Go With Your Gut

by Martina M. Cartwright, PhD, RD on Dec 12, 2013


Adding prebiotic and probiotic foods to your diet boosts beneficial bacteria and can improve overall health.

If your gut is in a rut, chances are your health is out of sorts too.

The gut, also known as the gastrointestinal (or GI) tract, hosts trillions of bacteria that can have profound effects on digestive health and overall wellness, which is why it’s a good idea to consume prebiotics and probiotics—dietary dynamos that work in concert to populate the gut with “microflora” that keep mind and body healthy.

Research offers clues on cultivating a healthier gut environment. Eating a variety of prebiotic-rich vegetables and probiotic fermented foods every day may improve mood, reduce cholesterol and promote weight loss. As a nutrition or fitness professional, you can help fitness-conscious clients select foods that promote health at “gut level.”

The City Inside You

The human body is a thriving metropolis of bacteria with 10 resident microbes for every human cell (Sommer & Bäckhed 2013); most live in the gut and do no harm, but a few troublemakers can cause diseases. The uniqueness of the GI tract’s microbial profile rivals that of fingerprints.

It’s hard to define a “healthy” microflora environment, because the type and amount of bacteria in the gut vary widely between individuals and geographical regions (Clemente et al. 2012). Diet has a huge impact: People consuming high-fat, high-sugar Western diets tend to have less bacterial diversity than those eating high-fiber, plant-based diets (Sommer & Bäckhed 2013). Furthermore, age, pregnancy, genetics and environment cause flora to fluctuate (Duncan & Flint 2013).

Medications also have a strong impact on gut microflora. Antibiotics frequently shrink populations of friendly bacteria, leaving the GI tract vulnerable to less-friendly bacterial species, inflammation and diarrhea (Sommer & Bäckhed 2013).

On the Defensive

The entire human digestive system is built to fight infection. The mouth serves as a physical blockade against germs (Sommer & Bäckhed 2013), and immunoglobulin A—an antibody— is secreted into oral mucous. Many species of friendly bugs, like those of the Lactobacillus family, thrive in the stomach, where powerful acid fights off unfriendly bacteria. The intestines harbor 70% of our immune system (Sommer & Bäckhed 2013).

Mucosal-associated lymphoid tissue (MALT) and gut-associated lymphoid tissue (GALT) form a roadway along the entire length of the intestines, fending off invaders by storing and secreting immune cells. The inner lumen of the intestines is coated with a biofilm colonized by hundreds of bacterial species (Sommer & Bäckhed 2013) that block bacterial villains by competing with them for nutrients and space (Saad et al. 2013).

Disease, illnesses and antibiotics disrupt the delicate microflora environment, allowing more potentially harmful bacteria to populate the intestinal walls. But a healthier gut environment is possible through symbiotics—the practice of combining prebiotics and probiotics (Ceapa et al. 2013).

Prebiotics: Fuel for Your Flora

Prebiotics are naturally occurring nondigestible carbohydrates, or soluble fibers, that nourish the growth of specific beneficial bacteria. Unlike probiotics, prebiotics are not live organisms. All prebiotics are fiber, but not all fibers are prebiotics. When prebiotics ferment in the intestines, they release fuel that enables friendly bacteria like Lactobacilli and Bifidobacteria to thrive. To be called a prebiotic, the substance must

  • resist gastric acid, hydrolysis by mammalian enzymes, and absorption in the upper gastrointestinal tract;
  • ferment with intestinal microflora, and
  • selectively stimulate growth and/or activity of intestinal bacteria potentially associated with health and well-being.

The most common prebiotics are in the inulin-type fructan family. Inulins are long-chain saccharides that are slowly degraded in the intestines. Smaller-chain inulins include oligofructose, fructooligosaccharides and galactooligosaccharides. All inulins resist digestion in the upper GI tract, so they are intact and fully fermentable by the time they reach the colon. Galactooligosaccharides are found in some legumes, but they are mostly made in the body from lactose (Kelly 2008).

About 5–8 grams a day of inulin prebiotics is enough to support growth of all Bifidobacteria species (Slavin 2013). Inulins are nearly calorie-free and do not raise blood sugar or insulin. Prebiotics have few side effects but may cause gas and bloating. The health benefits of prebiotics are still being investigated, but studies suggest they can

  • reduce the prevalence and duration of infectious, traveler’s and antibiotic-associated diarrhea (Slavin 2013);
  • reduce inflammation and symtoms of inflammatory blwel disease (Slavin 2013);
  • protect against colon cancer (Slavin 2013);
  • enhance the bioavailability and uptake of minerals, including calcium (Coxam 2007);
  • lower some risk factors for cardiovascular disease, such as cholesterol (Ooi & Liong 2010); and
  • promote satiety and weight loss to prevent obesity (Slavin 2013; Kovatcheva-Datchary & Arora 2013).

Probiotics: Alive and Well

Probiotics are live, active bacteria and/or yeasts that can

  • remain viable during processing, transport and storage;
  • ferment with intestinal microflora, and
  • colonize the GI tract;
  • antagonize pathogenic bacteria; and
  • produce demonstrated clinical health outcomes.

The most common strains of probiotic bacteria are the Lactobacillus and Bifidobacteria families, which use lactose to prevent harmful bacteria growth, serve as a physical barrier, compete with bad bugs for nutrients, and alter intestinal pH to tackle bacterial villains (like diarrhea-producing Clostridium difficile) that thrive in a neutral pH environment. Friendly bacteria also stimulate the immune system and curb inflammation (Sommer & Bäckhed 2013).

