Fast and Furious – About Healthy Metabolism

Fast and Furious – About Healthy Metabolism

Anil Kumar, PhD
Created On
Dec 07 2020
Last Updated
Jan 19 2023

What is metabolism?

Whenever we eat a meal, the body starts digesting it to give all the energy we need for daily activities.

Depending on the age, diet, and excess calories, some of that food converts into muscles, bones, and fat. Rest of the unusable parts leave the body in various forms of waste. This whole process is called metabolism.

Our metabolic rate scales with the body weight, and follows Kleiber’s law, shown in the image above.

A metabolism test is designed to understand the efficiency of this process.

Anatomy of metabolic process

It can be a fascinating to learn how each of these activities is carried out inside the body. The small part that converts food into energy involves breaking down the ingredients into basic components and then using the energy released from this break down for daily activities. Consuming sugar to generate energy, as athletes do when they drink glucose during heavy work outs, is just one simple example.

The second part of metabolism involves maintaining and building various organs, bones and muscles.

An example is weightlifters eating meat and other proteins to build muscles. This process will utilize final products of metabolism and build complex tissues that form bones and muscles. This part will also convert the excess energy left from food into fat and store it for future.

Anything else that’s not useful is excreted out.

The nuts and bolts of these processes are highly complex but they work as a well-oiled machine. This machine does have certain knobs that are constantly tweaked to ensure the processes function properly.

A metabolism test helps check these critical knobs.

Variables for healthy metabolism


Thyroid is one of the key glands that regulates this process. In combination with hypothalamus and pituitary in the brain, it monitors key hormones that maintain a stable body temperature, energy balance and mental health.


Adrenal cortex, a small gland on top of the kidneys, releases another key hormone called cortisol. This stress hormone plays a critical role in breaking down the food into basic building block that are used by the body to generate energy and to store fat for future use. One of the interesting properties of cortisol is its daily rhythm that follows the 24-hour cycle. Cortisol levels are highest in the morning and then drop slowly throughout the day to hit their lowest in the night.

Measuring cortisol levels in the morning is a great way to assess proper functioning of adrenal gland. Measurements taken throughout the day might even be more useful in systematic analysis of the 24-hour diurnal rhythm of cortisol.

High cortisol is the reason why we feel more energetic in the morning and the slow decline explains why afternoons start to feel tiring. It is also the hormone responsible for causing fear of public speaking.

Cortisol levels shoot up quickly whenever the body senses a danger, often termed as the fear or flight mode.


The third and final key hormone is the male sex hormone, testosterone. Despite the name, both men and women produce it though levels in men are almost ten times higher than in women. Testosterone is the key hormone responsible for building healthy bones and muscles. It is also responsible for development of sexual organs in men during puberty. Levels rise with age, peaking in twenties and then slowly decline throughout the adult life.

Similar to cortisol, testosterone also demonstrates a 24-hour trend, with a characteristic morning peak that slowly declines throughout the day. An early morning sample, collected 15-20 minutes after waking up is the best way to determine healthy cortisol and testosterone levels.

Ways to increase metabolism

Certain food allergies, dysfunctions of the glands, aging, and key ingredients in our diet–e.g., low iodine levels–can have dramatic impact on these crucial knobs designed to controlled our well-oiled machine. Whenever in doubt, it’s a useful to check these key hormones.

A simple and easy at-home metabolism test, that uses a morning saliva sample along with a few drops of blood with finger prick, can easily help assess a healthy metabolism.