This article was first published in The Montreal Gazette
I have a long-standing relationship with bacteria. These single-celled living organisms have wedged their way into my lectures ever since I started teaching in the 1970s. I have told many a story about Antonie van Leeuwenhoek observing little “animalcules” through the microscope he invented back in the 17th century, Louis Pasteur’s linking bacteria to disease, and Alexander Fleming’s accidental discovery of penicillin. With the exception of Ilya Mechnikov’s speculations about the supposed longevity of Bulgarian peasants due to lactobaccili in yogurt, historically bacteria have mostly been portrayed as villains that make us sick and spoil our food.
That impression was altered when the Human Microbiome Project, launched by the National Institutes of Health in 2007, revealed that we share our body with an astounding number of bacteria, some of which turned out to be “good.” These not only keep disease-causing “bad” bacteria in check, but also protect the mucus layer that lines our intestine while cranking out chemicals like butyric acid that nourish the immune system.
The Human Microbiome Project spawned an explosion of research that unveiled a number of other links between gut bacteria and our physiology. It seems that the specific bacterial composition may play a role in conditions ranging from chronic fatigue syndrome, allergies and inflammatory bowel ailments to cardiovascular and neurological disease. The diversity of bacteria in our microbiome may even affect mental state, response to chemotherapy, and, grippingly, aging.
While there is still great interest in antibiotics to tackle the one per cent of bacteria that are known to cause disease, there is also much curiosity about using bacteria therapeutically.
In one area curiosity has already borne fruit. “Rebyota” is a rectal infusion of bacteria isolated from the feces of healthy humans that is used to treat the violent diarrhea and inflammation of the colon caused by recurrent Clostridioides difficile infection. This can happen after a regimen of antibiotics wipes out the “good” bacteria that keep C. diff in check. It seems the healthy bacteria multiply in the colon and compete for nutrients with C. diff, resulting in the latter being crowded out.
As far as the seductive link to aging goes, we know that as we age, the balance of bacteria in our gut changes. Species linked to inflammation increase and ones that have an anti-inflammatory effect decline. Whether these changes cause the symptoms that we associate with aging or are a result of aging isn’t known.
We do, however, get a clue from some studies with mice. Like us, mice age and experience changes in the elasticity of their skin, a weakening of muscles and shrinkage of their brain. When older mice have feces from younger mice squirted down their throat twice a week, they seem to grow younger. Their skin retains more moisture, their muscle strength improves, and there is even a modest reversal of their age-related brain shrinkage. It’s certainly noteworthy, but the mouse microbiome is very different from that of humans. Mice live in the same environment, eat the same food day in and day out, meaning they have a less diverse and more limited microbiome than we have.
While mice don’t have much of a way of objecting to being fed fecal matter, it is doubtful that people would welcome the idea of eating poop. That story could be different if the specific “rejuvenating” bacteria were identified, isolated, and marketed as a “probiotic.” Probiotics are the “good” bacteria that are touted as having beneficial effects on the body and are widely hyped either in pill form or as components of fermented products such as yogurt, kefir and kombucha. While there is some evidence for benefits, mostly in bowel disease, there are many difficulties. Bacteria have to survive passage through the acid environment of the stomach in numbers large enough to colonize the intestine. Also, it isn’t clear which of the hundreds of species of bacteria in the gut, each having numerous strains, are the beneficial ones.
Taking a probiotic supplement is really a crapshoot. Does it contain the right strain of the right bacterium? Does it contain enough live bacteria to colonize the gut? Evidence indicates that even if the bacteria make it to the colon, they only frolic there temporarily, meaning that they have to be continuously supplied. This, of course, is not frowned upon by manufacturers.
Rather than taking probiotic supplements, or relying on fermented foods, a better approach is to adhere to a diet that fosters a diversity of colonic bacteria, especially ones that have some evidence of being linked to health. We get an indication of what that diet might look like from a study that examined stool samples donated by some 21,000 people in the U.S., Italy and the U.K. Some were vegetarians, some vegans and others omnivores. Data was also obtained about the subjects’ body mass index (BMI), blood pressure and cholesterol levels — all of which are risk factors for cardiovascular disease. Signature microbes of meat eaters were found to correlate with an increase in risk factors, while the microbes that typify a vegan diet correlated with favourable blood pressure, blood cholesterol and BMI. It seems that plant-based foods lead to a healthier microbiome.
Is it because these foods contain “good” bacteria that they deliver to the colon, or that they offer some nutrient that fosters the growth of beneficial bacteria that already inhabit the colon? A common feature of plants is fiber, the mix of cellulose, resistant starch and polyphenols that we cannot digest, but which serve as tasty morsels for gut bacteria, particularly ones associated with good health. Numerous clinical trials have shown that eating more fiber lowers all-cause mortality by as much as 30 per cent over the study period. Based on such studies, we should be consuming at least 25 grams of fiber a day, an amount of which most people run woefully short. More whole grains, nuts, fruits and vegetables, and especially beans are indicated.
Much is still to be learned about our microbiome. Some studies have suggested that babies born via C-section are more prone to obesity, allergies and asthma because they are not exposed to vaginal bacteria. Breastfeeding also has an influence, promoting the growth of Bifidobacteria that block colonization of the gut by harmful bacteria. Poor sleep, stress and artificial sweeteners have been shown to affect the gut microbiome unfavourably, while intermittent fasting has the opposite effect.
Believe it or not, our social life also affects our microbiome. We pick up bacteria from other people, making our microbiome more diverse, which is believed to be a good thing. Could biblical King David’s servants have been onto something when they searched for a young woman to lie by the aging king’s side? Maybe Abishag infected David with some youthful bacteria. After all, the king lived to 70 years old, which was impressive in those days. Dogs also harbour all sorts of microbes and having a dog has also been found to have a positive effect on our microbiome, although the King David regimen seems to be more inviting.
Before we get carried away with the benefits of microbes, let’s also mention that mice raised in a microbe-free environment live longer. Keep in mind also that the bacteria in our gut are ready to eat us when we stop feeding them. Within 30 minutes of death, they chomp away on our tissues eventually leaving only the bones.
