According to exercise experts, the fat-burning zone is where you exercise at close to fifty to seventy per cent of your maximum heart rate – almost 50 per cent of the full intensity. Now if that makes you believe that you need to limit your full intensity to burn fat, it may not be the whole story.
Let’s first see how our body functions. Our system is constantly turning carbs as well as fat into energy for our cells to use. This is a constant process and your body chooses the more dominant energy source (remember, keto?). So if you have a high-carb meal, your body will convert carbs into energy, but if there is fat in abundance, the body will burn fat. So regardless of how much you are working out in the fat burning zone, your body will burn fat as well as carbs – the latter more likely in a higher proportion – if your diet is more carbs than fats.
Now getting deeper into the science of things – our cells convert fats and carbs into a useful form of energy called ATP, aka adenosine triphosphate. Our body cells require oxygen to produce ATP and whether they are burning fat or carbs for energy depends on our activity levels. When we are at rest, oxygen is easily available and the body can burn ‘stored fat’ (the greatest fuel source) at a steady pace. It is adequate to release slow burning energy when you are at rest. This also happens when you workout at a slow intensity.
BUT if your workouts are more intense, the body will use carbs as the preferred fuel. The reason is because when you are working out, your body needs to quickly turn nutrients into ATP and the reason it prefers carbs is because it doesn’t always need oxygen to turn carbs into ATP. Our body has the tendency to store carb for cases when oxygen is scarce – which naturally become the preferred fuel choice.
When you workout at a high intensity, you lose more calories but when you workout at a moderate intensity, your chances of burning fat are more.