New year is often the time to make lifestyle changes that most commonly include dietary restrictions to stay healthy and happy. It is no surprise, to most of us, that these alterations impact us as well as our gut microbiome – the microbial community associated with the human digestive tract. Several studies have underpinned the role of the gut microbiome in regulating our physiology including metabolic functions and immune response. As a consequence, variations in the gut microbiome have been associated with autoimmune disorders, cancer, obesity and cardiovascular diseases. In order to understand how the gut microbiome influences our health, a fundamental question that remained to be answered was – what dietary components influence our microbiome. Scientists (Holmes AJ et al) in a recent publicationin the journal Cell metabolism have made some insightful observations to address this question. The researchers used experimental as well as simulation models to thoroughly investigate the influence of 25 different dietary compositions on the gut microbiome of 858 mice fed over a period of 15 months. One of the key findings from this study was that the microbial diversity is dependent on the energy density as well as nutrient distribution of the food i.e. the ratio of protein to carbohydrate. The study also showed that this diversity is largely governed by the utilization of nutrients by our body and their subsequent availability to the gut microbiome. In simpler terms, the complex proteins and carbohydrates we consume is broken down into end products that are primarily made up of carbon and nitrogen. These products are reabsorbed for our metabolic activities and physiological functions. The microbiome, however, has two major sources of nutrients which include (i) endogenous secretions in our gut such as mucin and (ii) digestion-resistant or partially digested carbohydrates and proteins present in our diet. Interestingly, the researchers were able to generate ‘guilds’ that constitute bacterial species that vary in their utilization of substrates for nutrients. For instance, a high protein to carbohydrate intake led to an increased abundance of Firmicutes that utilized dietary carbon and nitrogen for their metabolism. On the other hand, Bacteroidetes were more abundant in a low protein to carbohydrate diet where host endogenous secretions was the primary source of nutrients. Further analysis revealed that nitrogen that constitutes the protein diet played a key role in governing these microbial shifts in the gut. This suggests that the ratio of protein to carbohydrate is critical in mediating the gut diversity. Previous studies by the same group indicated that low protein intake by mice is associated with better immune response and intestinal function. In addition, other studies have revealed that the abundance of Bacteroidetes to Firmicutes helps in regulating obesity. Overall, this study has tremendous implications as we usher into an era of host-gut-diet interactions to understand disease processes. It is imperative to acknowledge that such studies are difficult to recapitulate in humans where several confounding variables exist within the diet. Nevertheless, they have begun to provide an understanding of the qualitative and quantitative aspects of our diet that can predict microbiome composition and consequently our health. In a period where precision medicine is the new norm, it will not be surprising if precision diet regimens might be generated for an optimal symbiotic relationship between the us and our gut microbiome for healthy living. Ultimately, while these findings warrant further study, you might want to think twice before you completely exclude those carbs and indulge in your legumes. Remember, it’s all relative !
Andrew J. Holmes, Yi Vee Chew, Feyza Colakoglu, John B. Cliff, Eline Klaassens, Mark N. Read, Samantha M. Solon-Biet, Aisling C. McMahon, Victoria C. Cogger, Kari Ruohonen, David Raubenheimer, David G. Le Couteur, Stephen J. Simpson. Diet-Microbiome Interactions in Health Are Controlled by Intestinal Nitrogen Source Constraints. Cell Metabolism, 2017 Jan 10;25(1):140-151. 1016/j.cmet.2016.10.021
Radhika Raheja and Isha Verma
Ipsa Jain (Illustration)