Alternative proteins in pet food: a scientific review
Veganism and sustainability are hot topics in both human and pet nutrition. But can dogs and cats thrive on diets using unconventional protein sources?
There is growing consumer concern around more traditional pet foods, from the perception that they are ‘unnatural’, to their ecological footprint and ethical considerations around the welfare of farm animals. This has led to the consumer-driven development of alternative pet foods containing substitute protein sources.
Emerging alternative protein sources
There are a growing number of pet foods using non-traditional sources of protein. But are these diets suitable for dogs and cats long term?
Vegan diets
Owners often prefer to feed their pets in alignment with their own dietary preferences and ethical beliefs. This often results in pet food trends following human diet trends, and veganism is no different. Vegan pet diets are a relatively new concept, meaning there are no large-scale studies on the effect of plant-based diets on health markers dating pre-2020, and none studying long-term effects.
The first large-scale study was in 2021, when 1,325 questionnaires were completed by cat owners. The study, reported in BMC Veterinary Research, was subject to both bias and methodological limitations, so could only conclude that “cat owner perception of the health and wellness of cats does not appear to be adversely affected by being fed a plant-based diet”.
In response to this study, and the resultant media storm, the British Veterinary Association (BVA) released a statement stating: “Cats are obligate carnivores and should not be fed a vegetarian or vegan diet as they require animal-sourced ingredients to provide essential nutrients, such as taurine and preformed vitamin A, which are minimal or even absent in plant ingredients.” The BVA also expressed concern as to the bioavailability of supplements added to vegan diets, and whether they could adversely affect the action of other nutrients.
A 2022 study from researchers at the University of Winchester in the UK surveyed 2,639 dog owners with the aim of assessing whether health outcomes vary between dogs maintained on vegan or meat-based diets.
A similar, more recent study (by the same authors) surveyed 1,418 cat owners. The studies claimed that both dogs and cats fed nutritionally sound vegan diets are healthier overall than those fed conventional meat-based diets; with owners reporting reduced veterinary visits, medication use, health disorders and severe illnesses.
However, there were multiple limitations to both these studies, including their subjective nature and the potential for owner unconscious bias. Additionally, the diets were not fed exclusively – in the case of the cats, around a third may have been hunting themselves, or also eating elsewhere. Furthermore, very few of the results were statistically significant. A low percentage of the owners surveyed were feeding vegan diets. Many of the pets in both studies also received dietary supplements.
A 2020 study from Brazil looked at the macronutrient, fatty acid, amino acid and essential mineral content of vegan dog and cat foods on the Brazilian market, and compared the results with European pet food body FEDIAF and Association of American Feed Control Officials (AAFCO) recommendations.
The exact protein requirements of dogs and cats vary depending on age, activity levels, any underlying medical conditions and the quality of the protein.
◆ AFFCO guidelines
Cats preferentially use protein as an energy source, meaning they have a greater dietary protein requirement than dogs. According to AAFCO guidelines, adult dogs require a minimum 18% protein as dry matter (or 45g per 1,000 kcal ME), whereas adult cats require a minimum 26% protein as dry matter (or 65g per 1,000 kcal ME). Interestingly, kittens not only have greater protein requirements for growth, but they are also more affected by the quality of the protein (and amino acid profile) than adult cats.
◆ Biological values
The ‘biological value’ of a protein source is the fraction of amino acids that are absorbed, retained and used by the body (i.e. not excreted). So, the biological value assesses the number and type of essential amino acids and the digestibility of a protein source. The lower the biological value, the more protein a diet must contain to meet the essential amino acid requirements. Protein from animal sources has a higher biological value than plant-based proteins.
◆ Cats are obligate carnivores
Cats cannot gain all their essential nutrients from plant material. Cats and dogs need 10 essential amino acids from their diet: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Unlike dogs, cats also cannot synthesize taurine, meaning they rely solely on dietary sources for this, too.
◆ Importance of taurine
Taurine deficiency in cats can lead to serious health issues, including heart disease and retinal degeneration. Plant-based protein sources lack taurine, meaning cats’ diets must contain some animal-based protein. Alternatively, the diet must be supplemented with taurine, but this comes with concerns as to bioavailability.
The study found that all the foods analyzed had at least 1 nutrient below the recommended levels, raising concerns about dietary deficiencies in vegan pet foods. A similar study back in 2004 looked at 2 commercially available vegan cat diets and found that both diets had multiple nutrient deficiencies when independently analyzed and compared with the AAFCO nutrient profile. Of most concern was that both diets contained insufficient levels of taurine – an essential amino acid.
Insect-based diets
Insects are a good source of highly digestible protein for dogs and have the potential to be useful as a novel protein source for hypoallergenic diets.
However, the nutritional composition of insects varies depending on species, diet and stage of the lifecycle. There are also some concerns over the level of manganese (a trace mineral) in insects, and their potential to harbor microorganisms such as bacteria and parasites. At present, there are limited studies in dogs and very scarce information for cats, so more studies are needed to draw accurate conclusions.
Other protein diversification
While currently rare, 2024 may well see a rise in other alternative protein sources, such as yeast, fungi and possibly seaweed. Cell-cultured meat is also predicted to consolidate in the pet food market this year.
Sustainability and ethics
Plant-based diets for humans are considered better for the planet, with lower greenhouse gas emissions, and reduced land and water use. However, it’s worth noting the counter-argument: that the meat used in pet food is often the by-product of the human food chain. This can be viewed as a sustainable way to use protein with high nutritional value, which would otherwise be wasted.
Furthermore, plant-based ingredients can come with higher air miles and contribute to deforestation. In the case of cats, there is also the ethical consideration that comes with enforcing a vegan diet on an obligate carnivore.
The farming of insects has a lower carbon footprint than that of conventional farm animals, such as chickens. However, studies are lacking on large-scale insect production, meaning the overall environmental impact of insect farming is unknown.
More evidence needed
The future looks promising for vegan dog food and insect-based diets, with the vegan pet food market predicted to reach a value of almost $16 million (€14.6M) by 2028. However, large-scale studies using objective data, such as laboratory results and veterinary clinical assessment, are needed to assess the safety and potential benefits of these diets. The jury is still out on vegan cat food, which has become a highly emotive topic, but the overriding opinion currently is that vegan diets are not suitable for felines.
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