The Impact of Vegan Diets on Indicators of Health in Dogs and Cats: A Systematic Review

SIMPLE SUMMARY: There has been controversy within the scientific literature, and in the popular press and online media, around the safety of feeding vegan diets to dogs and cats. With an increase in adherence to meat-free diets in the human population, many guardians may be considering providing these diets to their companion animals. Concerns arise due to dog and cat gut physiology which has adapted to a complete meat-based diet (cats) or largely meat-based diet (dogs). Particular concerns have been raised around deficiencies in certain amino acids such as taurine, and vitamins such as B12 (cobalamin) and B9 (folate). To date, there has been no formal assimilation of the scientific evidence on this topic, with a focus on actual health impacts of diets, as opposed to nutritional composition. In this review, we conducted a formal assessment of the evidence in the form of a systematic review. We found that there has been limited scientific study on the impact of vegan diets on cat and dog health. In addition, the studies that have been conducted tended to employ small sample sizes, with study designs which are considered less reliable in evidence-based practice. Whilst there have been several survey studies with larger sample sizes, these types of studies can be subject to selection bias based on the disposition of the respondents towards alternative diets, or since answers may relate to subjective concepts such as body condition. However, there is little evidence of adverse effects arising in dogs and cats on vegan diets. In addition, some of the evidence on adverse health impacts is contradicted in other studies. Additionally, there is some evidence of benefits, particularly arising from guardians’ perceptions of the diets. Given the lack of large population-based studies, a cautious approach is recommended. If guardians wish to implement a vegan diet, it is recommended that commercial foods are used. ABSTRACT: There has been an increase in vegetarianism and veganism in human populations. This trend also appears to be occurring in companion animals, with guardians preferring to feed their animals in accordance with their own dietary values and choices. However, there has been controversy amongst vets and online commentators about the safety of feeding vegan diets to carnivorous species, such as cats and dogs. In spite of this controversy, to date there has been no systematic evaluation of the evidence on this topic. A systematic search of Medline, Scopus, and Web of Science was performed, identifying 16 studies on the impact of vegan diets on cat and dog health. Studies were appraised for quality using established critical appraisal tools or reporting guidelines. There was considerable heterogeneity in the outcomes measured, and study designs employed, with few studies evaluating key outcomes of interest. Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was utilized for assessment of certainty in the evidence, with the evidence for most outcomes being assessed as low or very low. Whilst the quality and amount of evidence needs to be considered in formulating recommendations, there was no overwhelming evidence of adverse effects arising from use of these diets and there was some evidence of benefits. It is, however, recommended that future high-quality studies, with standardized outcome measures and large sample sizes, be conducted. At the current time, if guardians wish to feed their companion animals vegan diets, a cautious approach should be taken using commercially produced diets which have been formulated considering the nutritional needs of the target species.