How your metabolism works

Discover the many ways our bodies stay energised

We often mistake our metabolism as something that happens in a certain part of the body, such as in the digestive system, and something you can boast about at the gym. However, this isn’t the case. Metabolism occurs within every one of the 37.2 trillion cells that make up each human body and describes a myriad of different biochemical reactions, not just how fast you burn fat.

Your metabolism is the combination of two types of biochemical reaction. Catabolic reactions break down the molecular nutrients, such as carbohydrates, vitamins and fats, from the foods we eat for energy release, whereas anabolic reactions assemble different molecules for energy storage. These two types of reaction work in tandem to maintain a biological harmony in the human body called homeostasis.

While the nutrient molecules of water, minerals, proteins, fats and vitamins are vital for our survival in other ways, such as physically building our bodies, the release of energy comes from the metabolism of carbohydrates. On a cellular level, glucose molecules, found in carbohydrates, are broken down to release energy in the form of a compound called adenosine triphosphate (ATP). ATP is essentially the driving force of your body’s metabolism, converting energy from digested glucose or using up glucose that has been stored in the body as long-chain molecules called glycogen.

However, not everyone’s metabolism is the same. Genetics mostly determines the rate of metabolism, irrespective of a body’s size. There are many factors that can either speed your metabolism up or slow it down, such as age and gender. To function normally, the amount of energy needed, referred to as the basal metabolic rate (BMR), is around 7,100 kilojoules (kj) per day for the average man and 5,900 kj per day for the average woman. When we provide our bodies with more nutrients than we need to fulfil this energy demand, we store it as fat, and when we don’t supply our body with enough energy our metabolism uses the stored fat.