Over thousands of years, our bodies have evolved to not only live in harmony with the bacteria, fungi, and viruses in and on our bodies, but also to depend on them for certain essential metabolic functions—especially gut bacteria.
As you would expect, our intestinal microflora performs specific functions that improve our ability to digest, absorb, and eliminate the foods we eat; however, the benefits of these bacteria extend well beyond digestion. We’ve yet to understand just how extensive this connection is between gut flora and health, but here are some of the known relationships:
- Improves immune health
- Improves mood and mental health
- Boosts energy levels
- Improves cholesterol levels
- Regulates hormone levels
- Reduces yeast infection occurrences
- Supports a healthy weight
- Improves oral health
- Contributes to longer life
How Gut Bacteria Improves Immune Health
One of the most well-known non-digestive benefits of good gut bacteria is a stronger immune system. This happens in a number of ways, but generally is the result of our microflora’s ability to prevent pathogenic organisms from taking hold in our bodies.
As a natural byproduct of their own metabolism, the microbes living with us produce substances that our bodies use to fortify our defenses against bacteria, yeast, and other invasive organisms. Research has shown, for example, that the bacteria lining your intestines reinforce the barrier that prevents pathogens from seeping out of your GI tract and into the body. This is particularly important in your large intestine, where fecal matter accumulates before being excreted. Without a strong barrier in place, toxins from your feces can be reabsorbed, placing an additional burden on your immune system. (This is often referred to as leaky gut syndrome.)
See a list of all articles about Gut Bacteria in the Gut Bacteria and Probiotics Index
This protective mechanism depends on a fatty acid known as butyrate (or butyric acid), which is produced by the Lactobacillus and Bifidobacterium species of gut bacteria. One of butyrate’s main functions is to promote the growth of the mucus membranes that line the intestines and to increase their production of “mucking.” Mucking is a component of mucus that lines and protects the walls of the intestines. The mucus constantly sloughs off and carries pathogens with it.
Gut bacteria also support immune health by keeping the digestive tract at a pH level where it’s difficult, if not impossible, for undesirable bacteria, such as salmonella (which causes food poisoning), shigella (which causes diarrhea), and E. coli (which can cause intestinal disease and chronic kidney failure), to take root and grow. Healthy gut flora also produces a volatile fatty acid which, along with other byproducts, makes it difficult for fungus and yeast to survive.
Finally, good gut bacteria also help keep you regular. The shorter your bowel transit time, the less opportunity there is for toxins to be reabsorbed into your blood stream.
Read more about why balanced microflora is the cornerstone of immune health.
How Gut Bacteria Improves Mental Health
If you don’t believe that there’s a connection between our gut and our mood, try describing how you felt the last time you were nervous, afraid, or angry. If you use phrases like “butterflies in the stomach” or a “stomach tied in knots,” you’ve just proven how true this is.
Within the body, we actually have a “second brain” called the enteric nervous system (ENS). The ENS controls and regulates our intestinal tract and senses environmental threats. It reports information to the brain via the vagus nerve, the longest cranial nerve in the body. The vagus nerve links a number of organs with the brain, but about 90 percent of the signals passing along it are traveling from the gut to the brain.
Researchers have known for a long time about this “gut/brain axis,” but for some reason they have always focused on the impact the brain can have on the gut—or control from the “top down.” Even the pharmaceutical companies quickly realized that more than half of individuals with irritable bowel syndrome also have mood disorders. This is why antidepressants are some of the most common pharmaceutical treatments for irritable bowel syndrome. (J Psychiatry Neurosci 09;34(3):230–231)
It may seem strange that there is a neurological connection between the gut and the brain, and that you can treat the brain with antidepressants and see improvement in bowel problems. But what’s even stranger (to me anyway) is that until recently, conventional medicine never considered directly treating bowel problems to improve mood disorders. It’s a two-way street between the brain and the gut, after all. If you change one area, it makes a difference in the other.
Just recently, researchers in France proved that mood disorders can be controlled from the “bottom up” using two specific strains of probiotic bacteria (Lactobacillus helveticus Rosell-52 and Bifidobacterium longum Rosell-175). In other words, you can effectively treat depression, anxiety, and behavioral problems by normalizing the bacteria in the bowels.
The bacteria combination produced anti-anxiety characteristics in animals as well as beneficial psychological effects in human volunteers. Laboratory and numerous standardized psychological tests revealed lower levels of the stress hormone cortisol, a significant decrease in symptoms such as depression, anxiety, anger/hostility, obsessive-compulsive actions, phobias, and paranoia, and an improvement in sleep.
Depression, anxiety, and sleep disorders are just of few of the more common problems that have been closely linked to intestinal problems. As to which came first—the gastrointestinal disorder or the psychiatric illness—it’s hard to tell. But based on trends over the past few decades, I can’t help but think the constant assault on our intestinal flora is the underlying cause of many of the psychological problems we’re now experiencing. Read more about why mood disorder treatment should begin with gut bacteria.
