How does body produce energy – a detailed article

Human body gets energy from food. The structure of our body is also build using components from food. Food cravings also mean that you might be addicted to food. Cooking for someone is an ultimate sign of love.

Food and body connect together for the most important activity of metabolism. Is it a necessary evil that what gives us the daily means to survive is also the reason for lifestyle ailments. But to understand food and its effects better, you need to first get to know how food is converted in energy in our body.

Short version

Before we proceed any further, this is not a short article and there cannot be one. Food digestion and metabolism is a complex process and also depends on the type of food we are eating.

At this point of time you should keep in mind just one thing, one important thing. What you have heard or read till now is all wrong. This article will attempt to clear some of those wrong and myths.

List of topics which we shall cover

• Defining metabolism, combustion and oxidation
• Energy synthesis
• Reactive Oxygen Species aka free radicals
• Anti Oxidants

Defining metabolism, combustion & oxidation

Conversion of food to energy by our body is called metabolism.

It is similar to burning or combustion of fuel. In the presence of oxygen, any fuel burns to give carbon dioxide, water and energy.

Oxygen is also a reactive element. When it comes in contact with any atom, molecule or ion, one electron is removed and this process is called oxidation. Iron metal reacts with oxygen to convert to iron oxide. Another famous example is a cut apple turning brown with time.

Food is oxidised to provide energy to our body. 

The digestion of food begins with the mouth, gets broken down in the stomach and absorption begins in the small intestines. Enzymes in the intestine begin their breaking down action of converting protein to amino acids, carbs into glucose and fats into fatty acids and glycerol.

Energy generation happens only at cellular level by mitochondria. These are the core of energy production which combine oxygen and glucose to give the same end products, carbon dioxide, water and energy. 

Energy is measured in units called ATP. ATP stands for Adenosine triphosphate.

Conversion of food molecules to energy

Let us begin with the unit of energy we mentioned, the ATP. It has three bonds which are ready to be broken. Bond breaking releases lot of energy. Breaking of one bond of Adenosine triphosphate releases energy and gets converted to ADP or Adenosine diphosphate. ATP comes from glucose.

Molecules of carbon, hydrogen and oxygen coming together in various ratios is glucose. Carbohydrates in our food is digested and broken down into glucose. This glucose molecule is floating around in our blood so that it is an available source of energy for the hundreds and thousands of cells in our body.

Step 1 – Glycolysis

Glucose breaks down through a process called glycolysis into a molecule called pyruvate, another molecule called NADH and ATP which is also a molecule.

Glycolysis gives us net yield of two ATP molecules. We also have two each of the pyruvate and NADH which we saw earlier. Even though it is not an efficient process, it is still a good start for more better things to come.

Also glycolysis happens in the outer area of the cell called cytoplasm. This happens without the presence of oxygen which is why it is anaerobic.

Glycolysis is the precursor for bigger and better things to come.

Step 2 – Oxidative phosphorylation

Pyruvate, NADH and ATP thus produced by glycolysis are pushed into the inside of the cell where the mitochondria kicks into action.

Pyruvate has three carbon atoms, one of which is removed by a chemical reaction to create a molecule with two carbon atoms called Acetyl-COA. This merges with another four-carbon molecule to make a six carbon molecule called citrate. All these chemical reactions are facilitated by enzymes. In the end of the first round we get four molecules of ATP, ten molecules of NADH and two molecules of FADH2.

NADH and FADH2 start with transferring their electrons in a series of steps called electron transport chain. They lose their electrons to the mitochondria from where these electron travel inside the mitochondria. This process sets up hydrogen ions on the outside of the mitochondrial membrane. These power an enzyme ATP synthase that puts up a phosphate on ADP to create an ATP.

We started with two molecules of ATP from glycolysis and two more ATPs from the stage one. Each of the ten molecules of NADH gave us three ATPs (adding to total of 30) and two molecules of FADH2 gave two ATPs each. That makes it a total of 38 ATPs from every molecule of glucose.

End products are water and carbon dioxide. Oxidative phosphorylation happens in the presence of oxygen and it is a much more productive way of creating energy.

For this kind of energy be created you need a constant supply of glucose as well as oxygen. Long distance runners or cyclists keep their blood glucose levels high by sipping energy drinks while they are doing their routine. If your breathing is under control and your exercise does not demand too much of oxygen, then you will keep producing 38 units of energy after burning one molecule of glucose.

Step 3 – Glucose alternative – glycogen

Liver converts glucose in our blood to glycogen which is stored in the liver itself and between or behind the muscles called visceral fat. Glycogen is a form of fat which is denser than glucose. Glycogen can be tapped quickly by the muscles and other parts of the body from the fat storage. This fat is again broken down into fatty acids and glycerol.

Something similar happens to fat which we eat. It is broken down into fatty acids and glycerol which is available for the cells as a source of fuel. However, as a rule glucose is toxic for the blood and the body as a whole which is why glucose is burnt first. But more about that later.

