This article originally appeared on The Conversation. You can read it here.

When it comes to losing weight, people often want know the best way to shed excess pounds – and there's no shortage of fad diets or fitness crazes claiming to have the "secret" to fat loss. One theory even suggests that exercising at around 60% of your maximum heart rate will bring our bodies into a so-called "fat burning zone", optimal for losing weight.

But does this "fat burning zone" even exist?

First, it's important to understand a little about our metabolism. Even if we were to sit at our desk all day, our body still needs "fuel" to meet energy demands. This energy comes from carbohydrates, proteins, fats and phosphates. However, the rate at which we use them, and how much we have available, varies between people. It depends on a number of factors, such as dietary intake, age, sex and how hard or often we exercise.

Generally, exercising at lower intensities – such as sustained walking or light jogging – doesn't require as much effort by our muscles as sprinting, for example. This means the amount of energy needed by the body is lower, so energy supply predominantly comes from fats.