How a Good Gut Keeps You Healthy

You've heard the rumblings about bacteria. Once seen as just dirty germs, these microbes are now more accurately divided into two categories: disease-causing agents, or "bad" bacteria, and health-promoting "good" bacteria.

Research is showing that digestive tract bacteria, in particular, play a role in both digestive wellness and overall health. In other words, the same tiny microbes that help ward off food poisoning, get your system back on track after a bout with the stomach flu and help digest food may also contribute to a stronger immune system, weight management and even mental resilience. Below are just some of the ways these "good" gut bacteria affect us in positive ways--even beyond digestive health.

Bolstering Immune System Function
According to a study on mice from the University of Pennsylvania's School of Medicine, helpful gut bacteria can help prime the immune system, allowing it to respond effectively to harmful microbes it encounters. This might explain why secondary infections develop after the use of antibiotics, which kill off both good and bad bacteria.

How does this happen? Basically, white blood cells that recognize bacteria are primed or "warmed up" when in the presence of healthful bacteria, and can respond appropriately when harmful bacteria invade the body. Researchers hypothesize that broad-spectrum antibiotics, which kill of a range of bacteria rather than targeting a specific strain, detract from this priming by eliminating this baseline level of function.

Think of it as you would think about running: It's hard to go from standing to sprinting, but you might be able to switch into a sprint if you're already jogging. In this example, an antibiotic is an agent that keeps your body's white blood cells standing still, rather than jogging to warm up.

Staving Off Infection
Research evidence is mixed (it tends to vary by condition), but much investigation is being done to uncover how a healthy balance of gut bacteria might contribute to infection prevention. For example, some studies have shown that using probiotics to re-colonize the gut, especially after a course of antibiotics, can prevent diarrhea associated with antibiotic use.

In other infections caused or perpetuated by an imbalance of gut bacteria (such as yeast infections, urinary tract infections and bacterial vaginosis, a type of vaginal infection) probiotics are being tried as possible preventatives. This means that supplementing the body with the appropriate strain of "good" bacterial may help rebalance the body, thereby allowing it to fight off infection-causing agents on its own. In other words, a healthy gut really can boost your overall health.

Stopping Food-Borne Illness
If you've ever carefully washed a cutting board after slicing raw chicken or passed on the platter of deviled eggs that's been sitting at room temperature for who knows how long, you've done your part to prevent Salmonella infection, a type of food poisoning.

Now, scientists at Arizona State University say they've found evidence that Lactobacillus reuteri, bacteria that naturally live in a healthy gut, produce a substance called "reuterin," which wards off Salmonella poisoning. The exact mechanism is unknown, but reuterin appears to help keep cells lining the intestinal walls of mammals safe from salmonella.

Regulating Stress
We know that there is a connection between the brain and the gut, which is why a stressful day can cause indigestion or anxiety can increase irritable bowel symptoms, for example. But it is newly thought that this communication may not be simply from the brain to the gut, but a two-way sharing of signals. Animal studies have shown that good bacteria help facilitate resistance to stress, particularly early in life, when bacteria are first being introduced. And the way we tolerate stress tends to persist over our lifespan, so the bacteria that the body is exposed to when we are very young may well have lifelong consequences.

Preventing Obesity
A study led by a Washington University School of Medicine researcher compared the gut bacteria of twin siblings in which one twin was obese. They introduced the gut bacteria of each twin to mice, and found that the rodents gained weight or stayed lean according to which bacteria they were exposed to.

Interestingly, allowing the mice with differing bacteria to interact with each other helped obese mice return to a healthy weight—but only when that interaction was paired with a healthy diet. In other words, obese mice exposed to the "lean" promoting bacteria did not lose weight on an unhealthy, high-calorie diet.
Although much of this research is in its early stages, today's studies hint that a gut filled with "good" bacteria can have a range of health-promoting impacts, from supporting the immune system to allowing us to better cope with stress.

American Psychological Association, "That Gut Feeling,", accessed on December 6, 2013.
Arizona State University, "Beneficial Bacteria May Help Ward Off Infection,", accessed on December 6, 2013.

International Foundation for Functional Gastrointestinal Disorders, "Antibiotics & Diarrhea,", accessed on December 6, 2013.
Jane A. Foster and Karen-Anne McVey Neufeld. "Gut-Brain Axis." Trends in Neurosciences. 2013 May;36(5):305-12.
National Institutes of Health, "Gut Microbes and Diet Interact to Affect Obesity,", accessed on December 6, 2013.
Penn Medicine, "'Good' Bacteria Keep Immune System Primed to Fight Future Infections,", accessed on December 6, 2013.
Reid G, Howard J, Gan BS. "Can Bacterial Interference Prevent Infection?" Trends in Microbiology. 2001 Sep;9(9):424-8.
The Harvard Medical School, "Health Benefits of Taking Probiotics,", accessed on December 6, 2013.
University of California Los Angeles, "Changing Gut Bacteria Through Diet Affects Brain Function,", accessed on December 6, 2013.