Plan a food change before the old bag runs out. Check the new food’s suitability, agree portions and keep a record of symptoms. If your dog is unwell, contact your vet before treating a switch as the solution.
This guide covers planned transitions for a dog who is well, and the signs that need veterinary advice. It provides general information; your veterinary team decides the plan for a dog with symptoms or a medical condition.
Reasons worth switching for
Check that the food fits your dog’s life stage. Ask your vet when a puppy should move from growth food to adult maintenance. Growing large-breed dogs have particular nutritional needs; pregnancy and nursing also require an appropriate diet.
Discuss the diet with your vet if your dog has a medical condition. Your team may recommend a therapeutic diet or another feeding plan. Follow the advice for your dog instead of substituting a shop-bought food.
Persistent loose stools, reduced energy, unintended weight change or a change in coat can have causes beyond food. Contact your vet for advice. A six-to-eight-week trial of a new bag cannot tell you whether your dog needs assessment.
Food availability can change. Keep enough of the old food for the planned transition and contact your vet if you need another option for a therapeutic diet.
Reasons that are not reasons
Check for a change in appetite or discomfort before assuming boredom. Keep a consistent feeding routine and discuss reduced intake with your vet. Our article on coping with a picky eater covers related questions.
Words such as holistic or premium do not establish nutritional adequacy. Read the adequacy statement and check manufacturer information. The FDA explains the complete-and-balanced claim and the limits of endorsements.
Compare the adequacy statements, then check calories, manufacturer information and fit for your dog. Matching statements do not establish that two foods are equivalent. WSAVA’s selection guide (PDF) also covers formulation, quality control and research.
Should you switch?
| Situation | Next step | What to do |
|---|---|---|
| Puppy is reaching adult size | Discuss the timing | Check growth and life stage with your vet; agree a transition |
| Vet has diagnosed a condition | Follow the individual plan | Ask which food and portions fit the treatment plan |
| Loose stools or another ongoing symptom | Vet advice | Record symptoms and seek assessment before another food experiment |
| Low energy or unintended weight change | Vet advice | Do not wait weeks for a new food to prove itself |
| Dog seems less interested in food | Check appetite and comfort | Ask your vet about reduced intake or pain while eating |
| A new brand looks more premium | Compare evidence | Check adequacy, life stage, calories and manufacturer information |
Labelling points from the FDA on complete and balanced pet food. The verdicts are our own editorial position.
Plan a gradual transition
A gradual change can reduce digestive upset. PDSA’s feeding guidance (PDF) gives seven to fourteen days as a general guide. Agree the pace with your vet when your dog has special needs. Diarrhea during a change still needs attention.
One transition example for a dog who is well
Use the pace and portions agreed with your veterinary team. The example does not set a deadline for a dog with symptoms or a therapeutic diet.
| Days | Old food | New food | Watch for |
|---|---|---|---|
| 1 to 2 | 75% | 25% | Appetite, stools and any new symptoms |
| 3 to 4 | 50% | 50% | Appetite, stools and any new symptoms |
| 5 to 6 | 25% | 75% | Appetite, stools and any new symptoms |
| 7 onward | 0% | 100% | Appetite, stools and any new symptoms |
If stools loosen, contact your vet for advice on the food and transition. Do not assume the switch is the only cause. Seek advice sooner for a puppy or a dog who seems unwell. PDSA diarrhea guidance explains the warning signs.
Change one thing at a time
Do not start a new food in the same week you board your dog, move house, add a puppy, or begin a supplement. When something goes wrong you will have no idea which change caused it.
Keep enough of the old food for the agreed transition. Discuss any need to change the plan with your veterinary team.
Record the start date, each food’s measured portion, appetite and stool changes. Include treats, chews, supplements and medicines so your vet can interpret the record.
Before you open the new bag
- Check the adequacy statement says complete and balanced for your dog’s life stage
- Confirm you have enough of the old food for the agreed transition
- Record calories and the measured portions agreed with your veterinary team
- Pick a quiet week with nothing else changing
- Write the start date somewhere you will find it
- Keep both bags until the transition is finished
- Photograph both labels in case you need to discuss them
Portion sizes change with the food
Different foods have different calorie densities, so the same volume is not the same energy. A cup of one food can be meaningfully more than a cup of another.
Use the food label and your veterinary team’s advice to set the daily allowance. If the label lists kcal/kg, divide that figure by 1,000 to get kcal per gram. For each food, divide its share of the daily calories by its kcal per gram to find the portion in grams.
