[hazeii]

The 'detox' side of it is very likely garbage (but a great way to sell); on the other hand, 5-hour bike rides without fuel will deplete your glycogen stores and there'll come a point where the differnce becomes obvious (see 'bonk-training').

A 24-hour fast is different; your body will burn fat at sufficient rate to avoid glycogen depletion (it's pretty simple; the harder you exercise the less energy comes from fat and more from 'carbs').

From a weight-less perspective though all that matters is calories out exceed calories in - it's quite possible though that fasts end up making you less hungry than hard exercise does.

Long-distance cyclists don't worry about any of this though - the approach is actually pretty simple:-

Press food to face.

Suck.

Repeat.

Edit: formatting.

[_0w8t]

In one of his articles Ray Cronise gave some numbers that even with light jogging or even fast walking for fuel body uses carbohydrates exclusively. So cardio exercises are a bad way to loose weight. They made people hungry. And as people eat all the fat from the food is stored as body fat and may not be burned until the next exercise.

[hazeii]

That's pretty much it; although at higher intensities the calories per unit time is higher, the higher the intensity the more comes from short-term stores (glycogen) than from long-term (fat).

The numbers suggest 60 to 70 per cent of max heartrate (which is pretty easy) is the sweet spot for general fitness and fat burning (i.e. weight loss). For improved endurance, spend a lot of time in that zone; for improved performance spend shorter periods (well) above it.