Along with carbohydrates and proteins, fats comprise the three most important macronutrients that are essential for our body. Primarily, fat molecules comprise carbon and hydrogen atoms and, hence, they are hydrophobic in nature. Fats are soluble in all organic solvents, but they don't dissolve in water. Some of the best and most common examples of fat include cholesterol, triglycerides and phospholipids. In fact, fat is essential for the optimum health of our body and mind. As a result, it is important that we include them in our diet as a part of nutrition. In the absence of fat life would be impossible. In other words, we are not able to survive without ingesting fats.
Our body needs small quantities of "beneficial fat" to enable it to function optimally as well as to thwart off various diseases. Nevertheless, several present day diets include fats in excess than what is actually required by our body. Excessive fat, particularly too much of the harmful type of fat in the body, may result in grave health problems, which includes high blood pressure, obesity and elevated levels of cholesterol in the bloodstream. All these conditions can result in increased risks of developing heart disease.
Often fat is considered as an enemy and it is something that most people want to avoid. However, in the absence of fats, humans would actually freeze. Fats also insulate our nerves. If our nerves remain uninsulated, as it would be in the absence of fat, they would rattle us with crisscrossed communications from the different neurons. Moreover, we would not be in a position to store crucial vitamin supplies, especially some specific vitamins. At the same time, our immune system would also not be functioning as it does now. At the level of cells, fats are responsible for developing the membranes that enclose the cells and serve as messengers that attach to proteins, thereby enabling a variety of reactions.
Keeping this in mind, it needs to be underlined that the unassuming fat cells appear to be somewhat miraculous. Adipocytes, are molecules that include fats as well as related substances and they store any additional lipids. Hence, it is said that these molecules are appropriately named adipocytes.
There was a time when it was thought that adipocytes were somewhat uninteresting energy sacks. However, researches undertaken in the last few decades have shown that these molecules have several important roles in our body. They not only regulate nutrients, but also govern the release of hormones that affect our blood pressure, functioning of the thyroid gland and also have a role in reproduction.
Seen under a microscope, it was found that fat cells resemble little bulbous spheres. Similar to other cells in our body, each fat cell comprises a cell membrane and a nucleus. On the contrary, their bulk comprises stored triglyceride droplets, each of which comprises three fatty acid molecules that bind to a solitary glycerol molecule.
Fat cells are also called lipocytes or adipocytes and they form the basic structure of our body fat, also known as adipose tissue. Fat cells are focused on storing energy in the form of fat. In fact, adipose tissues are of two dissimilar types and they comprise two different kinds of fat cells - white adipose tissue and brown adipose tissue.
The white adipose tissue comprises unilocular fat cells. On the other hand, brown adipose tissue comprises multi-color (plurivacuolar or multilucolar) cells. It is worth mentioning here that aside from storing fat, adipocytes or the fat cells also generate the hormone called estrogen. Moreover, a fat tissue is also a variety of connective tissue - a group that includes blood, cartilage, bone, ligaments and tendons.
Interestingly, even after an adult undergoes weight loss, the number of fat cells or adipose remains relatively constant in his/her body.
A unilocular (while fat cell) or monovacular fat cell comprises a solitary lipid droplet enclosed by a cytoplasm layer, which is also known as intracellular liquid. Moreover, the cell's nucleus is flatted against one side of the cell wall. The lipid droplet in white adipose tissue more often than not comprises triglycerides in addition to cholesterol ester. In fact, white adipose tissue comprises roughly 20% of the weight of an adult male, while they make up about 25% of a female's weight.
It has been found that people having less amount of brown adipose tissue may actually be more overweight compared to people having higher levels of this type of fat. This was revealed by the findings of some studies.
The structure of the brown (plurivacular or multilocular) fat cells are different from the white or unilocular fat cells in several important ways. While the white fat cells have a round shape, the brown fat cells are polygonal and they also enclose additional cytoplasm compared to the white fat cells. The brown fat cells also contain several lipid droplets all over the cell. The nucleus of multilocular fat cells is round as well as off the center. On the other hand, the nucleus of the white fat cell is placed on the edge - flattened at the side of the cell membrane. The multilocular (brown) fat cells have a rich amount of mitochondria and capillaries compared to the white fat cells, since their requirement for oxygen is more.
As mentioned earlier, fat cells stock up energy as fat and this energy is used when our body requires additional fuel. White adipose tissue (unilocular) stores up energy and also insulates the body to sustain the body's heat. On the other hand, the brown fat tissue (multicular) is present in abundance in newborns and infants. In addition, it also helps to prevent a condition known as hypothermia, since infants are more vulnerable to cold compared to the adults. It is worth mentioning here that there are 30 billion white fat cells in an adult's body and they are present all over the body. Contrary to this, just a few adults have little deposits of brown fat tissues in their neck and upper chest. Interestingly enough, it has been found that the number of fat cells or adipocytes remain stable even after an adult has undergone significant weight loss.
When one consumes foods containing fat, more often than not triglycerides, it passes through the stomach as well as the intestines. When in the intestines several unhealthy things take place. Some of them are discussed below.
In the intestine, outsized fat droplets mix with bile salts released from the gall bladder through a process known as emulsification. These fat and bile salt mixture breaks down the big fat droplets into smaller ones known as micelles. This, in turn, increases the surface area of fat.
Our pancreas releases enzymes known as lipases, which assault the exterior of each micelle and breaks down the fats into different parts, such as fatty acids and glycerol. These parts of fat are taken up by the cells that form the intestinal lining.
Within the cells of the intestine, fatty acids, glycerol and other fat parts reassemble to form fat molecule (triglycerides) packages with a coating of protein, which are known as chylomicrons. These protein coatings help the fat to dissolve in water more easily.
Subsequently, the chylomicrons are discharged into the lymphatic system. In fact, chylomicrons don't directly enter the blood stream since they are quite big and therefore unable to pass through the capillary walls.
Eventually, the lymphatic system join together with the veins and this is the juncture when the chylomicrons enter the bloodstream.
One may wonder why the molecules of fat are broken down into fatty acids and glycerol when they again reassemble in a different form. The answer to this is rather simple. This happens because the molecules of fat are actually very big to pass through the cell membranes. Therefore, when these molecules pass from the intestine via the intestinal cells and into the lymph, or when they pass through any cell barrier, it is necessary that the fats be broken down into smaller parts. However, when fats are transported through the lymph or the bloodstream, it is always better that a few large molecules of fat remain instead of all being broken down into fatty acids. This is because the large fat molecules neither dissolve in water nor attract too many water molecules through osmosis compared to the smaller fat molecules.