Adverse food reactions in dogs and cats: What really matters in diagnosis and nutritional management

Adverse food reactions in dogs and cats: What really matters in diagnosis and nutritional management – Part 2

Ecommercy
2026-09-22
15:41
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The role of an elimination diet in diagnosis and treatment

An elimination diet plays a key role in the diagnosis and management of adverse food reactions because it is the only method that allows the relationship between diet and the body’s response to be assessed directly. Unlike laboratory tests, which provide only indirect information, elimination followed by a controlled food challenge assesses the patient’s actual response under everyday feeding conditions and encompasses the full spectrum of mechanisms involved, both immunological and non-immunological.

An elimination diet involves the temporary and strict removal of potentially reactive ingredients. If clinical signs clearly improve or resolve during the elimination phase and recur after a particular ingredient is reintroduced, a diet-related component of the disease can be confirmed with a high degree of confidence. This approach avoids the limitations of indirect diagnostic methods and provides a clinically useful answer regarding the role of food in an individual case.

At the same time, an elimination diet already serves a therapeutic purpose during the diagnostic process. In many patients, the reduction of clinical signs during elimination improves quality of life and reduces the need for anti-inflammatory or antipruritic medication. In this sense, an elimination diet is not simply a diagnostic test, but also the first stage of treatment, helping to assess the potential of nutritional intervention as part of long-term management.

Another important advantage of an elimination diet is the ability to assess the clinical relevance of individual ingredients. In some patients, eliminating a single protein results in complete remission of clinical signs, whereas in others the improvement is only partial, suggesting the presence of additional factors such as environmental allergies, impaired intestinal barrier function or secondary infections. This allows the nutritional component to be considered within the broader clinical context rather than treated as the sole cause of disease.

From a practical perspective, an elimination diet also helps structure the diagnostic process. Clear improvement confirms the involvement of diet, whereas the absence of improvement despite a correctly conducted elimination trial provides valuable information that can redirect further diagnostics and prevent unnecessary prolongation of dietary restrictions.

Selecting patients for an elimination diet

Appropriate patient selection is essential to the diagnostic and therapeutic value of an elimination diet. It is not a universal intervention that should automatically be introduced in every animal presenting with dermatological or gastrointestinal signs. Rather, it is a diagnostic tool that requires appropriate timing, preparation and careful consideration of clinical limitations. Its effectiveness depends on the patient’s stability, preliminary exclusion of other causes of clinical signs and the practical feasibility of maintaining strict dietary restrictions.

The main indications for an elimination diet are chronic or recurrent clinical signs that do not respond fully and consistently to symptomatic treatment or that occur without a seasonal pattern. In dogs, these primarily include chronic pruritus, recurrent otitis externa, persistent skin lesions despite parasite control and management of secondary infections, and chronic gastrointestinal disorders. In cats, indications include chronic pruritus of the head and neck, miliary dermatitis, eosinophilic lesions, symmetrical alopecia and unexplained chronic gastrointestinal signs. Importantly, these signs should persist despite appropriate basic diagnostic and therapeutic measures.

The timing of the elimination diet should be determined pragmatically. The best conditions for introducing it occur when the patient is relatively stable, after acute inflammation, severe skin infections or severe diarrhoea have been brought under control. Starting a restrictive diet during a significant disease flare-up can make it difficult to assess the clinical response and increase the risk of failure, so stabilising the patient beforehand is often appropriate. On the other hand, if a food-related allergic reaction is contributing to the severity of clinical signs, earlier removal of the inflammatory trigger from the diet may help the patient stabilise more quickly.

In animals with severe clinical signs in which symptomatic treatment cannot be discontinued, an elimination diet may be conducted alongside pharmacological therapy. However, the results must be interpreted cautiously because medications, particularly anti-inflammatory and immunomodulatory drugs, may mask the response to dietary intervention. In these cases, the full effect of the elimination diet can only be assessed after treatment has been gradually reduced, provided the patient’s clinical condition allows this.

