While histamine is part of the body’s natural immune response to allergies, you might be surprised to know that histamine can also be found in varying amounts in food! Histamine is a vasoactive amine that is chemical signalling molecule released by the immune system to trigger an inflammatory response. It’s this response that is what causes the classic allergy signs of itchiness, redness, swelling, and changes in heart rate and blood pressure. As histamine is found in foods, consuming large amounts of histamine can result in similar allergic reactions, or in pets who already have allergies, it can worsen their symptoms considerably.
With this in mind, when we are choosing a diet for a patient with atopy or severe allergies, we need to consider the level of histamines being ingested in conjunction with other key nutritional factors, as well as how we should be selecting a diet for atopic pets.
Fish actually isn’t the answer
A common mistake I see pet owners and professionals making, is adding fish oils or tinned fish like sardines or mackerel to the current diet, or simply switching an itchy patient to a fish-based diet. Let’s talk about why this isn’t the solution to your itchy pets problems:
- Fish is high in histamine – while the levels in different fish does vary, species such as tuna, mackerel, skipjack and bonito are very high in histamine. This is significantly increased if the fish is canned, pickled, fermented or preserved in some way. Shellfish are also very high in histamine. Surveys on histamine levels in pet food have consistently shown that fish based foods (particularly moist cat foods) contain the highest levels of histamine.
- Fish in pet food is usually not single protein – this problem is two fold, the combination of multiple protein sources (even if in trace amounts) can be an issue if you are trying to eliminate allergens from the diet as you can’t guarantee the patient is only being exposed to that one protein, and the second issue is that most fish based diets will use a ‘fish meal’ which could contain a combination of fish which also could be a combination of high and low histamine species.
- Fish oils can still be problematic, even if they don’t contain histamines – fish oil itself does not naturally contain high levels of histamine, however, histamine formation can occur during the processing and storage of fish oil, leading to potentially elevated histamine levels in the final product. Fish oil can also be problematic if you are adding it on top of a diet with a balanced omega 3:6 ratio.
But what about omega 3? The reason most pet owners and professionals recommend switching to a fish based diet is for the omega 3 content. While it is true that pets with skin disease need a higher level of omega 3, and omega 3 definitely can help to reduce a lot of the symptoms of allergies we need to look at alternative ways to support these patients nutritionally, that do not impact their histamine levels and consider a stepwise approach to managing their overall condition.
What else should I avoid?
Some fruits and vegetables are also very high in histamine or contain histamine-like compounds that can have a similar effect on itchy pets. Its recommended to avoid ingredients such as spinach, eggplant, tomatoes, beans and pulses (common in grain free or boutique ‘limited ingredient’ diets)
It’s for this reason using a ‘limited ingredient’ or boutique diet for an atopic patient in the first instance can be an issue. The main ingredients in these diets are usually exotic proteins, often using multiple different protein sources which could be high, low or moderate histamine content, meaning the end result could actually be higher in histamines, or using different carbohydrate or vegetable proteins that could also significantly contribute to the patient’s histamine and allergen load.
So while a limited ingredient diet sounds great in theory, it’s probably not as limited as you think. Many of these diets when tested have returned trace proteins of common allergens, so again these diets are unsuitable for pets who have allergies.
What should I feed my itchy pet?
So first things first, when we are thinking about nutritional support for itchy pets, we should first consider conducting a food elimination trial.
Why? Around 30% of atopic pets will have some level of food allergy. If the patient has been itchy for some time, the destruction of the skin barrier allows more allergens in, further overwhelming the immune system and elevating histamine levels.
So this is where a hydrolysed diet comes into play – these diets use a single novel protein source that is then hydrolysed (enzymatically broken down) into amino acids so the body cannot recognise the protein to launch a reaction to it. Because these diets are truely hypoallergenic, they help to also reduce the body’s allergen load and calm the immune system. We feed this diet exclusively for a period of 8-12 weeks and watch for any signs of improvement. If there is some improvement, food is likely contributing to the patient’s symptoms, so we move into the challenge phase where we try to determine which protein is the issue and try to provoke a response. We use the flowchart below to begin treatment for these allergic pets.
