Hi Cameron Joseph Mann

In my opinion...

Yes, the relationship between systemic lactate and Veillonella is an interesting aspect of the exercise-induced microbiome changes. Veillonella is a genus of bacteria that can metabolize lactate, which is produced in muscles during high-intensity exercise. It has been proposed that the abundance of Veillonella increases in the gut microbiota of endurance athletes due to their high lactate production.

The idea that increased aerobic capacity is conferred via fecal/microbiome replacement stems from studies where fecal microbiota transplantation (FMT) from athletes to sedentary mice resulted in improved exercise performance in the recipient mice. This suggests that the microbiome may play a role in exercise performance, although the exact mechanisms are not yet completely understood.

The turnover rate of Veillonella may indeed be favored by the presence of lactate, as it serves as an energy source for these microbes. However, it is important to note that the abundance of Veillonella is only one factor among many that can influence exercise capacity, and further research is needed to determine the precise mechanisms and extent of this relationship.

As for the mechanism of intestinal entry for systemic lactate, lactate produced in muscle tissue during exercise can be transported into the bloodstream, where it can be taken up by other tissues such as the liver for gluconeogenesis, or by the heart and skeletal muscles as an energy source. Lactate can also be transported into the gastrointestinal lumen, although the exact mechanisms are not entirely clear. It is thought that lactate may passively diffuse across the gut epithelial cells, facilitated by monocarboxylate transporters (MCTs), or be actively transported by other transport mechanisms. Once in the gastrointestinal lumen, lactate can be utilized by Veillonella as a substrate for metabolism.

These articles are worth reading:

Please note that these references may not directly address all of the statements I made in the answer, but they may provide relevant and contextual information about the topic at hand. For a more complete understanding, I would recommend reading these and other related studies.