Since prebiotics seem to play a role in nourishing a healthy gut microbiota, what does that mean for smart eating choices? Not all fiber provides prebiotic benefits, as we discussed in part one of this series, which summarizes where today’s research stands on prebiotics’ potential health benefits.
Let’s focus now on the practical take-home steps following that update. What food choices are doable ways to nurture gut bacteria that promote good health?
Translating Prebiotic Research to Food Choices
Prebiotics seem to protect health through direct effects on the gut microbes they support and through substances those gut microbes produce from the prebiotic. By definition, a prebiotic is a substance supports specific gut microorganisms that provide a health benefit.
Here’s a brief summary of the very complex science, showing some of the challenges in translating laboratory studies to practical tips for healthy eating. The most well-supported choices come from controlled studies, which show prebiotic benefits from two particular carbohydrates: inulin-type fructans and the galacto-oligosaccharides (GOS), although many others are under investigation.
- Inulin-type fructans can be extracted from plants, produced by breaking down inulin in plants to form oligofructose, or produced from sucrose (forming “FOS”, fructo-oligosaccharides, sometimes used as an alternative sweetener in yogurt or other dairy products).
- Galacto-oligosaccharides (GOS) are found in pulses (dried beans, peas and lentils). However, prebiotic research often uses a specific type that’s commercially produced by treating lactose (the carbohydrate in milk) with a particular enzyme. It’s not clear whether its effects on gut bacteria are the same as GOS from whole foods.
Mounting research shows that diets high in plant foods and dietary fiber can change the bacteria that make up the gut microbiota. We also have studies linking such microbiota changes to lower levels of markers of inflammation and to other indicators of good health. The challenge now, while research is still limited: How can we put together the puzzle pieces….
What Eating Habits Support a Healthy Microbiota?
Foods with Identified Prebiotics
Foods that provide inulin, inulin-type fructans, FOS and GOS, when a large enough part of the diet, tend to increase the variety of gut microbes (a beneficial effect).
- Jerusalem artichokes (also called “Sunchokes”) ~ try them roasted or mashed
- Globe artichokes (what most people think of when they hear “artichokes” ~ contain only about half the prebiotic compounds as Jerusalem artichokes, but still a delicious option with more prebiotics than most vegetables
- Onions ~ provide about 25% of the naturally occurring inulin and oligofructose in the American diet
- Pulses ~ dried beans (for example, kidney, navy and black beans), lentils, split peas and chickpeas (garbanzo beans)
- Garlic and Leeks ~use these to flavor almost any vegetable, pulse or other main dish or side
- Asparagus ~ delicious grilled, roasted, steamed, in stir-fries or salads, or with eggs ~ try frozen when fresh is not in season
- Bananas ~ look beyond breakfast, a portable pick-up snack with nuts, a thickener for smoothies
Foods with Potential to Feed a Healthy Microbiota
Certain types of dietary fiber can be fermented by gut bacteria to produce short-chain fatty acids (SCFA) that nurture the cells lining the colon, help strengthen the barrier that protects colon cells, and inhibit growth of harmful microbes. These fermentable fibers don’t meet the precise definition for prebiotics, but studies do suggest potential health benefits from these SCFAs .
Foods with Beta-Glucan (a viscous fiber that can also help lower elevated blood cholesterol and slow blood sugar rise after eating):
- Oats ~ hot or cold (have you tried “overnight oats”?), often overlooked as a snack
- Barley ~ hearty choice for soups and casseroles, terrific side dish in place of white rice
- Mushrooms ~ especially shiitake, chanterelle and oyster mushrooms, but also common white and brown button mushrooms. And mushroom stems contain even more beta-glucan than the caps.
- Seaweed ~ Do you get seaweed salad when you pick up sushi?
- Whole-grain wheat and rye also contain beta-glucan, although whole oats and barley provide more.
Foods with Sorbitol and Mannitol (natural carbohydrates classified as “polyols” that are another type of fermentable fiber):
- “Stone fruits” ~ Peaches, Nectarines, Plums, Apricots, Cherries ~ so nice in salads
- Apples and Pears ~ put slices in a sandwich anywhere in place of jelly
- Raisins ~ portable snack, delicious sweet flavor in chili
- Mushrooms (contain these polyols in addition to the beta-glucans noted above) ~ perfect addition to any stir-fry, roast like a dream, eggs’ perfect partner
Foods with Resistant Starch (a type of starch that is hard for our digestive enzymes to break down, which allows it to pass to the colon where gut bacteria ferment it to form SCFAs):
- Pulses – dried beans, peas and lentils – In addition to providing the known prebiotics listed above, much of the starch in pulses is resistant starch. So there is potential for double-benefit for health-promoting gut microbes.
- Whole grains, such as oatmeal, brown rice and whole wheat, reportedly have greater amounts of resistant starch than their refined versions.
- Potatoes, when cooked and cooled (as for potato salad), some of the easily digested starch becomes resistant starch.
