June 2012 Issue

Gut Health and Immunity — It’s All About the Good Bacteria That Can Help Fight Disease
By Lori Zanteson
Today’s Dietitian
Vol. 14 No. 6 P. 58

The gut is hardly cocktail party conversation, but some would argue that it’s on its way to becoming just that. Not only is gut health a popular topic in scientific research, it has a following in food circles. An understanding of the association between food and the gut for increased immunity and overall health is gaining momentum, as is the RD’s role in preventing disease through the promotion of a gut-healthy diet.

The Basics
Everything we eat and drink passes through the gut along the gastrointestinal (GI) tract. It seems simple enough, but the tubelike GI tract, lined with a thin, sticky mucous, is embedded with millions of bacteria that live, grow, and metabolize (digesting and absorbing) in what’s considered a complex ecosystem comprised of both beneficial and harmful bacteria. According to A. Venketeshwer Rao, MSc, PhD, professor emeritus in the department of nutritional sciences at the University of Toronto, “It’s the predominance of the beneficial bacteria referred to as the probiotic bacteria, such as bifidobacteria and lactic acid bacteria, that ensure good health and prevent diseases of the gut and other organs in the body.”

Recent evidence, Rao explains, shows a close involvement of gut microflora and various aspects of health, such as nutritional status, behavior, and stress response. “[The gut microflora] accomplish this via several mechanisms,” Rao says, “but primarily by metabolizing our dietary constituents to either detoxify them or activate them into toxic forms. A presence of pathogenic bacteria requires a well-functioning and strong immune system to prevent infections. In this way, the nature and composition of the gut microflora can influence our immune system.”

These beneficial probiotic bacteria do several things that contribute to good health and immunity. As Rao mentioned, their most basic function is to fight harmful foreign substances that enter the body by detoxifying them and easing their elimination. Probiotics can prevent the growth of harmful bacteria, which thrive and grow within a neutral pH environment, by producing organic acids such as acetic and lactic acids that, in turn, lower the pH of the large intestine. This lower pH also prevents the metabolism of cholesterol and bile acids in the colon. “Since cholesterol and bile metabolites act as cancer-causing agents,” Rao explains, “they can play an important role in the prevention of cancers of the GI tract and other organs as well.” These helpful bacteria, he continues, can even lower serum cholesterol levels along with cardiovascular disease risk by preventing the activity of an enzyme involved in the synthesis of cholesterol.

What Is Gut Health?
While there’s no clear definition of gut health other than a general absence of disease or GI issues, “Gut Health: A New Objective in Medicine?” published in the March 2011 issue of BioMed Central Medicine, lists five criteria that provide a positive basis for understanding (see sidebar).1

Intestinal microbiota, or gut flora, and the gut barrier determine gut health. Inside the gut are about 100 trillion live microorganisms that promote normal GI function, protect the body from infection, and regulate metabolism and the mucosal immune system. In fact, they comprise more than 75% of the immune system. Also important is their role in maintaining and protecting the GI barrier. An intact GI barrier maintains gut health, while a problem with its microbiota composition will affect the body’s defense systems and can create a condition known as leaky gut syndrome, which can compromise gut health and lead to diseases such as inflammatory breast cancer, obesity, chronic fatigue syndrome, and depression.

Maintaining Gut Health
When it comes to gut health, Kathie Madonna Swift, MS, RD, LDN, coauthor of The Inside Tract: Your Good Gut Guide to Digestive Health, said in the March 21, 2012, webinar “Functional Nutrition and the Gut” that “diet and nutrition therapy should be the first route [to obtaining gut health], not the alternative. In Western medicine, they [prescribe] medicine.” Based on several studies, the current medical focus is on treatment rather than prevention. Several drugs exist to treat acute inflammatory bowel disease (IBD), for example, but none to prevent it.

The research behind what’s known as the hygiene hypothesis says an imbalance within the gut will impair the gut barrier and increase risk to gut health and of developing disease. Conditions that cause imbalance can be an unbalanced diet but also may be lack of exercise or chronic stress. Recent studies have shown that high dietary fat and high fructose disturb the GI barrier, which can lead to fatty liver disease and inflammation.1 On the other hand, positive changes in the diet have been shown to help prevent major diseases such as obesity, allergy, and cancer.1 As more research shows the key role that diet and lifestyle play in maintaining gut health and preventing GI diseases, including infection, IBD, and food allergies, Swift says, “We [dietitians] have to be the change agent to make this happen.”

Swift says processed foods and today’s grains vs. ancient grains have a big impact on gut function. To help improve it and prevent disease, she counsels clients to feed gut flora by “plant centering the plate” and eating foods that are nutrient dense, high in fiber, and have a low glycemic load.

As a proponent of the RD’s role in public health, Rao agrees. Dietitians would do well to counsel clients to eat “health-promoting diets and, in particular, diets that help promote the predominance of the beneficial bacteria,” he says. Because probiotic bacteria use complex carbohydrates such as dietary fiber and harmful bacteria use dietary proteins and fats to produce toxins that can damage good health, Rao suggests a diet that’s a “good source of complex carbohydrates and low in red meats, which are sources of protein and saturated lipids. Good food sources of complex carbohydrates include fruits, vegetables, legumes, and cereals. Another important recommendation is to include foods that are rich sources of antioxidants such as fruits and vegetables.”

 “Food is central, but supplements can be helpful,” Swift adds. Most notable in supporting gut health are supplements containing probiotics or prebiotics. Though the number of studies is limited, probiotics have been shown to maintain gut health and prevent chronic bowel diseases such as IBD and restore leaky gut. While it’s still premature to recommend these supplements as a preventive measure, current evidence indicates a “strong rationale for using probiotics, possibly also in synergistic combinations with prebiotics, to maintain gut health.”1

RDs always have understood and counseled clients on the importance of food as preventive medicine and a maintainer of overall health. By recommending a balanced diet, exercise, and strategies to reduce stress as well as prebiotics and probiotics, RDs can support gut health in their practice. Now that medical research is beginning to make that food and gut-health connection, RDs will play a key role in what will hopefully be a shift in focus from treatment of GI disease to prevention.

— Lori Zanteson is a southern California-based food and health writer whose work has appeared in various publications.


1. Bischoff SC. ‘Gut health’: a new objective in medicine? BMC Med. 2011;9:24.


Five Criteria for a Healthy GI Tract1

Specific Signs of Gastrointestinal (GI) Health
• Normal nutritional status and effective absorption of food, water, and minerals

• Regular bowel movement, normal transit time, and no abdominal pain

• Normal stool consistency and rare nausea, vomiting, diarrhea, constipation, and bloating

Absence of GI Illness
• No acid peptic disease, gastroesophageal reflux disease, or other gastric inflammatory disease

• No enzyme deficiencies or carbohydrate intolerances

• No inflammatory bowel disease, celiac disease, or other inflammatory state

• No colorectal or other GI cancer

Normal and Stable Intestinal Microbiota
• No bacterial overgrowth

• Normal composition and vitality of the gut microbiome

• No GI infections or antibiotic-associated diarrhea

Effective Immune Status
• Effective GI barrier function, normal mucus production, and no enhanced bacterial translocation

• Normal levels of immunoglobulin A, normal numbers and normal activity of immune cells

• Immune tolerance and no allergy or mucosal hypersensitivity

Status of Well-Being
• Normal quality of life

• Qi (ch’i), or positive gut feeling

• Balanced serotonin production and normal function of the enteric nervous system

— LZ