The Cecum: The adaptive pouch of the past and the future

The cecum is a pouch located at the beginning of the large intestine right next to the ileum. This locale is at the center of the human ‘gut flora’ or ‘microbiome’, with the beginning of the higher concentrations of bacteria in the digestive system occurring here (1). The microbiome has gripped health sciences research recently, as studies have discovered it is at the foundation of human health, with correlations with infant outcomes (2), obesity and cardiovascular risk (3), chronic disorders (3) and even mental health (4).

The cecum can be used by many animals to ferment food allowing for the retrieval of additional nutrients not absorbed by the small intestine. Human ceca no longer have the ability to break down cellulose, in fact, the appendix hanging off the cecum was once thought, by Charles Darwin (5), to be a second cecum used by our ancestors for the additional breakdown of fibrous materials, but was left neglected as humans were able to get easier nutrients from their advancing agriculture, and now the appendix sits off the cecum bored with no purpose at all.

Birds also have ceca, most often two of them, which are important in digesting harder to break down materials. The mono-gastric (i.e., one-way-through) digestive system of most birds processes food quickly with most things in-and-out in less than 24 hours. While they are not as talented fermenters as ruminants, they can hold on to things like fibrous grass for greater than 24 hours in their cecum, fermenting, absorbing and even synthesizing nutrients there. Then, in one go, they can eject all the contents out; our chickens have two distinct droppings, a well-formed, black-brown decomposed-grain ball with a white smear on top (that is its pee), but they also have a runny green-brown ceacal dropping.

While the domestication of humans altered, and may still be altering, the ceacal domain, the domestication of birds can also cause significant changes to the cecum. Wild birds have significantly larger ceca, with higher micro-flora presence, than domesticated birds, and the transfer from the former to the latter condition almost instantaneously switched the ceacal condition (6). But birds’ ceca are incredibly adaptive and a chicken fed on whole natural grains that require more digestion produce cecums with characteristics more like those of wild birds (6). In an incredible demonstration of the flexibility and adaptive nature of the cecum, the ptarmigans’ cecum doubles in size over the winter (6), when food is scarce and a more fibrous diet is consumed.

So, our hope for the chicken future, is that someday, somewhere, someone figures out the importance of ceacal health and breed chickens that grow big fat cecums based on diet and grazing. For now we will continue to give our chickens access to pasture which encourages cecum activity through the consumption of grass and a more fibrous diet. Meanwhile, good fibre has become a major indicator of a good human diet (7,8), likely due to its influence on ceacal activity and in turn an enhanced microbiome. If we try hard enough to increase our dietary fibre (e.g., asparagus planting this year!) maybe we can take a trick from our chickens and grow our own cecum. Maybe if we can get everyone on board, in many generations, we’ll start using that appendix again to help with all that dietary fibre we have convinced ourselves to eat.

(1) Gorbach. Microbiology of the Gastrointestinal Tract. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston

(2) Tamburini et al. 2016. The microbiome in early life: implications for health outcomes. Nature Medicine. Vol 22, 713–722

(3) Aron-Wisnewsky and Clément. 2016. The gut microbiome, diet, and links to cardiometabolic and chronic disorders. Nature Reviews Nephrology. Vol 12, 169–181

(4) Malan-Muller et al. 2018. The Gut Microbiome and Mental Health: Implications for Anxiety- and Trauma-Related Disorders. OMICS: A Journal of Integrative Biology Vol. 22, No. 2 Review Articles

(5) Smith et al. 2017. Morphological evolution of the mammalian cecum and cecal appendix, Comptes Rendus Palevol, Vol 16, Issue 1.

(6) Clench and Mathias. 1995. The Avian Cecum: A Review. The Wilson Bulletin, 107(1), 93-121.

(7) Veronese et al. 2018. Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses, The American Journal of Clinical Nutrition, Vol 107, Issue 3, 436–444

(8) Threapleton et al. 2013. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ 347.