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Luís Pereira-da-Silva 1-3

1 - Medicine of Woman, Childhood and Adolescence, NOVA Medical School, Universidade NOVA de Lisboa;
2 - NICU, Hospital Dona Estefânia, Centro Hospitalar de Lisboa Central;
3 - Dietetics and Nutrition, Lisbon School of Health Technology, Lisbon Polytechnic Institute. Lisbon, Portugal

- 8th International Congress of the Union of European Neonatal and Perinatal Society (UENPS) Bucareste, Roménia, 05/10/2018 (Mesa redonda)

Proteins are transformed into amino acids, carbohydrates in monosaccharides, and lipids in glycerol and fatty acids. For terminal oxidation of these macronutrients Acetil-CoA is a masterpiece linking the three pathways - deamination, glycolysis, and beta-oxidation. In addition to produce energy (ATP) through oxidation, sufficient intake is necessary for anabolism and synthesis of glycogen, RNA and DNA, phospholipids, triglycerides, and substrates for amino acids synthesis.
Several hormones and peptides participate in the balance between energy intake and energy expenditure: the anabolic hormones insulin and IGF-1; their antagonists glucagon and catecholamines; hypophysis peptides participating in central regulation, such as the neuropeptide Y and agouti-related peptide; and peptides regulating the peripheral signaling, such as adiponectin, leptin, and ghrelin.
Infants need energy to support the basal metabolic rate (BMR), growth, physical activity, and thermic effect of food. In clinical setting, indirect calorimetry is the most feasible method to measure energy expenditure, providing measurements of resting energy expenditure (REE) and respiratory quotient (RQ). Several factors affect REE measurement in infants, particularly in preterm infants. The RQ provides an indication of the macronutrient that is preferentially oxidized; a value <0.75 suggests underfeeding and preferential use of fatty acids and a value >1.0 suggests overfeeding, preferential use of carbohydrates, and lipogenesis.
Complementary assessment of body composition can contribute to interpret indirect calorimetry measurements and guide the nutrition support. Air displacement plethysmography is an example of a convenient method for body composition assessment, since it is non-invasive, fast, and allows movements. As a bi-compartmental method, it provides measurements of fat mass (FM) and fat-free mass (FFM); from these, it calculates automatically the %FM, a measure of adiposity.
Energy expenditure is an expression of metabolically active tissue that is included in FFM (organs and muscle), but it is not an expression of FM. Therefore, it is more accurate expressing the REE as Kcal/ Kg FFM than as Kcal/ Kg body weight. When indirect calorimetry (REE and RQ) is combined with body composition assessment (adiposity), a better insight on the effects of amount and proportion of macronutrients on the nutritional status are provided.

Palavras Chave: Body composition; Neonate; Indirect calorimetry; Metabolism; Nutrition;