Do antibiotics make you fat?

I've blobbed about the spendthrift attitude we've had to antibiotics but mainly in the the context of wasting a precious resource by inappropriate widespread over-use: to promote growth in pigs and chickens (it works!), to deal with viral infections (it doesn't work) and to treat manifold childhood infections which previous generations used to just suck-it-up (it works as a sledge-hammer cracks a nut). By using the available spectrum of antibiotics we are robbing our grandchildren of life-saving treatments as all infectious microbes become resistant.

But until I read a piece in my Nature back-log (whoop paywall alert! try Wired for similar) by Maryn McKenna.  The Nature article is couched as a review of a book Missing microbes: how the overuse of antibiotics is fuelling out modern plagues by Martin J Blaser, but it serves as a vehicle for McKenna's long held views on the matter. She herself has written a book called Superbug; I wonder if Blaser has reviewed it somewhere, they are both on the same page. When I wrote about C.diff. a couple of months ago, I mentioned that you often get sick of C.diff after a course of antibiotics often in hospital. That's clearly a pretty direct downside for clearing up your ear-ache, or in fairness, your life-threatening septicemia. And having read my trib to Warren and Marshall you'd be tempted to agree that Helicobacter pylori is a pretty convincing black-hat for causing stomach ulcers (and its cancerous sequelae) and should be curbed if not killed as soon as detected.  BUT, there is evidence that the presence of H.pylori is associated with reduced incidence of asthma, allergy and debilitating reflux disease.  H.pylori is readily treatable in most cases with a short course of antibiotics and over the antibiotic decades the incidence of this microbe has decreased - even when the medicine is applied for that ear-ache or cold rather than to kill Helicobacter. But get this; over the same period the rate of esophageal cancer has gone up.  It's a complex ecosystem down there, we know very little about it and we trick about with it at our peril.

We now know that obese mice and humans have different intestinal microbiota. For just one example,  Ridaura et al. have found Little and Large twins (thus genetically and environmentally very close) and made fecal transplants from each into batches of identical germ-free mice. The mice receiving a dose of fat-poo promptly inflated.  It's all (or partly) in the Bacteroidetes, chaps.  When we encourage growth in farm-animals it is referred to as 'fattening up', despite the fact that we-the-eaters in the West don't really like fatty meat.  The number of people who cut the fat off their chops and leave it on the side of their plate shocks and surprises me.  McKenna and Blaser and others have taken this metaphor literally and hypothesise that profligate use of antibiotics (the average Western child will have 20 prescribed doses before they reach voting age) is the cause of the epidemic of obesity. You don't kill every microbe with, say, teramycin but you do cry havoc and let slip the dogs of lard on a delicately balanced ecosystem down there. I think it's a more fruitful avenue for research than the idea that Ikea is responsible because it supplies all the world's sofas.