What is Metabolism?

Written and Reviewed by: Elysium Health

What is Metabolism?


Key Takeaways:

  • Metabolism is the sum of every chemical reaction that happens inside the body and is influenced by various factors like age, genes, stress levels, sleep, and exercise.

  • Maintaining a balance in metabolism is essential, given the constantly changing physiological environment. Fluctuations in the type and amount of food eaten, the level of exercise, and aging can affect this balance.

  • Mitochondria play a central role in metabolism, producing almost 95% of the cell's energy. Mitochondrial function, however, declines with age. 

  • Maintaining a healthy level of NAD+ can help support mitochondrial and metabolic health. 

Related Product:

  • Signal: Contains the NAD+ precursor NMN to boost NAD+ levels. Signal also contains honokiol and viniferin, which work together with NAD+ to activate SIRT3, a key mitochondrial enzyme essential for maintaining mitochondrial and metabolic health.


Metabolism is the sum of every chemical reaction that happens inside the body. Scientists understand metabolism as the sum of the processes of breaking down, known as catabolism, and of building up, or anabolism, that sustains life. Metabolism is influenced by a variety of factors, including age, genes, stress levels, sleep, and exercise.

Popular ideas about metabolism aren’t doing us any favors. The suggestion in most articles (Google search: “how metabolism works”), that metabolism is inherently tied to gaining- and losing-weight isn’t wrong. But it does miss the forest for the trees. Metabolism is the sum of every chemical reaction that happens inside the body, an enormous web of interactions on the molecular level that aim to keep the organism (you) in what biologists call homeostasis: a state of balance, best illustrated by our near constant body temperature, which persists even in a wide range of circumstances. 

Scientists categorize most of the chemical reactions that make up metabolism into two processes that happen simultaneously and constantly. In catabolism, large molecules (many from food) are broken down to extract energy and form smaller molecular building blocks. In anabolism, the energy acquired is used to assemble those building blocks into larger complexes which can be used to build cells, tissues and organs.  

This is a delicate balancing act, and a constant effort by your body to produce the right amount of energy and the right raw materials to survive. Along with your genes, metabolism and the inputs that influence it make you who you are. While it doesn’t have the same familiar ring as “you are what you eat, ” “you are your metabolism” might be closer to the truth. 

What are catabolism and anabolism? 

Digestion is actually the important first step that takes you from chewing your food to absorbing valuable molecules in the intestines. Catabolism begins inside the cell, once the large molecules (also called macromolecules) like carbohydrates, fats, and proteins—the basic components of a piece of food—get broken down further into their building blocks. Those are called monomers and they include fatty acids, amino acids, nucleotides, and monosaccharides. 

This all happens in strings of chemical reactions called metabolic pathways, where enzymes react with a molecule and then pass it off to another enzyme for the next reaction, like an assembly line (or disassembly line, in the case of catabolism). Enzymes are proteins that speed up each reaction (like a catalyst), and many of these enzymes require coenzymes, or helper molecules such as NAD+, to help them function. These series of reactions continue until the molecule is converted into a form that can be used immediately or stored for later use. During many of these reactions, energy is released as a by-product in the form of adenosine triphosphate, or ATP. ATP is the primary source of energy for most biological processes in the body. The end result is a bunch of molecular building blocks of the food you ate, plus ATP, all of which get used in the other half of metabolism: anabolism. 

Anabolism uses many (but not all) of the same enzymes and metabolic pathways as catabolism. This means many parts of catabolism and anabolism happen simultaneously within the same cell. During anabolism, enzymes use the ATP-based energy, unlocked during catabolism, to combine the monomers back into larger macromolecules. These larger molecules are then used within the body as materials to repair and build cells, organ tissues, bone, and muscle. 

The important thing to remember is that metabolic pathways are part of a highly intricate system with a goal of keeping you in balance. Maintaining balance is non-trivial, given the constantly changing physiological environment. Fluctuations in the type and amount of food you eat, how much you exercise, and many other factors such as aging all affect this balance.  

Another way of thinking about reactions on the molecular level is by comparing them to your own behavior on the surface level. When you get cold, you put on another layer; when you go for a run, you get thirsty and drink water. Likewise, the chemical reactions that make up metabolism react to their conditions on the cellular level to keep you humming along. 

So, how do you maintain a healthy metabolism? 

First, we need to understand where the majority of these reactions take place. Mitochondria are critical organelles inside your cell that act as a hub for many of the metabolic reactions and play a central role in metabolism. As a matter of fact, almost 95% of the cell’s ATP is produced inside mitochondria. NAD+, the coenzyme mentioned previously, is an essential molecule in mitochondrial function, as are sirtuins, a class of NAD-dependent enzymes that act as molecular sensors of cellular energy balance and play an important role in regulating metabolism.  

We can help support our mitochondria, and the enzymes and metabolic reactions within, by maintaining a healthy level of NAD+ and providing nutrients that help support mitochondrial function. This is especially important because NAD+ levels and mitochondrial function decline as a normal part of aging. One way to maintain our NAD+ and support mitochondrial function is with our product Signal

Signal provides an NAD+ precursor molecule called NMN (nicotinamide nucleotide), which is efficiently converted to NAD+ by the cell, as well as a SIRT3 activation complex—honokiol, isolated from the bark of Magnolia officinalis, and viniferin, derived from grapevine. This complex works together with NAD+ to activate SIRT3 and help maintain overall mitochondrial and metabolic health.  

Likewise, sleep, exercise, and living relatively in sync with our natural circadian rhythms (think: getting sunlight in the morning and avoiding bright light after dark) are all supportive for metabolism. In contrast, eating a diet high in refined sugar, eating late at night, being sedentary, and sleeping at inconsistent hours can all put stress on the metabolic system.


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