What is metabolism?

In the everyday life you often hear phrases like "You must have a good metabolism! You can eat all you want and still not gain weight" or "My metabolism is so slow. I don't burn any calories". But what does the term "metabolism" actually mean?

Metabolism refers to the entirety of all build-up and breakdown processes in the body. This includes the chemical conversion of nutrients taken in with food into energy-poor end products. The body uses the energy released during this conversion for vital functions [Lang & Ranke 2013], such as maintaining body heat or activity. Metabolism is therefore a constant process of building and breaking down molecules in the body: breaking down nutrients to build cells for different processes. Metabolism constantly adapts to fluctuations in food intake and even prepares for foreseeable changes in nutrient availability. The brain integrates various signals from the body with those from outside to meet current and future energy needs [Brüning & Fenselau, 2023]

More information about "Which neural circuits are involved in metabolism?" can be found here.

Metabolism is often divided into two main phases: catabolic and anabolic metabolism. Catabolic metabolism (catabolism) refers to the breakdown of nutrients to produce energy. Anabolic metabolism (anabolism), on the other hand, refers to building up processes. The body can switch between catabolic and anabolic metabolism depending on nutrient availability and energy needs [Christen et al., 2016].

Metabolic disorders

Metabolic disorders are diseases that affect one or more metabolic processes. They can be innate and genetic, or develop over a lifetime as a result of environmental factors. Metabolic disorders can lead to a variety of disease patterns. Probably the best-known metabolic disorder is diabetes mellitus, which is divided into type 1 and type 2 diabetes.

While type 1 diabetes occurs mainly in childhood and adolescence and is caused by a lack of insulin, type 2 diabetes is a disease that develops over the course of a lifetime and is characterised by a reduced insulin effect and/or a reduced insulin production that is insufficient to cover the increased insulin requirement [Bundesministerium für Gesundheit, 2023].

You can find more information about diabetes on the website of the German Centre for Diabetes Research.

Type 2 diabetes is also closely linked to obesity, with the risk of developing type 2 diabetes increasing linearly with increasing BMI. Type 2 diabetes may be favoured (or even caused) by obesity-related insulin resistance, combined with a decrease in insulin secretion by so-called beta cells [Klein et al, 2022; Boutari et al, 2023].

More information on obesity-related diseases can be found here.

Certain genetic variations can also affect metabolism by promoting obesity. Mutations, which are genetic changes, in the so-called FTO gene correlate with an increase in BMI and thus also with weight gain in both children and adults, regardless of gender [Hess & Brüning, 2014]. The causes of weight gain associated with the FTO gene mutation are increased energy intake [Cecil et al., 2008; Haupt et al., 2009], impaired satiety [Wardle et al., 2008] and increased food intake [Velders et al., 2012].