Ask your veterinary team how to monitor weight and adjust portions. Report unintended weight loss or other symptoms instead of waiting for a monthly checkpoint. Our guide to feeding schedules and portions covers the routine.
Contact your vet for advice about these changes. Seek emergency care for severe illness, collapse, repeated unproductive retching or a swollen or painful abdomen. Cornell emergency guidance describes these signs.
- Diarrhea that persists, blood or mucus, or a dog who seems unwell
- Repeated vomiting, or vomiting with lethargy
- Reduced appetite, refusal to eat or pain while eating; a diabetic dog refusing one meal needs urgent advice
- New itching, paw chewing, or recurring ear infections
- Weight loss you did not intend
Never start an elimination diet on your own to chase a suspected allergy. Those trials only give a usable answer when they are run properly, and a shelf-bought limited ingredient food is not the same as a diagnostic diet. Ask your vet before switching a dog with kidney disease, pancreatitis, diabetes, bladder stones or a diagnosed allergy.
Give it long enough to judge
Your veterinary team sets the monitoring period for your dog and the reason for the change. A planned transition and a diagnostic elimination trial have different purposes. VCA food-allergy guidance explains why a diagnosis requires a controlled trial and follow-up.
Keep a consistent record and follow the agreed plan. Ongoing symptoms, reduced appetite or unintended weight loss need advice while the plan is in progress.
Our articles on reading a dog food label and feeding problems worth watching for sit either side of this one.
Copy the record below before starting. Bring it and photos of both labels if you need to discuss the change with your vet.
Food-change record to copy
| Record | What to write | Why it helps |
|---|---|---|
| Food and date | Exact product, start date and label photos | Distinguishes formulas and changes |
| Portions | Daily calorie goal agreed with your vet, kcal/gram and grams of each food | Checks the energy allowance across the mix |
| Other intake | Treats, chews, table food, supplements and medicines | Shows other exposures that may affect assessment |
| Symptoms and action | Appetite, stools, vomiting, weight, onset dates and veterinary advice | Helps your vet judge the pattern without another unsupervised trial |
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Ask your vet before using a supplement such as Purina Pro Plan FortiFlora. A probiotic does not establish the cause of diarrhea or replace assessment.
Questions people ask
How do I switch my dog to a new food without upsetting their stomach?
Agree the pace and daily calorie allowance with your vet. The table gives a seven-day example for a dog who is well, using calorie shares. Convert each share to the measured portion for that food; equal volumes of different foods may supply different energy. Your dog may need another plan.
What should I do if my dog gets diarrhea during a food change?
Contact your vet about diarrhea during a change, especially if it persists or your dog is young, old or unwell. Seek prompt advice for blood, vomiting, low energy, reduced appetite, pain or unintended weight loss. Your team can advise on feeding while they assess the cause.
When should I switch my puppy from puppy food to adult food?
Ask your vet when your puppy is ready for adult maintenance food and which formula meets their needs. Growth timelines vary, including for large breeds. Check the adequacy statement and agree a gradual transition with the appropriate daily allowance.
Should I change my dog’s food because they seem bored with it?
Check whether your dog is eating less or seems uncomfortable before assuming boredom. Contact your vet promptly for reduced appetite, refusal to eat or pain while eating. A diabetic dog refusing one meal needs urgent advice. VCA appetite guidance explains these concerns.
How long should I try a new dog food before deciding if it works?
Ask your vet how long to monitor the change and which results matter for your dog. Keep the food, portion and symptom record. Report clinical changes as they occur; a general trial period cannot rule out illness. Follow the prescribed duration if your vet has arranged a diagnostic diet trial.
Sources
- ASPCA, explains that dogs of different ages have different food needs and recommends vet guidance when illness or special needs affect the diet.
- FDA, says the FDA regulates pet food safety and labeling, and directs questions about a dog’s health or product use to a veterinarian.
- FDA complete-and-balanced guidance, on adequacy statements and life stages.
- WSAVA selecting pet foods (PDF), on calories per gram or serving, formulation and manufacturer information.
- PDSA feeding guidance (PDF), on gradual food changes as general guidance.
- PDSA diarrhea guidance, on young or unwell dogs and signs requiring advice.
- VCA appetite guidance, on prompt assessment and diabetic animals refusing a meal.
- VCA food-allergy guidance, on veterinary elimination trials and follow-up.
- Cornell emergency guidance, on emergency signs.
Updated October 14, 2026. We removed fixed trial and symptom-waiting rules, corrected the example’s calorie basis, added a food-change record and revised the supplement recommendation and disclosure.