Lipids.
Lipid metabolism
Lipid transportation.
Lipids are a group of molecules, which include fats, waxes, sterols,
monoglycerides, diglycerides, triglycerides, fat soluble vitamins etc,
Fats are a subgroup of lipids called triglycerides.
In common usage, fats and lipids, are used as synonyms.
Lipids can be classified in various ways.
Some common nomenclature of lipids are :
Free fatty acids.
Saturated fatty acids.
Monounsaturated fatty acids.
Polyunsaturated fatty acids.
Monoglycerides.
Diglycerides.
Triglycerides.
Essential fatty acids.
Trans fatty acids.
Cholesterol.
Fats are mainly composed of carbon, hydrogen, and oxygen.
Fats are however different from carbohydrates.
Fats have more number of carbon atoms, in relation to the number of oxygen atoms.
Palmitic acid is an example of a fatty acid.
It has the molecular formula,
C16, H32, O2 .
Fats are an important source for energy, for the human body.
Fats are metabolised to release energy.
For example, palmitic acid is oxidised, in human metabolism.
C16, H32, O2, +, 23 O2, results in, 16 CO2, +, 16 H2O.
Many types of cells in the human body, can use glucose or fats to generate ATP,
which is a store house of energy.
However fats generate much more energy than carbohydrates.
Fats provide about 9 food calories of energy, per gram.
This is much higher than the 4 food calories,
that carbohydrates provide, per gram.
Fats are thus more energy dense, or energy rich.
A human body uses fat to store energy.
It can also metabolise fat, in the cells , to provide energy.
Fats are organic chemical compounds.
Fats can be more easily understood if we are aware,
of the constituent chemical compounds.
Some of the main compounds are :
Aliphatic compounds.
Carboxyl acid.
Glycerol.
Glycerides.
Aliphatic chemicals, are compounds of carbon and hydrogen.
Carbon and hydrogen can form simple compound like methane,
with the molecular formula CH4.
Methane has 4 hydrogen atoms, with single bonds, with carbon.
Carbon and hydrogen can also form long chains, of hydrocarbon chemicals.
These chemical compounds can be classified as :
Alkynes.
Alkenes.
Alkanes.
Alkynes are hydrocarbons, with a triple bond.
Ethyne is an example of an alkyne.
It has the molecular formula C2, H2.
Carbon has a valency of 4, and hydrogen has a valency of 1.
The two carbon atoms, are joined by a triple bond.
Each carbon atom, is joined to a hydrogen atom, with a single bond.
Alkene are hydrocarbons, with a double bond.
Ethene is an example of an alkene.
It has the molecular formula C2, H4.
The two carbon atoms, are joined by a double bond.
Each carbon atom, is joined by two hydrogen atoms, with a single bond.
Alkane are hydrocarbons, with a single bond.
Ethane is an example of an alkane.
It has the molecular formula C2, H6.
Two carbon atoms, are joined by a single bond.
Each carbon atom, is joined by three hydrogen atoms, with a single bond.
The examples of ethyne, ethene, and ethane, are examples,
a short chain aliphatic hydrocarbons.
Alkynes, Alkenes, Alkanes, can also be long chain aliphatic hydrocarbons,
with many carbon and hydrogen atoms.
Alkanes are called as saturated hydrocarbons.
Alkanes have single bonds.
Since the valency of carbon, is satisfied with the hydrogen atoms,
they have no scope, for adding more atoms.
So, they are called as saturated hydrocarbons.
Alkenes and Alkynes are called as unsaturated hydrocarbons.
They have double bonds, are triple bonds.
Unsaturated hydrocarbons have scope, for adding more atoms,
by breaking the double or triple bonds, in the carbon atoms.
For this reason they are called as unsaturated aliphatic hydrocarbons.
A carboxylic acid, is a organic compound, that has a carboxyl group.
The carboxyl group, has the molecular formula (C(O)O H).
The general molecular formula for a carboxylic acid is, R-,(C(O) O H).
The “R” refers to a compound.
For example acetic acid, which has the molecular formula C H 3, (C(O) O H).
Compound “R” can be a large compound.
A fatty acid is carboxylic acid, with a long aliphatic tail.
When they are not attached to other molecules,
they are called as, free fatty acids.
Fatty acids are an important source of energy, for the human body.
When metabolised they yield large amounts of ATP.
Many cell types, in the human body, can use either glucose,
or fatty acids, for generating ATP, and energy.
