The thing is, is that infants internals aren't yet fully functioning. The liver (your bodies chemical processing plant) hasn't established all of the reactions and pathways to process things yet. There are some pretty critical things needed in these early days.

Stomach, intestines ... all of it. Needs pretty gentle input of the right stuff.

Like someone said (sammy I think ?) breast milk is the most fine tuned for this. Some of the better formulas do well also. I haven't looked at the vegan ways to create homemade formula for infants but I would be very very skeptical of them. Their guts aren't yet fully functioning. Maybe there are some "recipes" worth while. I wouldn't guinea pig MY infant with them though.

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Something wicked this way comes.