I seemed to have jumped the gun in my first basic science post! I followed the route that most textbooks (the ones I could easily find online) set out: highlighting the importance of glucose as the fuel needed for our body to function and that the metabolism of glucose is akin to the metabolism of fuel. And then later on there is a short chapter on the role of fats and keto acids, often paired with the phrase starvation mode.

So through this unintended marketing ploy, I already assume that glucose is the one and only preferred fuel of my body. I have heard that it can survive off of my stored fat, but this is only in case of emergency…

Let’s do it a bit differently, then.

As I outlined in my previous post, our cells need the molecule ATP to survive. This molecule is the food our cells need to function and perform all their tiny tasks. The food our bodies need to create ATP is often grouped into what people call macronutrients.

Food is our fuel.  What we eat can be divided into three main sources of energy: carbohydrates, proteins and fats.

Food is our fuel.
What we eat can be divided into three main sources of energy: carbohydrates, proteins and fats.

These macronutrients are luckily words we’re all familiar with: carbohydrates, protein and fats. Interestingly enough, alcohol also provides energy, but I think we can all agree that we can’t live off a diet of pure alcohol, even though we sometimes try…

In the end, all three of these macronutrients have to be converted to the ATP molecule so that our cells can function. The journey from food as a body fuel to a potential cell fuel occurs through digestion. Carbohydrates get stored as glycogen, protein as amino acids and fats as triglycerides.

Once broken down into these compounds, they can be metabolised, chemically transformed, into the type of energy an individual cells can use. Each compound has its own path that it must follow to be metabolised. These are called metabolic pathways, and as you can see in this chart, I am greatly simplifying all the processes happening. And that chart should give you some idea of the headaches biochemistry students surely must endure.

In simple terms, carbohydrates and protein can form glucose, while fats can form keto acids (also called ketone bodies).


Two paths to a working body: glycolysis and ketosis.

The cells can use either glucose or keto acids to create ATP. When you’re body has any reserve glycogen stored up, or available glucose in the bloodstream, it will choose to run on glycolysis. When your body sees that there is no more stored glycogen and no available glucose in the blood, it will naturally switch to ketosis and use the stored fatty acids to form keto acids for energy.
This switch between processes is not a strange or frightening occurrence. In fact, most people switch into ketosis at night since the body is not getting fresh glucose supplied from food.

Something to note is that ketosis is not your body’s starvation mode if you are on a high-fat, carbohydrate-restrictive diet. How can it be if you are actively putting fuel into your mouth? Starvation is only starvation when you are actually starving.

Now, how about your brain?

Your brain needs fuel, too!

Your brain needs fuel, too!

Your brain also needs fuel to thrive, and like your cells, it will run on glucose as long as it is readily available.

However, your brain can also tap energy from keto acids! Just as in the rest of your body, your brain changes its metobolism method in order to use the keto acids as its source of fuel.

There is a catch, though. Your red blood cells need glucose to create ATP. Luckily, as mentioned in the previous post, your body can produce enough glucose through gluconeogenesis for the red blood cells to function, even while running on ketosis. It’s amazing, really!

Is ketosis dangerous? Well, in the case of Type 1 diabetics it can be! In their special case, they can develop ketoacidosis. This happens when they can no longer produce enough insulin to tell their bodies to metabolise glucose, so their bodies over-produce keto acids while also retaining high levels of blood glucose. Total energy confusion, it seems.

This state only poses a threat to people who don’t know that they have type 1 diabetes. This is not a concern for the average human able to produce insulin. However, as always, if you are worried go see a medical doctor for a check-up! But please go prepared and read up on type 1 diabetes.

I hope this post gave some insight into what happens after we eat! As always, this is a incredibly simplified outline, but I hope it gives a reasonable, bare-bones overview of what goes on inside.

Don’t fear fat. It is fuel. 🙂