1 0 % ▁to ▁ 2 0 % ▁higher ▁than ▁adult ▁levels ▁and ▁those ▁for ▁inf ants ▁can ▁be ▁as ▁much ▁as ▁ 1 5 0 % ▁higher ▁in ▁the ▁first ▁year ▁of ▁life . ▁C yst e ine ▁( or ▁sul fur - cont aining ▁am ino ▁ac ids ), ▁ty ros ine ▁( or ▁a rom atic ▁am ino ▁ac ids ), ▁and ▁arg in ine ▁are ▁always ▁required ▁by ▁inf ants ▁and ▁growing ▁children . ▁ ▁Rel ative ▁am ino ▁acid ▁composition ▁of ▁protein ▁sources ▁Food st uff s ▁that ▁lack ▁essential ▁am ino ▁ac ids ▁are ▁poor ▁sources ▁of ▁protein ▁equival ents , ▁as ▁the ▁body ▁tends ▁to ▁de amin ate ▁the ▁am ino ▁ac ids ▁obtained , ▁converting ▁prote ins ▁into ▁f ats ▁and ▁car bo h yd r ates . ▁Therefore , ▁a ▁balance ▁of ▁essential ▁am ino ▁ac ids ▁is ▁necessary ▁for ▁a ▁high ▁degree ▁of ▁net ▁protein ▁util ization , ▁which ▁is ▁the ▁mass ▁ratio ▁of ▁am ino ▁ac ids ▁converted ▁to ▁prote ins ▁to ▁am ino ▁ac ids ▁supplied . ▁ ▁Complete ▁prote ins ▁contain ▁a ▁bal anced ▁set ▁of ▁essential ▁am ino ▁ac ids ▁for ▁humans . ▁Animal ▁sources ▁such ▁as ▁meat , ▁p oul try , ▁eggs , ▁fish , ▁milk , ▁and ▁che ese ▁provide ▁all ▁of ▁the ▁essential ▁am ino ▁ac ids . ▁Near - complete ▁prote ins ▁are ▁also ▁found ▁in ▁some ▁plant ▁sources ▁such ▁as ▁qu ino a . ▁ ▁The ▁net ▁protein ▁util ization ▁is ▁prof ound