When it is attached to a saturated aliphatic compound,
it is called as a saturated fatty acid.
When it is attached to a unsaturated aliphatic compound,
it is called as an unsaturated fatty acid.
Glycerol is commonly called as glycerin.
Glycerol is a simple sugar alcohol compound.
It has the molecular formula C3, H8, O3.
Glycerol is soluble in water, and is hygroscopic.
It has three hydroxyl groups.
A hydroxyl group is a O H molecule.
Glycerol is the backbone for all fats, called glycerides.
When a hydroxyl group, in glycerol, is replaced with a fatty acid,
the resulting organic compound, is called as a monoglyceride.
When two hydroxyl groups, in glycerol, is replaced with two fatty acids,
the resulting organic compound, is called as a diglyceride.
The fatty acids which replace, the hydroxyl group, can be different.
Palmitic acid and oleic acid are examples of fatty acids.
A diglyceride can have palmitic acid, and oleic acid, attached to it.
A mix of diglycerides, and monoglycerides, are used as food additives.
These food additives, are used as emulsifiers.
Emulsifiers help to mix oily substances, with water,
which otherwise don’t blend very well.
They are often used, in products like, ice-cream, peanut butter, chewing gum,
bakery products, whipped toppings, confections, and candies.
Typically nutritional labels do not mention, the presence of monoglycerides,
and diglycerides.
When three hydroxyl groups, in glycerol, is replaced with three fatty acids,
the resulting organic compound, is called as a triglyceride.
Each fatty acid can be different.
So, we have a variety of natural triglycerides.
Most natural fats, contain a complex mixture, of individual triglycerides.
Vegetable oils, and animal fats, are a mix of triglycerides.
Since triglycerides are the most commonly present glycerides, in fats,
sometimes the term “fats” are used to refer to triglycerides.
Most of the fat that we eat, comprises of triglycerides.
The body also synthesises the triglycerides, that it uses.
Saturated fats are triglycerides, which have only saturated fatty acid components.
Unsaturated fats are triglycerides,
which have unsaturated fatty acid components.
Natural fats have a mix of saturated, and unsaturated fats.
Some food items have a high proportion of saturated fats.
Examples of naturally occurring foods, with high proportion saturated fats are,
cream, cheese, butter, ghee, coconut oil, and palm oil.
Many prepared foods, are also high in saturated fats.
Examples, pizza, dairy products, deserts, sausages, etc.
Many vegetable oils have a higher proportion, of unsaturated fats.
Fats can be synthesised by the body.
A carbohydrate like sugar, can be a raw material for synthesising fat.
Most fats can also be derived from the fatty food we eat.
However, a few fatty acids cannot be synthesised by the body.
These are called essential fatty acids.
The important essential fatty acids are :
Linoenic acid called as omega-6, fatty acid.
Alpha linolenic acid, called as Omega-3, fatty acid.
These fats have to be supplied by our nutrients.
Flax seeds, soya oil, pumpkin seeds, sunflower seeds, canola oil,
leafy vegetables, walnuts, and fish, are sources of essential fatty acids.
It is good for health, to have essential fatty acids, in our diet.
Trans fats do not occur in nature.
They are manufactured by industrial food processing.
Most vegetable cooking oils, are liquid in nature.
Food processors, hydrogenate these oils.
This causes the oil, to be solid at room temperature.
This makes it easy for storage, and transportation.
Hydrogenated fats are called as trans fats.
Trans fats can be found, in margarine, snack food, packaged baked food,
fried fast foods, some commercial sweets, etc,.
Trans fats are harmful for health, and are associated with coronary heart disease.
It is best, to completely avoid trans fats, in our diet.
Cholesterol is a lipid molecule, with the formula C27, H46, O.
It is a modified steroid called sterol.
Cholesterol is synthesised in many cells, in the body.
Cholesterol can also be derived from dietary sources, like cheese, eggs, and meat.
Cholesterol is an essential biomolecule.
It is used by the cells to construct cell membranes.
It helps the cell membrane to have structural integrity, and fluidity.
Cholesterol is also used to biosynthesise, steroid hormones, bile acids and vitamin D.
Bile helps in digesting, and absorbing fat,
and fat soluble vitamins A, D, E and K.
Cholesterol is transported in lipoprotein molecules.
These are called LDL and HDL, which stands for low density,
and high density lipoproteins.
Unregulated cholesterol, in LDL, is considered as harmful to health.
