Can the growing obesity epidemic be linked to over-prescribed antibiotics?
You don't have to look far to get a sense that many Americans are overweight and even obese. Just drop by a mall on any weekend or for a more personal view, a glance in the bathroom mirror might suffice. If you want more objective data: According to a 2012 report of the Centers for Disease Control and Prevention, about 69 percent of all adult Americans are overweight or heavier, and almost 36 percent are obese. Incredibly almost 17 percent of U.S. children and adolescents are obese as well.
At home it’s been decades in the making. According to one peer-reviewed paper published in the American Journal of Medicine in 2007, the "incidence rates of overweight increased 2-fold and that of obesity more than 3-fold over 5 decades" since the 1950s. What I bet most of you did not know is that concerns about a rising population of overly rotund Americans dates back to the 1950s*, as a Life magazine article from 1954 entitled "The Plague of Overweight" attests.
This and the fact that obesity rates are now sharply rising in developing economies has led many health experts to hypothesize that something about the modern western lifestyle is at the heart of the problem. An obvious culprit could be the relatively sedentary, exercise-poor lives we Westerners tend to live. Others have speculated that it is caused by the meat-rich, high-calorie, sugary, soft-drink laden, processed-food diets we eat. All reasonable candidates.
But perhaps there is another culprit to add to the mix -- antibiotics. It is not as far-fetched as you might think. How could this be? It starts with the microbiome.
Our Microbiome, Ourselves
We have already waxed poetic about the microbiome on TheGreenGrok:
"Who are we anyhow? A body; a brain, a heart, other organs. There's skin and bones. And there are thoughts; consciousness. Some might even say a soul. But it turns out that that's not all. Not by a long shot. We are also our microbiome- the trillions of microbes (affectionately referred to as bugs) that live in our gut, on our skin, and who knows where else. If you were to count cells in your body--you'd find that 90 percent of them belong to microbes rather than you; or at least what you think of as you. With respect to genes, the number of microbe genes in our body outnumber our "own" genes by a factor of 100.
And a good fraction of these bugs are not just squatters - taking up residence in our bodies and not paying rent. They're symbionts, carrying out critical functions for us like digesting our food, fending off infections, helping to build organs like your heart as well as possibly influencing our diet and behavior."
Microbiome Diversity and Obesity
A growing body of evidence suggests there is a link between the robustness of our microbiome and our health and more specifically with the state of our adipose or body fat. (See here, here, and here.)
This link was strengthened last week with the publication of two papers in Nature, one by Emmanuelle Le Chatelier of the French National Institute for Agricultural Research and colleagues and the other by Aureilie Cotillard of the French Institute of Health and Medical Research and colleagues.
A Paucity of Bacterial Diversity May Lead to a Paunch-ity
The key finding in both papers:
Individuals with less diverse populations of bacteria in their gut were more likely to be overweight or obese.
The Le Chatelier et al. paper was based on a study of almost 300 Danes. In addition to finding that obesity was correlated with a lack of bacterial diversity, they also found that those individuals with less bacterial diversity in their guts had more metabolic markers of related diseases like type 2 diabetes and heart disease. Cotillard and co-authors' results were from a dietary intervention study of 49 overweight and obese French. An interesting aspect of their findings was that dietary interventions were able to increase the genetic richness of gut bacteria for many of their subjects with low bacterial diversity.
Of course studies like these that show a correlation of one thing to another always raise the question of cause and effect. Is lack of gene richness from bacteria diversity in the gut causing obesity or does obesity lead to a lack of gene richness? Le Chatelier at al. argue for the former by noting that previous studies have shown that "the obese phenotype can be transmitted by gut microbiota transplantation in mice, indicating that gut microbial populations may have an active role in obesity pathogenesis."
Is There an Antibiotic Connection?
So what have we got? There's all these bacteria hanging out in our guts; and many of those guys are doing good things, keeping us healthy -- including, as these studies suggest, helping us keep the weight off. Now imagine what happens when we take antibiotics. Sure, the antibiotics kill some nasty bugs and that's what we want them to do, but they also kill some of the good guys as well. So it seems reasonable to speculate that taking antibiotics decreases the genetic diversity of our microbiome and maybe even makes us more susceptible to obesity.
Okay, I'd be the first to admit that I am going out on a bit of a limb here. The studies discussed above link a lack of bacterial diversity in the gut to obesity. Nothing specific about antibiotics. But there are other studies. For example in a paper published last year in Nature, the authors found that administering subtherapeutic doses of antibiotics to young mice increased their body fat. In another study investigators found that antibiotic exposure correlated with an increase in body fat for infants. (More info here.)
And perhaps it's just mere coincidence, but it is interesting to note that widespread antibiotic use began in the mid-1940s just a few years before Life magazine sounded the alarm about "The Plague of Overweight" in 1954.
Be Good To Your Bugs
Obesity or not, it is important to keep in mind that antibiotics can be lifesavers. If you're sick with a bacterial infection, taking an antibiotic may be the appropriate medication. But the problem is we take antibiotics when it isn’t necessary. How often have you heard of someone taking antibiotics for a cold -- a viral infection for which antibiotics are useless? One study from 2007 reported that more than 80 percent of patients diagnosed with acute sinusitis receive antibiotic prescriptions, even though sinusitis is often caused by a virus. (Read more here and here.)
It is estimated that Americans take more than two times the amount of antibiotics than necessary. And that does not include all the antibacterial stuff we buy in consumer products -- like triclosan in toothpaste and soaps.
The rise of superbugs like MRSA is one serious consequence of overusing antibiotics. Obesity just might be another. Food for thought before you decide to make war on your -- or your kid’s -- bacteria by ingesting antibiotics when they aren’t necessary.