Switching Dog Food — How to Do It Without an Upset Stomach

Switching your dog's food is usually straightforward — as long as you give the stomach time. The most common reason a food change ends in loose stools is simply that it happened too fast. Your dog's stomach and its gut flora need time to adjust, and that takes a few days.

Transition over 7–10 days

The tried-and-tested method is to mix the old and the new food, gradually increasing the proportion of the new:

• Days 1–2: roughly 75% old food, 25% new
• Days 3–4: 50% / 50%
• Days 5–6: 25% old, 75% new
• Days 7–10: 100% new food

If your dog has a sensitive stomach, or you've seen trouble during previous switches, take it even more slowly — stretch the transition out over two weeks. There's rarely anything to gain from rushing.

Why slow matters

The bacteria in the gut are adapted to what your dog usually eats. An abrupt switch gives them no time to adjust, which often shows up as loose or slightly slimy stools during the first few days. A gradual transition lets the flora adapt at a calm pace — and it also makes it easier to notice if the new food genuinely doesn't agree with your dog.

If the stomach acts up anyway

Slightly looser stools during the first few days are common and usually settle on their own. Here's what to do if it happens:

1. Take a step back. Return to the previous mix for a couple of days before increasing again.
2. Stretch out the timeline. Continue the transition more slowly than planned.
3. Change one thing at a time. Don't switch food and amount and routine all at once — otherwise you won't know what caused what.

When to hold off on the switch

Timing matters. Try to avoid changing food while something else disruptive is going on:

• During stress — moving house, travel, a stay at a kennel
• If your dog already has an unsettled stomach
• Right after a period of illness, before the stomach has had a chance to recover

Switch when life is calm and stable instead, so the signals are clearer.

When it isn't about the switch

If the stools don't return to normal within a few days, or if blood, vomiting, lethargy, or fever appear — then it's no longer about a food change, and your dog belongs at the vet. The same goes if the same dog reacts strongly every time you try to switch: it may be worth investigating with a veterinarian rather than continuing to guess on your own.

NutriDog gives you step-by-step plans for everyday feeding questions — including how to switch food without an upset stomach — and is clear about where the line lies for when a veterinarian needs to be involved.