You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Outcome", "Participant", "Intervention"].

Please return the output as a JSON object of the format: {"Participant" : ["patients with COPD", ...], "Intervention" : ["Atenolol", ...], "Outcome" : ["blood pressure", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Nutrient retention in preterm infants fed standard infant formulas . Our purpose was to compare nitrogen , mineral , and zinc balance in preterm infants fed standard infant formulas , Similac With Iron and Similac With Whey + Iron . Nitrogen and magnesium balances were similar during both feeds , and met estimated fetal requirements . Infants absorbed and retained ( milligrams per kilogram per day ) more calcium , phosphorus , and zinc when fed Similac With Iron . However , retention of calcium , phosphorus ( both formulas ) , and zinc ( Similac With Whey + Iron ) was inadequate to meet estimated fetal requirements . These findings are important in the rapidly growing preterm infant , who is already at risk for the development of rickets and zinc deficiency and may be fed either formula on discharge from the newborn nursery .
{"Intervention": ["Similac With Iron", "standard infant formulas", "Similac With Iron and Similac With Whey + Iron"], "Outcome": ["calcium , phosphorus , and zinc", "Nitrogen and magnesium balances", "compare nitrogen , mineral , and zinc balance", "retention of calcium , phosphorus ( both formulas ) , and zinc"], "Participant": ["preterm", "preterm infant"]}