I’ve previously written about how dysbiosis can lead to insulin resistance, weight gain, and obesity. While I’ve focused on the detrimental effects of the increased use of antibiotics in humans, the fact is that around 80% of the antibiotics consumed in the U.S. goes to farm animals (1). Drugs aren’t only given to livestock to treat disease, but since farm animals often live in cramped, unsanitary conditions, low-level daily doses of antibiotics are given to ward of infections and fatten the animals up. Both antibiotics and antibiotic resistant bacteria found in farm animals reach humans through food, the environment, and direct contact, and could play a key role in the modern obesity epidemic.
Antibiotics alter “the second genome”
Antibiotics change the balance of bacteria that live in the gastrointestinal tract of farm animals, and the species that survive are typically those that have adapted and built up resistance to the antimicrobial drug. So, the detrimental effects of antibiotics are two-fold: They promote a state of dysbiosis, with less diversity and a potential overgrowth of pathogenic microbes, and they increase the numbers of bacteria with antibiotic resistant genes.
Just like in human, dysbiosis can initiate weight gain in animals through several different mechanisms. One of the adverse effects of broad-spectrum antibiotics is an increased translocation of bacterial endotoxins from the gut into systemic circulation. This “endotoxemia” can initiate a vicious cycle of weight gain, insulin resistance, and obesity.
Antibiotic resistant genes are transferred into the human microbiome
We know that microorganisms are able to transfer genes between each other through horizontal gene transfer, and we’re slowly starting to learn the implications of this gene transfer for human health. Since a bacterial cell that acquires resistance to antibiotics is able to transfer antibiotic resistant genes to other microbes, it’s no surprise that more and more health disorders and infections both in humans and animals can longer be treated successfully with antimicrobial drugs.
Scientists are desperately trying to keep up with the spread of antibiotic resistant genes by creating new and more powerful drugs, but we’re now learning that we’ve dealt with the trillions of microbes in and on our bodies in the wrong way. Instead of trying to eradicate bad bugs with broad-spectrum antibiotics and antifungals, it’s clear that the best approach to deal with disease and microbial infections usually is to restore a healthy microbiome. When normal microbial communities are introduced, beneficial bacteria naturally suppress the growth of pathogenic microbes (e.g., by lowering the pH) and we avoid dysbiosis and spread of antibiotic resistant genes.
The fact is that the millions of pounds of antimicrobials that have been pumped into food production and humans have altered the microbial ecosystems around us, and antibiotic resistant genes are transferred into the human microbiome through food products, direct contact with animals, and the environment. While this spread of antibiotic resistant bacteria is a serious problem in itself, we’re now learning that exposure to low-residue antibiotics in food products could be an even bigger issue.
A new hypothesis for the development of obesity
Obesity seems to be primarily driven by excess intake of highly palatable modern foods, but several other factors are needed to explain the mechanisms underlying the modern obesity epidemic. Chronic low-grade inflammation seems to be especially important in that regard, and the human microbiome – which makes up 90% of the cells in our body and 99% or our genome – has a significant impact on the inflammatory mileu in the body.
A group of researchers at the University of California just published an article where they hypothesize that the obesity epidemic in the United States is partly driven by exposure to food containing low-residue antimicrobial agents (2):
The rapid increase in obesity prevalence in the United States in the last 20 years is unprecedented and not well explained. Here, we explore a hypothesis that the obesity epidemic may be driven by population-wide chronic exposures to low-residue antibiotics that have increasingly entered the American food chain over the same time period. We propose this hypothesis based on two recent bodies of published reports – (1) those that provide evidence for the spread of antibiotics into the American food chain, and (2) those that examine the relationship between the gut microbiota and body physiology. The livestock use of antimicrobial agents has sharply increased in the US over the same 20-year period of the obesity epidemic, especially with the expansion of intensified livestock production, such as the concentrated animal feeding operations. Observational and experimental studies support the idea that changes in the intestinal microbiota exert a profound effect on body physiology. We propose that chronic exposures to low-residue antimicrobial drugs in food could disrupt the equilibrium state of intestinal microbiota and cause dysbiosis that can contribute to changes in body physiology. The obesity epidemic in the United States may be partly driven by the mass exposure of Americans to food containing low-residue antimicrobial agents. While this hypothesis cannot discount the impact of diet and other factors associated with obesity, we believe studies are warranted to consider this possible driver of the epidemic.
Another reason to choose organic
The amount of antibiotic residue in the food you eat depends on several factors, such as where you live, if the meat is organic or not, which types of drugs that have been used, withdrawal times, and how you prepare the food.
Meat is routinely tested for antibiotic residue as part of the U.S. National Residue Program, but it’s unclear whether the established tolerance levels for antibiotic residue is actually a safe level to ingest over time. Several studies show that antibiotics are present in eggs, beef, and pork and chicken meat (3,4,5,6,7).
Legislations vary around the world, and while the use of antibiotics as growth promoters is banned in the European Union, other countries have less strict rules regarding the use of drugs in animal feed (8). The Food and Drug Administration recently put in place a major new policy to phase out the indiscriminate use of antibiotics in livestock, but it’s unclear whether these new rules will actually limit the quantity of antibiotics used on farms (9,10).
Even animals who are raised on organically certified farms receive antibiotics when they are sick, and sometimes ingest drugs found in soil and streams. However, the use of low-level daily doses of antibiotics is banned in organic farming, and buying grass-fed, organic produce is the best approach to avoid low-residue antibiotics.
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