Key links emerging between antibiotics and childhood obesity

​By Diane Carman

It’s a crude comparison, but maybe it’s the easiest way to understand Dr. Martin Blaser’s tantalizing hypothesis.

Farmers feed chickens, hogs and cattle antibiotics to make them gain weight quickly. Some actually have found that the livestock gain weight twice as fast when eating a diet laced with antibiotics.

By over-prescribing antibiotics, we may be doing the same thing to our children.

Dr. Martin Blaser

Dr. Martin Blaser

Blaser, author of “Missing Microbes: How the Overuse of Antibiotics is Fueling our Modern Plagues” and a professor of medicine and microbiology at New York University, lays considerable blame for the exploding epidemic of childhood obesity on the overuse of antibiotics.

“We humans have co-evolved with our microbes, and since World War II, we’ve been screwing it up,” he said.

Last week, Blaser spoke to a packed auditorium at Children’s Hospital Colorado in the keynote lecture of a session on “Big Ideas for Combating Colorado Childhood Obesity.”

Blaser is among an international group of physicians and scientists working on one of the most promising fields in medicine and microbiology – the Human Microbiome Project.

The researchers are cataloguing the spectacular array of microbes found in the human body and working to understand the role they play in human health and development.

Blaser provided an overview of research by his colleagues, Dr. Ilseung Cho and Laurie Cox, who have demonstrated the relationship between antibiotics and increased body fat in mice.

They also found that early antibiotic use permanently affected the microbial diversity in mice, Blaser said, causing “lifelong consequences.” They have found that the cumulative effect of diverse microbes affects the genetics of the host.

“We need to understand the roles of microbes and how they are signaling our cells.”

In one of the most dramatic illustrations of a perceived relationship between antibiotics and obesity, Blaser offered two maps of the United States. One showed the states with highest and lowest rates of use of antibiotics; the other depicted obesity rates. The maps were surprisingly consistent.



Antibiotic prescriptions

Antibiotic prescriptions








Obesity rates

Obesity rates









“We’ve gone overboard in our use of antibiotics,” Blaser said. “We think all germs are bad.”

The cost of overusing antibiotics

For decades, when a worried mother brought a child with a painful ear infection to the doctor’s office, the physician would send them away with a prescription for antibiotics figuring “it may not help, but it can’t hurt.

“Now we’re pretty sure this is wrong,” Blaser said. “There’s a cost every time.”

Each time we take an antibiotic, “there’s probably a species of microbes that goes extinct, and then another and another,” he explained. “Now we’re four generations into this” and only beginning to comprehend the consequences.

“Microbes know how to talk to the host and the host talks back,” Blaser explained. Beneficial microbes – and some not-so-innocent ones – play important roles in the development of a healthy immune system and countless other functions in the human body.

Blaser is married to microbiologist Maria Gloria Dominguez-Bello, who is also involved in the microbiome research, which is supported by the National Institutes of Health. She works closely with University of Colorado microbiologist Rob Knight.

Among their dramatic findings is evidence of the important role vaginal delivery plays in protecting children from developing asthma, Type 1 diabetes, celiac disease and obesity.

The microbial bath the babies receive when they pass through the birth canal is thought to be essential to healthy development.

As the number of deliveries via C-section increased, Blaser said, “this was something that was just not on anybody’s radar screen. No one understood the biological cost.”

He said physicians need to stop doing elective C-sections, encourage mothers to breast feed since breast milk contains components that encourage the growth of important gut microbes, curtail their use of antibiotics unless they are clearly medically indicated and stop bathing infants with “antibacterial everything.”

He speculated that there may be reasons even to reconsider the practice of bathing newborn infants immediately.

“We wash the vernix (the waxy substance that covers an infant’s body) off the baby immediately and we don’t even know what’s in there,” he said.

In some primitive cultures, mothers traditionally licked the vernix off the newborn baby, Blaser said, transferring more microbes to the infant from the mother. “There may be some rationale there.”

Changes needed for doctors and patients

While the research is far from complete, the evidence is clear that much of our use of antibiotics is not merely ineffective, it’s harmful, he said. That message needs to be communicated to physicians and patients to stop the casual use of antibiotics when they are not indicated, such as for treatment of colds and other viral infections.

“I want to change the interaction in the doctor’s office,” he said.

Blaser even criticized the use of hand sanitizers outside of hospitals or health care facilities.

“Putting them in offices and supermarkets doesn’t make any sense to me. We’re getting rid of the good guys that help defend us against the bad guys.

“There’s a reasonable probability that we’re doing more harm than good,” he said.

While much work remains to understand the role microbes play in obesity, the correlations are strong.

The microbial diversity found in subjects studied in the U.S. is markedly less than that found in subjects studied in remote, largely uncontacted cultures in South America and Malawi, Blaser said. Of the top eight prescriptions given to children in the U.S., five of them are​ antibiotics.

And while obesity in those populations in South America and Malawi remains rare, the obesity rate in the U.S. has grown dramatically in the last three decades.

“We’re doing so many things that conspire against health,” Blaser said. “That’s why I wrote the book. Once we’re aware of these issues, we can deal with them.”








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