It has been known for a long time that there are many bacteria that grow on the body membranes that cover our outer (skin) and inner body surfaces (mouth, gastrointestinal tract, vagina). Many of them will cause disease when they overgrow an area, while others will never harm us or can even help protects us from disease causing microbes (so-called pathogens). We knew that some pathogens can cause severe diseases when introduced into our gastrointestinal system, such as food poisoning. It has also been known for quite some time that some of these bacteria help us break down certain food we eat, which can be beneficial, but also cause irritation and embarrassment (beans, beans the magic fruit…). However, there were also indications that at least some bacteria have an even greater and more beneficial influence on what is going on inside our body, such as strengthening our immune system.
Over the last 10 years or so our understanding of and appreciation for the bacterial garden, especially inside our mouth and the large intestine has grown a lot. We now estimate that for each cell in our whole body we have 10 bacteria colonizing our large intestine. Researchers have found that there are many different bacteria that together form a so-called microbiome. Which bacteria are dominant in a person’s microbiome is of great importance for how their body processes food, how many calories they extract from the food they eat and how their body weight develops.
Over the last few decades almost all developed countries experienced an ever increasing weight problem. Although no one really knows what a “normal” weight is, long-term research has shown that overweight people are at a higher risk to develop certain diseases. The Body Mass Index (BMI) or Quetelet index is used to classify people based on body weight and height into normal body weight (BMI below 25), overweight (BMI between 25 and 30) and obese (BMI above 30). Even though those ranges aren’t a law of nature and may be changed depending on future research, we still know that the heavier people get the more likely they are to develop diseases of the cardiovascular system, diabetes mellitus type II, and osteoarthritis. Currently approximately 1/3 of Americans are of normal weight, 1/3 is overweight, and 1/3 is considered obese.
Because of the negative long-term effects for overweight and obese people themselves as well as the enormous financial burden treatment of their obesity-related diseases puts on society as a whole, there have been many attempts at educating people about the dangers of obesity and the benefits of weight loss. Still, the percentage of overweight and obese adult and children keeps rising steadily. Researchers looking into these issues kept coming across people who seemed to do everything right, they ate healthy food in recommended amounts and exercised, but couldn’t lose weight or even gained some more, whereas others seemed to do everything wrong, from eating too much unhealthy food to not exercising at all, and yet didn’t gain any weight. We couldn’t find any reason for these differences when we measured how much energy they burnt at rest (basal metabolic rate, BMR) or when active (total metabolic rate, TMR), which indicated that there had to be something to the way how these different people digested food and absorbed nutrients.
The first hints about the importance of our gut bacteria for our body weight came from twin studies. They showed that “lean” twins and “obese” twins had different bacterial floras. When they ate the same kind and amount of food the lean twins would stay lean, while the obese twins gained more weight. We also saw the importance of a healthy microbiome when we looked at the reasons for severe bacterial infections of the large intestine caused by antibiotics given for the treatment of bacterial infections. One of the most surprising findings, however, was the importance of natural birth and breast feeding on the long-term body weight of babies and children. Babies born via C section and babies raised on formula instead breast milk have a much higher chance of becoming overweight or obese. Looking into that we realized that babies pick up a healthy bacterial flora on their way through the birth canal of the mother. These bacteria colonize the skin, the mouth and the large intestine of the newborn and establish a healthy environment. Breastfeeding encourages further growth of this healthy microbiome. Babies delivered via C section don’t pick up bacteria on their way out of the womb and babies fed on formula grow bacteria that breast-fed babies start growing once they transition to solid food. As their immune system had time to develop first they are more likely to being able to resist and suppress unhealthy microbes.
Based on these findings some researchers in Europe are experimenting with transferring healthy gut bacteria from lean patients to overweight patients to help them lose weight. Most doctors, however, want to wait and find out first which bacteria really are the good guys so we can isolate them and then introduce them into the body of people with weight issues. But, there are situations where a transfer of gut flora is a potentially life-saving procedure. Some patients on antibiotics or after gastroenteritis develop a Clostridium difficile infection in their bowels, which can cause vomiting, diarrhea and abdominal pain, and even be fatal in severe cases. One way to treat this disorder is to perform a fecal microbiota transplant – sometimes jokingly referred to as transpoosion. In this procedure a fecal sample of a healthy donor is introduced into the rectum of the patient. In a recently reported case from the United Kingdom a mother suffering from this condition was given a fecal transplant from her overweight daughter. The transplant did its job, the bowel infection healed, but the mother gained 36 lbs of weight over the next sixteen months going from a BMI of 26 (just above normal weight) to a BMI of 34.5, which is classified as obese, under the same diet as before.
There is still a lot to be learned about how bacteria influence our body as a whole and how we can use them to treat and prevent acute and chronic disorders. But, we can already say that bacteria, not dogs, should be considered men’s best friend.
© Peter Reuter 2015