Objective: The objective of the present research is to compare the nutritional status, weight gain, length of hospital stay, and development of some complications in very low birth-weight (VLBW) infants who received and did not receive olive oil supplementation enterally.

It is known that nutrition of very low birth-weight (VLBW, <1500 g) neonates is as crucial as the treatments they receive in the neonatal intensive care unit to prevent problems that may develop in long-term follow-ups and increase their quality of life. VLBW neonates need parenteral nutrition as an energy source to ensure optimal growth, and lipid emulsion represents an indispensable part of total parenteral nutrition [1]. VLBW neonates with an underdeveloped immune system and antioxidant defense due to preterm birth are vulnerable to oxidative stress, which takes an important part in the development of diseases, e.g., chronic lung disease (CLD), retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC), and intraventricular hemorrhage, which may increase the risk of morbidity [2,3]. Prematurity also causes the insufficient supply of long-chain polyunsaturated fatty acids (LC-PUFAs), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), most of which are transferred to the fetus during the third trimester of pregnancy [4]. These LC-PUFAs are essential and important for visual and cognitive development and reducing thrombotic and inflammatory responses [5].

The continuation of intrauterine growth and development in the extrauterine period without interruption may be possible by providing parenteral and enteral nutrition support in the early period and maintaining this support uninterruptedly [6]. Studies have proved that breast milk is the gold standard for feeding neonates under all conditions. However, despite its enormous benefits, unsupplemented breast milk can be nutritionally inadequate for preterm infants for various reasons. First, breast milk does not have a sufficient amount of some nutrients required to ensure the rapid growth of preterm infants [7], and nutrient concentrations can fluctuate over time. Of these, fat is one of the most variable nutrients [8]. Studies have demonstrated that there are temporal and interindividual differences according to the mother's diet, time of day, and breastfeeding duration (e.g., a richer fat content of hindmilk) [9,10]. When breast milk alone cannot meet these needs, it is recommended that special nutritional supplements in the form of powder or liquid be added to breast milk and given to the infant [11].

Due to its content, olive oil has antioxidant, cell regenerative, and anti-carcinogenic properties that help digestion [12]. There are clear pieces of evidence indicating that parenterally administered oil emulsions can be well tolerated by VLBW and even extremely low birth-weight infants from the first day and even from the first 1-2 hours of life [13-15]. The objective of the current research was to compare the nutritional status, weight gain, length of hospital stay, and the development of some complications (BPD, ROP, GIS intolerance, etc.) in preterm neonates who received and did not receive olive oil enterally for calorie support.

Inclusion Criteria:

Preterm infants;

• Between the 28th-36th weeks of gestation
• Weighing over 1000 g during the study
• Stable vital signs
• Being able to consume 75% of the total protein and energy through an orogastric tube
• Fed with breast milk and breast milk fortifiers

Exclusion Criteria:

Presence of;

• Necrotizing enterocolitis
• Pneumothorax
• Skull fracture
• Major congenital anomalies
• Suspected or diagnosis of metabolic disease
• History of pathological jaundice (jaundice developing in the first 24 hours),
• History of surgery that might affect the residual
• Using muscle relaxants, analgesics, sedative or inotropic drugs

Double blinding was used in the study. For this purpose, the participants were not specified in which group they belonged to the research. Therefore, a separate informed consent form was prepared for each group. In order to avoid bias in the analysis of the research data, statistician blinding was also applied. While coding the research data, the research groups were coded as A and B, and the statistician was prevented from knowing which letter represented which group.