How Gut Bacteria Boosts Energy Levels
When your body is absorbing nutrients and ridding itself of toxins more effectively, it stands to reason that you will feel an overall improvement in your energy level. But this is also supported by science, which has shown us that probiotics can be an effective way to fight fatigue—particularly chronic fatigue.
Blood and saliva samples were taken for one month in eight athletes who had fatigue and declining performance. All were shown to have a reduced secretion of interferon, and most were found to be infected with the Epstein-Barr virus (EBV). (Most adults are carriers of this virus.)
When the athletes were given a probiotic supplement (Lactobacillus acidophilus) for a month, not only did their interferon levels improve to levels found in healthy individuals, but only one was found to exhibit EBV shedding in the saliva. Also, the fatigue disappeared, and athletic performance noticeably improved. (Brit J Sports Med 06;40(4):351–354)
Admittedly, few of us are athletes—but there’s still a takeaway here. Restoring bacterial flora to optimal levels can have a profound effect on your overall energy level and health. The Epstein-Barr virus is associated with chronic fatigue syndrome, and studies have shown that interferon helps keep the virus in check in healthy individuals. The regular use of a good probiotic supplement is one of the easiest and least expensive ways to improve interferon levels. This, in turn, often becomes a very effective tool for managing problems involving chronic fatigue.
How Gut Bacteria Improves Cholesterol Levels
Much of the cholesterol produced by your liver is converted into bile acids, which are stored in the gallbladder and used to help digest fats. Ultimately these acids end up in the colon, where they are either destroyed or excreted in bowel movements.
People who don’t eat enough fiber (one of the habits that damage gut bacteria) often have too much pathogenic microflora in their GI tract. One of the things those unwanted bacteria do is attack bile acids. Specifically, they break the acids down into several substances, including a toxic product called lithocholate. Lithocholate causes the liver to convert less cholesterol into bile acids.
From here, a couple of things happen. When less cholesterol is converted to bile acids, it begins to accumulate in the blood stream, and levels rise. Also, less cholesterol reaches the colon where it can be excreted in bowel movements. This is especially dangerous because bowel movements are the body’s main method of ridding the body of unwanted cholesterol.
Eating a high-fiber diet effectively supports the good bacteria that leave passing bile acids intact. As a result, your body excretes more cholesterol, and in effect is “tricked” into creating more bile acids.
How Gut Bacteria Regulates Hormone Levels
I could write a book on this topic, but it would probably put us both to sleep—so I’ll keep it short.
Normally, as much as 60 percent of the estrogen circulating in the blood is picked up by the liver and "deactivated." It is then dumped into the gallbladder and released with bile into the intestines for excretion. In the GI tract, an enzyme produced by our good gut bacteria, called Beta-glucoronidase, reactivates the estrogen so it can be reabsorbed into the body.
When the bacterial flora is out of balance, the estrogen is neither reactivated nor reabsorbed. Instead, it is lost in the stool. Low estrogen levels have been linked to osteoporosis, PMS, water retention, breast soreness, severe menstrual cramps and heavy flow, slow menstrual cycles, migraine headaches, etc.—all problems that women (and the men they live with) want to avoid.
A similar process occurs with many other hormones, as well as folic acid, vitamin B12, bile acids, cholesterol, and vitamin D.
How Gut Bacteria Reduces Yeast Infection Occurrences
Apart from residing in the intestinal tract, beneficial bacteria also reside in the vagina and urinary tract, where they deter the growth of pathogenic bacteria and yeast. They are a primary defense against urinary tract infections (UTIs) and acute cystitis. Approximately 60 percent of women in the United States experience UTIs or acute cystitis during their lifetimes, and 30 percent of those women have multiple occurrences.
We know that the beneficial bacteria reach the vagina by migrating from the colon, out of the body, and into the vagina and urinary tract. Although there are multiple species residing in the vagina, Lactobacillus is the most prominent. As it does in the gut, the lactic acid that these bacteria produce help to keep the pH level of the vagina and urinary tract slightly acidic, which reduces the growth of yeast and harmful bacteria—including E. coli, one of the chief bacteria that cause UTIs.
If we look at women’s genitourinary health from this perspective, it’s easy to understand why some women experience recurring problems with UTIs. If the balance of bacteria is off in some way, pathogens are more likely to adhere to the bladder wall and cause infection.
Though antibiotics will effectively clear up the symptoms of a UTI, they also will kill off the friendly microflora that is needed to protect the urinary tract in the first place. This sets the stage for an ongoing cycle of infection.
The most effective way to break this cycle is not additional medication, but rather re-establishing healthy flora by eating fermented foods and/or taking probiotic supplements high in the Lactobacillus species. Once restored, it’s reasonable to assume that subsequent infections will be much less frequent.
How Gut Bacteria Improves Oral Health
The primary benefit of probiotic flora in the oral cavity—the mouth, throat, and by extension, the nose, sinuses, and ear canals—is in support of our immune system, since often our first exposure to viruses and bacteria comes through the mouth and nose.
