It's been a while since I've written a blog post but there has been a lot of talk about Zinc in social media lately.
Zinc is often low in homemade ratio diets so it's important to understand what it does, where we source it and why the body may not be able to absorb it in the diet even if on paper it claims to meet requirements.
Zinc is an essential micromineral in all animals’ diets, it plays a key role in immune function, cell replication, skin health and wound healing, the metabolism of proteins, lipids and carbohydrates, taste acuity and vision. Zinc is metabolized in the small intestine and provides a protective effect on the epithelial barrier in the gastrointestinal tract and supports microbial diversity in the GI tract making it an important nutrient for gastrointestinal health.
Deficiency is often first seen in poor skin and coat health which can include skin lesions particularly on the foot pads, around the eyes and mouth, this is particularly common is northern breeds like Huskies and Malamutes. Coat changes can include dullness, course hair and fading coat colour. Deficiency also causes growth retardation and poor reproduction performance. The eye contains high concentrations of zinc in the retina where it interacts with Vitamin A and the amino acid Taurine to serve several functions including acting as an antioxidant, deficiency can lead to blurred vision. As Zinc has a protective effect on the epithelial barrier in the Gastrointestinal tract it is important for optimal gut function, some studies suggest the Zinc supplementation can be beneficial to individuals who are suffering diarrhea, Irritable Bowel Disease, Leaky Gut/Dysbiosis, Infectious gut issues and other gut diseases.
How much Zinc do our pets need?
According to the National Research Council (NRC) our dogs and cats should be receiving:
Puppies: 25mg/1000kcal ME
Adult Dogs: 15mg/1000kcal ME
Kittens & Adult Cats: 18.5mg/1000kcal ME
Where can we find wholefood sources of Zinc?
Zinc is most bioavailable in meat and seafood, plant-based zinc is less bioavailable largely due to phytates, so we want to aim at providing our dogs and cats with animal sources of zinc. Some of the richest sources of wholefood zinc include:
· Oysters – According to USDA cooked oysters contain as much as 91mg/100g
· Red Meat – Beef contains aprox 4.45-6.76mg/100g, Lamb aprox 3.8-4.28mg/100g, Goat loin aprox 3.98mg/100g. Kangaroo meat aprox 3.05mg/100g
Sardines (canned in water, drained) contain around 1.71mg/100g
Blue Mussels – cooked in moist heat contain around 2.67mg/100g
Eggs – A Raw chicken egg yolk contain around 3.7mg/100g with a whole raw duck egg containing around 1.41mg/100g.
Hemp Seeds*- contain around 9.41mg/100g
Pumpkin Seeds* - contain around 7mg/100g
Sunflower Seeds*- contain around 6.3mg/100g
*Indicates plant based foods that may not be as bioavailable as meat based options due to phytates.
This list isn’t exhustative but gives some examples of foods from different food groups that we can use in combination to meet nutrient needs with whole foods.
What effects Zinc absorption?
Like all nutrients some nutrients work synergistically with others, and some inhibit the absorption of other nutrients.
Zincs Friends: Zinc works synergistically with magnesium, with magnesium helping to regulate the absorption of zinc, a diet low in magnesium may struggle to absorb zinc optimally even if appropriate levels are provided. Zinc enhances quercetin a plant derived flavonoid which acts as an antioxidant and antihistamine.
Zincs Foes: When we have high levels of calcium in the diet and especially when paired with phytates this can impact how much available zinc is absorbed as both bind to zinc making is less bioavailable. Phytates are found in many plant-based foods including seeds, nuts, legumes and grains but not in animal-based foods. Phytates are a plants natural defense mechanism and can be neutralized by soaking them overnight which kick starts the germination process, some foods also require cooking to help eliminate it, so if you are including some plant-based foods known to have phytates preparing them appropriately to remove the risk of them binding to zinc is wise.
Iron competes with zinc for absorption pathways, when supplemental iron is taken this can impact how much available zinc is absorbed, dietary iron seems less problematic, however.
Medications can also impact absorbability of zinc, if your pet is on medications ask your vet if it can affect how their body absorbs zinc and supplement if necessary.
Gut issues will also impact zinc absorption, if your pet has acute or chronic gut health issues chat to your vet about whether you may need to supplement zinc.
Zinc Supplementation-
If your pets diet is low in zinc or a medical condition requires supplementation, Zinc is most bioavailable when bound to amino acids so if you need to use a supplement choose a zinc chelate or zinc proteinate supplement such as Zinc Picolinate or Zinc Bisglycinate that is bound to an amino acid. Ultimately you will want to have an assessment of the diet before supplementing zinc to ensure you supplement as appropriate levels, a vet versed in wholefood nutrition or someone trained in wholefood animal nutrition can help with this.
Can we have much Zinc in our pets diets?
