I mean I've seen "low calorie bread" that was basically industrial bread cut with cellulose which is analogous to very fine sawdust.
> In human nutrition, cellulose is a non-digestible constituent of insoluble dietary fiber, acting as a hydrophilic bulking agent for feces and potentially aiding in defecation.
https://en.wikipedia.org/wiki/Cellulose
Workshop sawdust would be a bad idea though.