It is common to refer to LDL cholesterol, as “Bad cholesterol”.
Under some conditions the LDL cholesterol, attach themselves,
as foamy particles, to arterial walls.
This can potentially block blood flow to the heart,
leading to cardio vascular disease.
HDL cholesterol is believed to transport the cholesterol back to the liver,
where it can be appropriately reused.
It is common to refer to HDL cholesterol as good cholesterol.
Fats are one of the three essential macro nutrients.
The human diet has a mix of carbohydrates, fats and proteins.
Fats are metabolised in the human body, before being used.
A long series of metabolic processes happen, before a fat is finally used by the body.
Fats are an important source of energy for the body.
The body also stores energy, as fat, for future use, in adipose tissue.
Adipose tissue are composed of adipocytes.
Adipocytes are fat cells.
Fats are also used, to biosynthesise cell membranes.
Fats are digested and absorbed in the human digestive system.
Bile is a fluid synthesised in the liver.
Cholic acid is a primary bile acid.
Bile is stored in the gallbladder.
After eating, bile is discharged, into the duodenum in the intestine.
Bile aids in the digestion of lipids.
The enzyme lipase, is synthesised in the pancreas.
It is released into the duodenum.
Lipase digest fats, by breaking it down.
The triglycerides are broken down into monoglycerides, and fatty acids.
Fatty acids are the most widely used fats in the body.
Fats are water insoluble.
Fats are packaged with lipoproteins.
The resulting molecule is called chylomicron.
Chylomicron eventually enters the blood stream.
It can be used by body cells, to generate energy or to store energy.
The body has special cells to store energy.
They are called adipocytes.
In these cells almost the entire cytoplasm,
is filled with a single large fat droplet.
Clusters of adipocytes form adipose tissue.
Most of this is located in deposits underlying the skin.
The function of adipocytes is to synthesise and store triglycerides,
during food uptake,
and break them down, between meals, or during physical activity.
When chylomicrons enter adipose tissue,
adipose tissue synthesises triglycerides from the fatty acids, and stores them.
Adipose tissue serves as energy storage cells, in the form of fat.
The fat can also reach the liver.
The liver can choose, to store the fat cells,
or to circulate it in the blood stream.
The liver packages fat in molecules called low density lipoproteins .
This helps to emulsify the fat, and transport it, in the blood stream.
Cells can absorb the fatty acid to generate energy.
Adipose cells absorb the fatty acids, and convert them to triglycerides,
for storage.
After eating a meal, nutrients is harvested from the food.
Most of the cells, absorb relevant nutrients, to generate energy for the cells.
This is called as the absorptive state.
After the meal is fully digested, there is no more direct supply of nutrients.
The body enters the post absorptive state.
In this state, the body has to draw energy, from its energy stores.
The most important energy store, of the body is the fat in the adipose cells.
Hormones signal the need for energy.
Adipose cells, respond to these signals.
They breakdown the store triglycerides into fatty acids.
This process is called as lipolysis.
This fatty acid enters the blood stream, and can be absorbed by the other cells,
to generate energy.
It is interesting to know that cells can use either glucose, or fatty acids,
to generate energy.
When a cell needs energy, it can absorb fatty acid from the blood stream.
The fatty acid is catabolised.
It is broken down into smaller and smaller molecules, in multiple steps.
At some point, in this process the molecule, acetyl, Co A, is created.
Acetyl Co A, stands for acetyl coenzyme A.
Acetyl Co A, enters the Krebs cycle.
The Krebs cycle is the same cycle, that generates ATP and energy, from glucose.
Fatty acids through a series of metabolic reactions, can also be converted,
to ATP and energy.
Fats produce much more energy than glucose.
1 gram of fat, can produce 9 kilo calories of energy.
1 gram of carbohydrates, can only produce 4 kilo calories, of energy.
Plants do not move around.
They store energy in the form of starch.
Animals and human beings, move around.
They also engage in physical activity and work, which requires more energy.
They also require a more efficient way, of storing energy.
Fats are energy dense.
They are an efficient way, to store energy.
This is the reason , that animals, including human beings ,
store energy in the form of fat.
However, many modern human beings, do not engage in physical activity.
A sedentary life style can result, in an energy imbalance.
When more food is consumed, then energy expended,
the unused energy is stored as unwanted fat, in adipose tissue.
This can result in obesity, and related health problems.