While Zinc is considered low in toxicity, in human literature zinc at high doses long term can damage the retinas and is a neurotoxin, the neurotoxic effects may be more to do with the knock-on effect of copper deficiency however it is important to note that zinc should be offered at recommended doses and not at grossly over exceed guidelines.
Just how much do our pets need?
I don’t think anyone knows definitively just how much zinc is required in our dogs and cats’ diets, especially wholefood diets. While guidelines such as NRC mentioned above give us minimum and recommended values, what isn’t clear is what type of zinc was used to establish those guidelines. As these guidelines were developed to support the processed pet food industry to ensure essential nutrients are present in sufficient amounts after processing, often low grade and synthetic nutrients are used to meet the required guidelines this pose bioavailability issues as well as interactions that may inhibit what is available to the pet. We know that many of these commercially used supplements have a lower bioavailability so chances are wholefood diets may in fact require less to nourish the body. Inorganic zinc such as Zinc Oxide has poor bioavailability compared to organic Zincs. In a study by Lowe et al, it showed that Zinc chelate was twice as bioavailable compared to Zinc Oxide. When we consider that a cat needs 18.5mg/1000kcal we really need to know in what form this was established. In a fresh food diet where we are offering Zinc in wholefoods with animal-based proteins do we actually need less than that 18.5mg/1000kcal? If it was established via use of Zinc Oxide then that answer may very well be yes, but we just don’t know and that is the frustrating side of pet nutrition.
We also need to take into account that our pets are individuals, they metabolise nutrients as individuals so one cat may thrive on recommended guideline amounts, another may need more, another may thrive on less. Genetic factors can also play a role in how well an individual processes nutrients. Gut health is another a major factor in how zinc is absorbed in the body, if there are acute or chronic gut issues, zinc may need to be supplemented in the diet to support ongoing gut health and provide enough for other vital processes in the body in either the long or short term.
Another consideration is what is the overall diet is comprised of, as we understand there are factors that reduce the absorption rate of zinc, a diet high in phytates and/or calcium will significantly decrease the available zinc. When we need to retain a diet like this supplementation may be required to prevent deficiency.
Summary
Wholefoods diets can meet Zinc requirements if we are mindful in selecting suitable species appropriate food options, we must also remember to provide diversity over time. When we rotate our ingredients and spread out various food items so that we are not always feeding the exact combination of foods at once it give our pets bodies opportunity to metabolise various nutrients naturally and minimize interactions. For example, with my own puppy Wilfred, he receives his meaty bone which is his main source of calcium for breakfast often with a little additional meat and sometimes some organs. Dinner is then more meat, organs, and various other ingredients in rotation such as mussels, oily fish, eggs and plant matter. This helps the body to absorb calcium away from his main zinc sources that may otherwise be bound and less bioavailable to him.
References:
1. Zinc-Responsive Dermatosis in Dogs
By Krista Williams, BSc, DVM, CCRP; Robin Downing, DVM, DAAPM, DACVSMR, CVPP https://vcahospitals.com/know-your-pet/zinc-responsive-dermatosis-in-dogs
2. Zinc and gastrointestinal disease. Skrovanek et al. 2014. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4231515/
3. Case, LP et al. (2011) Canine and Feline Nutrition: A Resource for Companion Animal Professionals, Third Edition. Missouri, USA, Mosby Elsevier.
4. National Research Council (2006) Nutrient Requirements of Dogs and Cats. Washington, DC. The National Academies Press
5. Zinc and the eye. Grahn et al., https://pubmed.ncbi.nlm.nih.gov/11349933/
6. USDA Food Database https://fdc.nal.usda.gov/index.html
7. New Zealand Food Composition Data https://www.foodcomposition.co.nz/
8. How Zinc and Quercetin Work Together. https://blog.bioticsresearch.com/how-zinc-and-quercetin-work-together
9. Zinc. Oregon State University. https://lpi.oregonstate.edu/mic/minerals/zinc
10. Zinc in Dog Nutrition, Health and Disease: A Review. Pereira et al., (2021). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8066201/
11. Effects of Zinc Source and Enzyme Addition on the Fecal Microbiota of Dogs. Pereira et al., (2021) https://www.frontiersin.org/articles/10.3389/fmicb.2021.688392/full
12. The Essential Toxin: Impact of Zinc on Human Health. Plum et al., (2010) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872358/
13. Zinc: Why Too Much of a Good Thing May Be Bad. Tolentino (2019) https://www.optometricmanagement.com/newsletters/nutritional-insights-for-clinical-practice/february-2019
14. Zinc absorption by young adults from supplemental zinc citrate is comparable with that from zinc gluconate and higher than from zinc oxide. Wegmuller et al., (2020) https://pubmed.ncbi.nlm.nih.gov/24259556/