The signs that a dog's food is making them sick are mostly boring and chronic: soft stools that never quite firm up, gas, vomiting more than once in a while, year-round itching, recurring ear infections, and weight that creeps up on the same portion. None of those prove it is the food, but together they are a reason to run a proper diet trial instead of switching bags at random. This post is the checklist, what each symptom usually means, and how to test the food in a way that gives you an answer.
First, the base rate
True food allergy is less common than the internet suggests. Tufts veterinary nutritionist Cailin Heinze puts it bluntly: food allergies are uncommon.1 Dogs react far more often to other things about a food, in her words, "other factors in the diet such as the amount of fat or fiber or the overall digestibility."1 Merck agrees that "Among pets, food allergies are less common than airborne allergies."2 So when you go through the list below, keep two explanations in mind: the food does not agree with your dog (common), or your dog is allergic to something in it (less common). The test is the same for both.
The checklist
Digestive signs
- Soft or loose stools most days. VCA lists "Changes in diet or food intolerances" among the common causes of diarrhea.3 If it started when you opened a new bag, or a new batch of an old bag, that is your first suspect.
- Vomiting more than once or twice a month. Occasional grass-and-bile vomiting happens. Regular vomiting after meals does not, and fat is the usual culprit. Tufts: "If you've been feeding a higher fat diet...you can try one that is at least 25% lower."1
- Gas that clears a room. Usually poorly digested protein or fermentable fiber reaching the colon. A food with better digestibility fixes this more often than a "sensitive stomach" label does.
- Eating grass, licking floors, gulping air. Nausea behaviors. Not specific to food, but worth noting on the log.
Skin and ear signs
- Itching that does not change with the season. Merck: "Signs of food allergy are similar to airborne allergies except there is little variation in the intensity of itching from one season to another."2 A dog who itches in April and October alike is more suspicious for food than one who only itches in pollen season.
- Recurring ear infections. VCA: "In the dog, the signs of a food allergy are usually itchy skin, paws, or ears or digestive disturbances such as vomiting or diarrhea."4 Ears that get treated, clear, and come back every few months are a classic pattern.
- Paw licking, red belly, face rubbing. Same category. Our post on dog itchy skin causes works through the non-food explanations too, because fleas and environmental allergies are more common.
Weight and energy signs
- Gaining on the same portion. The food may be more calorie-dense than the last one, or the treats crept up. The AVMA's line is to "limit treats to less than 10% of your pet's daily calorie needs."5 Weigh the food. Count the treats.
- Dull coat, flaky skin. Often low fat or low omega-3 in the diet, or a food that is not complete and balanced. Check the label for the AAFCO statement; the FDA says that when it references "either an AAFCO nutrient profile or a feeding trial using AAFCO procedures," you are "better assured that the 'complete and balanced' claim is valid."6 A food without one is a topper, not a diet.
- Sudden refusal to eat a food they liked. Sometimes the dog is right. Check the FDA recalls and withdrawals list for the brand and lot before you assume pickiness.7 We explain how to read one in dog food recalls and what they mean.
What is not on the list
Blood and saliva "food sensitivity" tests. Merck: "Blood and skin tests are not reliable for diagnosis."2 They produce a long list of foods to avoid and no useful information. Save the money for the diet trial.
How to actually test the food
Switching from one bag to another with the same chicken, the same fat level, and a different logo tells you nothing. A real trial changes one variable and controls the rest.
- Log for two weeks first. Tufts: "Keep a journal of the symptoms for a couple of weeks as a baseline, including an inventory of everything that you feed your pet."1 Stool score, vomiting, scratching, ears. You need a before.
- Pick one change. If the signs are digestive, try a lower-fat food or a more digestible one before you chase allergens. If the signs are itching and ears, pick a protein your dog has never eaten, or ask your vet about a hydrolyzed diet. Merck: "The foods dogs are most often allergic to include beef, chicken, eggs, corn, wheat, soy, and milk."2 A dog who has eaten chicken kibble for six years is not going to be tested by a different chicken kibble.
- Transition over several days. Cornell suggests starting "by feeding 75% of the old diet mixed with 25% of the new diet. The next day, feed 50% of each diet, then on the third day feed 25% old and 75% new."8 Go slower for a dog with a touchy gut.
- Control everything else. This is where most home trials fail. Tufts: "The successful elimination diet trial has to control everything that goes into your pet's mouth, such as treats, rawhides, dental chews and toothpaste, table food, dietary supplements, and flavored medications."9 Yes, toothpaste. Brush with water or a paste that matches the trial protein.
- Give it long enough. Tufts: "Most veterinary specialists recommend an elimination diet trial of at least 8-12 weeks for pets with skin issues and 3-4 weeks for those with digestive issues."9 Gut signs answer fast. Skin signs are slow.
- Beware "limited ingredient" bags. Tufts notes that "several studies have shown high rates of contamination with common proteins in over-the-counter 'allergy' or 'limited ingredient' diets."9 For a suspected allergy, a veterinary diet is the reliable tool. For a plain intolerance, a well-made single-protein food is usually enough. Our guide to dog food for sensitive stomachs covers how to pick one.
If the signs resolve, you have a working diet. If you want to know exactly which ingredient was the problem, add the old foods back one at a time and watch. Most owners stop at "it works," which is fine.
Where Truva fits
Every food we carry has passed The Truva Standard, and the first two checks are about the ingredient panel: a named animal protein first, and nothing on the label we cannot defend. Those checks reward foods whose ingredient panel matches what the front of the bag promises, which is the thing a diet trial depends on. The limitation is that passing the Standard does not make a food right for your dog. A lamb food that passed is still the wrong choice if your dog is reacting to lamb. If you email us the symptoms and the history at hello@truvapets.com, we will narrow the options to ones that make sense as a trial.
When to call the vet
Go in before you start a trial if there is blood in the stool or vomit, if diarrhea has lasted more than two days (VCA's threshold3), if your dog is losing weight, or if a puppy or senior is involved. Parasites, pancreatitis, and inflammatory bowel disease all look like "the food" from the outside and need a different fix. And if you suspect a true allergy, the vet is the only source of a properly controlled hydrolyzed diet.
Sources
- Tufts Cummings School of Veterinary Medicine, Petfoodology, "Figuring Out Food Sensitivities," 2019. sites.tufts.edu
- Merck Veterinary Manual, "Allergies in Dogs." merckvetmanual.com
- VCA Animal Hospitals, "Diarrhea in Dogs." vcahospitals.com
- VCA Animal Hospitals, "Food Allergies in Dogs." vcahospitals.com
- American Veterinary Medical Association, "Your pet's healthy weight." avma.org
- U.S. Food and Drug Administration, "'Complete and Balanced' Pet Food." fda.gov
- U.S. Food and Drug Administration, "Recalls and Withdrawals (Animal and Veterinary)." fda.gov
- Cornell University Riney Canine Health Center, "Re-evaluating your dog's diet." vet.cornell.edu
- Tufts Cummings School of Veterinary Medicine, Petfoodology, "Think Your Pet has a Food Allergy? Eliminating Mistakes in Elimination Diet Trials," 2022. sites.tufts.edu