Particular attention is required in patients receiving glucocorticoids or other immunosuppressive medications. These drugs are not an absolute contraindication to an elimination diet, but they may lead to a false-negative assessment of its effectiveness. If possible, doses should be reduced before starting the elimination trial; otherwise, the diet should initially be regarded as a preparatory stage.

Concurrent diseases must also be considered when selecting patients, including chronic enteropathies, pancreatic disease, endocrine disorders and kidney disease, as these may require modifications to the diet. Practical factors are equally important, particularly the owner’s willingness and ability to adhere strictly to the recommendations. Poor dietary compliance significantly reduces the diagnostic value of an elimination trial and may lead to incorrect conclusions. Assessing whether the diet can realistically be followed is therefore an integral part of patient selection.

Stages of an elimination diet – a practical approach

An elimination diet is a multi-stage process whose success depends not simply on choosing the right food, but on correctly completing every stage. Its diagnostic and therapeutic value relies on consistency, careful planning and informed interpretation of clinical responses. Omitting any stage significantly reduces the reliability of the entire process.

The preparation stage is fundamental to success. It involves taking a detailed dietary history covering all previous diets, treats, chews, supplements, medications with food-based flavourings or carriers, and accidental exposures. This makes it possible to determine which ingredients the patient has previously encountered and to plan the elimination trial appropriately. At the same time, educating the owner, clearly explaining the dietary rules and determining whether the restrictions can realistically be maintained for several weeks are essential.

The elimination phase involves completely excluding potentially reactive ingredients and basing the diet on a strictly defined feeding plan, most commonly using one protein source and one carbohydrate source or a hydrolysed diet. Absolute consistency is essential, with no foods or additional ingredients outside the agreed diet. The elimination phase must last long enough for the inflammatory response to subside, and clinical improvement, particularly in dermatological disease, may occur gradually. Regular assessment of clinical signs and the patient’s overall condition is therefore essential throughout this period.

A crucial but frequently overlooked stage is the food challenge. This involves the controlled, individual reintroduction of ingredients into the baseline diet while monitoring the patient’s clinical response. Each ingredient must be tested separately and for an appropriate period. Recurrence of clinical signs confirms a clinically relevant reaction and provides a basis for permanently excluding that ingredient. Common mistakes include introducing several foods simultaneously, observing the patient for too short a period and failing to return to the baseline diet to confirm the causal relationship.

The final stage is to establish a long-term diet based exclusively on ingredients that have been identified as safe. The diet must not only be well tolerated but also nutritionally complete and balanced, particularly when it contains a limited number of ingredients. Home-prepared diets require individual formulation and appropriate supplementation. Long-term nutrition should be regarded as part of the overall treatment strategy, with the aim of achieving lasting control of clinical signs and maintaining a good quality of life.

Types of elimination diets

In clinical practice, an elimination diet is not a single standardised approach, but a strategy that can be implemented in several ways. The choice of diet should take into account the patient’s dietary history, severity of clinical signs, concurrent diseases and the owner’s practical circumstances. Each type of elimination diet has advantages and limitations that may affect its diagnostic value.

Novel-protein diets are one of the most commonly used strategies, particularly in patients with a well-documented dietary history. Their effectiveness relies on selecting proteins to which the animal has not previously been exposed. Advantages include good palatability and the option of using either commercial foods or home-prepared diets. Limitations include the decreasing availability of genuinely novel proteins and the risk of cross-reactions or trace amounts of undeclared proteins in commercial foods.

Hydrolysed diets are an alternative when previous elimination trials have failed or when a genuinely novel protein cannot be reliably selected. By breaking proteins down into smaller fragments, hydrolysis reduces the likelihood that they will be recognised by the immune system. Their advantages include standardisation and ease of use. However, the degree of hydrolysis varies between products, and some patients may fail to improve or may have problems accepting the food, particularly cats.

Home-prepared diets provide the greatest degree of control over ingredients and are particularly useful in patients with a complex dietary history or concurrent diseases. At the same time, they are the most demanding in terms of preparation and are particularly susceptible to errors. Even minor deviations, uncontrolled additions or inadequate nutritional balancing can significantly reduce their diagnostic value. When used for longer periods, they require appropriate supplementation and collaboration with an animal nutritionist.

