The use of antibiotics — crucial as they are — in our earliest years of life has increasingly been suspected of fueling later health problems, particularly obesity. Now, a new study published Tuesday in The Lancet Diabetes & Endocrinology suggests that it’s actually childhood infections that may be to blame.

Researchers at California-based Kaiser Permanente, the country’s largest managed healthcare company, studied the electronic health records of more than 200,000 children born between 1997 to 2013. They specifically looked at children who came down with bacterial infections in the first year of life but avoided antibiotics and compared their risk of developing later obesity to children with no documented infections. The former group of children had a 25 percent increased risk on average, they found, while more infections predicted a greater risk. Conversely, there was no difference in risk between children who took antibiotics in the first year of life and those who went untreated, further supporting their findings.

"In previous studies, antibiotics used to treat infant infections have been associated with weight gain. However, we separated the two factors and found that antibiotics do not, themselves, appear to be associated with childhood obesity," said lead author Dr. De-Kun Li, a reproductive and perinatal epidemiologist at Kaiser Permanente’s research division, in a statement.

Whichever is the real culprit, neither infections nor antibiotics seem to directly cause our bodies to balloon up. Rather, scientists theorize it’s the effect either has on our microbiome — the vast community of generally harmless or even beneficial microorganisms that live in and on us, particularly in our guts — that can trigger weight gain.

In exchange for a comfy home, gut bacteria typically help our body function in any number of ways, including digestion. When this delicate balance is disturbed, however, things can go awry. In particular, it might wreak havoc with our metabolism or hormone production, making it easier to become fat or adopt an unhealthy appetite. It should be noted, though, that not all research supports this theory, and the exact role of the microbiome in obesity is still being hotly debated.

Regardless, Li’s team hopes their findings bring us one step closer to settling these vital questions.

"Our study is one of the largest analyses of the interplay among infections, antibiotic use and childhood obesity, and adds important evidence to a small but growing body of research on how the microbiome, or gut bacteria, may be affecting children's development," said Li.

Source: Li, et al. The Lancet Diabetes & Endocrinology. 2016.