Add to collection
  • + Create new collection
  • Food’s macronutrients undergo chemical breakdown as they move through the digestive system. Learn more about the digestion process and its hormonal control with these explanations of the key concepts encountered when using our digestion chemistry resources.

    Human digestive system

    The human digestive system consists of a long muscular tube and several accessory organs. It is responsible for food ingestion and digestion, absorption of digestion products and the elimination of undigested materials.


    Digestion of food involves both mechanical and chemical processes. Through digestion, large food particles are converted into smaller components that can be readily absorbed into the bloodstream.

    Digestive enzymes

    Digestive enzymes speed up the breakdown (hydrolysis) of food molecules into their building blocks (components).

    Enzyme activity

    Because enzymes are protein molecules with a specific shape and chemistry, their activity is pH and temperature sensitive.


    Hydrolysis is a chemical process in which a certain molecule is split into 2 parts by the addition of a molecule of water. The catalytic action of enzymes allows the hydrolysis of proteins, fats, oils and carbohydrates.

    Resting metabolic rate

    The amount of energy needed to keep the body functioning in a resting, awake and fasting state in a comfortably warm environment is called the resting metabolic rate (RMR). RMR varies from 1 person to another.

    Energy balance

    Balancing energy intake by eating food with output through resting metabolism, growth, exercise and digesting food is 1 of the key components of maintaining health and well-being.


    Mitochondria are organelles inside cells that are involved in releasing energy from food. Keeping them functioning well is thought to be important for avoiding premature ageing and degenerative diseases.

    Adenosine triphosphate (ATP)

    ATP is often referred to as the energy currency of the cell. It stores energy derived from food, and this can then be used to drive the body’s complex chemical, mechanical and electrical systems.

    Gut hormones

    The gut is the body’s largest hormone-producing organ. It releases over 20 hormones, some of which have a key role in controlling food intake and energy expenditure.


    Satiety is the lack of appetite or hunger following a meal. It is controlled by the release of hormones in response to food in the gut as well as the nutritional health of the individual.


    Satiation is the feeling of fullness achieved during food consumption that promotes an end to eating. Foods and food supplements have been developed to enhance this effect to reduce energy intake.

    Gut bacteria

    Gut bacteria play important roles in nutrient digestion, vitamin synthesis, energy metabolism and immune responses.

    Colonic fermentation

    Bacteria in the large intestine (colon) ferment undigested carbohydrate (fibre), releasing short-chain fatty acids along with gases such as carbon dioxide and methane.

    Short-chain fatty acids (SCFAs)

    SCFAs are produced in the colon by bacterial fermentation of undigested carbohydrate. They serve as an energy source for cells lining the colon as well as playing a role in colonic health.

      Published 30 October 2016 Referencing Hub articles
          Go to full glossary
          Download all