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Metabolic cost of growth in very low-birth-weight infants
Insights
Energy expenditure in very low-birth-weight infants increases with growth, with a metabolic cost of approximately 2.3 kJ/g weight gain. Macronutrient oxidation shifts from carbohydrates to lipids during the first six weeks of life.
Area of Science:
- Neonatal physiology
- Pediatric nutrition
- Metabolic research
Background:
- Very low-birth-weight infants have unique metabolic demands.
- Understanding energy expenditure is crucial for optimizing growth and development in preterm infants.
Purpose of the Study:
- To quantify energy expenditure and its relationship with weight gain in very low-birth-weight infants.
- To determine the metabolic cost of growth.
- To analyze substrate oxidation patterns in early neonatal life.
Main Methods:
- Conducted 48 energy expenditure measurements in 15 very low-birth-weight infants over the first 6 weeks of life.
- Monitored birth weight, gestational age, and weight gain.
- Analyzed substrate oxidation (carbohydrate, lipid, protein) as a percentage of total energy expenditure.
Main Results:
- Mean energy expenditure increased from 170 kJ/kg/day in week 1 to 252 kJ/kg/day in week 6.
- Significant positive correlations were found between weight gain and energy expenditure (r=0.58) and net weight gain and net energy expenditure (r=0.80).
- The metabolic cost of growth was estimated at approximately 2.3 kJ/g of weight gain. Carbohydrate oxidation decreased from 80% to 65%, while lipid oxidation increased from 14% to 30% over the study period.
Conclusions:
- Energy expenditure is closely linked to growth in very low-birth-weight infants.
- The metabolic cost of growth is quantifiable and provides insight into nutritional requirements.
- Substrate utilization shifts towards lipids as infants mature, reflecting changing metabolic adaptations.
Abstract:
Forty-eight measurements of energy expenditure were performed in 15 very low-birth-weight infants during the first 6 wk of life. Their mean birth weight and gestation age was 1223 g and 31 wk respectively. Their mean weight gain was 11.2 g/kg . d (range: -6.6 to +15.9 g/kg . d.). The mean energy expenditure increased from 170 kJ/kg . d (wk 1) to 252 kJ/kg . d (wk 6). There was a significant relationship between weight gain and energy expenditure (r = 0.58, P less than 0.001) and also between the net increase in body weight gain and the net increase in energy expenditure (r = 0.80, P less than 0.001). From the slopes of these regression lines, the metabolic cost of growth was found to be approximately 2.3 kJ/g of weight gain. Carbohydrate oxidation represented 80% of energy expenditure at the second wk and decreased to 65% the 6th wk, whereas lipid oxidation during the same period increased from 14 to 30% and the relative protein oxidation remained unchanged, covering 5-6% of the energy expended.