Scholars have linked higher IQ at early school age to weight gain and increased head size in the first month of a baby's life.

The results were determined - as apparently intelligence is - by analyzing data from more than 13,800 children who were born full-term.  

The findings in Pediatrics were that babies who put on 40% of their birth weight in the first four weeks had an IQ 1.5 points higher by the time they were six years of age, compared with babies who only put on 15% of their birth weight. Those with the biggest growth in head circumference also had the highest IQs.

 Thus another post hoc, ergo propter hoc study was born.

"Head circumference is an indicator of brain volume, so a greater increase in head circumference in a newborn baby suggests more rapid brain growth," says the lead author of the paper, Dr Lisa Smithers, a philosopher and nutritionists from the University of Adelaide's School of Population Health. "Overall, newborn children who grew faster in the first four weeks had higher IQ scores later in life.

"Those children who gained the most weight scored especially high on verbal IQ at age 6. This may be because the neural structures for verbal IQ develop earlier in life, which means the rapid weight gain during that neonatal period could be having a direct cognitive benefit for the child."

Various papers have found an association between early postnatal diet and IQ, but this is the first to claim IQ benefits from rapid weight gain in the first month of life for healthy newborn babies.

Smithers says the study further highlights the need for successful feeding of newborn babies. "We know that many mothers have difficulty establishing breastfeeding in the first weeks of their baby's life. The findings of our study suggest that if infants are having feeding problems, there needs to be early intervention in the management of that feeding."