When talking about the 3 diets that work I realized that it's important to cover our basics and to lay down a proper foundation for good understanding of their effects and effectiveness for weight loss. So today, I'm going to talk about metabolism.
So, what is metabolism? The leanest definition of metabolism would be the sum of all biochemical processes happening in our bodies. These processes include digestion and absorption of nutrients, breakdown and building of new proteins, tissue reparation, nutrients breakdown and storage or utilization, mobilization or storage of fat and glycogen, gluconeogenesis (creation of glucose from non-carbohydrate substrates) and many others. These processes can be divided into two categories - anabolism and catabolism. To put it simply, anabolism is creation of new tissues, catabolism is their breakdown. As you can imagine, some of these processes require energy and some of them generate energy.
Metabolism is a very complex set of processes, both anabolic and catabolic, and there are many ways to describe it, but the very basic way of quantifying it would be using energy balance. I'll make an analogy to a state economy - there are number of companies and individuals producing and consuming goods and services, there are regulators such as government, there are things that have to be done to maintain the state in general - to support health care, there is taxation and redistribution of wealth and social services etc. We can look at a number of indicators of economy to describe it, but to get a general understanding of the state of economy they usually use the currency to measure the interactions between different parties and to calculate the gross domestic product as an overall indicator of the country's economy. Similarly, when we are talking about metabolism, we can use energy, measured in calories, as a common denominator for all metabolic processes and the total daily energy expenditure (TDEE) to measure one's metabolism as a whole.
When we are talking about metabolic processes, we measure the amount of energy produced or spent in calories and I would like to explain in detail what calorie is. Calorie is a unit of energy, which is defined as the amount of energy (actually, heat) that is needed to spend in order to raise a temperature of 1 gram of water by 1 degree Celsius. In physics, we normally use Joules and 1 calorie equals approximately 4.2 Joules. I must note that there are small calories and large calories, which are denoted as cal and Cal, respectively. Large calorie is 1000 calories (1 Cal = 1000 cal). Usually, when we talk about metabolism and nutrition we are using large calories, but it's not always that obvious and I'd like to mention it here to avoid confusion in the future.
Nutrition is one important aspect of metabolism - we consume various foods, that can be broken down to simple constituents - macronutrients and micronutrients. Micronutrients are vitamins, minerals and other items that do not serve as major sources of energy. Macronutrients can be further broken down into carbohydrates, lipids, and proteins, which can be used as energy sources and building blocks for our body. They contain significant amount of energy in them - 1 gram of carbohydrates or proteins carries 4 Calories, 1 gram of lipids (fat) contains 9 Calories.
These nutrients have to be processed in our digestive tract, then absorbed into our blood stream, undergo some transformations in our liver and then they are either used to produce energy for metabolic processes, or used as building blocks for our tissues - proteins are broken down to individual amino acids and become building blocks for muscles and virtually all other tissues, lipids and carbohydrates are being reorganized and repackaged and can be stored as adipose tissue (fat) or glycogen in the liver or muscles (carbohydrates). Then can also be transformed into each other under certain circumstances, with some limitations and energy loss.
All these processes are necessary to maintain our health and along with getting energy from food and our own tissues we must spend energy to maintain functioning such as breathing, oxygen exchange, bowel health, heart beating and other basic processes. The energy required for these basic processes is called basal metabolic rate (BMR), which is defined as energy expenditure for maintaining basic metabolic process over the course of 1 day (24 hours). It is very similar to resting metabolic rate (RMR). The difference between these two is very small - resting metabolic rate is always bigger than BMR as it includes some very basic activities and the procedure of capturing BMR is stricter. For our purposes (weight loss, body transformation) they are essentially the same.
In addition to maintenance, we spend energy to move and do other things (like being emotional for example) that are beyond BMR/RMR. We use TDEE to capture these. There were a number of experiments that allowed for measurement of BMR/RMR and TDEE in laboratory setting and now we have a good understanding of how much energy we spend and how much energy we can get from food. We can use special equations to estimate all these indicators and I would encourage you to check the toolbox page where we have these essential tools for you.
There are also aspects of hormonal regulation of metabolism and this is an important topic for future discussion - I will definitely talk about them in my future blogs as well as about the nutritional value and metabolic effects of various nutrients, sleep and exercise. I hope the things that we covered today are a good overview of metabolism in general and will help you understand the big picture and apply it to your body transformation goals.