Dietary Diversity & the Whole-Food Matrix: Why Food Structure Matters

Nutrition involves considerably more than supplying individual vitamins, minerals, proteins and fats. Every whole food contains a complex combination of nutrients, fiber, phytochemicals and naturally occurring structures that influence how its components interact and become available during digestion. This collection of peer-reviewed research explores the concept of the whole-food matrix, demonstrating that the physical form of a food and the diversity of ingredients within a diet can influence nutritional and physiological outcomes. Studies examining whole nuts, intact grains, fresh fruits and dietary plant diversity illustrate why foods cannot always be evaluated solely by their nutrient labels. For companion bird owners, this research provides an important foundation for understanding the potential value of offering a varied selection of suitable whole foods, while recognizing that different species have different nutritional requirements. Although much of this research comes from human nutrition, it identifies important principles worthy of consideration and further investigation in avian nutrition. Ultimately, a thoughtful feeding program should consider not only which nutrients are present, but also their sources, the physical structure of the foods providing them, and how different ingredients contribute to a nutritionally balanced, species-appropriate diet.

1. Jacobs & Tapsell (2007): Why foods are more than the sum of their nutrients

Jacobs, D. R., Jr., & Tapsell, L. C. (2007). Food, not nutrients, is the fundamental unit in nutrition. Nutrition Reviews, 65(10), 439–450.

What this means for the animals we feed: Whole foods contain combinations of nutrients and other compounds that interact within the food itself and during digestion. This review supports considering the complete food, not just a list of isolated vitamins and minerals, when selecting ingredients for the animals we feed.

2. Jacobs, Gross & Tapsell (2009): Food synergy

Jacobs, D. R., Jr., Gross, M. D., & Tapsell, L. C. (2009). Food synergy: An operational concept for understanding nutrition. The American Journal of Clinical Nutrition, 89(5), 1543S–1548S.

What this means for the animals we feed: Nutrients and plant compounds occur together in whole foods, where their interactions can influence how they function in the body. Offering a variety of suitable whole foods provides these naturally occurring combinations rather than focusing exclusively on individual nutrients.

3. Fardet (2015): Preserving the structure of grain foods

Fardet, A. (2015). A shift toward a new holistic paradigm will help to preserve and better process grain products’ food structure for improving their health effects. Food & Function, 6, 363–382.

What this means for the animals we feed: The physical structure of grains influences how digestive enzymes reach their nutrients and how quickly those nutrients become available. This review supports considering intact grains and preparation methods that preserve useful food structures when choosing appropriate whole-food ingredients.

4. Ellis et al. (2004): The natural structure of whole nuts

Ellis, P. R., Kendall, C. W. C., Ren, Y., Parker, C., Pacy, J. F., Waldron, K. W., & Jenkins, D. J. A. (2004). Role of cell walls in the bioaccessibility of lipids in almond seeds. The American Journal of Clinical Nutrition, 80(3), 604–613.

What this means for the animals we feed: The natural cell walls of almonds influence how much fat is released during digestion. Whole nuts therefore behave differently from extracted oils or finely ground nut products, demonstrating that the physical structure of a food matters alongside its nutrient content.

5. Mandalari et al. (2008): How almond cell walls affect nutrient release

Mandalari, G., Faulks, R. M., Rich, G. T., Lo Turco, V., Picout, D. R., Lo Curto, R. B., Bisignano, G., Dugo, P., Dugo, G., Waldron, K. W., Ellis, P. R., & Wickham, M. S. J. (2008). Release of protein, lipid, and vitamin E from almond seeds during digestion. Journal of Agricultural and Food Chemistry, 56(9), 3409–3416.

What this means for the animals we feed: Almond cell walls influence how protein, fat, and vitamin E are released during digestion. This shows why the natural structure of a whole nut is an important part of its nutritional characteristics, not merely packaging around its nutrients.

6. Gebauer et al. (2016): Whole almonds and almond butter behave differently

Gebauer, S. K., Novotny, J. A., Bornhorst, G. M., & Baer, D. J. (2016). Food processing and structure impact the metabolizable energy of almonds. Food & Function, 7(10), 4231–4238.

What this means for the animals we feed: In a feeding study, whole almonds provided less absorbable energy than almond butter, even though both came from almonds. The finding demonstrates that grinding a whole food can change how its nutrients are released and used, making food structure relevant when selecting and preparing nuts.

7. Haber et al. (1977): Intact apples versus apple purée and juice

Haber, G. B., Heaton, K. W., Murphy, D., & Burroughs, L. F. (1977). Depletion and disruption of dietary fibre. Effects on satiety, plasma-glucose, and serum-insulin. The Lancet, 2(8040), 679–682.

What this means for the animals we feed: In this study, intact apples were more filling and produced a different insulin response than apple purée or fiber-free juice. The results demonstrate that removing or disrupting a fruit’s natural fiber structure can change its physiological effects, supporting the value of offering suitable fruits in their whole form.

8. Flood-Obbagy & Rolls (2009): Whole fruit versus processed fruit

Flood-Obbagy, J. E., & Rolls, B. J. (2009). The effect of fruit in different forms on energy intake and satiety at a meal. Appetite, 52(2), 416–422.

What this means for the animals we feed: Participants felt fuller after eating whole apple pieces than after consuming applesauce or apple juice, even when the foods were matched for several nutritional characteristics. This illustrates how offering fruit in its intact form preserves physical properties that influence the eating experience and the body’s response.

9. Musa-Veloso et al. (2021): The importance of intact grain structure

Musa-Veloso, K., Noori, D., Venditti, C., Poon, T., Johnson, J., Harkness, L. S., O’Shea, M., & Chu, Y. (2021). A systematic review and meta-analysis of randomized controlled trials on the effects of oats and oat processing on postprandial blood glucose and insulin responses. The Journal of Nutrition, 151(2), 341–351.

What this means for the animals we feed: Studies found that intact oat kernels and thick oat flakes produced more favorable blood-glucose and insulin responses than refined-grain controls, while finely processed oats did not show the same effects. This supports preserving the natural structure of appropriate grains when choosing how to offer them.

10. Reynolds et al. (2020): Whole-grain particle size matters

Reynolds, A. N., Mann, J., Elbalshy, M., Mete, E., Robinson, C., Oey, I., Silcock, P., Downes, N., Perry, T., & Te Morenga, L. (2020). Wholegrain particle size influences postprandial glycemia in type 2 diabetes: A randomized crossover study comparing four wholegrain breads. Diabetes Care, 43(2), 476–479.

What this means for the animals we feed: Even when foods contained the same whole-grain ingredients and similar nutrients, differences in grain structure affected blood-glucose responses in the human participants studied. The findings reinforce that a food’s physical form matters and that preserving intact grain structure can offer nutritional characteristics not captured by an ingredient list alone.

11. McDonald et al. (2018): Plant-food diversity and the gut microbiome

McDonald, D., et al. (2018). American Gut: An open platform for citizen science microbiome research. mSystems, 3(3), e00031-18. What this means for the animals we feed: In this large microbiome study, people who reported eating a greater variety of plant foods had more diverse gut microbial communities than those eating fewer types of plants. The association provides a rationale for investigating dietary plant diversity as a way to support microbial diversity, while offering animals a broad assortment of appropriate whole-food ingredients.