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Unnecessary Antibiotics Could Contribute to Weight Gain


Antibiotics are powerful medicines can save lives when used properly. Unfortunately, there is some inappropriate prescribing of the drugs that have led to bacterial resistance and could be contributing to the obesity epidemic. Two new studies show how antibiotics can affect our nutrient absorption and potentially cause weight gain.

"We typically consider obesity an epidemic grounded in unhealthy diet and exercise, yet increasingly studies suggest it's more complicated," says one study researcher Dr. Leonardo Trasande, associate professor of pediatrics and environmental medicine at New York University School of Medicine. "Microbes in our intestines may play critical roles in how we absorb calories, and exposure to antibiotics, especially early in life, may kill off healthy bacteria that…would otherwise keep us lean."

Dr. Trasande’s study evaluated the medical records of more than 11,000 newborns in Britain who were followed during the 1990’s. Those who received antibiotics before they were six months old were 22% more likely to be overweight by the time they were toddlers. Interestingly, those children who received antibiotics after six months of age were no more likely to be obese than other children not given the drugs, suggesting a “window of special vulnerability to exposure.”

“Antibiotics disrupt the development of the healthy flora in our gut. The earlier the exposure occurs, the more disruptions occur,” Trasande explains. “It seems the first few days and months are important. It is difficult to reconstitute that in later life.”

A second study, conducted by Dr. Martin Blaser of New York University, involves the feeding of antibiotics to animals. Farmers have long known that giving low doses of antibiotics to cattle and chickens make them fatter.

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In a study of laboratory mice, Dr. Blaser’s team discovered that the drugs were accelerating calorie absorption from food. The mice were given varying combinations of penicillin, vancomycin, and chlortetracycline. Those who received the antibiotics gained weight even though they did not eat any more than the mice not given the drugs.

The gastrointestinal tract is the center of hormone production, Dr. Blaser says. It is possible that altering the organisms in the intestines – called the microbiome -- could help people better absorb nutrients and calories from “indigestible” foods such as cellulose, thus leading to excess intake and weight gain.

Keep in mind, though, that “We are just beginning to scratch the surface,” says Dr. Ilseung Cho, who worked with Dr. Blaser’s team. “Obesity is multifactorial.” Whether antibiotics are contributing to weight gain by “10 percent or 70 percent,” we just don’t know, so don’t forgo that prescription if your doctor finds it is necessary to combat a bacterial infection.

But do keep in mind that antibiotics do not fight infections caused by viruses, such as colds, flu, most coughs and bronchitis and sore throats (unless caused by strep). Taking an antibiotic when you do not need it will ultimately do more harm than good.

Journal References:
L Trasande et al. Infant Antibiotic Exposures and Early-Life Body Mass, International Journal of Obesity, (21 August 2012) | doi:10.1038/ijo.2012.132
Martin Blaser. Antibiotic Overuse: Stop the killing of beneficial bacteria. Nature 476, 393–394 (25 August 2011) doi:10.1038/476393a

Additional Resource:
Medline Plus, US National Library of Medicine (National Institutes of Health)