High versus low medium chain triglyceride content of formula for promoting short-term growth of preterm infants

Most very low birth weight infants grow slowly in hospital after delivery. This causes concern because poor growth can link to neurodevelopmental impairments including decreased cognitive ability (IQ), speech, and reading skills when school-aged. Fat provides about half of the energy source (calories) in human breast milk, mostly as long-chain fatty acid triglycerides (LCT). As a way of improving growth, fat can be added to formula used to feed preterm infants. Fats in formula can contain triglycerides with long chain fatty acids or shorter medium chain fatty acids (MCT). MCT are more easily absorbed by the newborn infant with an immature digestive system. LCT are still important in the development of visual acuity and development of cell membranes and the brain. The review authors searched the medical literature. They found eight small controlled randomized studies looking at short-term growth (weight, length, and head circumference gain) in preterm infants fed with varying amounts of medium chain fats. The pattern of growth in infants fed exclusively with high MCT or low MCT formula for at least one week did not differ (five studies with 182 infants). These infants had a mean gestational age between 29 and 32 weeks, mean birth weights between 1 kg and 1.5 kg, and were aged one to six weeks. One study found a high degree of gastrointestinal intolerance with high MCT content and another did not. Development of necrotizing enterocolitis was not different. No studies addressed long-term growth or neurodevelopmental outcomes.

Authors' conclusions: 

There is no evidence of difference between MCT and LCT on short-term growth, gastrointestinal intolerance, or necrotizing enterocolitis. Therefore, neither formula type could be concluded to improve short-term growth or have less adverse effects. Further studies are necessary because the results from the included eight studies are imprecise due to small numbers and do not address important long-term outcomes. Additional research should aim to clarify effects on formula tolerance and on long-term growth and neurodevelopmental outcomes, and include larger study populations to better evaluate effect on NEC incidence.

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Background: 

In-hospital growth of most very low birth weight infants remains below the 10th percentile of reference intrauterine growth curves (Ehrenkranz 1999). To improve growth, fat is added to preterm formula in the form of medium chain triglycerides (MCT) or long chain triglycerides (LCT). MCT are easily accessible to the preterm infant with an immature digestive system while LCT are beneficial for central nervous system development and visual function. Both have been incorporated into preterm formulas in varying amounts, but their effect on the preterm infant's short-term growth is unclear.

Objectives: 

To determine the effect of high MCT as opposed to low MCT (high LCT) formula on short-term growth rates in preterm formula fed infants.

Search strategy: 

MEDLINE (1966 - 2007), CINAHL (1982 - 2007), Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2007), conference proceedings, and reference lists of articles were searched.

Selection criteria: 

All randomized trials comparing the effects of exclusive feeding of high versus low MCT formula (for a minimum of one week) on the short-term growth of healthy, preterm infants.

Data collection and analysis: 

The reviewers assessed each study's quality and extracted data on growth parameters as well as adverse effects from included studies. All data used in analysis were continuous; therefore, weighted mean differences with 95% confidence intervals were reported.

Main results: 

Eight randomized trials studying a total of 182 infants were included.

There was no evidence of difference in short-term growth parameters when high and low MCT formulas were compared. The meta-analysis of weight gain based on five studies yielded a WMD of -0.35 g/kg/d (95% CI -1.44, 0.74). Similarly, meta-analysis of weight gain in g/d based on two studies showed no evidence of difference (WMD 2.09 g/d, 95% CI -1.46, 5.64). Length gain, based on five studies, showed a non-significant WMD of 0.14 cm/wk (95% CI -0.04, 0.31). Head circumference gain, based on data from five studies, showed a non-significant WMD -0.03 cm/wk (95% CI -0.15, 0.08). Only one study reported a statistically non-significant skin fold thickness gain, with a mean difference -0.15 mm/wk (95% CI -0.41, 0.11).

Subgroup analyses according to % MCT in the high MCT formula, by 10% intervals showed no evidence of effect of high MCT on short-term weight gain within any subgroup.

There are conflicting data (two studies) as to formula tolerance.

There is no evidence of effect on incidence of necrotizing enterocolitis (NEC), based on small numbers in two trials.

No studies were located addressing long-term growth parameters or neurodevelopmental outcomes.

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