TORONTO - It's a natural substance that has such a high "phew" factor that most people hold their noses and turn away. But for a group of researchers from Stanford University, getting the inside scoop on baby poop was something to relish.

The team of researchers spent more than a year analyzing diaper dump to see what kind of microbes take up residence in a baby's gut after birth.

At the time of birth, an infant's intestinal system is completely sterile - the bacteria that will help the system separate nutrients and waste products have yet to colonize the gut.

"It's an amazing thing trying to figure out how we go from a completely sterile gut to having a microbial ecosystem that will be with us for the rest of our lives," senior author Dr. Patrick Brown, a professor of biochemistry at Stanford, said in a statement.

"What could be more fundamental than that?"

To get the microbial lowdown on baby caca, the researchers asked the parents of 14 healthy, full-term babies - including one set of fraternal twins - to take periodic samples from their child's diapers from birth to just past their first birthday. An average of 26 samples were taken per youngster over the year.

The scientists then analyzed the bowel movement samples, pinpointing genetic markers for thousands of possible bacteria known to inhabit the human gut.

What they found is that the gut of a baby is a rapidly evolving environment, but each baby had vastly different microbes colonizing their intestinal tracts as they matured.

Within days of an infant's delivery, microbes take up residence in the gut and create a population that soon outnumbers the baby's own cells tenfold, a ratio that continues throughout life.

Lead author Chana Palmer, a PhD graduate in genetics who worked in Brown's lab during the study, said the results set a kind of baseline for what constitutes a "healthy" baby, at least bowel-wise - and it shows that "the definition of a healthy baby is pretty broad."

"Babies had things (microbes) that adults had, but we also found a couple of other things that maybe were not so common to find in adults, in at least as high numbers," Palmer said in an interview from Stanford, Calif.

"Things were relatively unstable (in the early days after birth) and then you'd have a rapid reorganization of the (microbial) population and then it would stabilize again."

But by the end of the first year of life, she said that while each baby's overall intestinal ecology remained unique, it contained colonies of microbes similar to those found in the intestines of mature adults.

Those swarms of microbes in the intestines are vital to health: not only do they help break down nutrients from food and separate out waste products, they also help the immune system develop and protect the gut from being colonized by more harmful bacteria.

The Stanford team's research, published Tuesday in the July issue of the Public Library of Science-Biology, is the most extensive survey yet of how microbes establish flourishing communities in what began as a sterile environment.

Palmer said bacteria enter the baby's digestive tract through food and environmental contact, but those can differ from baby to baby.

All the babies in the study were breastfed, so it's not known if bottle-fed babies would harbour different bacteria, said Palmer, noting that comparing the two types of feeding and their effects on gut flora is one area of future research.

Researchers could also investigate microbial differences in the feces of infants who were born full-term versus prematurely and those delivered by C-section versus vaginally, she said.

"The twins were the only babies born by a planned caesarean section, so the implication of that is that the babies never travelled through the mother's vaginal canal and were exposed to microbes that way."