Most people end up here after a small, worrying change: a cat that’s vomiting, passing runny stools, straining in the litter tray, or bringing up hairballs more often than usual. Sometimes it settles. Sometimes it’s the first hint of dehydration, parasites, a food intolerance, or a blockage.
Cat digestion is quick, efficient, and a little unforgiving. This guide lays out what “normal” looks like, the common patterns that turn up at home, and the moments when it’s safer to ring your vet rather than wait.
How a cat’s digestive system works
A cat’s gut is built for animal tissue: short, acidic, and geared towards protein and fat. Food is taken in, broken down in the stomach, then nutrients are absorbed mostly through the small intestine. The large intestine finishes the job by absorbing water and shaping faeces.
The digestive tract, in plain terms
- Mouth: Grabs and tears food; chewing is brief compared with herbivores.
- Oesophagus: Moves food to the stomach.
- Stomach: Uses acid and enzymes to start serious breakdown.
- Small intestine: Main site of digestion and nutrient absorption.
- Large intestine: Absorbs water and forms stools.
Common digestive problems (and what they usually look like)
Hairballs
As cats groom, they swallow loose hair. Hair can’t be digested, so it can gather in the stomach into a lump (a trichobezoar). Often it’s vomited up; occasionally it irritates the stomach or contributes to an intestinal blockage, especially in long-haired cats.1
Vomiting
An occasional vomit can happen with hairballs, eating too fast, or a mild dietary upset. Repeated vomiting, vomiting plus diarrhoea, or vomiting with lethargy is a different shape of problem and needs a closer look.
Diarrhoea
Loose stools can follow sudden diet changes, parasites, infections, stress, food intolerance, or underlying disease. Cats can dehydrate quietly, particularly kittens and older cats.
When to call the vet (quick triage)
Use your cat’s overall state as your compass. A bright cat with one vomit may only need monitoring. A dull cat, or one losing fluids, should be seen sooner rather than later.
Seek veterinary help urgently if you notice:
- Vomiting that lasts more than 24 hours, or repeated vomiting in a day.2, 3
- Diarrhoea that lasts more than 24 hours, or any blood (red or black/tarry).4
- Your cat can’t keep water down, won’t drink, or looks dehydrated (dry gums, marked lethargy).2, 4
- Possible foreign body ingestion (string, thread, toys, bones) or suspicion of poisoning.2, 5
- Marked belly pain, bloating, collapse, pale or yellow gums, or sudden weakness.2
- A cat that isn’t eating for a day (especially if overweight, unwell, or also vomiting) — prolonged inappetence can trigger serious complications and shouldn’t be brushed off.6
How vets investigate digestive issues
Most work-ups start with the basics: history (diet changes, access to rubbish, plants, strings), a physical exam, and a check of hydration. From there, your vet may recommend:
- Faecal testing for parasites and infections.
- Blood tests to assess hydration, inflammation, and organ function.
- Imaging (X-ray and/or ultrasound) to look for obstruction, constipation, or organ changes.
The goal is to separate a self-limiting upset from problems that need targeted treatment, such as parasites, pancreatitis, inflammatory bowel disease, or an intestinal blockage.
Diet basics that support healthy digestion
Cats are obligate carnivores. In practice, that means a complete and balanced commercial cat food is usually the safest foundation, because it’s formulated to meet essential nutrient requirements without guesswork.7
Ingredient lists can be seductive, but they don’t reliably tell you whether a food is nutritionally appropriate. Look for evidence of nutritional adequacy (such as a complete-and-balanced statement) and feed to your cat’s life stage and health needs.7
Gentle habits that make a difference
- Change foods slowly over several days to reduce diarrhoea and vomiting.
- Measure portions to prevent obesity, which is linked to several health problems.
- Feed in a way that suits the cat (smaller meals, puzzle feeders, or slow-feeding strategies for cats that bolt food).
Hydration: the quiet partner in digestion
Water keeps intestinal contents moving and helps prevent constipation. Many cats take in more total moisture when they eat wet food, which can be useful for cats that are reluctant drinkers.
Practical ways to boost water intake
- Offer fresh water daily and wash bowls regularly (some cats avoid stale-smelling water).
- Set out multiple bowls in calm, separate spots.
- Consider a water fountain if your cat prefers running water.
- Use wet food (or add water to food) if advised by your vet and tolerated by your cat.
Probiotics and supplements: useful, but not automatic
Some cats benefit from veterinary-recommended probiotics during certain bouts of diarrhoea or after antibiotics, but “more supplements” isn’t always better. Give your vet the full picture (diet, treats, medications, and any supplements already used) and ask what has evidence for your cat’s situation.7
Avoid starting multiple new products at once. If your cat worsens, you want to know what changed.
Foods to avoid (digestive upsets and true toxins)
Many human foods are simply too rich for cats and can trigger vomiting or diarrhoea. A smaller group is genuinely toxic and needs stricter prevention.
Common “problem” foods
- Milk and dairy: many adult cats don’t digest lactose well and can develop diarrhoea.8
- Fatty scraps and trimmings: can cause gut upset and may contribute to pancreatitis risk.9
- Cooked bones: can splinter and cause injury or obstruction.9
Toxic foods to keep away from cats
- Onion, garlic, chives and leeks (Allium family): can cause gastrointestinal irritation and damage red blood cells.8, 9
- Chocolate and caffeine: toxic; risk depends on dose and type.9
- Grapes, raisins, sultanas and currants: can cause serious illness; the toxic mechanism is not fully understood.8, 9
If you think your cat has eaten something toxic, contact your vet immediately or call the Australian Animal Poisons Helpline for advice (24/7).5
Preventing digestive trouble (the steady, everyday approach)
The healthiest cat guts are supported by small routines: a consistent diet, gradual changes, regular parasite control, and a close eye on litter tray patterns.
Simple prevention that suits most households
- Brush regularly, especially long-haired cats, to reduce swallowed hair and hairball risk.1
- Keep strings and chewable clutter out of reach (thread, hair ties, ribbon, and soft toys can become dangerous fast).
- Monitor the litter tray: stool frequency, firmness, and any straining are often the earliest clues.
- Book routine vet checks so weight, dental health, and chronic issues (like kidney disease) don’t quietly undermine appetite and digestion.
References
- Merck Veterinary Manual (table): Managing hairballs in cats
- Vet Help Direct (AU): Vomiting in cats — when to see a vet
- Pet Circle (Dr Kes Holliday, DVM): Why is my cat vomiting? (Updated 5 Dec 2025)
- My Corner Vet Nedlands: Diarrhoea in cats — causes and when to see a vet
- Animal Poisons Helpline (Australia): 24/7 poisons advice service
- Merck Veterinary Manual (pet owner): Liver disease in cats (includes hepatic lipidosis and inappetence risk)
- WSAVA: Global Nutrition Guidelines
- Agriculture Victoria: Human foods to avoid for cats
- Agriculture Victoria: Human foods to avoid for cats and dogs (toxicity and digestive risks)
Veterinary Advisor, Veterinarian London Area, United Kingdom