Matthew 5:6 -- "Blessed are those who hunger and thirst for righteousness, for they will be filled."
Matthew 6:16 -- “When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show others they are fasting. Truly I tell you, they have received their reward in full. 17 But when you fast, put oil on your head and wash your face, 18 so that it will not be obvious to others that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward you."
A little more detail as to context: https://en.wikipedia.org/wiki/Matthew_6:16
Fasting has been beneficial to my incurable medical condition. I'm quite encouraged by the association between fasting and religion. To me, it suggests there is something fundamentally wise about the practice and important to human health.
That may be the interpretation under Judaism, but outside of Judaism I think people can take a decent stab at understanding.
Whilst it's true that these concentrate in carnivores this is not a reason why we eat mostly herbivores.
Herbivores were plentiful and less dangerous to hunt. Then, herbivores are much easier and more economical to breed (you would need to breed herbivores first if you wanted to breed carnivores...)
You'll note that these decisions were made long before people even knew about heavy metals or had pesticides.