Cellulose
A plant-derived insoluble fibre used as a bulking agent. Most commonly sourced from wood pulp, cotton, or peanut hulls. It adds volume without adding meaningful nutrition.
Why manufacturers use it
Cellulose is cheap and inert. It adds physical bulk to dry and wet formulas, creates a feeling of fullness, and helps bind kibble. It also dilutes calorie density, which is sometimes marketed as a benefit for weight management.
What the evidence says
Cats cannot ferment insoluble fibre and derive no nutritional value from cellulose. At low concentrations (under 2–3%) the impact on digestibility is minimal. At higher levels, cellulose can interfere with mineral absorption and reduce the digestibility of protein and fat — the nutrients cats actually need. A 2001 study by Fahey et al. found that cellulose at 7.5% of dry matter significantly reduced apparent digestibility of crude protein and fat in cats.
Why it's not a scored risk factor
Cellulose is not toxic. At the levels typically found in commercial cat food it is unlikely to cause direct harm. The issue is one of quality, not safety: cellulose displaces ingredients of actual nutritional value. Products high in cellulose will score lower through the protein ranking and grain-filler pillars, which already capture the dilution effect.