Dietary fats contain about 150 gm of fat mainly in form of Triglycerides, phospholipids, Cholesterol. About 5 gm of the fat is removed from faeces daily. In blood, lipids always exist in combination with proteins and such a combination is called as Lipoproteins (Lipid + Proteins). Lipids are easily stored in the body. They serve as a source of fuel and are an important constituent of the structure of cells. Cholesterol, triglycerides, phospholipids, free fatty acids are transported as lipoproteins in combination with proteins.

 

 

 

What is LDL (Bad) Cholesterol?

LDL cholesterol (LDL-C) or the "bad cholesterol” consists mainly of cholesterol. It has three fates. It can be engulfed by some cells or organs where cholesterol part can be converted to various hormones like in Liver, Adrenal glands etc. LDL particles can be removed from the bloodstream by macrophages that deposit these particles on the blood vessels. This is done via an enzyme called as acyl-CoA-cholesterol acyltransferase (ACAT) which converts excess of the intracellular cholesterol into cholesterol esters, for intracellular storage. High cholesterol intake in diet can lead to Excess of the cholesterol esters in the cells and hence can lead to disease called as atherosclerosis. If a clot forms and blocks a narrowed artery, heart attack or stroke can result.

Most LDL particles are absorbed from the bloodstream back into liver by receptor present on the liver called as LDL receptors. Diets high in saturated fats and cholesterol decrease the uptake of LDL particles into the liver.

 

What is HDL (good) Cholesterol?

High-density lipoproteins (HDLs) are a separate group of lipoproteins that contain more of the protein and less of cholesterol than LDL. HDL cholesterol (HDL-C) is also called "good cholesterol."  HDLs are synthesized in the liver and small intestine. The newly formed HDLs don’t have any cholesterol or cholesteryl esters. But these HDL particles acquire cholesterol from the cells and become HDL-Cholesterol (HDL-C) via an enzyme present in liver called as lecithin: cholesterol acyltransferase (LCAT). This process has the effect of lowering the level of intracellular cholesterol, which will be used for formation of Plaques by the cells and cause atherosclerosis.

Function of HDL cholesterol is to remove cholesterol from cells especially deposited within arteries and transport it back to the liver for excretion or re-utilization. The process is called as REVERSE CHOLESTEROL TRANSPORT. So HDL-bound cholesterol is sometimes called "good cholesterol", or HDL-C.

 

A high level of HDL-C seems to protect against cardiovascular diseases, and low HDL cholesterol levels (less than 40 mg/dL) increase the risk for heart disease.

 

Written by Dr Vaishalee Punj