and cause toxic like effects like chornic neuropathy, night blindness, narrowing of the visual field, skeletal abnormality and cardiac complication.
- Trans fatty acids: ingestion of excessive amount of trans fatty acids results in the following metabolic disorders:
- Disturb the metabolism of available essential fatty acids.
- Decrease the concentration of essential fatty acids in heart muscle.
- Symptoms of essential fatty acids deficiency are aggravated.
- Long chain medium unsaturated fatty acids : Some naturally occurring edible oil contains appreciable quantities of medium unsaturated fatty acid like Erucic acid (C 22:1). Rapessed oil and mustard oil contains Erucic acid which adversely affect the heart muscles.
- Oxidized fats: Heating of unsaturated fats results extensive chemical changes and generates a wide range of polymerized compounds. It affects liver, kidney and heart organs.
- Role of dietary lipids in disease processes:
- Cardiovascular disease: It is a collective name for a number of diseases which affect the supply of blood to the heart.
- Obesity: Excessive accumulation of fat in the adipose tissues of the body results obesity. It occurs when the intake of energy is not precisely matched by energy expenditure. High fat diets play an important role in the development of obesity. Hence too much dietary fat should be avoided.
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