Food is so complex… all we can do is learn what we can, and focus on the things that make the most sense for us individually, and prioritize as best we can.
In my experience, citrulline in a low dose is good for me. (less than 0,4 - 0,8 gr). Combined with low-dose arginine, it works even better for elderly people to improve their circulation and the oxygenation of the tissues in their body.
But swirling around beet juice in my mouth is the way to go if the aim is to increase endurance.