Peter Reuter, MD, PhD
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 protect us from disease causing microbes (so-called pathogens). We knew that some pathogens could 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 can 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 tremendously. 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 we extract from the food we eat and how our body weight develops.
Over the last few decades almost all developed countries have 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 cardiovascular system diseases, diabetes mellitus type II, and osteoarthritis. Currently approximately 1/3 of Americans are of normal weight, 1/3 are overweight, and 1/3 are 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 this difference 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 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 breastfeeding on the long-term body weight of babies and children. Babies born via C section and babies raised on formula instead of breast milk have a much higher chance of becoming overweight or obese. Looking into this topic, 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. In this way, we can isolate them and then introduce them into the body of overweight people. 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
Body Mass Index: https://www.youtube.com/watch?v=1PyrXtYON1k
Microbe: Microorganism that can cause disease or fermentation on carbohydrates
Pathogen: Also known as infectious agent. General term for anything that can cause disease in a human, animal or plant. Most often used for microorganisms, such as bacteria, viruses, fungi, and parasites.
Gastrointestinal system: Also known as digestive system. Organ system consisting of the gastrointestinal tract (mouth, gullet, stomach, small and large intestine) and accessory structures, such as teeth, tongue, salivary glands, liver, gallbladder and pancreas. It has to break down (digest) foodstuff and drinks to prepare nutrients, such as glucose, to be taken into our body.
Large intestine: Also known as large bowel and (mistakenly) colon. The last part of the digestive tract starts with the cecum, a blind-ending sack with a worm-like appendage called appendix vermiformis, and end with the anal canal. The longest part, the colon, starts at the right lower abdomen. It has four parts, ascending, transvers, descending, and sigmoid colon. The rectum, so called because it is straight, connects colon and anal canal. The colon isn’t important for nutrient uptake, apart from water and salt, which is why it is not essential to life and can be removed completely if needed.
Basal metabolic rate: The amount of energy expended by the body while at rest in a neutrally temperate environment. It is higher during childhood and teenage years and keeps declining throughout adulthood. Women have a fairly constant BMR between approx. 25 and 45, which makes it easier for them to keep their weight constant compared to men, who have a higher BMR during teenage years and early adulthood.
Total metabolic rate: The total amount of energy used by our body when we’re active. It depends on our basal metabolic rate (higher for men than women) and the level of physical activity, the more active we are the more energy we use and the more energy (calories) we can consume without gaining weight.
Bacterial flora: All the bacteria living in our digestive system form one big ecosystem. Depending on where we life, what we eat and drink and so on the composition of this flora changes. While most of the bacteria are harmless or beneficial for us, some of them can cause serious illness when they overgrow the others. Intestinal bacteria that find their way into the bladder or other parts of the urinary tract are by far (up to 90%) the most common cause of urinary tract infections (UTI).
Antibiotics: Substances that can fight and sometimes kill microorganisms, especially bacteria, that can cause diseases in human, animal, or plants.
C section: Also known as Caesarean section. A surgical intervention to deliver the baby through the wall of the abdomen and the womb (uterus). The surgeon has to cut through the abdominal wall and the wall of the womb to get access to the unborn baby. The surgeon has to work fast, because of the danger to mother and child, but also be careful not to cause harm to the baby when cutting through the womb.
Gastroenteritis: Originally to describe any inflammation (-it is) of the stomach (gaster) and guts (enteron) the term is now mostly used for any illness of the digestive tract that leads to diarrhea, nausea, vomiting, and/or crampy abdominal pain. Most cases are caused by viruses, such as an outbreak of Norwalk virus on cruise ships, or bacteria (classic food poisoning).
Clostridium difficile: Bacterium that lives in our intestines without causing any issue until it overgrows other bacteria, which is often caused by antibiotics therapy. Infection can cause severe gastroenteritis and death in rare cases. It is related to Clostridium botulinum, which produces a variety of toxins among them botox, which has found a lot of uses in medicine.