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What is Metabolism?

At any given moment, there is an incredible amount of metabolic pathways, enzymes, and reactions happening in a eukaryotic cell to keep it going. Many people try to hack their metabolism with the latest fad diet. But what exactly is metabolism?

Metabolism is energy.

Metabolism is the art of transforming molecules we eat into useful molecules that energize cells, store energy, communicate, and so much more. Metabolism captures the energy in our food to be able to do all of this through controlled reactions, which produce metabolites. Different metabolites have different functions.

Food is energy. Metabolism captures and uses it
Food is energy. Metabolism captures and uses it.

Metabolism can be broken down into anabolism and catabolism.

Anabolism is building molecules from other ones, like legos. An example is making the energy needed to produce all the extra items that a cell needs during cell division.

Catabolism is breaking molecules down into the legos used in anabolism. For example, when you eat sugar, your body must break it down a little before it can do anything with it. A trick to remember what anabolism and catabolism do is that a cat breaks things into pieces while Ana builds.

The balance between catabolism and anabolism is important in overall metabolism. Metabolic pathways, such as glycolysis, often use the relative amounts of metabolites as a method of regulation. So if the balance of the catabolic and anabolic steps is thrown off somewhere in the pathway, you can get metabolic diseases, like diabetes.

Some of the most important metabolic pathways include:

  • Glycolysis - This is THE central metabolic pathway. Breaks down glucose for energy and branches off to many other pathways.

  • Citric Acid Cycle (AKA Krebs or TCA Cycle) - Can follow glycolysis. Generates intermediate metabolites and more energy.

  • Gluconeogenesis - Makes glucose from other sources, like fat and protein, for energy production when the availability of glucose is low.

  • Glycogenesis - Energy storage of excess glucose as glycogen.

Cellular metabolism ensures cells remain powered and responsive to the ever-changing needs of the organism. It is the intricate web that connects the food we eat to the energy we use constantly. The role it plays in diseases and disorders makes it a fundamental process worth exploring further in the biomedical context, which we will do.

Interesting Fact

Zero-calorie/zero-sugar drinks and foods do have energy from the sweetener, but not for us. These zero-calorie drinks use molecules that are close enough to certain sweet molecules that we can taste them but we cannot break them down. However, bacteria in our gut have metabolic pathways we do not so they may be able to break these sweeteners down, which can disrupt the balance in our microbiome by favoring whichever bacteria can use these molecules. The changes in the microbiome may cause serious domino effects on our own metabolism, which could lead to diseases [2].


Please see a nutritionist before deciding on major dietary changes. Many diets out there are not well-founded in science and, even the ones that are can cause health issues. For example, there is mounting evidence that fasting, vegan, and vegetarian diets are associated with higher bone fracture rates. High-protein and fat diets can cause heart disease and other complications. All of these diets can result in nutritional deficiencies, which can behave unpredictably with your unique body, so please work with an expert to minimize poor outcomes.


[1] Garrett, R. & Grisham, C. Biochemistry, 7th Edition. (Cengage, 2024).

[2] Le Roy, T. & Clément, K. Bittersweet: artificial sweeteners and the gut microbiome. Nature medicine vol. 28 2259–2260 (2022). DOI:


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