Lipids: Functions, Structure, Derivatives, and Optimal Dietary Intake

What is lipid?

Lipids are heterogenous group of organic compounds having a greasy and waxy consistency that dissolves in alcohol and other non polar organic solvents (acetone, ether, chloroform, benzene) but are insoluble in water. Lipids derivatives will be discussed in detail in this article

Lipid comprises of carbon, hydrogen and oxygen with different configuration having less oxygen atom as compared to carbohydrate. They are found naturally on the cellular components of plants, animals and microorganisms.

The four fat soluble vitamins are A, D, E and K which helps in absorption in the small intestine which provides more concentrated energy in comparison to carbohydrate diet.

Lipid provides an energy of 9 kilocalories per gram. 

Function of lipids

• Lipid is a complete structure of glycerol and fatty acid molecule that is a major structural component of the cells membrane.
• Lipids store energy in the form of triglycerides, fat cells and lipoproteins which provides enough energy for a body to function for several weeks.
• Steroid hormones are lipid derived hormones that acts as a chemical messenger and provides thermal insulation for testosteron and estrogens.
• Lipid beneath our skin help us in maintaining our body temperature and insulate our body.
• Lipid also provides protection to the vital organs like heart, liver, kidney from injuries by covering around them with a layer of fats.

Structure and its derivatives

Lipids are glycerol molecules that is bonded with a single or multiple hydrocarbon chain.

Lipids are of three types namely,

1. Triglycerides
2. Phospholipids
3. Sterols

Triglycerides (fats)

• Lipid consisting of a glycerol molecule with three chains of fatty acid linked with OH group by an ester bond. An example of simple triglyceride is tristearin because it contains only one type of fatty acid.
• However two or more types of fatty acid containing molecule is called mixed triglycerides.
• Depending upon the number of bonds in the hydrocarbon in the chain, the compound may vary as saturated and unsaturated fatty acids.
• Saturated fatty acids are straight chain even carbon number molecules with no double bond because they are saturated with hydrogen molecules. Butter, coconut oil and other animal fats are an example of saturated fatty acid that remains solid at room temperature.
• Unsaturated fatty acids are a chain of carbon molecules with one or more double bond between hydrogen molecules. If a fat molecules contain single double bond then it is monosaturated and polyunsaturated if two or more double bond are present.
• The fatty acid with double bond are less stable and remains liquid at room temperature. Monosaturated fats include plant based liquid oil such as canola oil, olive oil, sesame oil. Similarly, polysaturated fats include walnuts, flax seeds, fish, corn oil, sunflower oil.
• Adequate amount of triglyceride provides energy and aids in absorption and transporation of fat soluble vitamins but when taken in excess amount causes fatty liver disease as high triglyceride level thickens the arteries which increases the risk of heart diseases.

Sterols

• Sterols are found in plants as a mixture with β-sitosterol, campesterol and stigmasterol whereas it is found in animals and microorganims as cholesterol, zoosterol and mycosterols.
• Cholesterol is the most common sterol in animal body and is not essential to include on our diet because our liver can synthesize cholesterol enough to provide structure to the cell membrane and nerve sheath.
• Cholesterol containing animal products are meat, egg yolk, fish, poultry and dairy products. High amount of cholesterol deposition piles up in the wall of arteries and cause myocardial infarction and heart stroke.
• But most people think cholesterol is bad for health but taking adequate amount of cholesterol helps in bile and steroid homrone formation. Cholesterol also helps in the absorbtion and activation of UV light to synthesize Vitamin D in our body.
• Similarly, plant sterols are used to lower the cholesterol level and also reduces the risk of cardiovascular diseases but these sterols can build up in heart valves and cause stenosis.

Phospholipids

• Phospholipids are similar to triglycerides having a hydrophilic phosphate group and hydrophobic nitrogen containing compound such as choline, ethanolamine or serine.
•  Phospholipids are emulsifier that helps two liquid component i.e, water and oil to mix together. Lecithin is one of the example of emulsifier that are found in egg yolk, mustard, peanuts and liver.
• Phospholipid protects our brain and neurotransmitter. It helps in controlling the positioning of sensory neurons and acts as an insulator within the brain and spinal cord.

An excess amount of lipid intake causes fat deposits on the wall of arteries and leads to heart diseases. Therefore, according to the dietary reference intake (DRI), a healthy adult should include 20 to 35% of fat from total calories of food.

If you consume about 2000 calories a day then 44 to 77 grams of fat must be included on a diet.