Livestock drugs 'link' to obesity epidemic
Farmers may have fuelled the obesity epidemic by using antibiotics to fatten up livestock, a new study suggests.
This is based on a study published in Nature. I haven't read it because it's behind a paywall and I don't really care, but the salient points seem to as follows...
For decades since the 1950s, farmers have used low non-therapeutic doses of antibiotics to increase the body weight of cows, sheep, pigs and chickens.
They have indeed, although the EU banned the practice in 2006.
"The rise of obesity around the world is coincident with widespread antibiotic use, and our studies provide an experimental linkage," said lead researcher Professor Martin Blaser, from New York University School of Medicine in the US.
Hmm. Not the most compelling start. Correlation/causation and all that. Quite a lot of things coincided with the rise of obesity. Falling smoking rates and rising alcohol consumption fit pretty well, to take just two examples off the top of my head.
"It is possible that early exposure to antibiotics primes children for obesity later in life."
Anything's possible, Professor. So what is this research of which you speak?
The scientists administered common antibiotics such as penicillin and vancomycin to weaning mice at similar doses as those used in agriculture.
The treatment altered the composition of gut bacteria in the mice which in turn led to metabolic changes, such as increased production of fatty acids. After about six weeks the mice had gained about 10% to 15% more fat mass than untreated mice.
That's what one would expect to happen since the antibiotics are known to produce weight gain. What happened next? Were human subjects given a diet of these mice and carefully monitored for years to track changes in their body mass index?
They were not. It seems that fattening up the mice was the start and end of the experiment. So what does that tell us?
"By using antibiotics, we found we can actually manipulate the population of bacteria and alter how they metabolise certain nutrients," said co-author Dr Ilseung Cho, also from New York University.
Although it was known that antibiotics could fatten up animals, previously the mechanism involved was unclear.
Well, that's great and all, but identifying the biological mechanism behind a known effect is a little different from saying that antibiotics fed to livestock caused an international epidemic of human obesity.
All that's been shown here is that if you give certain drugs—which we know make large animals fatter—to small animals, then those animals will also put on weight. From this, you might speculate that if the same drugs were given to humans in equivalent quantities, they would also put on weight. That would depend on the doses, the type of antibiotics used and the length of time they were used for. It also relies on the assumption that humans will react to the drug in the same way as cows and mice.
If you were a reckless person—such as a Telegraph or Independent journalist—you could go out on a limb and imagine that eating slices of these animals might involve trace chemicals from the antibiotics entering the body and somehow having the same effect on weight gain, but that would be to indulge in wild speculation that is not supported by the study.
To repeat, I have not read the study, although this video of the author summarising its findings suggests that my description is fair. In it, he raises the possibility of antibiotics used in childhood being a possible explanation for childhood obesity. Essentially, he thinks that bacteria in the gut help prevent weight gain. That is a very tentative theory (although that doesn't stop the ever-irresponsible Daily Mail calling it "another very good reason for avoiding antibiotics") but it is not incompatible with the available evidence. What he does not do is suggest that there is some "passive" effect flowing from animals to humans. That appears to be an invention of the media and it should not be taken seriously.
Besides, everybody knows that obesity is caused by advertising. Didn't this guy get the memo?
