Wednesday, 18 April 2018

Dietary fats - Part two (Triglycerides digestion)

Many foods contains substantial amounts of dietary fats. Cooking oils (Sunflower, peanut, olive) got 100% fats as triglycerides. Butter and mayo - got more than 80% fat, bacon and sausages - around 40% fats, as opposed to fruits and veg - little to no fat.

We can have cholesterol only in foods of animal origin (highest amount in egg yolk and shrimps). Saturated fatty acids can be found in lard, butter, coconut oil, and unsaturated fatty acids in vegetable oils. Soy bean oil - has linolenic acids (C18:3), coconut oil - has medium chain fatty acids (8-12 chains, fish oil - has fatty acids with 20-22 chain length. Flax-seed oil is a good source of essential fatty acids (50% linolenic acids).

Fat digestion - we would talk especially about triglycerides digestion. The breakdown of a triglycerides molecule is done under the influence of an enzyme called lipase. It is broken in 2 fatty acids and one monoglyceride attached to a fatty acids. We got lingual lipase, in the mouth, with a role in fat taste detection more than digestion. The process starts in the stomach under the gastric lipase, and it is continued in the intestines, with the pancreatic lipase doing most of the job. When dietary fat enters in the intestines, a hormone called cholecystokinin (CCK) is released, to activate the gall bladder contractions, and the secretion of bile acids. Bile acids are made from cholesterol and are stored in the gall bladder with cholesterol and phospholipids, and has the role of an emulsifier, changing fat in little droplets, for pancreatic lipase easy access. The main bile acid is the cholic acid, can be attached easily to amino-acids like taurine and glycine (making taurocholate and glycocholate - conjugated acids). The broken down fatty acids and the monoglycerides resulted from the digestion of triglycerides form a special structure called mycelle and the bile acids play an important role in it. Then they are taken up by the enterocyte (intestinal cell) and reconverted into triglycerides via a process called re-esterification. Then they are packaged into special particles called chylomicrons - which carry the dietary fats through the body, using the lymphatic circulation (small vessels called lacteals) to reach the subclavian vein.

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