Eating foods with probiotics may reduce symptoms of irritable bowel syndrome, diarrhea caused by antibiotics, and traveler’s diarrhea (Guarner et al. 2008). Several probiotic strains used in conjunction with antibiotic therapy enhance eradication of ulcer-causing Helicobacter pylori (Guarner et al. 2008). Probiotics may prevent the common cold (Kang et al. 2013). Weight loss and prevention of obesity are linked to consumption of probiotics (Million et al. 2013). Beneficial bacteria may also improve athletic performance (West et al. 2009) and reduce anxiety (Tillisch et al. 2013).

In a review of the medical literature, Nichols (2007) could not find scientific evidence supporting probiotics as an ergogenic aid, though probiotics may benefit athletic performance indirectly (West et al. 2009).

Lamprecht et al. (2012) investigated the use of a probiotic supplement on markers of intestinal barrier and inflammation following intense exercise. Twenty-three trained male endurance athletes received a multispecies probiotic or placebo for 14 weeks. By the end of the study, markers of gut barrier and inflammation had improved over baseline levels.

Variations between probiotic products can be huge—up to 25,000%, according to (2013). Active colonies in supplements decrease over time, so check the “best buy” date. Those allergic to milk should note that some supplements are made from milk. Probiotic supplements are sensitive to heat, light and moisture and may require refrigeration. Check the label for storage recommendations.

Be Good to Your Gut

The depths of the digestive tract host a microbiome of bacteria that are key to good health and well-being. Supplying the gut with a daily dose of prebiotics and live probiotics nurtures a hidden for- tress that protects the body from harm. Encourage clients to support a healthy gut by eating a variety of prebiotic-rich vegetables along with fermented products with live cultures.


ACS (American Cancer Society). 2013. Kombucha tea.; accessed Sept. 18, 2013.

Ceapa, C., et al. 2013. Influence of fermented milk products, prebiotics and probiotics on microbiota composition and health. Best Practice & Research Clinical Gastroenterology, 27 (1), 139-55.

Clemente, J.C., et al. 2012. The impact of the gut microbiota on human health: An integrative view. Cell, 148 (6), 1258-70. 2013. Probiotics for adults, children and pets.; accessed Sept.10, 2013.

Coxam, V. 2007. Current data with inulin-type fructans and calcium, targeting bone health in adults. Journal of Nutrition, 137 (11 Suppl.), 2527S-23S.

Duncan, S.H., & Flint, H.J. 2013. Probiotics and prebiotics and health in ageing populations. Maturitas, 75 (1), 44-50.

Guarner, F., et al. 2008. World Gastroenterology Organisation Practice Guideline: Probiotics and prebiotics.; accessed Sept. 11, 2013.

Kang, E.J., et al. 2013. The effect of probiotics on prevention of common cold: A meta-analysis of randomized controlled studies. Korean Journal of Family Medicine, 34 (1), 2-10.

Kelly, G. 2008. Inulin-type prebiotics—A review: Part 1. Alternative Medicine Review, 13 (4), 315-29.

Kovatcheva-Datchary, P., & Arora, T. 2012. Nutrition, the gut microbiome and the metabolic syndrome. Best Practice & Research: Clinical Gastroenterology, 27 (1), 59-72.

Lamprecht, M., et al. 2012. Probiotic supplementation affects markers of intestinal barrier, oxidation, and inflammation in trained men: A randomized, double-blinded placebo-controlled trial. Journal of the International Society of Sports Nutrition, 9 (1), 45.

Million, M., et al. 2013. Gut bacterial microbiota and obesity. Clinical Microbiology and Infection, 19 (4), 305-13.

Nichols, A.W. 2007. Probiotics and athletic performance: A systematic review. Current Sports Medicine Reports, 6 (4), 269-73.

Ooi, L.-G., & Liong, M.-T. 2010. Cholesterol-lowering effects of probiotics and prebiotics: A review of in vivo and in vitro findings. International Journal of Molecular Sciences, 11 (6), 2499-2522.

Saad, N., et al. 2013. An overview of the last advances in probiotic and prebiotic field. LWT—Food Science and Technology, 50 (1), 1-16.

Slavin, J. 2013. Fiber and prebiotics: Mechanisms and health benefits. Nutrients, 5 (4), 1417-35.

Sommer, F., & Bäckhed, F. 2013. The gut microbiota--masters of host development and physiology. Nature Reviews Microbiology, 11 (4), 227-38.

Tillisch, K., et al. 2013. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology, 144 (7), 1394-1401.

Van Loo, J., et al. 1995. On the presence of inulin and oligofructose as natural ingredients in the Western diet. Critical Reviews in Food Science and Nutrition, 35 (6), 525-52.

West, N.P., et al. 2009. Probiotics, immunity and exercise: A review. Exercise Immunology Review, 15, 107-26.

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About the Author

Martina M. Cartwright, PhD, RD

Martina M. Cartwright, PhD, RD IDEA Author/Presenter

Martina Cartwright is a registered dietitian (R.D.) with a Ph.D. in Nutritional Science and Biomolecular Chemistry from the University of Wisconsin-Madison. She has more than 20 years experience in me...