Final answer:
The best indication for the use of a soy-based infant formula is galactosemia, a condition preventing the breakdown and proper metabolization of galactose, leading to serious symptoms when lactose-containing milk is consumed.
Step-by-step explanation:
The best indication for the use of a soy-based infant formula is galactosemia. Galactosemia is a condition where infants lack the enzyme needed to metabolize galactose, leading to its accumulation in the blood (galactosemia) and excretion in the urine (galactosuria). Symptoms of galactosemia include diarrhea and vomiting when the infant consumes milk containing lactose. Since soy-based formulas are lactose-free, they provide an alternative to milk-based formulas, which contain lactose that these infants cannot process. It is important not to confuse lactose intolerance with galactosemia; while they both result in difficulties digesting lactose, lactose intolerance typically stems from a deficiency in lactase, an enzyme that breaks down lactose in the small intestine.