When we exercise our body uses a combination of all three types of energy; carbohydrates, fat and protein. Different exercises will cause the energy system to shift towards using the most appropriate fuel, largely depending on the level of effort an individual produces during exercise. Anaerobic exercise causes the energy system to shift towards burning predominantly carbohydrates (carbs) simply because movements require more effort. Energy is needed quickly for fast and/or power movements and because sugars (carbs) burn much more easily they form the major source of energy for exercises with high effort such as weight training, squash or sprinting. As much as 90% carbs can be used during anaerobic exercises. Although bear in mind that high intensity exercise can only be performed for a limited time, depending on the fitness level of the individual, thus during periods of rest the energy system will shift back and a little more fat may be burned, although this is only a minor change. An example is weight training with frequent rest intervals between exercising; another is soccer, where a player may run around the pitch until out of breath (burning up to 90% carbs) then have slight periods of walking to aid recovery which reduces the percentage of carb usage.

Aerobic exercises which are generally performed at a slower pace and with less effort usually burn a greater degree of fat. Fat is a slow-burning fuel which requires oxygen and exercising at lower effort enables the cells to use this energy more efficiently, meaning a greater percentage of fat can be burned, up to 70% of total energy used when exercising aerobically. Obviously some people will have greater fitness levels and able to workout at a higher rate of effort and still be exercising aerobically, this will allow the fitter person to burn more calories. An example of this would be an experienced long distance runner. They are very lean because they burn lots of energy and still use mostly fat even though training is fairly intense. Individual fitness levels mean it is important to workout within your own Target Heart Rate when trying to lose fat weight. Or as a beginner a good tip to use when exercising is to make sure you can still manage a conversation during a workout. In other words you want breathing to be deeper than normal but not out of breathe so you cannot talk.

Protein is also burned during exercise but this is usually a small percentage. Protein usage may increase to as much as 20% during high intensity training. However again bear in mind that exercising at such high levels of effort are not maintained for long so the actual amount of protein used for energy will still be small in comparison to carbohydrates and fats.

At this stage you may be thinking that the best way to burn fat is to hardly move so the energy system shifts towards higher degree of fat burning. Yes good thinking, in fact resting will shift the energy system into fat burning mode but because there are so few calories burned at rest it doesn