Phytonutrients, Antioxidants & Plant Bioactives: Understanding the Nutritional Complexity of Whole Foods
Fruits, vegetables, seeds and other whole plant foods contain thousands of naturally occurring compounds that contribute to their nutritional complexity beyond essential vitamins and minerals. These substances, collectively known as phytochemicals or phytonutrients, include carotenoids, anthocyanins, flavonoids and numerous other plant compounds with diverse chemical structures and biological activities. The peer-reviewed publications presented here examine how these compounds occur in different foods, interact within the whole-food matrix, and undergo absorption and metabolism. They demonstrate that phytochemicals cannot be evaluated solely by their concentrations in foods or their antioxidant activity in laboratory experiments. Instead, their potential biological effects depend on numerous factors, including chemical structure, food composition, digestion and interactions with intestinal microorganisms. For companion-bird owners, this research provides a scientific foundation for understanding the value of selecting a diverse assortment of suitable whole plant foods. Offering different fruits, vegetables and other plant ingredients introduces a wider range of naturally occurring phytochemicals while providing opportunities for dietary and behavioral enrichment. This research identifies important principles that warrant further investigation in avian species and encourages a more comprehensive understanding of whole-food nutrition.
1. Liu (2003): The combined effects of plant compounds in whole foods
Liu, R. H. (2003). Health benefits of fruit and vegetables are from additive and synergistic combinations of phytochemicals. The American Journal of Clinical Nutrition, 78(3 Suppl.), 517S–520S.
What this means for the animals we feed: Fruits and vegetables contain numerous plant compounds that occur together rather than in isolation. This review supports offering a variety of suitable whole plant foods to provide those naturally occurring combinations.
2. Manach et al. (2004): Different foods supply different polyphenols
Manach, C., Scalbert, A., Morand, C., Rémésy, C., & Jiménez, L. (2004). Polyphenols: Food sources and bioavailability. The American Journal of Clinical Nutrition, 79(5), 727–747.
What this means for the animals we feed: Plant foods contain many different polyphenols, and the amount absorbed depends partly on each compound’s chemical form and the food in which it occurs. Offering diverse, suitable fruits, vegetables, and other plant foods introduces different polyphenols rather than relying on a single source.
3. Scalbert, Johnson & Saltmarsh (2005): Polyphenols do more than act as antioxidants
Scalbert, A., Johnson, I. T., & Saltmarsh, M. (2005). Polyphenols: Antioxidants and beyond. The American Journal of Clinical Nutrition, 81(1 Suppl.), 215S–217S.
What this means for the animals we feed: Polyphenols are studied for biological activities beyond their ability to act as antioxidants in laboratory tests. Including a variety of appropriate plant foods provides these compounds in their natural food sources without assuming that a high laboratory antioxidant score predicts a particular health benefit.
4. Manach et al. (2005): Not all polyphenols are absorbed equally
Manach, C., Williamson, G., Morand, C., Scalbert, A., & Rémésy, C. (2005). Bioavailability and bioefficacy of polyphenols in humans. I. Review of 97 bioavailability studies. The American Journal of Clinical Nutrition, 81(1 Suppl.), 230S–242S.
What this means for the animals we feed: This review found substantial differences in how various polyphenols are absorbed and metabolized. It reinforces the value of dietary variety while showing why the amount of a compound measured in a food does not, by itself, tell us how much an animal will absorb or use.
5. Saini, Nile & Park (2015): Carotenoids in colorful produce
Saini, R. K., Nile, S. H., & Park, S. W. (2015). Carotenoids from fruits and vegetables: Chemistry, analysis, occurrence, bioavailability and biological activities. Food Research International, 76(Part 3), 735–750.
What this means for the animals we feed: Fruits and vegetables contain different carotenoids, including compounds associated with yellow, orange, and red coloration. Offering a range of suitable colorful produce can introduce different carotenoids, although color alone does not reveal a food’s complete nutrient profile.
6. Castenmiller & West (1998): Carotenoid absorption depends on the food and the consumer
Castenmiller, J. J. M., & West, C. E. (1998). Bioavailability and bioconversion of carotenoids. Annual Review of Nutrition, 18, 19–38.
What this means for the animals we feed: The availability of carotenoids depends on factors including their chemical form, the surrounding food matrix, and the animal consuming them. This supports considering the whole ingredient and species-specific nutrient requirements rather than treating all carotenoid-containing foods as interchangeable.
7. Schweiggert & Carle (2017): The structure of plant foods affects carotenoid availability
Schweiggert, R. M., & Carle, R. (2017). Carotenoid deposition in plant and animal foods and its impact on bioavailability. Critical Reviews in Food Science and Nutrition, 57(9), 1807–1830.
What this means for the animals we feed: Carotenoids are stored in different physical forms within foods, and those structures influence how readily the compounds become available during digestion. Whole-food selection and preparation therefore matter alongside the measured carotenoid content of an ingredient.
8. He & Giusti (2010): Anthocyanins give many plant foods their vivid colors
He, J., & Giusti, M. M. (2010). Anthocyanins: Natural colorants with health-promoting properties. Annual Review of Food Science and Technology, 1, 163–187.
What this means for the animals we feed: Anthocyanins are a large family of plant pigments responsible for many red, purple, and blue colors in fruits and vegetables. Suitable foods with these colors can contribute anthocyanins alongside their other naturally occurring nutrients and plant compounds.
9. Rodriguez-Mateos et al. (2014): Berries contain several families of polyphenols
Rodriguez-Mateos, A., Heiss, C., Borges, G., & Crozier, A. (2014). Berry (poly)phenols and cardiovascular health. Journal of Agricultural and Food Chemistry, 62(18), 3842–3851.
What this means for the animals we feed: Berries supply multiple kinds of polyphenols, including anthocyanins, flavonols, and ellagitannins. Offering a variety of suitable berries introduces different combinations of these compounds.
10. Lila et al. (2016): Anthocyanins are transformed during digestion
Lila, M. A., Burton-Freeman, B., Grace, M., & Kalt, W. (2016). Unraveling anthocyanin bioavailability for human health. Annual Review of Food Science and Technology, 7, 375–393.
What this means for the animals we feed: Anthocyanins can be broken down and transformed into other compounds during digestion, so their biological activity cannot be judged solely by measuring the original pigments in a food. Suitable anthocyanin-containing whole foods provide these compounds as part of a broader food matrix.
11. Kay et al. (2017): Gut microbes contribute to flavonoid metabolism
Kay, C. D., Pereira-Caro, G., Ludwig, I. A., Clifford, M. N., & Crozier, A. (2017). Anthocyanins and flavanones are more bioavailable than previously perceived: A review of recent evidence. Annual Review of Food Science and Technology, 8, 155–180.
What this means for the animals we feed: Research shows that gut microbes help transform certain fruit-derived flavonoids into smaller compounds that can be absorbed. This highlights an interaction between dietary plant compounds and digestion.
12. Tsuda (2012): Anthocyanin-rich foods contain more than antioxidant pigments
Tsuda, T. (2012). Dietary anthocyanin-rich plants: Biochemical basis and recent progress in health benefits studies. Molecular Nutrition & Food Research, 56(1), 159–170. What this means for the animals we feed: This review examines anthocyanins as biologically active plant compounds while noting that their effects may depend on other constituents of the foods containing them. Offering varied, suitable whole plant foods preserves that broader combination of compounds instead of treating one pigment as the sole reason to select an ingredient.