In simple terms, metabolism is a vital process in which the body converts the food and drinks we consume from our diet into energy to fuel our bodies daily. This energy is essential for driving “basic” bodily functions (like the digestion and absorption of nutrients in our gut, breathing, our heart beating, blood circulating throughout our vasculature, etc.), complex physiological pathways in our cells and tissues (eg, RNA transcription into various proteins, DNA synthesis, neuron signals in our brain, etc.), and physical actions that require more energy (like physical activity, immune responses, and healing).
Metabolism and metabolic rate are closely related. Metabolic rate can be broken down into three different components: resting metabolic rate (aka resting energy expenditure, or REE), thermogenesis, and energy burned during physical activity. REE refers to the amount of energy (ie, calories) burned to keep all those “basic” physiological functions running when the body is at rest. REE happens to make up the bulk of our total daily energy expenditure, or use.
Thermogenesis describes the process of heat generation (the primary product of metabolism) that occurs as a result of food intake and activation of brown adipose (fat) tissue and supports whole-body energy balance. The third and final way we expend energy (ie, burn calories) is through physical activity—which includes any daily movement we engage in, no matter the intensity.
Daily metabolism and metabolic health are critical for promoting not only a healthy weight and body composition, but also overall health and well-being. There are many variables that influence the health and efficiency of our body’s metabolism and metabolic rate—including age, body composition, muscle mass, biological sex, thyroid health, physical activity, dietary patterns, and even our genetics and epigenetics.