A few other considerations:
- Without some pretty extreme surgery, it will be difficult to retain all the internal liquids within the severed leg until consumption is completed.
- Similarly, being able to ingest the entire leg prior to digestive breakdown may require, at the very least, unhinging your jaw, or perhaps simply converting your leg into a more readily digestible form – I'm pretty sure IT WILL BLEND.
- Any significant cooking/preparation of the limb for eating/drinking will result in at least some fat and muscle/bone-borne water loss.
Now, let's say you had one really SHORT leg, that could fit "whole" directly into your stomach. If we had a device that could instantly teleport it in there, while also cauterizing the pelvis/hip in the process "losslessly", or perhaps putting the open wound in statis, then there would certainly be at least an instant in which your before and after weights remained the same.
The more interesting question, to me, is "how long would the weight remain the same, and what would the self-digestion weight loss curve look like over the next hour/day/week?"