[chimprich]

> I did a fast which lasted a few weeks (18days) [...] I lost 1kg a day

That seems unlikely.

1kg is 7,700 calories. You'd have to burn about 5,700 calories in exercise, which would be something like a 200km bike ride completed without eating anything.

Maybe a serious athlete who had specifically trained for that could do it for one day, but I don't think anyone could do that for 18 days. For a start, I don't think they'd be fit enough to do it if they had 18kg of excess weight they could lose.

[lazyier]

Your metabolism goes UP under fasting. Not down.

And everybody is different.

2500 is average male adult. That does not mean that he, or anybody else, actually uses 2500 calories per day.

Typically people can burn up to around 39 calories per kilogram of weight. Which means the bigger you are the more you burn.

90kg man, with an active lifestyle, would could need around 3900 calories to just maintain his body weight.

If he was a very large person who is overweight then 150 kg is not going to be very abnormal. I know plenty of guys that weigh like that don't look like fat blobs. They are just really big. Big frames, very tall, etc.

In that case then needing to consume 5500-6000 calories to maintain weight is not unreasonable. It is high, but not outside the expected range.

[chimprich]

> Your metabolism goes UP under fasting. Not down.

Short-term fasting might. Long-term, extreme fasting slows metabolism.

> In that case then needing to consume 5500-6000 calories to maintain weight is not unreasonable.

Let's assume that's correct, and the person in question is huge and needs 6,000 calories a day to maintain weight. To lose a kilogram a day you'd still need to eat nothing and do 1,700 calories of exercise a day above baseline to lose a kilogram a day.

You probably wouldn't be able to eat nothing for 18 days, so you'd actually have to burn the equivalent in exercise for whatever you ate.

Let's play with some numbers. Some of the heaviest athletes around are front-row rugby players. 150kg would be right around the top end of that range. If they were on a 50% calorie reduction diet they'd be needing to burn 4,700 calories a day. That's still about 100km of cycling even if you're 150kg. On a very restricted diet. For 18 days in a row.

I believe some Buddhist monks go in for multi-week extreme fasts, but I think they spend their time meditating rather than doing exercise.

[Terry_Roll]

All this talk about exercise and not one of you mentions my brain!