The dog's blog no. 14: Obesity and antibiotic use

Obesity and antibiotic use

There’s a growing interest in the relationship between the microorganisms (mainly bacteria) that inhabit the intestines, and health – in humans and animals. One aspect of this is the relationship between this intestinal flora (or microbiota) and body weight. 

Intestinal flora has many functions including metabolic actions and it seems to play a role in growth, energy metabolism and fat accumulation. The flora is formed at birth and evolves in the first years of life. It is affected by various factors including diet, digestive tract secretions and antibiotic treatment. Antibiotics affect the quantity and diversity of intestinal flora for days or weeks after treatment. An independent French organisation that reviews medicines (la revue Prescrire) recently looked at the published evidence examining a link between antibiotic use in the first years of life and the risk of obesity in later life in humans.

It found that the result of several studies, involving about 300,000 children, showed a statistically significant increase in the risk of obesity after at least one antibiotic course before the age of 2 years. The risk appears to increase proportionately with the number of antibiotic courses. Although the type of study that provided these results is not usually considered to be strong evidence (cohort studies), the results from the individual studies are generally consistent.  

These results are also in keeping with what is known about the function of the intestinal flora and with the results of animal experiments. In mice, the intestinal flora has been shown to play a role in growth, energy metabolism and fat accumulation; and transfer of intestinal flora from obese to non-obese mice causes weight gain due to an increase in fat mass. And tt has long been known that antibiotic use promotes weight gain in farm animals.

How relevant all this is to companion animals is not clear. But it is another good reason not to trivialise the use of antibiotics or prescribe them automatically without careful consideration, on a case-by case basis, with judgement of the harm-benefit balance. 


Antibiotics during infancy: a risk factor for obesity? Rev Prescrire 2017; 37 (410): 912-915

Our purpose... to provide vets with high-quality, independent, comparative information they won't find elsewhere. However, it costs money to do this. We are a small, self-funded company of two dedicated full-timers (Andrea Tarr and Carl Russell), together with a team of regular and occasional writers, editors, reviewers, verifiers and proofreaders, who support our rigorous editorial process. We are absolutely passionate about independent information and empowering vets by giving them what they need to make rational decisions about medicines. Buying a subscription supports independent information you can trust. If you are getting free information ask yourself who is paying for it and why!