What is metabolism?
Metabolism can be a confusing concept to understand, but it is critical to how children grow and develop. All the cells in a child’s body use a tiny amount of energy to divide and make copies of themselves, and the do it all by themselves. They do this by breaking down the nutrients and extracting the energy from them – this is called “metabolism”.
Some cells have a higher activity, like those that make up the muscles, heart, brain and eyes. Those use more energy, more quickly. Adding up all the billions of cells together, you will have a total amount of energy (in calories or kilojoules) per hour for the whole body, and this is called “metabolic rate” .
It is also what generates heat in the body. Metabolism is steady (also called “basal”) when kids are sitting down, but increases when they move around, run, jump and play. The energy used is controlled by the individual tissues, but they are all coordinated by a hormone called thyroid hormone. Another observation is that children also have a high metabolic rate for their body size than adults, because they lose more heat.
Which macro-nutrients are needed for making energy?
Metabolism has two sides to how it works:
- Breaking down: macronutrients (especially fats and carbohydrates) are broken down to make energy. These macronutrients have the highest energy value and are needed every day. The digestive system starts this process off, while the cells do the rest once they get the broken down nutrients.
- Building up: the energy from (1) is the used to build up tissues from other macronutrients (mainly protein). Protein has amino acids for new parts of tissues for growth.
Protein also has some energy value, meaning some of it can be broken down to make energy as well, because some amino acids are used for energy processes, like glutamine and aspartic acid.
Which micronutrients are needed for making energy?
Because (1) and (2) are integrated, all essential micronutrients are needed to keep this cycle going. Missing one or a few micronutrients may slow down the flow of energy to the tissues. Some nutrients with specific energy functions include:
- Magnesium & phosphorus – activate key parts of the process where energy is moved around
- B-vitamins – widely used in all processes of macronutrient breakdown
- Iron & copper – required in small amounts for processes that use oxygen
- Chromium – used in the breakdown of fats and carbohydrates
- Molybdenum – used to help process nucleotides in the body
- Carnitine – used for breakdown of fats into energy
Under-nutrition vs over-nutrition – how is it related to energy?
Metabolism runs at a balanced level when kids are at rest. This means they have a constant energy consumption – a bit like when a car sits at the traffic lights and slowly burns petrol. This is simple way to look at it.
- Under-nutrition is when there is a lack of nutrients needed for growth and development in children . When there is not enough carbohydrate, or energy forming nutrients, there is simply not enough to keep normal metabolism going. In extreme cases, the starts to break down its own tissues for energy (wasting). As a result, the whole “engine” slows down, growth lags behind, and illnesses become more common. Under the age of 3, this is also known as “failure to thrive” .
Consequences: slower growth, stunting, problems with development of muscular and skeletal systems, intestine, immune system, eyesight and cognitive ability.
- Over-nutrition  is the opposite – there is usually an over-supply of macronutrients, so that when there is more than what the body can break down, it is stored (as fat tissue). Also, the intake of foods with lower energy forming nutrients means even the breaking-down process is not working well, and although there is more than enough energy, other systems like the immune system may not work properly.
Consequences: overweight or obese, lower endurance, higher blood pressure, cholesterol problems, higher risk of infections, lower cognitive performance.
As you can see, both these nutrition states are harmful, especially if they are maintained for a long time, and may cause future health issues later in life.
Why do children feel tired when they are sick?
When there is an illness or infection, the energy that children normally use for growing is diverted for dealing with the illness, and sometimes this results in higher levels of spent energy than normal . The excess energy is sometimes lost through heat, such as when kids have a fever.
Furthermore, they also lack sleep, which delays recovery, and this can lead to children feel emotionally unmotivated, lazy or groggy.
Bottom line - nutrients feed metabolism
In summary, nutrients support metabolism, and metabolism supports how nutrients are used. During illness, metabolism changes the way energy and nutrients are used, so it may take time to get back to normal growth. This is a simple way of looking at an extremely complex process.