Lipids like fats, have to be transported, from the cells, and to the cells.
From the digestive system fats are transported, in a carrier called chylomicron.
The liver also plays a significant role in transporting lipids,
from the cells, and to the cells, via the blood stream.
Lipids are not soluble in water, and cannot be transported directly.
Lipids are packaged, in another biomolecule, called Lipoprotein.
This packaging helps to transport lipids.
Lipoproteins have a lipid component, and a protein component.
They have an interesting property which makes them specially useful,
to transport lipids.
One end of the lipoprotein molecule, is water loving, or hydrophilic.
The other end of the lipoprotein, is water phobic, or hydrophobic.
Lipoprotein clusters tend to organise themselves, into a circular shell.
The inner surface of the cell, is hydrophobic, but fat friendly.
The outer surface of the cell, is hydrophilic.
Lipids can be packaged in these lipoprotein clusters.
The liver generates the lipoproteins.
There are two significant lipoproteins, which play a role, in lipid transportation,
from and to the liver.
They are :
Low density lipoproteins, or LDL.
High density lipoproteins, or HDL.
LDL transports lipids from the liver, to the cells.
HDL transports lipids from the cells, to the liver.
Cells in the body absorbs, the required lipids from the LDL carrier.
Cells export lipids, in the HDL carrier.
The liver regulates the flow of lipids to and from the cells.
It must be emphasised, that fat is an essential macro nutrient.
In some cultures, being over weight, or obese, is a major health issue.
Due to this reason, it is sometimes misconceived,
that all fat is “bad.”
It is also misconceived that eating fat, is what makes one physically fat.
This is not true.
One can become physically fat, just by eating sugar.
A good diet, needs to have an healthy proportion, of fat .
Fats provide the raw material, for synthesise essential bio molecules.
For example, lipid molecule are required to synthesise, phospholipids.
Phospholipids are used to build cell membranes.
These membranes provide structural rigidity, and fluidity to the cell.
The cell membrane, also plays a very critical role,
in regulating the substances that can enter the cell, and leave the cell.
Fat is also, a very efficient way to store energy.
Many animals spend, a good part, of their waking day, foraging for food.
Human beings are engaged in other useful activity, during the day.
Metabolic processes, are continuously happening, in our cells,
every second, throughout the day.
This is called as the basic metabolic rate, or BMR, of the body.
If a cell does not have energy, even for a few seconds, it can die.
The body needs a very steady supply, of small doses of energy,
to keep the cells alive, and sustain the BMR.
This needs to be done, even when we are resting, or sleeping.
We might eat, about 3 meals a day.
Energy is harvested from these meals.
This energy has to be stored, so as to supply a steady stream of energy,
throughout the day.
This essential function, is elegantly performed by adipose cells.
There is a constant flux, of fatty acids, to and from adipose cells.
When there is excess energy, these cells store the energy as fat.
When there is a shortage, it releases fats, to produce energy.
This process helps us to engage ourselves, in other fruitful activity.
A normal diet, with a sedentary lifestyle, results in excess energy.
When this becomes a life style, the body tends to put on weight.
The excess energy is stored in adipose cells.
The number of adipose cells, in an adult is typically constant.
But, an adipose cell can increase, to about 4 times its weight.
Depot for adipose cells, exists in many places in the body.
One typical place is the belly.
When these adipose cells increase in size, the body tends to bloat up,
and put on extra weight.
When this becomes excessive, it can result in obesity.
Obesity is related to a number of health issues, like diabetes,
cardiovascular diseases etc.
The most sensible way to have a healthy life, is to have a physically active life.
Physical activity could be anything, like gardening, walking to the market,
playing, cooking, dancing, cleaning, etc, etc.
Spending as much energy, that we eat, is the simplest and most sensible way,
of maintaining a body, at the right weight.
The guidelines with respect to healthy body, related to fat could be summarised as:
Maintain an physically active life style.
Eat only that much food, that the body requires.
Eat a balanced diet with carbohydrates, fats and proteins.
Eat foods that have essential minerals, and vitamins.
Include dietary fibre, and water in food.
Minimise the amount of added sugar in food.
Avoid popular beverages, which has high sugar content.
Avoid so called energy drinks.
Avoid or minimise eating highly processed food, like typically found in fast food.
Include a higher proportion of unsaturated fats,
and a lower proportion, of saturated fats.
Avoid trans fats.
Minimise fried foods.
Include essential fatty acids, in the diet.