Energy Systems. What's happening to those macro nutrients when I run, bike or swim?

We have seen from the post "Nutrition 101" that our bodies are programmed to store fat and as a consequence of that we will burn carbohydrate before fat if both are available. Since carbs yield less than half the energy of fats, the question is "how can I access those fats for burning which will yield more energy and make me look in better shape?"

Since this is primarily a running blog lets take running as the example here but the story is the same for cycling, swimming and any other endurance activity.

The muscle cells store a small amount of glucose as does the liver. As we sit in work, lay in bed or watch TV our bodies use these glucose molecules for energy production, the energy is required to keep us ticking over (think of a car with the engine turned on and it's sitting still). This energy equates to our basal metabolic rate (the amount of fuel you will need to put in the car to keep the engine ticking over), as we get up from our desk, climb out of bed or get up off the sofa these muscle glucose stores will be burned up very quickly. The daily activities we do all require energy (remember the car, now you are beginning to press the accelerator) and this energy added to the basal metabolic energy equates to our metabolic rate (or metabolism). If you have eaten any carbohydrates you will be replenishing these stores all the time until you begin to run!!!

So you start running and you feel good for about 10-15mins because you have a lot of easy access glucose to burn. The part of the cell that converts glucose and oxygen into energy is called the mitochondria (think power station) and the trucks carrying the fuel to the power station are full of newspaper, fast burning low yield energy. Then from 15-20mins you feel like crap because your fuel stores are running low and your energy plummets. But then at about 20-22mins (you put some big wood logs on the fire) you start to burn the fats. Now your energy will increase and you will begin to feel good again. This energy surge will now depend on the amount of power stations you have active in your muscles.

If you increase the number of workouts and/or the duration, your muscle cells will build more (mitochondria) power stations and you will (like the Duracell Bunny) go for longer.

If you are new to running you need to understand that this will take some time and most importantly regular running however short the distance. If you are a runner but have taken some time off, the power stations are shut down if they are not used that's why you can no longer run as fast as before or for the same distance. It will take 2 -3 weeks of regular running to get your power stations reopened and fully functional.

If you keep your metabolism quite low by doing very little exercise the carbohydrates you eat will always prevent your fat stores from being used as fuel. This will give you low energy and you will feel tired and cold (newspaper burning does not give off heat for very long) most days. Some of the  carbs that are not burnt will be linked with fatty acids and stored as fats (no need for water). So yes carbs can and will be stored as fats. Excess carbs that have not be burnt or stored as fats are excreted (calories down the toilet). Another reason why calorie counting is an arbitrary weight loss plan.

The next entry I will discuss, how running can be used to lose weight and how you go about maintaining weight loss!