What happens after I consume omega oil supplements?
The absorption of dietary fats is a complicated process and requires many steps, including the transport of fat from the diet into the intestine cell, and then from the intestine cell to the lymphatic system and then to the blood. Typically fats in most food sources are found in their natural triglyceride (TAG) form. These fats are comprised of three fatty acids linked to a molecule of glycerol. Without glycerol, free fatty acids would be rapidly oxidised and therefore the glycerol backbone helps to stabilise the fat molecules and prevent breakdown and oxidation.
TAGs are too big to travel across cell membranes into the cells of the intestine and so, after consumption, bile fats and the enzyme pancreatic lipase digest dietary fat in the small intestine. The lipase enzyme breaks the TAG molecule into two free fatty acids and a monoglyceride (one fatty acid combined to the glycerol), which are then able to cross the membrane and enter the cells of the small intestine (enterocytes) where they are reassembled again as TAGs. These TAGs are then joined up with phospholipids (consisting of a glycerol bound to two fatty acids and a phosphate group), cholesterol and special proteins called apolipoprotiens to form carrier molecules called chylomicrons. These then transport the TAGs out of the enterocyte into the lymphatic channel and finally into the blood, where they are then delivered to various part of the body. The function of a chylomycron therefore is to simply enable fats and cholesterol to move within the water-based solution of the bloodstream. There are several types of apolipoprotein, and individual apolipoproteins actually govern which cells in the body receive the chylomicron. As the chylomicron travels throught the blood it is able to ‘swap’ components with another lipoprotein named high-density lipoprotein (HDL) (see cholesterol).
Fatty acids in ethyl ester form differ from TAGs. Ethyl esters are synthetically derived by reacting free fatty acids with ethanol. The fatty acids are removed from their natural glycerol backbone then linked (esterified) with a molecule of ethanol. The primary benefit of this method is that esterification concentrates EPA, meaning that one can consumer lower doses of fat in order to meet the required dose.
The digestion of ethyl-EPA fish oils is slightly different to TAGs due to the lack of a glycerol backbone. In the small intestine it is again the pancreatic lipase which breaks the fatty acids from the ethanol backbone; the fatty acid-ethanol bond is more resistant to pancreatic lipase, however, than to TAGs, but produces free fatty acids plus ethanol. The free fatty acids are then taken up by the enterocytes but must then be reconverted to TAGs in order to form chylomicrons, then leave the cell, enter the lymphatic system and then the blood. Because the ethyl-EPA does not have a glycerol back bone it must find one within the cell because TAG re-synthesis is not possible without one. For this reason the transport of ethyl esters is slower than that of TAGs. To increase absorption of ethyl-esters it is beneficial to consume them at the same time as a fatty meal as this will ensure that there is glycerol ‘pool’ for the free fatty acids to reform as triglyceride. Because ethyl-esters are more susceptible to peroxidation (going rancid) than TAG, it is important to include an anti-oxidant such as vitamin E to protect the oil.
After uptake EPA appears in the body in a variety of forms. Whilst some will be used directly as energy, the remaining is incorporated into lipoproteins (which carry cholesterol), into the phospholipids that make up cell membranes, some will become fatty acid esters and some will remain as triglycerides stored in adipose (fat) tissue.
Phospholipids are comprised of two fatty acids joined to a phosphate group (either ethanol, choline, serine or inositol) and a glycerol to form either: phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PE) or phosphatidylinositol (PI). The fatty acids can join on at either sn-1 or sn-2 position and polyunsaturated fatty acids such as EPA are located almost exclusively in the sn-2 position but EPA has to compete with other fatty acids such as omega-6 fats for this space. EPA only forms PE or PC and as a phospholipid can be measured in the blood around 4 hours after consumption, but it can take around a week before these phospholipids are incorporated into platelet membranes and for these levels to become stable at around 12 weeks after consumption.
The lymphatic system is a network similar to the cardiovascular system and carries a clear fluid called lymph, which has three main functions: the removal of cellular fluid (containing amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts and waste products from the cells and tissues), the absorption and transport of fatty acids to the circulatory system and the transport of immune cells.