How to switch your dog's food without an upset stomach

Switch gradually over about seven days: start with a quarter new food and three quarters old, move to half and half, then three quarters new, then all new. Go slower if your dog has a sensitive stomach, and stop and call your vet if vomiting or diarrhoea doesn’t settle.

A sudden change of food is one of the most common reasons for loose stools, vomiting or a dog going off its food for a day or two. The new food may have a different fat level, fibre type or protein source, and the gut needs a few days to adjust.

A seven-day schedule

Days	New food	Old food
1–2	25%	75%
3–4	50%	50%
5–6	75%	25%
7	100%	0%

This matches the schedule the American Kennel Club recommends. Several manufacturers give a similar window on their labels. Merrick’s labels, for example, say to mix the new food in “over 7 - 10 days”.

Measure both foods rather than guessing. “Half a bowl” of a dense food and “half a bowl” of a light one can be very different amounts of calories.

Get the amount right, not just the mix

Two foods can differ a lot in calories per cup. In our database, dry foods range from about 230 to over 500 kcal per cup, so one food’s cup can carry more than twice the energy of another’s. If the new food is more energy-dense, the same cupful is more food, and overfeeding during the switch can upset the stomach by itself.

Work out the daily amount of the new food before you start. Our Feeding Calculator uses the calories of the exact food you pick. During the switch, scale each food to its share: on days 3–4, give half the daily amount of the old food plus half the daily amount of the new one.

When to go slower

Stretch each step to three or four days, so the whole switch takes two weeks, if:

• your dog has a history of a sensitive stomach or loose stools,
• the new food is much higher in fat than the old one,
• you’re moving between very different formats, such as dry to wet or fresh,
• you’re switching a senior dog or a young puppy.

If stools go soft at one step, go back to the previous mix for a few days before moving on.

Switching because of an allergy or an elimination diet

If your vet has asked you to start a strict elimination diet, follow their schedule instead. Some vets prefer a quick, complete change so the trial starts cleanly. During the trial, treats, chews and flavoured medicines count too.

Before you buy the new food, check it really leaves out the ingredient you’re avoiding, including the other names it can appear under. Chicken, for instance, can come back as chicken fat, chicken broth or “poultry” ingredients; our guide to hidden chicken in dog food lists them. Paste any ingredient list into the Label Checker to see every match, or use the Food Finder to list foods without it.

Switching a puppy to adult food

Check the new food’s nutritional adequacy statement first. A puppy needs food that meets the growth (or all life stages) profile until it’s fully grown, and for large breeds that can be well past their first birthday. Our guide to what “complete and balanced” means shows how to read that statement.

When to call your vet

Call your vet if, at any point during the switch:

• vomiting or diarrhoea lasts more than a day, or there is blood in either,
• your dog stops eating for more than a day,
• your dog seems lethargic or in pain.

A gradual switch prevents most problems, but it doesn’t fix a food that doesn’t suit your dog. If the upset comes back every time you reach 100%, the new food may not be the right one.