This is going to be the final chapter of food facts. Today, we are going to focus on lipids. Many of us are familiar with the term lipids as fat or oils. Yes, lipids can be divided into two groups as fats and oils. The difference in here is the amount of saturation of the molecule. A lipid molecule is basically formed when 3 fatty acid molecules combine with a glycerol molecule forming an ester bond. And all lipids have one feature in common, that is they hate water which means in other words, they are mostly hydrophobic. Other than fats and oils, there are other types of lipids such as steroids, waxes, phospholipids etc. If we talk about the functions of lipids inside our body, lipid acts as storage energy just like carbohydrates. Lipids can release more energy though.
Fats and oils
The molecules formed by fatty acids and glycerol are of carbon chains which are sometimes saturated and sometimes unsaturated. What makes a saturated molecule is the single bonds of carbons in the molecule. They are called fats. When there are double bonds and triple bonds in the carbon chain, they are known as unsaturated lipids or oils.
Phospholipids
Phospholipids are made from glycerol, two fatty acids, and (in place of the third fatty acid) a phosphate group with some other molecule attached to its other end. The hydrocarbon tails of the fatty acids are still hydrophobic, but the phosphate group end of the molecule is hydrophilic because of the oxygens with all of their pairs of unshared electrons. This means that phospholipids are soluble in both water and oil.Our cell membranes are made mostly of phospholipids arranged in a double layer with the tails from both layers “inside” and the heads facing “out” on both surfaces.
Cholesterol
The general structure of cholesterol consists of two six-membered rings side-by-side and sharing one side in common, a third six-membered ring off the top corner of the right ring, and a five-membered ring attached to the right side of that. The central core of this molecule, consisting of four fused rings, is shared by all steroids, including estrogen (estradiol), progesterone, corticosteroids such as cortisol (cortisone), aldosterone, testosterone, and Vitamin D. In the various types of steroids, various other groups/molecules are attached around the edges. Know how to draw the four rings that make up the central structure.
Cholesterol is not bad people. Our bodies make about 2 g of cholesterol per day, and that makes up about 85% of blood cholesterol, while only about 15% comes from dietary sources. Cholesterol is the precursor to our sex hormones and Vitamin D. Vitamin D is formed by the action of UV light in sunlight on cholesterol molecules that have “risen” to near the surface of the skin. People should not shower immediately after being in the sun, but wait at least ½ hour for the new Vitamin D to be absorbed deeper into the skin. Our cell membranes contain a lot of cholesterol to help keep them “fluid” even when our cells are exposed to cooler temperatures.
Many people have hear the claims that egg yolk contains too much cholesterol, thus should not be eaten. An interesting study was done at Purdue University a number of years ago to test this. Men in one group each ate an egg a day, while men in another group were not allowed to eat eggs. Each of these groups was further subdivided such that half the men got “lots” of exercise while the other half were “couch potatoes.” The results of this experiment showed no significant difference in blood cholesterol levels between egg-eaters and non-egg-eaters while there was a very significant difference between the men who got exercise and those who didn’t.Lipoproteins
Lipoproteins are clusters of proteins and lipids all tangled up together. These act as a means of carrying lipids, including cholesterol, around in our blood. There are two main categories of lipoproteins distinguished by how compact/dense they are. LDL or low density lipoprotein is the “bad guy,” being associated with deposition of “cholesterol” on the walls of someone’s arteries. HDL or high density lipoprotein is the “good guy,” being associated with carrying “cholesterol” out of the blood system, and is more dense/more compact than LDL.
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