There's some evidence for benefit of fermentable fibers. Add pure inulin or resistant starch to rodent chow, good chance they'll do better. The insoluble fiber in most grains? Not so much. It's commonly used as a stock fiber source in lab chows.

There's a study done a few years back when ketogenic studies were just starting to kick off again. In mice, they had to restart when the mice were all dying off at six months. They switched to wheat bran instead of cellulose as a fiber source, and mice were then able to survive long enough to be useful. Benefits of wheat fiber? Hardly. Maybe it was a benefit of everything in the wheat bran that wasn't fiber, or at least wasn't cellulose.


Another study looked at longevity in mice on 25 different diets, high or low in protein, fat, carbohydrate, all sorts of different ratios. Also high in energy density or low in energy density. Energy density was controlled by altering cellulose content, the low energy, high fiber animals didn't fare well for lifespan. Seven groups were in the lowest energy/highest fiber category, six of these were in the bottom six for maximum lifespan, also sucked for median lifespan, those same six are in the bottom seven for that. So of course the main claim made by the authors is;



Cellulose kills looks way more consistent in that study than protein to carb ratio meaning much of anything.

http://www.cell.com/cell-metabolism...14)00065-5#app2