Cleanliness causing obesity?

A story making the rounds of the popular media is that a new study has found an association between household use of disinfectants and childhood fatness. (1)

These researchers from the University of Alberta reported in the Canadian Medical Association Journal (CMAJ) that they found a linear association between the amount of use of household disinfectants and excess weight in 3-year-old toddlers. They followed 757 infants and asked their mothers how often they cleaned with disinfectants at home. They also asked about “eco-friendly” household cleaners that presumably kill fewer germs and that was not associated with more fatness of their babies. They also found a certain bacteria, Lachnospiraceae, that was more abundant in the stools of the babies in the disinfectant exposed houses and in the bigger rounder babies. There were also lower populations of other bacteria types. These bacterial profiles however did not seem to be the reason that eco-friendly exposed babies were not as often obese. So the specific bacteria profile of the cause of this association, if indeed there is a causal connection, could not be conclusively determined. Remember association is not causation. The CMAJ started the media hype themselves with a press release. (2) But this observational study adds to the growing evidence that the germs who live in us and around us may be an important part of the story of the obesity epidemic. For example, another recent study found by collecting gut and oral samples of bacteria of 226 two-year-old children by swabbing their mouths and taking stool samples that those children with rapid infant weight gain – a growth pattern which is a key indicator of whether a baby will become obese – were found to have a less diverse range of microbes in their mouths. (4)

There’s a thing called the hygiene hypothesis that uses the observation that kids who live on farms or have lots of pets in the house seem to have less asthma and allergies to hypothesize that living with fewer germs, as our modern society has embraced, may be why we are having more asthma and allergies. Maybe the epidemic of obesity could also explained by a hygiene hypothesis. Maybe we need to get dirtier.

1. Tun MH et al. Postnatal exposure to household disinfectants, infant gut microbiota and subsequent risk of overweight in children. CMAJ September 17, 2018 190 (37) E1097-E1107; DOI:



4. Craig SJ et al. Child Weight Gain Trajectories Linked To Oral Microbiota Composition. Scientific Reports, volume 8, Article number: 14030 (2018)