In part one of this short series, I explained why we seem to snack against our own better judgement. It’s our physiology working against us. Those of us that are involuntary snackers are physiologically, sugar burners.
Remember sugar burners preferentially burn carbohydrate for fuel and fat burners preferentially burn fat for fuel.
Let’s get a little sciencey for a minute. In part one I outlined that when we snack, we spike our blood sugar which in turn spikes our insulin. Insulin replenishes glycogen stores, meets all of our cells’ energy requirements, and stores the excess energy as fat.
In a process called lipogenesis (Lipo = fat; genesis = to make new) our body stores excess glucose as fat in the form of triglycerides. A triglyceride consists of 3 short chains of fat, called fatty acids that are stuck on a structural backbone called glycerol (not to be confused with glycogen or glucose.) These fatty acids vary in length but most have between 12 – 18 links. When we ‘chew on body fat’ (burn body fat), a process called fatty acid oxidation, each triglyceride molecule can generate over 300 molecules of ATP, our cells preferred energy source. (To put this into perspective, one glucose molecule generates 38 molecules of ATP. A single 16-link fatty acid generates 106 molecules of ATP.)
So fatty acid oxidation is extremely efficient, generating loads of energy. All of the cells of your body can burn fatty acids, except your red blood cells and your brain cells, which we will talk about shortly. Our cells do not run out of fuel, so… no snack attack.
When you are a fat burner, you can easily access your body fat for fuel. Instead of demanding a quick supply of energy from sugar, your body can easily chew on a little body fat for energy between meals, so… no snack attack.
In addition, fatty acids and ketones (more on ketones coming up) do not spike our blood sugar, so our insulin levels remain low. Low insulin means no rebound sugar lows, so… no snack attack!
While it is true your RBCs and your brain cannot use fatty acids for fuel, there is no need to worry about wilted RBCs and shrivelled up brain cells if you don’t eat every two hours. You will not get short of breath or confused.
The sole job of red blood cells (RBCs), those life-saving iron containing oxygen delivering doughnut shaped cells, is to deliver oxygen to our tissues and remove the cellular waste product, CO2. They must be flexible enough to squeeze through tiny little capillaries – so they do not have a nucleus or any mitochondria. Without mitochondria, the energy generating powerhouses of our cells, RBCs are totally dependent on glucose for their energy needs. This is where the glycerol backbone of triglycerides comes in very handy. That back bone, very conveniently breaks down into glucose, maintaining our blood glucose levels in the healthy range, keeping our RBCs very happy, even when we were starving between successful hunts.
Fatty acids are large molecules, and as such, do not cross the blood brain barrier – that ever so important filter that keeps all kinds of toxins out of our brain. But, again, the liver comes to the rescue! When the liver is depleted of glycogen – its emergency glucose supply, it converts fatty acids into ketones. Those ketones are able to cross the blood brain barrier and the brain gets lots of clean burning fuel.
Interestingly, only muscles, the heart and the brain can burn ketones for fuel. RBCs get glucose. Everyone else gets fatty acids. Isn’t it amazing how the body prioritizes its energy distribution system? Enough science for now.
So how can we make the switch from sugar burner to fat burner? It’s simple, but not easy.
More on that in part 3
Have a fantastic week,
Dr Karen
