Australasian Science: Australia's authority on science since 1938

Fatter Babies Are Smarter

By Stephen Luntz

Parents worrying that early weight gain may be a sign of subsequent obesity might be reassured to know that fast-growing offspring are also more likely to have the brains to take on life’s challenges, poor health included.

Dr Lisa Smithers of the University of Adelaide’s School of Population Health has reported in the journal Pediatrics that children in the top quartile of weight gain over the first 4 weeks of life had IQs 1.5 points higher by the age of 6 than those in the bottom quartile. The study was done on 13,800 children born full-term and with normal birth weight.

The IQ difference is small compared with the variation in weight gain – the top quartile gained 40% of birth weight on average, while the bottom group gained just 15%. The group is too large for the effect to be caused by children with developmental delays or feeding problems.

“Those children who gained the most weight scored especially high on verbal IQ at age 6,” Smithers says. “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.”

Smithers says the data her group had could not distinguish whether better nutrition drove both gains in intelligence and weight, or whether genetic factors were involved. She did show that the children whose heads grew the fastest ended up with the highest intelligence. “Head circumference is an indicator of brain volume, so a greater increase in head circumference in a newborn baby suggests more rapid brain growth,” she says.

Early weight gain has been associated with obesity and high blood pressure later in life, but Smithers says: “We’re balancing that argument, showing that while it can be problematic it is good for brains”.