Diet and Gut Microbiome and the Chicken or Egg Problem

Quantity and quality of the intestinal and fecal microbiome vary considerably between individuals and are dependent on a very large number of intrinsic and environmental factors. Currently, only around 15% of the variance in microbiome diversity can be explained by these factors. Although diet and individual food items have effects, other individual parameters such as gender, age, body mass index (BMI), but also plasma lipids and blood pressure reveal stronger associations with microbiome diversity. In addition, gastrointestinal functions that translate into changes in stool frequency, stool volume, and stool appearance rank very high as effectors of microbiome signatures. In particular, the intestinal/colonic transit time is a critical factor that alters the substrate load for bacterial growth and metabolism as it alters simultaneously stool volume, water content, bacterial mass, and diversity. Moreover, metabolic and neurological diseases are frequently associated with marked changes in intestinal transit time that may translate into the reported changes in gut microbiota. This review provides scientific arguments for a more comprehensive assessment of the individual's intestinal phenotype in microbiome studies to resolve the chicken or egg problem in these observational studies.

Automated summary

The quantity and quality of the intestinal and fecal microbiome vary greatly between individuals and are affected by numerous intrinsic and environmental factors. While diet does have an effect, other individual factors such as gender, age, BMI, as well as plasma lipids and blood pressure, are more strongly associated with microbiome diversity. Additionally, gastrointestinal functions, particularly the intestinal/colonic transit time, play a critical role in influencing the microbiome. Metabolic and neurological diseases are often accompanied by changes in intestinal transit time and may contribute to alterations in gut microbiota.