I keep saying that brain grows (BDNF, brain-derived neurotrophic factor is released into blood) when body encounter evolutionary familiar stress - hunger, need

I keep saying that brain grows (BDNF, brain-derived neurotrophic factor is released into blood) when body encounter evolutionary familiar stress - hunger, need for endurance and need for force exertion. Basically, brain was made for body to experience less of that stress. As an example of what BDNF does: endurance exercise is known for elevating serum BDNF levels long-term [1] and endurance exercise has been shown to help with Parkinsons' [2]. Thus, can it be that these speaking two languages experience more of that stresses thorough their life? The article does not suggest that these factors were, well, factored out. [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6613032/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6613032/ [2] https://pubmed.ncbi.nlm.nih.gov/28870627/ https://pubmed.ncbi.nlm.nih.gov/28870627/ PS https://www.researchgate.net/publication/260394068_Long_term_habitual_exercise_is_associated_with_lower_resting_level_of_serum_BDNF https://www.researchgate.net/publication/260394068_Long_term... - they suggest that habitual exercise does not produce more BDNF or it is not BDNF that acts on the brain, I counter that body utilizes it better, just like glucose in blood.