Tag: nutrition and diet

Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, phospholipids, and others. They are the most calorigenic among the biomolecules. Chemically lipids are hydrophobic.

On oxidation of 1gm of fat energy yield is 9.3 cal. For carbohydrate and proteins, the energy value is roughly around 4 cal. Vitamins are not energy yielding compounds.

The predominant lipids present in the biomembrane are phospholipids, having a polar water soluble phosphorous head and a non polar long aliphatic tail. The polar head is exposed on the surface while the hydrophobic tail remains buried inside.

Steroids like cholesterol are crystallisable lipids having four hydrocarbon rings (phenanthrene, consisting of three cyclohexane and one cyclopentane) and a long hydrocarbon side chain. Fatty acids are absent. Sterols are precursors of steroid hormone and vitamin D. They are essential for plant growth and flowering. Cholesterol forms bile salts and hence, essential for absorption of fatty acids.

Lipids (fats and oils) are compounds of carbon, hydrogen and oxygen where ratio of hydrogen and oxygen is less than that of the water. Lipids are esters of fatty acids and alcohol which form emulsion with water but are soluble in organic solvents. They are esters of three molecules of fatty acids and one molecule of trihydric alcohol glycerol, e.g., ghee, butter, cholesterol, carotene, eucalyptus oil.