Regardless of the chosen approach, the risk of cross-reactions and difficulties with dietary compliance in the home environment must be considered. Access to another animal’s food, treats, flavoured medications or testing new products during the elimination period are common causes of inconclusive results. The choice of elimination diet should therefore represent a compromise between the theoretically ideal approach and one that the owner can realistically and consistently maintain throughout the trial.

The most common mistakes during an elimination diet

Failure of an elimination diet is rarely caused by the method itself. Far more often, it results from organisational, communication or interpretation errors that distort the clinical picture and lead to incorrect conclusions. These errors can occur on the part of both owners and veterinary professionals and may result not only in failure to identify a food-related reaction, but also in unnecessarily prolonged symptomatic treatment or excessive dietary restrictions.

The most common problem is unintentional exposure to ingredients outside the elimination diet. Treats, chews, table scraps, supplements, medications with food-based carriers or flavourings, and gelatin capsules may be regarded as insignificant additions, even though a single deviation can trigger recurrence of clinical signs or make it impossible to assess the diet’s effectiveness. In particularly sensitive patients, occasional exposure can undermine several weeks of correctly conducted elimination.

Another common mistake is making the elimination phase too short. Resolution of chronic inflammation, particularly in dermatological disease, takes time. Prematurely concluding that the diet is ineffective may lead to the food-related component being incorrectly ruled out. This is particularly relevant in patients with long-standing pruritus, secondary infections or concurrent enteropathies.

Treats and chews are another frequent source of problems. Products labelled as “hypoallergenic” or “single-protein” are not necessarily free from cross-contamination, and giving them outside the agreed feeding plan reduces the diagnostic value of the diet. During an elimination trial, every ingredient matters, regardless of quantity.

Errors among veterinary professionals often involve interpretation of the clinical response. Temporary deterioration, fluctuations in clinical signs or delayed improvement may incorrectly be interpreted as treatment failure, while improvement resulting from intensive pharmacological therapy may mistakenly be attributed to the diet. A lack of standardised assessment, reliance solely on subjective owner reports and inadequate documentation can further complicate interpretation.

Another important systemic problem is inappropriate timing. Treating an elimination diet as a “last resort” may result in starting the trial under unfavourable clinical conditions, while introducing it too early without excluding basic differential diagnoses can lead to false conclusions. The effectiveness of an elimination diet therefore depends not simply on the concept itself, but on the quality of its planning, implementation and interpretation.

Patient monitoring and assessment of effectiveness

Monitoring during an elimination diet is essential both for assessing its diagnostic effectiveness and for ensuring the animal’s safety and comfort. Without systematic and reasonably objective assessment of clinical changes, the diet can easily become an intuitive intervention based primarily on the owner’s subjective impressions, significantly reducing the reliability of any conclusions. The aim of monitoring is not simply to determine whether improvement has occurred, but to assess the dynamics and clinical significance of the changes observed.

Regular, repeatable assessment of dermatological signs is fundamental. In dogs, semi-quantitative scoring systems for pruritus and skin lesions can help compare the patient’s condition before the elimination trial with subsequent follow-up assessments. In cats, although there is no single standard, the severity of excessive grooming, extent of alopecia, eosinophilic lesions and frequency of flare-ups can be documented systematically. Consistency is essential, ideally with assessments performed by the same person at regular intervals.

Monitoring gastrointestinal signs is equally important. Simple diaries maintained by the owner and recording stool consistency, defecation frequency, the presence of mucus or blood, and episodes of vomiting can help objectify changes and distinguish genuine improvement from natural fluctuations. In practice, gastrointestinal improvement often occurs earlier than improvement in dermatological signs and may be the first indication that the diet is effective.

Body weight and body condition should also be assessed routinely. Weight loss, deterioration in muscle condition or changes in appetite may indicate that the diet is inadequately balanced or poorly accepted, while excessive weight gain may create additional health problems. Regular weighing allows early dietary adjustments to be made.

In selected cases, laboratory testing may also be appropriate, particularly in patients with concurrent diseases, chronic enteropathies or when an elimination diet is being considered as a long-term solution. Laboratory parameters may help assess nutritional status and organ function, but they should always complement rather than replace clinical assessment.

