We extend our deepest gratitude to Dr Kelkar for sharing his insights with us and taking out time to educate us about such an important topic. We are humbled by his extensive knowledge and detail about the subject. It has been a pleasure and an honour to be mentored by him.
Fat is one of the important energy source derived from foods. 1 g of fat gives us 9Kcal of energy. Most lipids found in the human body from ingesting food are triglycerides and cholesterol. More than 95% of dietary fat is long-chain triglycerides (complex fats). Most cells in our body can produce cholesterol on their own. Only a few cells need cholesterol supply. Cells need cholesterol to maintain its structure.
Now let us see how a complex molecule of Fat is Metabolized
Fats Metabolism I: Through Gastrointestinal Tract
Fats or Lipid metabolism is the synthesis and degradation of lipids in cells, involving the breakdown or storage of fats for energy.
Lipogenesis is the process of synthesizing fats. Lipids are hydrophobic molecules, they need to be solubilized before their metabolism begin. Lipid metabolism often begins with hydrolysis, which is the process of breaking the triglycerides (complex fat units) down into smaller monoglyceride (simple fat units) with the help of lipase enzymes.
When fat is ingested, the digestive system breaks it down into its component parts, i.e. Free fatty acids and monoglycerides. Digestion of fats begins in the mouth through chemical digestion by lingual lipase. Lipids then continue into the stomach where chemical digestion continues by gastric lipase and mechanical digestion begins.
The majority of lipid digestion and absorption occurs once the fats reach the small intestines. Chemicals from the pancreas are secreted into to the small intestines to help breakdown the triglycerides, along with further mechanical digestion, until they are individual fatty acid units able to be absorbed into the small intestine’s epithelial cells.
Absorption is the second step after the hydrolysis. In this, the fatty acids are absorbed into the epithelial cells of the small intestinal wall. In the epithelial cells, fatty acids are packaged and transported to the rest of the body. Once the triglycerides are broken down into individual fatty acids and glycerol, along with cholesterol, they will aggregate into structures called micelles to enter the epithelial cells.
In the cytosol of epithelial cells, triglycerides and cholesterol are packaged into bigger particles called Chylomicrons. Chylomicrons are the transportation system for fats through which fats travel through the blood stream to enter adipose and other tissues in the body. Due to the hydrophobic nature of membrane lipids, triglycerides and cholesterols, they require special transport proteins known as lipoproteins. Chylomicrons are one sub-group of lipoproteins which carry the digested lipids from the small intestine to the rest of the body.
Fats Metabolism II: Through Liver
Hepatocytes (liver cells) are metabolic overachievers in the body. They play critical roles in synthesizing molecules that are utilized elsewhere to support homeostasis (balance in physiological processes), in converting molecules of one type to another, and in regulating energy balances.
The liver is extremely active in oxidizing triglycerides to producing energy. The liver breaks down many more fatty acids than the hepatocytes need and exports large quantities of acetoacetate into the blood where it can be picked up and readily metabolized by other tissues. A bulk of the lipoproteins are synthesized in the liver. The liver is the major site for converting excess carbohydrates and proteins into fatty acids and triglyceride, which are then exported and stored in adipose tissue.
The liver synthesizes large quantities of cholesterol and phospholipids. Some of this is packaged with lipoproteins and made available to the rest of the body. The excess is excreted in bile as cholesterol or after conversion to bile acids. The excess caloric intake overwhelms the liver’s ability to metabolize fat in a normal fashion, which results in fat accumulation in the liver
The accumulation of fat in the form of lipid droplets within the hepatocytes results in hepatic steatosis which, indeed is a hallmark of liver diseases such as non-alcoholic fatty liver disease, alcoholic fatty liver, acute fatty liver in pregnancy, and hepatitis C.
This is how the fats get metabolized in our body and are utilized for their various functions like padding around internal organs for shock absorption, insulating the body, maintaining body temperature, transporting fats soluble vitamins, maintaining and giving cells their structure and rigidity and finally energy to our body.
Minimum or lower amounts of fat is required by our body for its normal and healthy functions. The problem arises when it is in excess. The excess of fats does not get easily used up in the body, instead, it is stored in for a long time causing various dreadful diseases which damage the organs and many times these damages are irreversible. Hence, we should be very careful while choosing our diets. Choose a diet high in Protein and Low in carbs and fats.
Stay tuned for more amazing insights by Dr Kelkar. Over the next couple of weeks, Dr Kelkar is going to educate us on key ingredients of our diet and management of the same. I hope that you are as excited as we are to get the next article up and running.