Our large intestine harbors more than last night’s left overs - trillions of friendly bacteria also reside in harmony with our bodies. And with the progression in microbiota research, it has been shown that our gut microbiota is an essential organ that is involved in many biological activities such as immunity, metabolism and has even been associated with longevity1. Recent study have shown that a population accustomed to Western diet, which consists of high fat, protein and low fibre intake, has a significantly lower microbiota diversity compared to a population with traditional dietary patterns2. Traditional dietary patterns involve high dietary fibre intake such as grains and beans rich in complex carbohydrates also known as microbiota-accessible carbohydrates (MACs). MACs, as the name suggests, are the main sources of energy for the friendly bacteria residing in our gut.
In order to investigate the effect of different diets on microbiota diversity, Sonnenburg and colleagues3 used mouse-models with humanized gut microbiota and manipulated their diets to resemble either Western or traditional dietary patterns. The authors hypothesized that low-MACs diet, which represents the Western diet, would drive the loss of diversity in the gut microbiota.
The authors started with two groups of mice that were fed a high-MACs diet that showed similar gut microbiota diversity. Then, a group of mice was switched to a low-MACs diet and a significant difference in bacterial abundance arose between the two groups. The group that experienced the diet switch showed a decrease of 60% abundance in taxa. In addition, the taxa did not fully recover with the re-introduction of high-MACs diet. The authors then proposed that diet-induced loss in microbiota abundance would be magnified over generations, even to a point of “taxa extinction”. The two groups of mice independently generated offspring that followed their parents’ diet, and this was repeated for four generations. The results demonstrated that prolonged low-MAC diet over generations led to extinction of bacterial taxa which could not be recovered with the re-introduction of high-MAC diet. With each generation, the microbiota composition of the diet-switching group showed progressive loss in diversity. This diversity was only fully restored with a fecal transplantation from the control group that was continuously under high-MACs diet. The authors also suggested that increased loss of bacteria taxa seemed to be correlated to decrease in carbohydrate degrading capacity of the microbiota, which will be further investigated.
In modern Western society, the predominant diet involves high fat and protein consumption. In addition, our fitness obsessed culture promotes low-carbohydrate diet as an effective weight-loss method, popularizing carbohydrate-shaming. However, we need to be reminded that, complex carbs such as brown rice, whole grains and fruits – not white bread, are actually one of the essential food groups that flourish our gut microbiota that plays a significant role in maintaining good health.
1. Guo, L., Karpac, J., Tran, S. L. & Jasper, H. PGRP-SC2 promotes gut immune homeostasis to limit commensal dysbiosis and extend lifespan. Cell 156, 109–22 (2014).
2. De Filippo, C. et al. Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proc. Natl. Acad. Sci. 107, 14691–14696 (2010).
3. Sonnenburg, E. D. et al. Diet-induced extinctions in the gut microbiota compound over generations. Nature 529, 212–215 (2016).