Lipids are hydrocarbon molecules constituting an essential part of living systems by serving as the building blocks of their structure and function.
In biological and biochemical terms, the individual molecules of lipids contain both polar and non-polar constituents in them, making them almost entirely soluble in non-polar solvents while partially soluble in polar solvents (forming micelles).
Typical examples of lipids are: oils (unsaturated lipids / having lesser hydrogens in their hydrocarbon chains), fats (saturated lipids / having maximum hydrogen content in their hydrocarbon chains), waxes (malleable lipophilic solids), and some of the important vitamins (vitamin A, D, E and K).
The position of lipids as essential biological molecules points towards their indispensable functions they carry out. Let us explore them one by one in the context of some relevant and noteworthy examples where applicable.
While carbohydrates function to serve as an instant energy source for the human body, lipids function to serve as major energy reserves of the body. Thereby, these two molecules function to provide a major portion of energy to the living organisms.
The energy from carbohydrate molecules is stored as glycogen but it cannot be stored in huge amounts in the body. Also, the glycogen molecules are continuously formed and broken down as per the intake of carbohydrates by the body thus serving as instant energy reserves.
On the other hand, when the superfluous amounts of carbohydrates are available and the glycogen limit is also exceeded then the extra amount is first converted into glucose which is then further processed to for the fat molecules being ultimately stored in the fatty cells known as adipose tissue. Also, the amount of energy stored as fat or lipids is much greater than that of the carbohydrates or proteins.
For example, one gram of lipids yields about 9 kcal of energy as compared to 4 kcal by carbohydrates or proteins, on average.
Mostly lipids are stored in the body in the form of triacylglycerol molecules. These are highly concentrated reserves of metabolic energy and contain lipids in anhydrous and reduced form.
This is another reason why fatty acids yield more energy than proteins and carbohydrates because the latter is usually stored in water-bound or hydrated from. Therefore, as the amount of water molecules increases, the actual content of the energy-providing molecules becomes less and less.
In mammals, the triacylglycerols are stored in the cytoplasm of the fat cells also known as adipose cells. These cells are specialized not only for triacylglycerols’ synthesis and storage but also function to provide these fuel molecules to other tissue via blood when needed.
An excellent example of the lipids as energy reservoirs and their utilization comes by looking at its consumption by migratory birds. Some of these birds (e.g., American golden plover) can travel distances up to hundreds of kilometers without feeding. All thanks to fatty acids which provide energy during such tasks.
Since lipids are hydrophobic in nature or insoluble in water, they also function to provide insulation to both plants and animals from the environment.
In plants, for example, the outer cuticle layer of the plant leaves secretes wax. Apart from leaves, this layer is also present in the young shoots and some other aerial parts of the plant.
This waxy layer not only functions to cloth the tissue from which it is being secreted but also functions to reduce water loss, protection of photosynthetic cells and insulation against heat and cold.
If we talk about insulation provided by fats in animals, the best example comes from marine mammals. There is an insulating layer of fat present under the skin of all marine mammals (e.g., seals, walruses and whales) known as blubber. Not only it functions to provides thermal insulation to these mammals but also provide buoyancy too.
Lipids are accumulated in different modified forms in the fat tissue or adipose tissue of the body. This adipose tissue functions to cushion the organs (e.g., liver, spleen, heart, kidneys, and lungs), bones and other tissues thereby protecting them from potential damage.
Omega 3 Fatty Acids in Preventing Heart Diseases
Omega 3 fatty acids are a type of polyunsaturated fatty acids. They typically contain 18-22 carbon atoms and a double bond at every third position from their methyl terminal. Since the human body cannot synthesize them de novo, they must be taken in diet.
One important function which omega 3 fatty acids perform is the reduction of inflammation in the body. This function has important consequences for various heart diseases and strokes as inflammation is a major reason for blood vessels’ damage and heart anomalies.
Besides, other functions of omega 3 fatty acids include:
- Reduction of depression and anxiety,
- Improvement of vision, brain and heart health,
- Fights inflammation and autoimmune diseases,
- Improves mental disorders and age-related memory declines,
- Reduces asthma and fatty liver disease,
- May help fight cancer, improves joint and bone health
Healthy Brain Function
A lack of adequate dietary and nutritional intake of lipids can have important consequence on brain health and function.
This is because lipids play structural and functional roles in neurons. As the neurons contain an insulating lipid layer that is used for fast transmission of signals across the brain, the sheer maintenance of this very basic phenomenon speaks for the importance of lipids in the maintenance of appropriate brain health.
Importance of Cholesterol
Cholesterol is an organic molecule and belongs to a class of lipids known as sterols. Animal cells can synthesize cholesterol and is found in all cells of the body because it constitutes an essential structural component of the cell membranes.
Moreover, it is also used to make some important vitamins needed by the body e.g., vitamin D.
There are two types of cholesterol: good and bad. Good cholesterol is also known as HDL (high-density lipoproteins) whereas bad cholesterol is known as LDL (low-density lipoproteins). The total cholesterol in the blood is a combination of both HDL and LDL.
Now why they are designated as good and bad cholesterols? The answer to this question lies with the development or prevention of heart diseases associated with each of these types.
While research has linked HDL with a protective role on blood vessels, its high levels are associated with keeping the body away from developing heart diseases. Contrasting is the case with LDL i.e., its high amount is indicative of higher risks for blocked arteries and related health problems.
Lung surfactants also known as pulmonary surfactants are lipoprotein complexes that form a layer on the surface of lung cells (alveolar cells). This layer of surfactants basically functions to decrease lung surface tension and thus helping in increasing lung compliance (an ability of a lung to expand or stretch).
The major lipid present in lipoprotein complexes of lung surfactants is dipalmitoylphosphatidylcholine (DPPC). Since it constitutes 80 – 90% weight of lung surfactant, it holds an essential position for normal pulmonary function.
How do DPPC molecules help in the distention of the lungs? This is an interesting question whose answer lies in the composition of the hydrocarbon chains of the DPPC molecules which are saturated.
Therefore, they have a tendency to extend without bending. Moreover, the close packing of DPPC molecules and their orientation within the layer prevents the lungs from collapsing when the air is exhaled.
Calcium Metabolism Regulation
Vitamin D is a lipid hormone that is also a sterol derivative. It is formed in animal skin via exposure to UV light coming from the sun. in its active form, it facilitates the uptake of dietary calcium via its absorption through intestines thus increasing the resultant deposition of calcium in bones and teeth.
Since it is water-insoluble, it is stored in the fatty tissue inside the body. But, excessive amounts or intake for longer periods of time can result in a disease known as vitamin D intoxication.
Consequently, the blood serum calcium levels become high which triggers calcification of various soft tissues as well as the formation of the kidney stones (which can ultimately lead to kidney failure).
It can be justifiably concluded that whereas lipids hold a prime position in the life of living organisms by performing various essential functions, an excess amount of various individual types of lipids can also lead to serious health consequences.
Therefore, one needs to have a balanced well-informed aptitude when adding lipids to their daily healthy meal plans so as not to intoxicate oneself from an overdose.