How can I tell a food reaction apart from a short-term stomach upset?

Acute gastroenteritis typically comes on quickly and resolves within a few days. If symptoms recur or seem to be time-linked to specific foods, ask your vet about further investigation.

How do I set up an elimination diet trial?

An elimination diet trial uses a single novel protein or hydrolyzed diet for 8–12 weeks with no other treats or foods allowed. Consult your vet with any questions during the trial period.

When should I bring my pet to the vet for vomiting or diarrhea?

See a vet promptly if vomiting or diarrhea lasts more than 24 hours, if dehydration, blood in the stool, or a marked drop in energy is noted. Mild, brief episodes can be monitored at home with careful observation.

What tests will the vet run at the appointment?

Typically a physical exam, blood work, and urinalysis are performed first. Abdominal ultrasound or X-rays may follow if needed, with specialist referral or advanced imaging for complex presentations.

How much do the tests and treatment usually cost?

Costs vary by clinic and region — ask your vet for an estimate before proceeding.

Disease Guide

Food Reaction in Dogs & Cats (Gastrointestinal): Symptoms, Diagnosis & Home Care [2025]

Adverse food reactions — including food allergies and food intolerances — can cause vomiting, diarrhea, and skin symptoms. Diagnosis requires an 8–12 week elimination diet trial. Avoiding the offending food effectively controls the condition.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

Pethealthmap Editorial Team

Sources: WSAVA, ACVIM, Taiwan Society of Veterinary Internal Medicine

When to See a Vet

Seek immediate veterinary care (emergency)

•Repeated vomiting for more than one day and unable to drink water
•Diarrhea persists and causes obvious dehydration or weakness
•Bright red blood in the stool or black, tarry stool

Schedule a clinic visit as soon as possible (within 24-72 hours)

•Repeated vomiting but still able to eat and drink small amounts
•Diarrhea lasting more than one day, but energy level is still acceptable
•Appetite has clearly decreased or picky eating continues for several days

01What symptoms indicate something is wrong?

Gastrointestinal food reactions most commonly present as vomiting, diarrhea, and changes in appetite. Some cases also show concurrent skin itching or hair loss.

Noticeably decreased appetite or persistent picky eating for several days
Repeated vomiting or frequently bringing up undigested food
Acute or chronic diarrhea with loose or mucus-laden stools
Skin itching, localized hair loss, or persistent scratching
Bloating, increased flatulence, or lethargy and low energy

Seek emergency care immediately if you notice the following symptoms:

⚠️ Continuous vomiting for more than one day with inability to keep water down
⚠️ Persistent diarrhea causing obvious dehydration or weakness
⚠️ Stools containing fresh blood or black tarry material

02What should you watch for at home, and when is it an emergency?

Observing and recording key information at home helps your vet quickly understand the disease course and possible triggers.

Record the brand of food, treats, and feeding times given recently
Take photos of vomit or stools and note the time they occurred
Count the number of vomiting and diarrhea episodes, including timing and intervals
Monitor changes in skin condition and where your pet is scratching
Observe changes in alertness, activity level, and water intake

03How will the vet diagnose this condition?

At the clinic, the vet will start with a physical exam and order blood work, imaging, or urinalysis as needed to rule out other causes.

Physical examination

abdominal palpation, hydration status, and temperature assessment

Blood work

evaluating for infection, inflammation, and organ function

Urinalysis

ruling out metabolic or urinary tract issues

Abdominal ultrasound or X-rays

assessing gastrointestinal and abdominal structures

Advanced imaging (CT) or specialist referral if indicated

04How is this condition treated and managed at home?

Treatment focuses on supportive care, with dietary adjustments or long-term monitoring planned based on the diagnosis.

Short-term IV fluids and supportive care to correct dehydration and electrolyte imbalances
Symptomatic medications for vomiting or diarrhea as assessed by the vet
Diagnosis-guided dietary modification or a structured elimination diet trial
Regular follow-up visits to monitor symptoms and repeat blood work if needed
Referral to a specialist for complex or recurring cases

05What should you prepare before the vet visit?

Bring photos of vomit or stools with timestamps

Note when symptoms started, how they progressed, and their frequency

List all foods, treats, and any recent diet changes

Describe changes in alertness, water intake, and bowel habits

Bring previous medical records or related test results

This content is for reference only and cannot replace a professional veterinary diagnosis. If your pet shows signs of illness, please seek veterinary care promptly.