Giving formula-fed infants a higher protein diet such as pureed meat can improve their early length growth, new research suggests. The findings, published in the American Journal of Clinical Nutrition, suggest that meat, such as pork, can be an important source of much-needed protein in an infant’s diet during the transition to solid foods.

“Meat, such as pork, provides important micronutrients, is an excellent source of protein and can be an important complementary food for infants who are ready for solid foods,” said lead study author Minghua Tang, Assistant Professor of Pediatrics at University of Colorado Denver-Anschutz, in the US.

“Our research suggests introducing higher amounts of protein and introducing meat, such as pork, into the diet at five months could be potentially beneficial for linear growth (length gain),” Tang said.

In the study, a small group of healthy, formula-fed infants ate meat-based complementary foods, such as pureed ham and beef, or dairy-based complementary foods from ages five to 12 months old, increasing their protein intake from two grams of protein per kg each day before the study up to three grams per kg each day during the study period.

While the protein increased, both calories and fat intakes stayed the same between the meat and dairy groups, regardless of protein source.

The researchers found the pureed meats promoted a greater rate of growth — with length of nearly one inch greater compared to the dairy-fed group at 12 months of age, with no increase in risk of being overweight at the completion of the seven-month study.

The rate of weight gain in early infancy, specifically in the first year of life, has critical influences on the obesity trajectory in childhood that carries on to adulthood . Infant dietary intakes have a significant impact on infant growth and weight gain. Some observational studies showed a greater weight gain in formula-fed than breastfed infants. In one study, breastfed and formula-fed infants were followed over the first year of life , and the average weight of breastfed infants was significantly lower than that of formula-fed infants after 6 months of age.

Because formula (∼1.5 g/100 mL) has a higher content of protein than breast milk (∼0.9 g/100 mL) (6), the difference in protein intakes has been considered a potential key contributor to the greater weight gain in formula-fed infants. A proposed potential mechanism includes the stimulation of insulin-like growth factor I (IGF-I). The correlation between weight gain and protein intake has been reported in breastfed infants and a greater weight gain in formula fed compared with breast fed infants during the first year of life .

Recently, Koletzko et al  conducted a large, randomized, controlled trial to examine the protein quantity on infant growth by using an isocaloric infant formula with different cow milk–based protein contents and reported a dose-dependent correlation between protein and weight gain. In a subsample from the study, the high-protein group also showed higher fat mass and possibly higher adiposity .

The sum of these and other findings has led to recommendations to limit protein to <15% of energy during later infancy and the second year of life . Although dairy protein has been acknowledged to potentially pose more risk of excessive weight gain than meat protein is, recommendations have not distinguished between the protein source or between formula fed and breastfed infants.

Complementary foods refer to nutrient- and energy-containing solid or semisolid foods fed to infants in addition to human milk or formula and are typically introduced between 4–6 mo of life. The complementary feeding period includes the largest proportion of the 1000-d critical window and may, thus, be a potentially critical period to influence obesity risks.

The protein content of human milk gradually declines over the course of lactation in contrast to the higher and unchanging protein content of infant formula. For infants who are breastfed only (no formula), meats not only are a good source of high-quality protein but also provide highly bioavailable iron and zinc at a time when human milk alone no longer meets the needs of infants .

Very limited evidence is available to evaluate the effect of protein quantity specifically from complementary foods on the growth of breastfed infants. Thus, the purpose of this report was to examine the effect of a lower- compared with higher-protein complementary feeding regimen, with animal flesh being the primary protein source, on infant growth and metabolic profile in older breastfed-only infants.


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