Spinach is at the top of the superfoods list — foods that provide natural antioxidants, bioactives, functional fiber and essential nutrients. Despite many of us growing up not liking spinach, today we find it in a wide variety of grocery products and in food service, usually served as a fresh vegetable in salads or as an addition to sandwiches in place of lettuce. Much of this thinking about the benefits of spinach in our own diets has now crossed over into pet food. We see superfood blends unapologetically promoted in product names and callouts with a nod to their benefit for our pet’s health, often with spinach as a lead. So, is it true? Does this vegetable add something to dog and cat food, treats, and toppers?
All about spinach
Spinach is a green leafy vegetable originating in central and western Asia. It is in the Amaranth family and related to beets and quinoa. The spinach plant is grown as an annual and harvested as leafy greens at various stages of maturity. There is a wide array of varieties, some of which are more suitable for commercial production. In the U.S., three basic types of spinach are produced: savoy (curly leaf), flat (smooth leaf) and semi-savoy (slightly curly leaves). They are all green leaved and differ primarily in their thickness or durability in handling. There are also new varieties being developed with more red coloration in the stems and leaves.
The largest producer is China with the U.S. as a distant second, though production and consumption have been growing steadily for the past 20 years to about 1.5 pounds per person. Current U.S. acreage is approximately 47,000 with California, USA, leading the way due to their ability for year-round production. On these commercial farms, unlike backyard gardens, the seeds are planted at a rate of 1.5–2.3 million seeds per acre and grown in wide beds of 40–80 inches to permit mechanical harvest.
There are specific guidelines for growing, harvesting and distributing spinach for human consumption (80 FR 74354, 21CFR112). This also applies to pet food considering most of the spinach in the supply chain comes through the same channels. It is sold as U.S. No. 1 or U.S. No. 2 with specific standards of identity. One can presume that U.S. No. 2 would be more appropriate for pet food use given it will be added to a mix that is going to be processed. Dried spinach flakes are also commonly used. For flakes, the harvested leaves are cleaned, dewatered and then dried either on trays or in drum dryers with moisture removed through heated air, then sized before packaging.
From a nutritional perspective, spinach is noted for the presence of some essential nutrients (USDA NDB SR) but for all intents and purposes it is mostly water (91.4%). This dramatically lowers the concentration of the macronutrients (e.g., 2.86% protein, 0.39% fat, 1.72% ash), though on a dry basis the functional nutrients are concentrated dramatically. For instance, the total dietary fiber is around 25% of the dry mass. The micronutrients such as potassium (6.74%), iron (315 mg/kg), folate (22 mg/kg), vitamin K1 (phylloquinone, 56 mg/kg), vitamin C (3,267 mg/kg), betaine (>12,000 mg/kg), and the carotenoids B-carotene (654 mg/kg) and lutein+zeaxanthin (1,418 mg/kg) are very high relative to other typical ingredients used.
Additionally, spinach contains several secondary metabolites from flavonoid derivatives that have anti-inflammatory properties. It also contains appreciable concentrations of phenolic acids such as p-coumaric and ferulic acid, and p-hydroxybenzoic and vanillic acid along with various lignans. All have antioxidant properties, among other functions. The green color in spinach is mostly from chlorophyll which has been demonstrated to delay stomach emptying, decrease ghrelin and increase GLP-1, the implications of which may benefit type 2 diabetes. Among the omega-3s, it contains stearidonic acid along with some EPA and ALA. Spinach can contain nitrates which were once thought to be detrimental but are now being considered as beneficial to health. It also contains oxalates which can contribute to stone formation in the bladder, although these can be reduced by cooking.
The use of spinach in pet diets
Published reports for spinach evaluation in dog diets go back as far as 1918 (McClugage and Mendel, 1918). More recent research has demonstrated that spinach chlorophylls are absorbed and transported to the tissue in dogs (Fernandes et al., 2007) and may benefit cellular oxidation and immune function. There are several other recent studies which indicate that spinach, as part of an antioxidant blend, may promote cognition.
So how do we get spinach into the diet? Generally, spinach in pet food is added as an accent or as a coloring agent in some treat applications. Whether as dried flakes or raw leaves, the addition level is generally small — around 0.1% or less, in part because it is expensive. It also does not hold up well in the processing steps, turning slimy as a raw leaf or disintegrating in dry flake form. However, this loss in visual appearance does not preclude the notion of value, though an effective dose that might impart an antioxidant, immune or nutritional contribution is probably diluted to insignificant at minimal inclusions. It would be beneficial to know what the effective dose is and whether dogs and cats would tolerate the change in aroma and flavor when those levels are present.
Spinach clearly has several applications in pet food: nutritional fortification, health maintenance and marketing appeal are but a few. There do not appear to be many down sides to its inclusion and the story as a “superfood” seems to have merit in modern dog and cat diets.
Briefly: top 5 takeaways
- Spinach is a green leafy vegetable originating in central and western Asia; the largest producer is China with the U.S. as a distant second.
- There are specific guidelines for growing, harvesting and distributing spinach for human consumption which also apply to pet food since most of the spinach in the supply chain comes through the same channels.
- On a dry basis, the macronutrients and micronutrients in spinach are significant.
- Research on the use of spinach in dog diets indicate that it may benefit cellular oxidation and immune function as well as cognition.
- There do not seem to be many downsides to the use of spinach in pet food, and its label as a “superfood” seems to have merit in dog and cat diets.