Introduction
By now, you probably know that we strongly believe that you can optimise your health on your own at home, with no doctor or hospital required. Of all the things to work on, metabolic health is perhaps one of the most critical things to get right. Metabolic health is closely linked to other health domains, and improvement in metabolic health has a huge array of positive downstream effects. Furthermore, poor metabolic health is one of the most important drivers for chronic diseases. Ok, this might sound familiar, but how does it actually work? We'll start with the basics of metabolism in this article. Let's dive right in!
Nutrition & metabolism
Metabolism deals with the conversion of food into energy, storage of energy and utilisation of energy. We take in food, because it provides us with the critical macro-nutrients (carbohydrates, proteins and fats) and micro-nutrients (mostly amino-acids, vitamins and minerals) for our bodies to function properly. The complex structures of food are broken down into macro-nutrients in our alimentary tract and liver, which in turn are exported through the bloodstream to the rest of our body. We’ll come back to the liver later, since it is the orchestrator of metabolism.
Food composition matters
The exact form and composition of our foods (including drinks) - together with the body’s demand at that exact time - has a huge impact on what happens with those macronutrients.
Let’s take a simple example to illustrate this point. Freshly pressed orange juice results in a rapid, huge spike in blood glucose. That’s the case, because it is ingested in a liquid form. This usually implies more oranges consumed in a smaller volume than you normally would, increasing carbohydrate concentration, and that higher carbohydrate (glucose and fructose) concentration reaches the liver much quicker due to shorter digestion time for liquid versus solid foods. Eating an orange leads to a much more modest spike in blood glucose, because you’ll eat less, need more time to digest it and it contains much more fibres, which slows down the carbohydrate release from the bowel to the liver.
Now you know this, you might see why a blind focus on calories intake or macronutrient composition can be very misleading. Good riddance ‘calories are calories’.
From macronutrients to energy
Most cellular processes in the body - like the synthesis of organic molecules or the transport of molecules across the cell membrane - require energy.
The currency of energy that you pay with to afford these processes is not glucose, protein or fat, but the molecule ATP, which stands for adenosine triphosphate. It contains energy stored in the chemical bonds between the three phosphate groups. When ATP is broken down to (i.e. metabolized) ADP (adenosine diphosphate), the energy of that one abolished phosphate-phosphate bond is released. Each mol of ATP yields approximately 30 kJ of energy. To put this into context. 1 calorie equals approximately 4J. ADP can also be broken down further into AMP (adenosine monophosphate), which approximately results in another 15 kJ. Don't worry, wel'll take it easy on the nerdy stuff now and continue the story.
We generate ATP by metabolising the carbohydrates (mostly glucose and fructose), fat (free fatty acids) and to a lesser degree proteins (amino acids) in the mitochondria. Perhaps the words Krebs cycle and electron transport chain ring a bell. You are lucky, we'll ignore those for now.
Storing energy
So, directly after we have broken down our food into macronutrients and have metabolised those, we have energy (ATP) to spend, right? Well, we usually don't need to spend the energy right away. What we want is to store the energy source so that we have sufficient storage for the following period that we are not eating and for when demand increases (for example when we exercise). When you get your income, you want it deposited in an account so that you have sufficient money for the month and for when rent is due, don't you?
ATP is not a great molecule for storage. Instead we store glucose in the form of glycogen in the liver and skeletal muscle, and we store fatty acids as triglycerides in white adipose tissue under our skin. When blood glucose level rises, the pancreas secretes the hormone insulin. This hormone brings down the blood glucose level by promoting the uptake of glucose in the liver and skeletal muscle, and facilitating the conversion of glucose into glycogen (glyconeogenesis). Under the influence of glucagon (stimulus) and insulin (brake), glycogen can be converted back into glucose when there is increased energy demand. That glucose is then metabolised to free up ATP which can be used in the cellular processes that require it.
Ok, that's a wrap. Now you have a very basic understanding of metabolism!
