While these studies didn’t prove that antibiotics directly cause obesity, the consistency in these correlations, as well as those observed in livestock, prompted scientists to have a closer look. What they found was astonishing. A simple transfer of intestinal bacteria from obese mice into sterile (“germ-free”) mice made these mice obese, too! We’ve heard before that many factors lead to obesity: genetics, high-fat diets, high-carb diets, lack of exercise, etc. But bacteria—really? This raised skepticism among even the biggest fanatics in microbiology, those of us who tend to think that bacteria are the center of our world. However, these types of experiments have been repeated in several different ways and the evidence is very convincing: the presence and absence of certain bacteria early in life helps determine your weight later in life. Even more troubling is the additional research that shows that altering the bacterial communities that inhabit our bodies affects not just weight gain and obesity, but many other chronic diseases in which we previously had no clue that microbes might play a role.
Let’s take asthma and allergies as an example. We are all witnesses to the rapid increase in the number of children suffering from these two related diseases. Just a generation ago it was rather unusual to see children with asthma inhalers in schools. Nowadays, 13 percent of Canadian children, 10 percent of US children, and 21 percent of Australian children suffer from asthma. Peanut allergies? That used to be incredibly rare, but is now so frequent and so serious that it has led to peanut-free schools and airplanes. As with the obesity research, it is now evident that receiving antibiotics during childhood is associated with an increased risk of asthma and allergies.
Our laboratory at the University of British Columbia became very interested in this concept and decided to do a simple experiment. As had been observed with humans, giving antibiotics to baby mice made them more susceptible to asthma, but what we observed next left us in awe. If the same antibiotics were given when the mice were weaned and no longer in the care of their mothers, there was no effect in susceptibility to asthma. There appeared to be a critical window of time, early in life, during which antibiotics had an effect on the development of asthma. When given orally, the antibiotic that we chose, vancomycin, kills only intestinal bacteria, and does not get absorbed into the blood, lungs, or other organs. This finding implied that the antibiotic-driven change in the intestinal bacteria caused the increase in the severity of asthma, a disease of the lungs! This experiment, as well as others from several different labs, came to the same conclusion: modifying the microbes that live within us at the beginning of our life can have drastic and detrimental health effects later in life. The discovery that this early period in life is so vulnerable and so important tells us that it’s crucial to identify the environmental factors that are disturbing the microbial communities that inhabit us during childhood.
One of these factors has been observed by comparing children raised on rural farms to those raised in a city. Several studies have shown that exposure to a farming environment makes children less likely to develop asthma, even children from families with a history of asthma, and scientists are now beginning to learn why. Farm-raised children are exposed to more animals, more time outside, and a lot more dirt (and feces!), all things that are known to stimulate the immune system. A critical part of the training and development of the immune system occurs in the first years of life. Asthma, characterized by a hyperactive immune system, seems to have a higher chance of developing in a child with a limited exposure to these immune stimulants, because without them, the immune system does not have all the tools for proper development. By cleaning up our children’s environments, we prevent their immune systems from maturing in the way they have for millions of years before us: with lots and lots of microbes. Life for our ancestors involved massive exposure to microbes from the environment, food, water, feces, and many other diverse sources. Compare that to our current way of life, where meat comes on sterile Styrofoam pans wrapped in plastic wrap, and our water is treated and processed until it’s free of nearly all microbes.
Kids Will Be Kids
A friend, Julia, moved to a small free-range pig and poultry farm when her first child was a preschooler. She observed firsthand how differently a kid grows up in a city and on a farm. She has always been outdoorsy, so even when she was living in the city she would let Jedd, her oldest child, play outside a lot. They would go to parks and playgrounds, where she would encourage Jedd to get dirty, play in sandboxes and mud puddles—she even allowed him to put (safe-sized) objects in his mouth, like big rocks or leaves. Her outdoorsy nature, she thought, would make their transition to rural life easier, and it did in many ways. But nothing prepared her for the things she’s seen her kids do on their farm. When her second baby was born, she would strap him on her back every morning so she could go to their chicken coop to pick up eggs. Jedd, timid with the animals at first, was now chasing and riding the chickens, tasting their feed and touching the fresh eggs. A couple of times she even caught him chewing on something he had picked up from the ground. Anyone who has stepped inside a chicken coop knows what’s on the floor, so she’s pretty sure Jedd has tasted chicken droppings at least a few times. Clearly, Julia freaked out at first, but it’s hard to prevent a five-year-old boy from getting dirty when you’re busy working and looking after a second child. After realizing that Jedd wasn’t getting sick from his newly acquired tastes of the farm, Julia relaxed a bit. Jedd, now eight years old, is responsible for gathering the eggs every morning. Newly laid eggs are often soiled and he doesn’t wear gloves. He washes his hands when he’s done, but it’s impossible that some of that stuff hasn’t made it into his mouth.
Julia’s second child, Jacob, was born and raised on the farm and, like his big brother, he was never the slightest bit hesitant to get dirty. He was once found playing knee-deep in a cesspool of pig waste. At fourteen months he swallowed a handful of fresh chicken droppings as Julia rushed towards him to prevent it. Her initial worry that her children were going to contract a disease from all this messiness dissipated as her kids remained healthy.
Nowadays, with her third baby strapped on her back, she doesn’t even flinch at the sight of the two older boys doing what all farm kids do: getting very, very dirty. Every single day, they come home with dirt, poop, feathers, and who knows what else caked onto their skin and clothes. They try their best to keep their farm boots for outdoor use only, but it inevitably happens that dirty boots make it onto the living room carpet. Julia makes sure to wash their hands before they eat and they rarely miss a daily bath (the color of the bathwater is a constant reminder of why daily baths are mandatory in their house).
Even if they play outside a lot, most children growing up in urban environments rarely ever reach the level of dirtiness that Julia’s kids experience on a daily basis. From this perspective, a farm kid (and his microbes) is very different from a city kid. We are by no means suggesting that we should all allow our kids to play with animal waste, as they could become sick from this. But farms in general provide a microbe-rich environment that has proven beneficial for the development of the immune system, and that really is akin to the way we used to live, which has been seriously altered only in the past few generations.
The vast majority of children have something in common with Jedd and Jacob, in that they all seek out dirt and enjoy getting messy and sucking on things. Why is that? Our natural behavior in the early years of life definitely tries to maximize our exposure to microbes: babies are in direct contact with maternal skin while breastfeeding, they are constantly putting their hands, feet, and every imaginable object in their mouths. Crawlers and early walkers have their hands all over the floor, and then in their mouths. It often seems that they’re waiting for the few seconds that parents take their eyes off them to almost magically find and put the dirtiest thing they can reach in their drool-dripping mouths. It makes us wonder: Are kids instinctually drawn to microbes?
Older kids love digging in the dirt, picking up worms, rolling on the ground, catching frogs and snakes, etc. Perhaps this is actually natural behavior designed to populate kids with even more microbes. Children rarely hesitate to lick anything or anyone. As would be expected, children also suffer more infections than adults. Their vacuum-like behavior ensures that they taste the microbial world and subsequently train their immune system to react to it accordingly. If they encounter a disease-causing microbe, also known as a pathogen, their immune system detects it, reacts to it in the form