The so-called "gut-brain axis" is the well-established bidirectional interaction between the gut microbiome and the brain. In other words, the microbiome in our gut has been found to influence many aspects of our brain: stress physiology and psychology, mood, cognition, and behavior.
A novel challenge has arisen from this finding. Namely, how can astronauts stay alert and healthy through their travels?
One issue is the inadequate intake of micronutrients, which is generally associated with increased inflammation and stress. It also leads to reduced functioning of the immune system. Although the space travelers’ diet is not yet optimized, considerable progress has been made. For instance, the average caloric intake has been significantly increased in recent years.
However, it remains a fact that during spaceflights, astronauts eat less and generally more poorly than on Earth. Several possible reasons include cultural habits, the palatability of food, space motion sickness, changes in light-dark cycle and appetite-regulating hormones.
Optimizing the gut's microbiome is hard enough on earth. Doing so in space requires much more research. But the physiological and cognitive benefits for a healthy gut mean that astronauts will be more effective when they are in optimal health.
From the article: "The upcoming exploration missions will imply a much longer duration than any of the missions flown so far. In these missions, physiological adaptation to the new environment leads to changes in different body systems, such as the cardiovascular and musculoskeletal systems, metabolic and neurobehavioral health and immune function. To keep space travelers healthy on their trip to Moon, Mars and beyond and their return to Earth, a variety of countermeasures need to be provided to maintain body functionality."