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The effects of different energy sources (such as high-glucose or high-fat diet) on lung function in adults are variable; an increased fat intake alters diffusion capacity (gas exchange), whereas an increased glucose intake elevates carbon dioxide production. In either case, the body is able to control these variations by metabolic adaptation, that is, changes in breathing and digestion patterns may keep the body functioning smoothly. The effect of a high-lipid or high-glucose diet on respiratory gas exchange of newborn infants under resting conditions has not been established previously. Ten newborn infants (ages 5 to 21 days) were selected on the basis of (1) the ability to breathe on their own, (2) weight and gestational age match, and (3) surgical placement of a feeding tube for delivering parenteral nutrition. The experiment was set up so that each infant could serve as its own control subject, with two five-day feeding periods during which the same nitrogen and energy content was delivered within a different energy source; one energy source was low in fat and high in glucose (LF) and, conversely, the other was high in fat and low in glucose (HF). Blood samples were collected and measurements, using a gas monitor to determine oxygen consumption (VO2) and carbon dioxide production (VCO2), were taken on the last day of the feeding period as the first four days let the infant adjust to the different nutrition. There was no difference in oxygen consumption values computed from either energy source, but carbon dioxide production increased during LF feeding. However, another measurement, the transcutaneous partial pressure of carbon dioxide (tcPCO2), was not affected during LF, which means the body adjusted adequately for the increase in carbon dioxide. During HF, the tcPCO2 was lower, suggesting that the body did not compensate for the changes brought on by the high-fat diet. The plasma levels of prostaglandins and thromboxanes, substances that affect blood flow by controlling the dilation of blood vessels, were also unchanged after each feeding. Although both LF and HF diets produced unwanted metabolic effects in newborn infants, HF effects on respiratory gas exchange are not as easily compensated for as LF effects. The advantages of using fat, and not glucose, as the primary dietary energy source are not clear. (Consumer Summary produced by Reliance Medical Information, Inc.)

Newborns who receive intravenous (parenteral) feedings are often begun on preparations which provide caloric content mainly from sugar (glucose). The metabolic and clinical consequences of changing from infusions high in sugar to one high in fats were studied in 11 infants with a mean birth weight of around six pounds born at an average of 37 weeks of gestation. The infants were treated for an average of eight days in an environment with constant temperature. Body and environmental temperatures were recorded over four-hour periods, and urinary excretion was measured and analyzed over a 24-hour period. When the babies were switched from glucose to lipid feeding, there was a significant increase in body temperatures. Analysis of the 24-hour urine collection indicated that excretion of urinary nitrogen increased during the second day of treatment, when the high-fat regimen was initiated. A decrease in nitrogen retention during the high-fat feeding may have been due to a reduction in metabolically available energy. It seems that newborns can adjust to the change from high glucose to high fat diet, but it takes a few days to make this transition metabolically.