What are nitrites primarily formed from in infants' guts?

Nitrites in infants' guts are primarily formed from the conversion of nitrates, which are naturally occurring compounds found in various foods and water sources. Nitrates can be converted into nitrites by certain bacteria present in the gastrointestinal tract. This process can be particularly significant in infants, as their gut microbiota is still developing and varies from that of older children and adults.

Nitrates, when consumed, can originate from various dietary sources such as vegetables (like beets and spinach) or drinking water that has been contaminated. The conversion of these nitrates to nitrites by bacteria is especially concerning in the context of infants because nitrites can interfere with the ability of blood to carry oxygen, potentially leading to a condition known as methemoglobinemia, or "blue baby syndrome."

The other options suggest different origins for nitrites that do not accurately reflect the primary biochemical process involved in their formation in the gut.