I think they both contain methylcellulose, which is considered benign but not digestible. In my experience it doesn’t cause major discomfort, but a mildly off putting sensation in my GI tract for a few hours. It might be something else, but it seems likely after narrowing things down for a while.

Cellulose? This is the modern equivalent of adding sawdust.

Fiber is good for you. Adding bulk into something that's supposed to be a mixture is only a problem when it's diluting the rest too much.

If you dig a little deeper you’ll find that methylcellulose has some interesting culinary properties, making it well suited to adding structure and firm texture to soft foods.

When mixed with water it transforms into a firm gel after heating, or it can be used to create extremely resilient emulsifications.

It’s practically flavourless, so it works well. I’m not convinced it passes through the GI tract with no impact whatsoever, but it appears so far to be relatively benign.

It’s nothing like sawdust or a filler, though. It’s also somewhat expensive so it wouldn’t be a good option for filler. My 500g bag was around $25, but if you wanted to use actual sawdust, well I think you could get that for close to nothing.

Thank you for your eloquent and well reasoned refutation!

I take that as a huge compliment! I find myself dreaming of Old Internet quite often these days, so thank you very much. Maybe we can restore the old ways one comment at a time.