In reply to GDes:
> Low fibre for a day = 1-2 kg?
Depends on your usual amount of fibre consumed. For some people, potentially yes. This number is more likely to be observed over 2-3 days for most with a balanced diet.
> Blimey. Is that solely fibre and not the old glycogen dumping/less water retention effect?
There is no glycogen dump with low fibre because you keep carbohydrate intake high - this makes it ideal for a short-term performance intervention because you can cut bodyweight by a few percentage points without affecting power output, mood or sleep quality.
> Would obviously require lots of care as long term effects of low fibre are clearly pretty bad, but that's pretty interesting.
Its just a short term intervention for a maximum 1-2 week period for when you need to get an edge on a project.
> So standard low fibre diet = protein and fat?
No, not at all. That's low-carb and totally different - low fibre is avoiding fibrous foods such as vegetables and fruits and wholegrains as the soluble fibre contained in these foods absorbs water in the gut and thereby increases bodyweight. It also takes a while to travel through the gut, hence why just a few days dietary shift can result in a noticeable change.
In general soluble fibre plays a crucial role in the function of our gut and prevents constipation etc so aside from the obvious health benefits of fibre consumption, there is also a practical 'window' after which this tactic stops being functional 😂
Hope this helps clarify.