Fresh Fruits, Vegetables & Leafy Greens: Understanding Their Nutritional Value

Fresh fruits, vegetables and leafy greens provide an extraordinary diversity of vitamins, minerals, fiber and naturally occurring phytochemicals that contribute to the nutritional complexity of whole foods. Different plant species, varieties and colors contain different combinations of these compounds, making dietary diversity an important consideration when selecting foods for companion birds. The peer-reviewed publications presented here explore the nutritional characteristics of fruits and vegetables, the phytochemical diversity found in berries and cruciferous vegetables, and the ways preparation and processing can alter their composition. Several studies demonstrate that heating can substantially reduce particular heat-sensitive nutrients, while others show that the effects of processing depend on the food, compound and preparation method. Together, these resources provide bird owners with a scientific foundation for understanding the value of offering a varied selection of suitable fresh produce. Although much of this research comes from human nutrition and food chemistry, it highlights important considerations that is easily extrapolated for selecting, preparing and preserving whole-food ingredients as part of a nutritionally balanced, species-appropriate feeding program for our birds.

1. Slavin & Lloyd (2012): Nutritional diversity in fruits and vegetables

Slavin, J. L., & Lloyd, B. (2012). Health benefits of fruits and vegetables. Advances in Nutrition, 3(4), 506–516.

What this means for the animals we feed: Fruits and vegetables provide different combinations of vitamins, minerals, fiber, and naturally occurring plant compounds. Offering a colorful variety of suitable fresh produce helps provide a broader range of these components than relying on only a few familiar foods.

2. Del Rio, Borges & Crozier (2010): The natural compounds found in berries

Del Rio, D., Borges, G., & Crozier, A. (2010). Berry flavonoids and phenolics: Bioavailability and evidence of protective effects. British Journal of Nutrition, 104(S3), S67–S90.

What this means for the animals we feed: Berries contain vitamin C alongside several families of plant compounds, including anthocyanins and other polyphenols. Offering a variety of suitable whole berries provides these naturally occurring compounds together in the fruit.

3. Rao & Snyder (2010): Nutritional compounds in raspberries

Rao, A. V., & Snyder, D. M. (2010). Raspberries and human health: A review. Journal of Agricultural and Food Chemistry, 58(7), 3871–3883.

What this means for the animals we feed: Raspberries contain nutrients and plant compounds, including anthocyanins and ellagitannins, that contribute to their nutritional characteristics. Including suitable berries among a varied selection of fresh fruits introduces additional plant compounds and food textures.

4. McKillop et al. (2002): Folate losses when vegetables are boiled

McKillop, D. J., Pentieva, K., Daly, D., McPartlin, J. M., Hughes, J., Strain, J. J., Scott, J. M., & McNulty, H. (2002). The effect of different cooking methods on folate retention in various foods that are amongst the major contributors to folate intake in the UK diet. British Journal of Nutrition, 88(6), 681–688.

What this means for the animals we feed: In this study, boiling reduced the measured folate in spinach and broccoli by approximately half. Offering these vegetables fresh, when appropriate for the species, avoids the folate losses observed with boiling.

5. Skrovankova et al. (2015): Different berries provide different plant compounds

Skrovankova, S., Sumczynski, D., Mlcek, J., Jurikova, T., & Sochor, J. (2015). Bioactive compounds and antioxidant activity in different types of berries. International Journal of Molecular Sciences, 16(10), 24673–24706.

What this means for the animals we feed: Strawberries, raspberries, blackberries, blueberries, and cranberries contain different combinations of vitamin C and plant compounds, including anthocyanins and other polyphenols. Offering a variety of suitable whole berries provides a broader selection of these naturally occurring compounds.

6. Rumm-Kreuter & Demmel (1990): Heat-sensitive vitamins in vegetables

Rumm-Kreuter, D., & Demmel, I. (1990). Comparison of vitamin losses in vegetables due to various cooking methods. Journal of Nutritional Science and Vitaminology, 36(Supplement 1), S7–S14.

What this means for the animals we feed: Heating vegetables can reduce water-soluble and heat-sensitive vitamins, with losses depending on the vegetable and how it is prepared. Offering suitable vegetables fresh avoids the vitamin losses associated with those cooking methods.

7. Yuan, Sun & Yuan (2009): Vitamin C and plant compounds in broccoli

Yuan, G.-F., Sun, B., Yuan, J., & Wang, Q.-M. (2009). Effects of different cooking methods on health-promoting compounds of broccoli. Journal of Zhejiang University SCIENCE B, 10(8), 580–588.

What this means for the animals we feed: Boiling, microwaving, and stir-frying broccoli reduced several measured nutrients or plant compounds, including vitamin C and chlorophyll, while steaming preserved more of them. Offering appropriately prepared fresh broccoli avoids these cooking-related losses and retains its naturally occurring combination of nutrients and plant compounds.

8. Pellegrini et al. (2010): Nutrient changes in broccoli, Brussels sprouts, and cauliflower

Pellegrini, N., Chiavaro, E., Gardana, C., Mazzeo, T., Contino, D., Gallo, M., Riso, P., Fogliano, V., & Porrini, M. (2010). Effect of different cooking methods on color, phytochemical concentration, and antioxidant capacity of raw and frozen brassica vegetables. Journal of Agricultural and Food Chemistry, 58(7), 4310–4321.

What this means for the animals we feed: Researchers found substantial vitamin C losses during cooking of the vegetables studied, along with changes in other plant compounds that varied by cooking method. Offering suitable fresh cruciferous vegetables preserves vitamin C that would otherwise be lost during these treatments.

9. Sablani et al. (2010): Anthocyanin losses during berry canning

Sablani, S. S., Andrews, P. K., Davies, N. M., Walters, T., Saez, H., Syamaladevi, R. M., & Mohekar, P. R. (2010). Effect of thermal treatments on phytochemicals in conventionally and organically grown berries. Journal of the Science of Food and Agriculture, 90(5), 769–778.

What this means for the animals we feed: Canning reduced the measured anthocyanins in raspberries and blueberries by as much as 44% under the conditions studied. Offering suitable fresh berries preserves these naturally occurring pigments that can be reduced during heat processing.

10. Rickman, Barrett & Bruhn (2007): Vitamin changes during produce processing

Rickman, J. C., Barrett, D. M., & Bruhn, C. M. (2007). Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compounds. Journal of the Science of Food and Agriculture, 87(6), 930–944.

What this means for the animals we feed: This review documents how the initial heating used in some produce-processing methods can reduce vitamin C and certain B vitamins. Offering suitable fresh produce without that heating step avoids those initial processing-related losses.

11. Pellegrini et al. (2009): Antioxidant changes during vegetable preparation

Pellegrini, N., Miglio, C., Del Rio, D., Salvatore, S., Serafini, M., & Brighenti, F. (2009). Effect of domestic cooking methods on the total antioxidant capacity of vegetables. International Journal of Food Sciences and Nutrition, 60(Supplement 2), 12–22. What this means for the animals we feed: Pan-frying generally reduced the measured antioxidant capacity of the vegetables examined in this study. Offering appropriate vegetables fresh avoids the changes associated with that preparation method and provides their naturally occurring plant compounds without heating.