Lauren Raine noticed something that growth charts miss: an infant's weight tells only half the story. The assistant professor at Northeastern University's Interdisciplinary Health, Body Composition and Neuroscience Lab is investigating whether what that weight is made of—fat tissue or lean muscle and bone—predicts how well babies will think and move, findings that could reshape how pediatricians assess early development.
For decades, pediatricians have relied on WHO growth charts to track whether infants are developing normally, measuring weight, head circumference, and length. An infant who scores higher on these charts typically performs well on cognition and motor function tests. But Raine suspected the composition of that weight matters more than the weight itself. "Looking at weight and not body composition doesn't tell us the entire story," she said.
Body composition includes fat mass and lean mass—the bones, muscles, and organs that make up the rest. While doctors use body mass index to estimate body composition, BMI doesn't reveal what type of tissue is actually driving development. An average healthy adult carries about 21 percent fat mass and 79 percent lean mass, but infants experience dramatic shifts early in life: roughly 10 percent fat at two weeks old, rising to 30 percent by six months before gradually declining.
To test her hypothesis, Raine studied 40 healthy infants older than 32 weeks, measuring their body composition using specialized, noninvasive machines that calculate fat and lean mass in minutes. She then compared these measurements against results from the Bayley Scales of Infant and Toddler Development, the standard tool for assessing cognition—memory, processing, executive function, attention—and motor skills like rolling, walking, and hand-eye coordination. Her preliminary findings, presented to more than 150 people at Northeastern's Institute for Cognitive and Brain Health in November, suggested that infants with greater lean mass performed better on certain neurological development tests.
This matters because excess body fat has been linked to poor cognition in adults and increased symptoms of anxiety and depression in children. Charles Hillman, director of the Institute for Cognitive and Brain Health, notes that while fat tissue serves essential functions—storing energy, insulating the body, protecting organs—too much of it carries risks beyond physical health. Raine's earlier research with children aged 8 to 11 found that those with lower body fat and greater aerobic fitness showed fewer anxiety and depression symptoms.
The research is still in the data-collection phase, but the implications reach beyond the clinic. If body composition proves to be a better predictor of cognitive and motor development than traditional growth measures, pediatricians could use it as an early indicator of which infants might benefit from intervention. Raine is collaborating with Laurel Gabard-Durnam, a developmental cognitive neuroscientist, to deepen the investigation. What begins as careful measurement in infancy could ultimately influence how we understand—and support—human development from our first weeks of life.