Regular and clearly focused communication with the owner remains an essential part of monitoring. Explaining what changes can be expected and within what timeframe reduces the risk of overinterpreting minor fluctuations or discontinuing the diet prematurely. Well-planned and consistent monitoring ultimately determines whether an elimination trial provides reliable and clinically useful information.

Long-term dietary management

Dietary management after the diagnostic phase is a key component of long-term treatment in patients with adverse food reactions. The aim is not simply to maintain the improvement achieved during elimination, but to achieve stable control of clinical signs while ensuring a nutritionally complete diet and a good quality of life. Diet should be regarded as an integral part of the therapeutic plan.

Long-term nutrition should be based exclusively on ingredients confirmed as safe during the elimination and challenge phases. Avoiding unnecessary restrictions is just as important as excluding confirmed triggers. An excessively narrow range of permitted ingredients increases the risk of nutritional deficiencies and reduces dietary flexibility, making long-term adherence more difficult.

If the patient’s tolerance allows, gradually introducing different protein sources that have previously been tested and confirmed as safe may be beneficial. This can help meet amino acid requirements, improve diet acceptance and reduce the risk of food aversion. Any expansion of the diet should, however, be based on documented tolerance rather than theoretical assumptions.

Particular attention should be paid to preventing nutritional deficiencies, especially when diets contain only a limited number of ingredients or are prepared at home. Deficiencies in vitamins, minerals or fatty acids may develop gradually and initially remain asymptomatic. Long-term diets should therefore be reviewed periodically for nutritional adequacy and supplemented where necessary, particularly in young and senior animals and those with concurrent diseases.

In selected patients, rotation between several previously tested and well-tolerated diets or protein sources may be considered to reduce prolonged exposure to a single antigen. However, this approach requires caution and is not appropriate for animals with a very limited range of tolerated ingredients or severe clinical reactions, in whom dietary stability may be more important than variety.

Regular clinical assessment and a willingness to modify the diet remain essential components of long-term management. Recurrence of clinical signs does not necessarily indicate a new food reaction and should be assessed within the broader clinical context, including environmental factors, secondary infections and age-related changes. This ensures that diet remains an actively managed therapeutic tool rather than a rigid set of restrictions.

Collaboration between the vet and animal nutritionist

Managing patients with adverse food reactions increasingly requires a comprehensive approach that extends beyond pharmacotherapy alone. In chronic, complex cases or those responding poorly to standard management, collaboration between the vet and an animal nutritionist can significantly improve the likelihood of an accurate diagnosis and successful long-term control of clinical signs.

The vet is responsible for the comprehensive clinical assessment of the patient, differential diagnosis and treatment of conditions that may mimic or exacerbate food-related reactions. This includes parasite control, management of secondary infections, endocrine disorders and other chronic diseases, as well as stabilising the patient during flare-ups. Without addressing these factors, even the best-planned diet may fail to produce the expected results.

The animal nutritionist is responsible for analysing the patient’s dietary history and designing elimination and long-term diets in a precise and safe manner. This role is particularly important in patients with extensive feeding histories, multiple reactions or concurrent diseases, where there is little margin for nutritional error. A carefully planned diet reduces the risk of elimination trial failure and long-term nutritional deficiencies.

This collaboration becomes particularly important when the response to dietary intervention is partial or inconclusive. Joint assessment can help determine whether the lack of improvement results from errors during the elimination trial, unintentional exposure, problems with nutritional balance or other underlying disease processes. This allows the strategy to be modified rationally without introducing unnecessary restrictions.

Consistent owner education is another essential element of this approach. Providing clear and consistent information about dietary rules, permitted ingredients and the duration of the elimination trial builds trust and improves adherence. In the long term, collaboration between the vet and nutritionist also enables informed nutritional planning, assessment of deficiency risks and adaptation of the diet to the patient’s changing needs, supporting stable control of clinical signs and a better quality of life.