Small Animal Clinical Nutrition, Chapter 31. Protocol for elimination-challenge trials for the diagnosis of adverse reactions to food.
What if it’s just environmental allergies?
If no improvement in the hydrolysed diet trial, we can be comfortable that food is not a trigger and the environment is what the patient is allergic to.
So instead, we can now move onto a diet specifically designed to manage their symptoms – for example a diet that targets atopic pets and has increased levels of omega 3, nutrients to improve the skin and hair (vitamins B and C, zinc, iron etc), and nutrients that support the body’s immune system. It’s important to note that these diets usually do not use novel proteins, but you will see that they do use relatively low histamine ingredients. For more information on diets that support the skin, check out my post here.
Of course, in conjunction with nutritional management, dermatological conditions will usually benefit from a multimodal approach that may include immunotherapy, topical products that soothe the skin and pharmaceuticals as directed.
But it’s so expensive!
While it may seem cheaper at first to feed a ‘limited ingredient’ diet available over the counter, rather than a scientifically formulated hydrolysed diet, let’s actually look at the potential cost to complete an elimination trial compared to feeding an OTC diet:
Diet A is a salmon based sensitive skin diet purchased through a pet store that costs $124 for a 7kg bag, and Diet B is an hydrolysed diet purchased through a veterinary clinic which costs $138 for a 7kg bag.
For a 10kg dog, the pet needs to be fed 170g of Diet A and 152g of Diet B.
A bag of Diet A lasts 41 days, so the cost per day is $3.06
A bag of Diet B lasts 46 days, so the cost per day is $3.00
So despite initially appearing more expensive, the cheaper diet is actually more expensive (albeit only by 6c) because the feeding amounts are significantly lower when feeding the hydrolysed food due to increased digestibility and higher kcal/g content.
Why is this important? Well, not only are you saving money by purchasing the “more expensive” product, you’ll also be moving to an accurate diagnosis and potentially improving the patient’s symptoms much faster – this means less medication, less shampoos and topicals, less trips to the vet, and less COST overall.
So don’t just judge a diet’s cost based purely on the price per bag!
References
Guilford, W. G., Roudebush, P., & Rogers, Q. R. (1994). The histamine content of commercial pet foods. New Zealand Veterinary Journal, 42(6), 201-204.
Altafini, A., Roncada, P., Sonfack, G. M., Guerrini, A., Romeo, G. A., Fedrizzi, G., & Caprai, E. (2022). Occurrence of Histamine in Commercial Cat Foods under Different Storage Conditions. Veterinary Sciences, 9(6), 270.
Montegiove, N., Calzoni, E., Cesaretti, A., Alabed, H., Pellegrino, R. M., Emiliani, C., … & Leonardi, L. (2020). BIOGENIC AMINE ANALYSIS IN FRESH MEATS AND MEAT MEALS USED AS RAWMATERIALS FOR DRY PET FOOD PRODUCTION. Scientific Bulletin Series F. Biotechnologies, 24(2).
Visciano, P., Schirone, M., & Paparella, A. (2020). An overview of histamine and other biogenic amines in fish and fish products. Foods, 9(12), 1795.
Paulsen, P., Bauer, S., Bauer, F., & Dicakova, Z. (2021). Contents of polyamines and biogenic amines in canned pet (dogs and cats) food on the Austrian market. Foods, 10(10), 2365.
Craig, J. M. (2019). Food intolerance in dogs and cats. Journal of Small Animal Practice, 60(2), 77-85.
Fossati LA, Larsen JA, Villaverde C, Fascetti AJ. Determination of mammalian DNA in commercial canine diets with uncommon and limited ingredients. Vet Med Sci. 2019;5(1):30-38. doi:10.1002/vms3.125
Jackson, H. A. (2023). Food allergy in dogs and cats; current perspectives on etiology, diagnosis, and management. Journal of the American Veterinary Medical Association, 261(S1), S23-S29. Retrieved Jun 29, 2024, from https://doi.org/10.2460/javma.22.12.0548