More than 600 species of bacteria have been identified within the oral cavity. Most of those species probably play a lesser role in health, but researchers have found that higher numbers of the more prominent beneficial species directly correlate to a reduced incidence of everything from bad breath and dental caries to ear infections, strep throat, and tonsillitis. (J Appl Microbiol 06;100:754–764) (J Med Microbiol 03;52:829–833) (Revista de Microbiol 99;30:332–334) (Scand J Infect Dis 93;25:31–35) (Ann Otol Rhinol Laryngol 97;106:571–574)
The most effective way to increase the number of good bacteria in the oral cavity is through the use of probiotic lozenges, particularly those which contain the species Streptococcus salivarius. Tests have shown that using a lozenge that incorporates the K12 strain can help restore the natural bacterial flora of the mouth and throat. These bacteria produce compounds referred to as “bacteriocin-like inhibitory substances” or BLIS, which act as natural antibacterials and help control the growth of invasive microorganisms that cause infections.
How Gut Bacteria Supports a Healthy Weight
More and more research is emerging that draws a direct link between our weight and the health of our gut flora (including its role in the success of gastric bypass surgery), but this shouldn’t be a surprise. The connection has been known, and manipulated, for years by the agricultural industry.
Antibiotics—which kill the natural bacterial flora in the human body that influences how we break down and absorb the nutrients that help keep us lean and healthy—are known as growth promoters. Farmers have been using antibiotics for more than half a century to fatten cattle, pigs, and chickens. With the use of these medications, animals gain more weight more quickly, on less food. I’ll say that again: antibiotics stimulate growth with less food.
There is other research on the topic of weight and gut flora as well, two of the more interesting and recent pieces being related to how gut bacteria influence which foods we crave. Here are a few more examples:
- Butyrate—one of the fatty acids produced by good gut bacteria—has been suggested to promote feelings of satiety (a feeling of fullness and satisfaction). (Nutr Rev 07;65(2):51–62) (Aliment Pharmacol Ther 08:27(2):104–119) This, obviously, can help prevent overeating.
- A Japanese company gave 87 overweight individuals 100 grams of fermented milk twice a day. The milk consumed by half the group contained the bacteria Lactobacillus gasseri. After 12 weeks, those individuals lost an average of 2.2 pounds—and there was no weight loss in the other group. (Eur J Clin Nutr 2010 March 10. [E-pub ahead of print PMID:20216555] Specifically, the participants lost 4.6 percent of their visceral fat (fat around the stomach) and 3.3 percent of their subcutaneous fat (fat just under the skin). Their hip circumference was reduced by 1.7 cm (almost ¾ of an inch) and their waist went down by 1.5 cm (just over ½ inch). Researchers feel that Lactobacillus gasseri somehow decreases the amount of fat absorbed from the intestines.
- Researchers evaluated the use of antibiotics in 11,532 children born in Britain’s Avon region in 1991 and 1992. Almost 30 percent of the infants were given antibiotics sometime during the first six months of their life. By age 38 months, the children in the antibiotic group had a 22 percent greater likelihood of being overweight. (Int J Obes (Lond) 21 October 2012 [Epub ahead of print]) Antibiotics. Doing it at such a critical period of development, such as early childhood, has long-lasting effects.
How Gut Bacteria Contributes to Longer Life
The more diverse our bacterial flora is, the more effective it is and the better our overall health tends to be. To see this, you need look no further than a study that examined gut microbes in the elderly.
When researchers looked at the gut bacteria of 178 elderly individuals over the age of 65 (average age 78, none of whom were being treated with antibiotics), they found that the microbes varied extensively depending on where the individual lived and the state of their overall health.
The people who lived independently in the community had the most varied microbacterial flora and were the healthiest. People who lived in long-term assisted living homes had less diverse microbacterial flora and were frailer.
The research team, led by Paul O’Toole of University College Cork in Ireland, tied this difference to the diet of each respective group. Though the foods eaten by people who moved into long-term residential facilities changed immediately upon entry (becoming much more uniform and based on government-issued nutritional data), it took about a year for the profile of their bacteria to change. It was during that transition time when the individuals’ health started declining the most. What makes this study so intriguing to me is the speed at which a person loses his or her health to a decline in the numbers and variety of intestinal bacteria. The clear takeaway from this is that eating a varied diet that includes fermented foods is a key to maintaining gut flora and, by extension, strength and vitality.
Read More About Gut Bacteria and Digestive Health
Gut Bacteria and Probiotics Article Index
See a full list of articles by Dr. Williams about gut flora, probiotics, and the microbiome. Read more
Gut Bacteria May Influence Food Cravings
Learn how gut bacteria manipulate which foods we crave, in order to get the foods they need to survive. Read more
Why Mood Disorder Treatment Should Begin With Gut Bacteria
Learn about the gut/brain axis and how signals from the gut influence our thoughts and feelings, including its role in depression, autism, and ADHD. Read more
Balanced Microflora Is a Cornerstone of Immune Health
Learn more about why efforts to fight disease should focus not on the disease itself, but on the body’s internal environment, which allows harmful bugs to flourish. Read more