Summary and practical conclusions

Adverse food reactions in dogs and cats can be difficult to diagnose conclusively because clinical signs are non-specific, chronic and variable, and both immunological and non-immunological mechanisms may be involved. In practice, it is important to move away from viewing food allergy as a single, uniform condition and instead adopt a broader, functional approach to diet-related reactions.

One of the key conclusions is that no laboratory test can replace a properly conducted elimination diet. IgE and IgG testing and allergy panels cannot reliably confirm a clinically relevant adverse food reaction and may lead to incorrect decisions. Elimination followed by a controlled food challenge remains the only method that directly assesses the relationship between diet and clinical signs.

An elimination diet should be regarded as a logical part of the diagnostic algorithm in patients with chronic pruritus, recurrent otitis and long-term gastrointestinal disorders rather than as a last resort. It serves both diagnostic and therapeutic purposes, and the absence of improvement after a correctly conducted elimination trial can provide just as much valuable clinical information as a clear positive response.

Long-term management requires a balance between avoiding immunologically relevant triggers and providing complete and balanced nutrition. Excessive restrictions increase the risk of deficiencies and make dietary recommendations more difficult to maintain, whereas carefully expanding the range of confirmed safe ingredients and periodically reviewing nutritional adequacy can support stable long-term control of clinical signs.

Clinical experience shows that the best outcomes are achieved through collaboration between the vet and animal nutritionist. This approach enables precise nutritional planning, appropriate interpretation of the clinical response and more effective management of patients with chronic and complex diet-related conditions.

Watch the webinar recording: “Food allergies in dogs and cats – how to recognise the problem and choose the right diet”

References:

Rejas López J., Goicoa Valdevira A. Skórne niepożądane reakcje na pokarm. Warszawa: Wydawnictwo Galaktyka; 2023.
Olivry T., Favrot C., Mueller R.S. Adverse Food Reactions in Dogs and Cats. Hannover: Schlütersche; 2015.
Olivry T., Mueller R.S. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Veterinary Research. 2016;12:225.
Olivry T., Mueller R.S. Critically appraised topic on adverse food reactions of companion animals (2): diagnosis. BMC Veterinary Research. 2017;13:275.
Mueller R.S., Olivry T., Prélaud P. Critically appraised topic on adverse food reactions of companion animals (3): prevalence. BMC Veterinary Research. 2018;14:70.
Verlinden A., Hesta M., Millet S., Janssens G.P.J. Food allergy in dogs and cats: a review. Critical Reviews in Food Science and Nutrition. 2006;46(3):259–273.
Favrot C., Steffan J., Seewald W., Picco F. A prospective study on the clinical features of chronic canine atopic dermatitis and food-induced allergic dermatitis. Veterinary Dermatology. 2010;21(1):23–31.
Hiller A., Mueller R.S., Olivry T. Diagnosis of adverse food reactions in dogs and cats. Veterinary Dermatology. 2017;28(1):1–12.
Hardy J.I., Hendricks A., Loeffler A., Chang Y.M., Verheyen K., Garden O.A., Bond R. Food-specific serum IgE and IgG reactivity in dogs with and without skin disease: lack of correlation between laboratories. Veterinary Dermatology. 2014;25(6):447–e70.
Roudebush P., Guilford W.G., Jackson H.A. Adverse reactions to food. In: Hand M.S., Thatcher C.D., Remillard R.L., Roudebush P., Novotny B.J., eds. Small Animal Clinical Nutrition. 5th ed. Topeka: Mark Morris Institute; 2010. pp. 609–635.
Ricci R., Granato A., Vascellari M., et al. Identification of undeclared animal species in canine dry foods used in dietary elimination trials. Journal of Animal Physiology and Animal Nutrition. 2013;97(Suppl 1):32–38.
Horvath-Ungerboeck C., Widmann K., Handl S. Detection of DNA from undeclared animal species in commercial elimination diets for dogs using PCR. Veterinary Dermatology. 2017;28(4):373–e86.
Gaschen F.P., Merchant S.R. Adverse food reactions in dogs and cats. Veterinary Clinics of North America: Small Animal Practice. 2011;41(2):361–379.
Rosser E.J. Diagnosis of feline allergic diseases. Journal of Feline Medicine and Surgery. 2010;12(11):861–868.