What does Metabolism Mean?

Picture a campfire. It keeps the body warm on a cold night and provides light. To ensure that the fire keeps burning, fuel needs to be added(pieces of wood in this case). When a small piece is added, the fire burns bright for a bit and then dies down unless more wood is added. But, if too many pieces are placed at a time, the fire escalates and burns for a longer time, without actually burning away all the pieces that have been added. Many of them, especially the larger chunks or damp pieces, remain unburnt. 

Now think of this campfire as the body’s metabolism; think of the warmth and light of the campfire as energy to walk, run, think, and breathe. The food consumed by a person is the wood that strokes the fire, fueling the body. How fast, or slow, the campfire burns is based on a person’s metabolic rate. Metabolism is the umbrella term for a series of chemical reactions in cells that help organisms change food into energy.  

A human body uses the energy it requires to sustain itself, and the rest gets stored as fat. If a person eats too little, he will have very little energy. If he eats too much, or an unbalanced diet, his body will store more fats than it needs, leaving him lethargic.  

Thus, too little or too much food can affect the metabolism, slowing it down to a point where energy conversion becomes inefficient, and the person gets a risk of becoming unhealthy and sick. Just as a right-sized wood should be added to the campfire at the right moment, the body needs the right food at the right intervals to produce and consume energy in the most efficient manner. 

Illustrations of the Metabolic Process

What does the Process of Metabolism look like? 

When the physical sensations of hunger are felt, one might even feel a sudden dip in energy. Suppose a person reaches for a slice of bread and eats it, kickstarting the process of digestion. How does it get converted into energy? 

Bread contains starch, a complex carbohydrate. Enzymes in the saliva start breaking down the bread’s starch molecules to convert them into smaller, simpler molecules. 

In this case, starch is broken down into sugars. The sugars enter the bloodstream and energize individual cells of the body. It gives an instant rush of energy, while also satiating the hunger for a short period.  

The process of digestion continues as the bread reaches the stomach, breaking down into several other smaller and simpler molecular substances, namely glycerol and fatty acids, and amino acids. Note that simple sugars are formed when complex carbohydrates break down, glycerol, and fatty acids are formed when lipids break down, and amino acids are formed when proteins break down.  

When the immediately required energy is consumed by the body, the rest is stored as fat for later use. The molecule used by cells to store this energy is called ATP or adenosine triphosphate. 

So, if there is a consistent calorie deficit (when the body is supplied with less energy than it requires for daily upkeep), loss in body weight can be observed. When the body is supplied with more calories than it can burn, it gains weight due to the accumulation of fats.  

Are there Different Types of Metabolism? 

Metabolism can be defined as the total amount of biochemical reactions required to synthesize energy from food sources to maintain life. As energy requirements for essential life processes vary across species and individuals, metabolic rates differ widely. 

There are two types of metabolism, namely catabolism, and anabolism. Catabolism is the process by which the body breaks down larger organic molecules into smaller ones. Energy is released from catabolic reactions. Anabolism, on the other hand, is the process by which this energy is synthesized and stored for later use.  

Metabolic pathways are irreversible and have a first committed step which is regulated. 

Even when at rest, the body has several essential functions that must continue to stay alive. The functions are performed by burning calories and expending energy. The amount of energy every individual requires to keep performing these basic life-sustaining functions is called basal metabolic rate or BMR. It is often confused with resting energy expenditure (REE) which is essentially the number of calories burnt by the body while at rest. Though there are subtle differences between the two, they are often used interchangeably. 

Quick Summary of Metabolism 

Metabolism is the rate at which the body breakdowns the food consumed into energy that the cells can immediately use or store for consumption at a later time. The energy can be used for several things, from cellular level growth, reproduction, maintenance, and repairs, to bodily functions and actions such as breathing, walking, talking, thinking.  

The digestive system is where all the metabolic action happens; the digestive system helps to break down food and convert it into energy through catabolic or anabolic reactions. Catabolism breaks down large molecules of food into smaller molecules, releasing energy in the process. During anabolic metabolism, the excess energy released from catabolic processes is stored in the body in the form of fats; more specifically, in the form of fatty acids and ATP. 

Common Misconceptions around Metabolism 

Several factors influence the rate of metabolism. BMR uses up about 50% to 80% of the energy to simply maintain its functions. Thus, it is a major component of metabolism. Factors that influence the BMR and therefore the metabolism include age, gender, genetic makeup, existing muscle to fat ratio, body size, hormones, physical activity, nutrition and diet, drugs and medication, environment.  

Quick-fix diets that claim to speed up metabolism can do more harm than good; they can not only slow down the metabolism but also cause insulin spikes which put the body at a greater risk of diabetes. 

While green tea is said to optimize metabolism or help your body burn fat, it only works when supplemented with adequate exercise, an active and mindful lifestyle, and a calorie-deficit diet. 

Context and Applications  

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for; 

• Bachelors in Zoology  
• Bachelors in Biochemistry 
• Bachelors in General Physiology  
• Masters in Human Physiology  
• Masters in Anatomy and Physiology