Can dogs eat tomatoes?

Why

Tomatoes belong to the nightshade family, and like their relatives they make natural pest-deterrent compounds called glycoalkaloids — solanine and its close cousin tomatine. These are concentrated in the living green parts of the plant: the leaves, stems, vines and the fruit while it is still hard and green. As a tomato ripens to red, those levels fall away sharply, which is why the soft red flesh sitting in your fruit bowl is a different proposition from the plant it grew on.

In a dog, glycoalkaloids act first as gut irritants — dribbling, a sore stomach, vomiting or loose stools. In larger amounts they interfere with the chemical signalling between nerves and muscles, which is where the more worrying picture comes from: wobbliness, weakness, tremors and an unsettled heart rate. Genuinely serious tomato-plant poisoning is uncommon, partly because the green material tastes bitter and most dogs lose interest. The dogs who get into trouble are usually garden raiders and greenhouse pottering types who chew vines, or who hoover up windfall green fruit. Size matters too: the same mouthful of leaves is a far bigger deal for a terrier than for a Labrador.

The bigger everyday risk is not the tomato at all — it is what tomatoes usually arrive in. Pasta sauce, ketchup, tinned tomatoes, soups, chutneys, pizza and leftovers are very often built on onion and garlic, which damage a dog's red blood cells and are far more dangerous than anything in the fruit itself. Add the salt, oil and sugar, and a bowl of bolognese is a genuinely poor idea even though tomatoes on their own are fine.

Even plain ripe tomato can be too much of a good thing. The flesh is acidic, so dogs with sensitive stomachs may get loose or gassy after more than a taste, and a whole cherry tomato is an easy thing for a small dog to gulp without chewing.

How much is sensible?

Treat ripe tomato as an occasional snack rather than a daily habit, and keep all treats and extras to roughly 10% of your dog's daily calories — the rest should come from their proper food. Use tomatoes that are properly red and soft, pull off the green stalk and any hard green shoulder, and chop the flesh up: a couple of small chunks for a Labrador-sized dog, a single cherry tomato quartered for a terrier or a similar small breed. Serve it plain — no salt, oil, sauce, dressing or seasoning — and if your dog has never had tomato before, offer a single small piece and see how their stomach handles it over the next day before offering more.

Signs to watch for

• Dribbling, lip-licking or turning away from food shortly after eating
• An upset tummy — vomiting, loose stools or obvious gurgling and discomfort
• Unusual tiredness, or a dog who seems flat and not themselves
• Wobbliness, weakness in the back legs, or an unsteady walk
• Muscle tremors or shaking
• A racing, slow or irregular heartbeat, or breathing that seems off

If your dog has had too much

If your dog has pinched a ripe tomato or two off the worktop, there is no need to panic — keep water available, skip any extra treats, and just keep an eye on them for a day in case of a soft stool. Ring your vet if your dog has eaten tomato leaves, stems, vines or unripe green tomatoes, if they have got into a tomato-based sauce or ready meal that may contain onion or garlic, if they are very small or have an existing health problem, or if any of the signs above appear. Have the details ready — what they ate, roughly how much, and when — as that is exactly what your vet needs to judge the risk. Do not try to make your dog sick unless your vet specifically tells you to, and if your dog is wobbly, trembling or collapsed, treat that as an emergency and ring your vet or an out-of-hours service straight away rather than waiting to see how things go.

Serving tips

• Only ever offer the fruit, fully ripe and red, with the green stalk and any hard green shoulder cut away and binned where your dog cannot reach it.
• Chop it, and always quarter cherry and baby plum tomatoes for small dogs — they are the perfect size to be swallowed whole.
• Fence off tomato plants, grow bags and greenhouses, or keep pots well above nose height. Pick up windfall green fruit rather than leaving it for a curious dog to find.
• Assume any tomato sauce, ketchup, tinned tomato or leftover dish contains onion or garlic unless you made it yourself and know it does not.

Common questions