Our weight normally fluctuates by upto 2kg over the course of a day. –
A 1 liter of water weighs 1 kg, so it depends on where you are in your input / output cycle :-).
Then there is the weight of the food in your digestive system, 800 calories of celery or salad weighs much more than 800 calories of cheese or meat.
The average domestic scale is not very accurate, even if it has a digital reading it is still basically a metal spring which can be effected by temp, humidity, how level, a stray coin or screw rolling under the scales.
Then on top of that as we keep our insulin levels down our bodies have a chance to heal, that includes growth hormone getting a chance to work as it should, so your body can heal – bones can get stronger, and muscles strengthen, both of which will increase weight.
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For all these reasons, monitoring progress by the scales is not a good idea. Far better to take photographs and take measurements and use those to monitor progress.