What it is, how it works and its relationship to food and exercise

If I had a penny for the number of times people tell me that they put on weight because their metabolism is too slow or that their friend has a fast metabolism because they never seem to put on weight no matter what they eat, I would be a very rich man. But I cant help thinking, how do they really know they have a slow metabolism and do they even know what metabolism is?

Its all about energy

Metabolism is a bit of a catch-phrase these days and it seems to have lost all its original meaning. Metabolism is derived from the Greek language for change.1 The scientific definition for metabolism is it ...involves all the chemical reactions of biological molecules within the body, including both synthesis (anabolism) and breakdown (catabolism).2 So, in your bodys terms, metabolism is the change created by chemical reactions such as the times when your body chooses to store fats (anabolism) or burn fats for fuel (catabolism).

The history of metabolism

Chemical reactions occur inside any living creature and these reactions either use or create energy. That energy is measured as heat, either in joules or calories.3 The joule is the internationally accepted scientific unit of measure and the calorie is now an outdated empirical unit. Metabolism was founded in classic experiments by Atwater and Rosa in 1899.

These two pioneers discovered there was an almost perfect relationship between the heat given off by a person (calories) and the oxygen they used. They used information collated more than a century before them by the scientist, Antoine Laurent Lavoisier, in 1777. This data forms the foundation of the discipline calorimetry, which measures the energy used by metabolic chemical reactions and demonstrates that the history of metabolic research is more than two centuries old.

How to measure metabolism

What this discovery means to you is that the only method for measuring your metabolism is calorimetry. From the turn of the 19th century onwards, scientists have commonly used the indirect calorimetry method, which analyses gases from the breath instead of heat because of its portability, convenience and also because it measures carbon dioxide. Carbon dioxide allows an expert to determine the type of calorie that is being used as fuel by the body. By type of calorie, I mean fats or sugars. Proteins are an insignificant energy resource.

When fats are burnt, they give off 25 per cent less carbon dioxide than when carbohydrate is used. By using this information, a trained specialist can tell you how efficient you are at burning fats, which is, of course, very important in weight loss. Alternatively, the expert can also use the same evidence to determine how well sugars are burnt, which is very important information for diabetics and athletes.

When assessing metabolism its very important to be completely at rest; normally, you would have to fast for a minimum of five hours with water only.5 You would also have to avoid exercise, coffee, tea and cigarettes during the fast. An assessment room that is quiet and low in light with a comfortable bed is especially good at helping you reach a rested state.