Fructooligosaccharides (FOS) in dog and cat food

Is it OK for dogs and cats?

Dogs

Generally fine in small amounts. In dogs, FOS raised faecal bifidobacteria and lowered faecal ammonia. Across 15 prebiotic studies in dogs, protein digestibility tended to dip as the dose rose, so the amount matters.

Cats

Fine at low amounts, but stools change at higher ones. At 0.5% of the diet, scFOS raised bifidobacteria without changing stool output or faecal protein breakdown products. At 4%, FOS gave softer stools and higher faecal ammonia and indole than a cellulose diet. At 6–9%, oligofructose, a related fructan, changed most faecal measures.

How settled this is: Depends on the amount

What fructooligosaccharides (fos) is

FOS are non-digestible oligosaccharides. The EU Catalogue of feed materials lists fructo-oligosaccharides as a product made from beet or cane sugar through an enzymatic process, or from physical treatment of fresh cultivated pasture grass. Oligofructose is made by partial hydrolysis of inulin from chicory roots, and it has its own entries. Some studies use the term short-chain FOS (scFOS).

Why it is in pet food

FOS is used as a prebiotic. In dog and cat studies, added FOS raised faecal bifidobacteria. It also changed the short-chain fatty acids and protein breakdown products found in stool. In dogs, a probiotic (Lactobacillus acidophilus) worked better when given with FOS than when given alone.

What it does in the food

FOS is non-digestible, so gut bacteria ferment it instead, producing short-chain fatty acids such as butyrate. Dogs given 2 g of FOS twice a day had more faecal bifidobacteria and butyrate. They also had lower faecal ammonia and branched-chain fatty acid concentrations. A meta-analysis of 15 dog studies found that prebiotics did not change dry matter or fat digestibility. They raised bifidobacteria and short-chain fatty acids, and crude protein digestibility tended to fall at higher doses. In cats, 0.5% scFOS did not change dry matter or fat digestibility.

Safety and limits

The EU lists fructo-oligosaccharides as a feed material, and the entry sets no maximum level. Stool effects grow with the amount. In cats, 0.5% scFOS did not change stool output, faecal dry matter or faecal protein breakdown products. FOS at 4% gave higher faecal scores (softer stools) than 4% cellulose, though faecal dry matter and output did not differ. Oligofructose at 6% or 9% changed almost all faecal measures, while 3% did not differ significantly from the control. Results for protein breakdown products differ between species, doses and studies. FOS lowered faecal ammonia in dogs, but 4% FOS gave higher faecal ammonia and indole than cellulose in cats. In cats, a lower apparent protein digestibility with fructans was traced to more bacterial nitrogen in the faeces.

What depends on the amount and the recipe

Dose is the main factor, as the cat studies show. The form matters too: in cats, oligofructose seemed to ferment more easily than inulin. Combining FOS with other ingredients changes the results. In cats, scFOS plus GOS lowered crude protein digestibility, while either one alone did not. In dogs, a probiotic worked better with FOS than alone. A dog meta-analysis found that bacterial changes were larger when starting numbers of beneficial bacteria were low.

Not the same as

• Oligofructose — Closely related, but made by partly breaking down chicory inulin rather than from sugar. The EU catalogue lists it as a separate feed material.
• Inulin (chicory root extract) — The fructan that oligofructose is made from. It is extracted from chicory roots and other plants and listed separately.
• Dried chicory root — The root itself, chopped, dried and ground. It is a source of inulin, not purified FOS.
• Galactooligosaccharides (GOS) — A different prebiotic oligosaccharide. Cat studies have tested it alongside scFOS.

Sources

1. Commission Regulation (EU) 2022/1104 amending Regulation (EU) No 68/2013 on the Catalogue of feed materials — EUR-Lex, Publications Office of the European Union, 2022. Entry 13.2.11 fructo-oligosaccharides (from beet or cane sugar by an enzymatic process, or physical treatment of fresh cultivated pasture grass). Entries 4.4.9 inulin and 4.4.10–4.4.11 oligofructose by partial hydrolysis of chicory inulin. No maximum level in these entries.
2. Swanson KS et al. Fructooligosaccharides and Lactobacillus acidophilus modify gut microbial populations, total tract nutrient digestibilities and fecal protein catabolite concentrations in healthy adult dogs. J Nutr 132(12):3721-31 — The Journal of Nutrition (American Society for Nutrition), 2002. In dogs, 2 g FOS twice daily raised bifidobacteria and faecal butyrate and lowered faecal ammonia and branched-chain fatty acid concentrations. L. acidophilus was more effective with FOS than alone.
3. Patra AK. Responses of feeding prebiotics on nutrient digestibility, faecal microbiota composition and short-chain fatty acid concentrations in dogs: a meta-analysis. Animal 5(11):1743-50 — Animal (Cambridge University Press), 2011. Across 15 dog studies, prebiotics did not change dry matter or fat digestibility. Crude protein digestibility tended to fall with dose, while bifidobacteria and SCFA rose. Responses were larger when initial bacterial numbers were low.
4. Kanakupt K et al. Effects of short-chain fructooligosaccharides and galactooligosaccharides, individually and in combination, on nutrient digestibility, fecal fermentative metabolite concentrations, and large bowel microbial ecology of healthy adult cats. J Anim Sci 89(5):1376-84 — Journal of Animal Science (American Society of Animal Science), 2011. scFOS are non-digestible oligosaccharides with a prebiotic effect. In cats, 0.5% scFOS raised bifidobacteria without changing faecal dry matter, output, digestibility or faecal protein catabolites (ammonia, indole, 4-methylphenol, biogenic amines). scFOS plus GOS lowered crude protein digestibility compared with the other treatments.
5. Barry KA et al. Dietary cellulose, fructooligosaccharides, and pectin modify fecal protein catabolites and microbial populations in adult cats. J Anim Sci 88(9):2978-87 — Journal of Animal Science (American Society of Animal Science), 2010. In cats fed 4% cellulose, FOS or pectin, FOS gave higher faecal scores (softer stools), ammonia, indole and butyrate than cellulose, raised bifidobacteria and lowered E. coli. Faecal DM% and output did not differ.
6. Hesta M et al. The effect of oligofructose and inulin on faecal characteristics and nutrient digestibility in healthy cats. J Anim Physiol Anim Nutr 85:135-41 — Journal of Animal Physiology and Animal Nutrition (Wiley), 2001. In cats, 6% and 9% oligofructose changed almost all faecal characteristics, and 3% did not differ significantly. Lower apparent protein digestibility was due to bacterial nitrogen. Oligofructose seemed more easily fermented than inulin.

Checked against these sources on 2026-10-15. Definitions are in our own words. This is a reading aid, not veterinary advice: a vet who knows your animal comes first.