A typical fat molecule with 16 carbons will have the following calculations. 21 molecules of ATP from NADH, 14 ATPs from FADH2 and 96 ATPs from Acetyl-COA. That makes it a total of 131 ATPs from just one molecule of fat.

Sugar adapted v/s Fat adapted

The body mechanism is so designed that first the glucose in the food enters the bloodstream and then it is burnt first. If your diet consists of excess carbs and sugars you will have a plenty of glucose in your blood. Once the glucose levels start to drop, you will feel hungry. You will crave for food even though you have sufficient fat reserves in the body.

Another reason for this problem is because you are eating too many times in a day.

However if you are going for longer period between meals or you are giving sufficient fasting between two meals, you body will start fat burning. A minimum of 15 hours of fasting is recommended to ensure you enter into fat burning.

In sugar adapted scenario you are eating at regular intervals and glucose is fuelling your cells. When blood sugar levels goes down, you eat something to raise it again.

In fat adapted scenario, first your food gets digested and then once the blood sugar levels drop, the liver starts converting glycogen to ketones which are used as source of energy. This allows you to go without food for longer intervals.

Glucose in your blood is toxic which is why the body consumes it first by burning it off. Blood sugar causes inflammation in the artery walls which leads to plague formation. It also makes the RBCs sticky because of which they find it difficult to enter the tiny blood capillaries. It makes all the right sense to give up carbs and sugars and to go back to the diet which we used to follow just a couple of hundred years ago.

Free Radicals – a necessary evil lurking out there

We eat food and that powers our body. One by-product of energy production is oxidative stress or the creation of free radicals. Let us examine reactive oxygen species in detail.

A by-product of the metabolism process is reactive oxygen species also called ROS or the more popularly known name as free radical. ROS are also called oxidants. The cell mounts an antioxidant response against the free radicals. 

As discussed in Step 2 we have NADH and FADH2 transferring their electrons by electron transport chain.

During this transfer of electrons there is a chance that a free electron can escape the cell and then it combines with an oxygen molecule to create a free radical. A kind of free radical is superoxide contains two oxygen molecules with one unpaired electron. 

Free radicals are very reactive. They can grab an electron from protein, fatty acids or even DNA. A free radical after grabbing an electron converts the other molecule into a free radical thereby setting off a chain reaction which cannot be stopped. 

Free radicals start damaging cell membranes and change the structure of cell proteins thereby affecting the very performance of the cells. 

Our body has a defence mechanism to take care of free radicals. There are antioxidants. Free radicals have one unpaired electron which makes it reactive. Anti oxidant has one free electron to donate which is how it neutralises the free radical. 

Normally the body is able to maintain a balance between the production of free radicals and neutralise them with antioxidants. 

It is able to do that within the cells by generating three types of enzymes.

• Superoxide Dismutases (SOD)
• Catalase
• Glutathione Peroxidases

There are also two antioxidants which are manufactured by the body.

• Glutathione
• Uric Acid

Anti-oxidants from the diet

• Vitamin A, C & E
• Carotenoids (esp beta carotene)
• Lipoic Acid
• Phenolic Acid
• Selenium

A large part of the requirement of antioxidants has to come from our diet. With so many chemicals and pollutants surrounding us, we cannot rely on the body to manufacture them on their own.

Human body also uses free radicals in a positive way. For example the immune system uses free radicals to fight germs and infection. It also uses this mechanism to heal an injury. Hydrogen peroxide is a signalling molecule which asks the immune system to respond after an injury. Hydrogen peroxide is also the free radical which is released on a bacteria to kill it. 

Another example of positive use of free radicals is when we exercise, there is oxidative damage to muscle tissues. That promotes tissue growth and encourages the production of antioxidants in the body. 

Brain is the largest consumer of oxygen. Which is why we have two largest arteries supplying blood directly to the brain. The brain cells use oxygen to perform metabolic activities in a heightened manner. But here the free radicals produced help in cell growth, neuroplasticity and cognitive function. Excessive free radicals can cause damage to cellular structure of the neural network leading to problems like Parkinson’s and Alzheimer’s disease. 

Before we talk about possible ways to reverse let us explore the contributing factors.

Environmental pollutants like chemicals, bad air, and radiation are the main contributing factors. Toxic chemicals like heavy metals, smoke, radiation, asbestos increase the amount of free radicals in the cells. Others are unhealthy lifestyle and wrong eating habits lessen the cellular ability to mount the antioxidant defence mechanism. 

Smoking and alcohol consumption are also one of the key factors. 

A keto diet is where you should begin. It is not another fad diet but the one which focuses on reducing carbs and sugar and eating healthy foods. It improves the ability of the cells to tackle the free radicals on their own. 

Keto diet also induces ketosis in the body. By a combination of fasting and depriving the body of carbs to induce fat burning fast. Ketones are known to accelerate the clearing up of free radicals. Damage can be taken care of by prolonged fasting which induces autophagy which activates the clean up crew within the cells. 

Lastly, the healthy version of keto involves lots of dietary and natural fats. These also help with the extra production of energy from fat burning. It also gets us into ketosis as early as possible.