Increased BMI after early antibiotics in life?

http://www.nature.com/ijo/journal/v38/n8/pubmed/ijo2013218a.html

http://www.cell.com/cell/pdf/S0092-8674(14)00821-6.pdf

It seems that it is a true effect of gut flora modifications and not of ATB per se.

Acquisition of the intestinal microbiota begins at birth, and a stable microbial community develops from a succession of key organisms. Disruption of the microbiota during maturation by low-dose antibiotic exposure can alter host metabolism and adiposity. We now show that low-dose penicillin (LDP), delivered from birth, induces metabolic alterations and affects ileal expression of genes involved in immunity. LDP that is limited to early life transiently perturbs the microbiota, which is sufficient to induce sustained effects on body composition, indicating that microbiota interactions in infancy may be critical determinants of long-term host metabolic effects. In addition, LDP enhances the effect of high-fat diet induced obesity. The growth promotion phenotype is transferrable to germ-free hosts by LDP-selected microbiota, showing that the altered microbiota, not antibiotics per se, play a causal role. These studies characterize important variables in early-life microbe-host metabolic interaction and identify several taxa consistently linked with metabolic alterations.

"Low-dose penicillin suppressed early-life Lactobacillus, Allobaculum, Rikenellaceae, andCandidatus Arthromitus. This finding suggests a protective role for these organisms in the modulation of host metabolism."

"All microbiota members do not equally impact the host; prior studies indicate that these four organisms have either metabolic and/or immunologic interactions which may contribute to the observed protection from weight gain in the control animals," 

http://www.medpagetoday.com/Endocrinology/GeneralEndocrinology/47252?