Our body needs fuel to meet its energy demands. This energy is derived from carbohydrates, proteins, fats and phosphates.

• We use less energy when we exercise lightly. This energy supply comes from fats.
• When we exercise more intensely, fat can't be metabolised fast enough to meet the energy demands, so the body uses carbohydrates.

The best heart rate for metabolising fat is between the rested state of around 70 beats per minute and the level of exercise intensity where the body switches to carbohydrates.

By measuring how much air a person exhales during an exercise that gets progressively harder, one can calculate how much fat is burned. The fat-burning zone is between 50 - 72% of a person's VO2 max (the maximum amount of oxygen a person can use during exercise) and around 24-46% of VO2 max for overweight people.

We burn surprisingly little fat during exercise. In studies with athletes, participants only burned about 0.5 grams of fat per minute at FATmax. That is approximately 30 grams of fat per hour. The average person burns between 0.1 and 0.4 grams of fat per minute.

However, following certain diets such as intermittent fasting or a ketogenic, high-fat diet and a longer exercise time can increase the amount of fat we burn.

Perhaps we should consider an individualised "sweet spot" we can use to improve our workout to lose weight.

Frequent physical activity at 30% - 60% of your maximal effort or an observed exertion level of one to four out of ten will likely aid our bodies to use fat for energy.