Studies in mice have shown that those exposed to antibiotics had higher total fat mass/body fat without additional weight gain.  In addition, a study of infants indicated that early antibiotic exposure may also be a risk factor for increased weight gain.

From Gastroenterology and Endoscopy News, June 2013: http://www.gastroendonews.com/ViewArticle.aspx?d=In%2bthe%2bNews&d_id=187&i=June+2013&i_id=961&a_id=23385

“Ilseung Cho, MD, MS, assistant professor of medicine, associate program director, Division of Gastroenterology, NYU School of Medicine, New York City, said, “Many investigators who study the gut microbiome think that it plays a significant role in the obesity epidemic in concert with a variety of other risk factors, such as poor dietary habits or a sedentary lifestyle. The microbiome plays a key role in a variety of host functions, including immune response and metabolism.”

Effect of Antibiotics

Dr. Cho was the lead investigator on a study in mice that demonstrated that antibiotics altered the gut microbiome in such a way as to affect murine metabolism and cause increased adiposity (Cho I et al. Nature 2012;488:621-626). Investigators administered subtherapeutic doses of penicillin, vancomycin, penicillin plus vancomycin, or chlortetracycline to young mice in their drinking water; a control group received no antibiotics. There were 10 mice per group. After an exposure period of seven weeks, the mice did not differ significantly in weight gain, but all four antibiotic-exposed groups had significantly higher total fat mass (P<0.05) compared with controls, and most (with the exception of the vancomycin group) had higher percent body fat (P<0.05).

The antibiotic exposure caused taxonomic changes in the microbiome, with the ratio of the phylum firmicutes to the phylum Bacteroidetes elevated in the antibiotic-exposed mice. Additionally, there was evidence of metabolic changes. For example, glucose-dependent insulinotropic polypeptide was elevated in the antibiotic-exposed mice, and glucose tolerance tests showed a trend toward hyperglycemia.

“In our paper, we describe a model where, by exposing mice to low-dose antibiotics, we were able to alter their microbiome,” said Dr. Cho. “Altering their microbiome resulted in a metabolic change in the mice that led to increased adiposity. The paper demonstrates that we are able to affect host metabolism by altering the gut microbiome.”

Around the same time that Dr. Cho and his colleagues published their results, a related paper about antibiotic exposure in infants was published in advance online (Trasande L et al. Int J Obes 2012 Aug 21 [Epub ahead of print]).

“Knowledge of the importance of the microbiome in human development raises new issues about antibiotic use in children, as such exposures may disrupt the microbial ecology,” the authors wrote.

In the longitudinal birth cohort study, investigators analyzed data from 11,532 children. Exposure to antibiotics during three early-life time periods (ages <6 months, 6-14 months, 15-23 months) was assessed by questionnaires that had been administered to the parents near the measured time interval. Body mass indices (BMIs) were examined at five time points (six weeks, 10 months, 20 months, 38 months and seven years).

Exposure to antibiotics during the period before 6 months of age—and only during that period, of those studied—was consistently associated with increases in BMI from 10 to 38 months. At 38 months, children who had been exposed to antibiotics before 6 months had significantly higher standardized BMI scores (P=0.009) and were 22% more likely to be overweight than children who had not been exposed (P=0.029). The researchers controlled for known social and behavioral risk factors for obesity.”

Related blog links:

• Microbial transfer for metabolic syndrome? | gutsandgrowth
• Microbiome and the risk of Kwashiokor | gutsandgrowth