- Bananas when less ripe still have some carbohydrate present as resistant starch
Research is still in early stages, and though promising, its benefit to the gut microbiota is not as easy to interpret as what’s seen with the inulin and fructan compounds, notes Patrice Cani, PhD. He’s a professor and researcher at the Université catholique de Louvain in Belgium investigating prebiotics, who graciously shared insights with me via email. There are five different types of resistant starch, and we need more study to clarify effects of amounts that are relevant to human diets.Another reason to eat pulses at least 3 times a week: They’ve got prebiotics for a healthy gut! Click To Tweet
For a Healthy Microbiota, Overall Diet Matters
Another expert on diet and the gut microbiota, Johanna Lampe, PhD, RD, of Fred Hutchinson Cancer Center, emphasizes, “There are a lot of other aspects of diet-microbe interactions besides fiber that are important.”
Don’t overdo the meat. Diets that are high in meat tend to promote higher levels of gut microbes that tolerate and feed off compounds generated with more meat intake, and these are not microbes that seem to support good health.
- In a study that exchanged customary diets for two weeks between two different populations, microbiota changed. Rural Africans switched to a high-fat, low-fiber “Western diet” experienced changes in gut microbiota that link to greater risk of colon cancer. Even in that short time, markers of inflammation increased, as did colon cell growth rates (associated with cancer risk). And these changes were related to the changes in microbiota. Part of that could stem from decreased fermentable fiber, but evidence suggests that diets high in meat add risk, too .
Focus on abundance and variety of plant foods. Polyphenols, a diverse group of natural compounds in plant foods, show potential to nurture a health-promoting gut microbiota. Reportedly 90 to 95 percent of polyphenols can’t be digested and absorbed in the small intestine, and pass through to the colon. Microbes in the colon break down these polyphenols into new compounds that demonstrate potential for important health protective effects.
- Walnuts provide one example: Rats in a recent study fed a diet with walnuts displayed greater diversity in the gut microbiota than those fed a diet that provided matching fat, fiber and protein, but no walnuts. This research is challenging, because looking at changes in gut microbes based on large categories can miss changes in more specific types within those broad groupings. But overall, increased variety and abundance of bacteria linked with health benefits suggests potential for a positive role.
- Other foods high in polyphenols that scientists are studying for possible protective interactions with the gut microbiota include berries, tea and coffee.
Many plant foods provide some level of polyphenol compounds, so this provides yet another reason that enjoying an abundance of whole plant foods is a smart move for health.Do polyphenol-rich foods like walnuts & berries offer prebiotic benefits? Maybe! Click To Tweet
What about Prebiotics in Functional Foods and Supplements?
Although studies show that basic changes in eating patterns can change gut microbiota, it’s possible that some people (yet to be identified) may benefit from higher levels of prebiotics than they can get in a healthy diet. They might choose to use certain “functional foods” that contain added prebiotics. Other people may not need added prebiotic carbohydrates, but might be pleased to know when checking food labels that ingredients added to improve texture or flavor may actually be providing prebiotic benefit, too.
Chicory root fiber, sometimes labeled as Inulin or Oligofructose, is the source of those carbohydrates noted above identified as prebiotics. But often these are added to foods for other qualities. Inulin enhances moisture and adds a creamy texture, so you may see it in low-fat ice cream, or non-dairy or reduced-calorie yogurt. Baked goods and gluten-free breads use it to improve texture. Inulin and oligofructose add a sweet taste without the calories of sugar. So you may also see it in granola and other cereals or bars. And if you ever go to New Orleans, the city’s famous coffee is actually a blend of coffee and chicory root powder.
Hi-Maize, a resistant starch powder, is made from corn. You may see it in some commercial bread, cereal, pasta and snacks that show higher fiber content. Hi-Maize also comes as a separate ingredient to use in baking, add to smoothies or oatmeal, or thicken soup.
Some sweeteners, Polydextrose (manmade from natural carbohydrates, added as a sweetener or to improve the texture of foods) and Arabinogalactose (produced from other carbohydrates to serve as a stabilizer, binder or sweetener) are examples of prebiotic carbohydrates that can be found as additives in common foods.
Fiber supplements containing psyllium or inulin are prebiotics. However, other brands contain other types of fiber that has different effects. Of course, supplements offer the opportunity to boost fiber, but do not provide the other nutrients found in foods that supply dietary fiber, resistant starch or polyphenols.
Special Cases: Prebiotics & the Sensitive Gut
Although prebiotics offer exciting potential for health benefits, what about people with gut sensitivity, such as Irritable Bowel Syndrome (IBS)? As I noted in part 1 of this series on prebiotics, people with IBS may see themselves forced to decide between eating choices that improve their symptoms and choices that promote long-term health. Some types of fiber are fermented quickly and may lead to excess gas and bloating, even in people without IBS. Others are large molecules, fermented more slowly and less likely to bring these effects.Must people w/ IBS choose eating for improved symptoms OR long-term health? Thx @KateScarlata_RD Click To Tweet
I turned to my colleague, Kate Scarlata, RDN, a digestive health expert dietitian and New York Times best-selling author for insights. Given the known health benefits of prebiotics for gut health, she incorporates them in smaller amounts in the diet of IBS patients, and increases gently to a patient’s tolerance. She notes, “In clinical practice, I have found that some IBS patients can tolerate resistant starch better than short chain prebiotic fibers such as fructans and GOS, so we start with small amounts of raw oats or unripe bananas initially.”
Fortunately, she reports that tolerance to FODMAP-containing foods can change over time. (FODMAP is an acronym for these carbohydrates: Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols.) “In clinical practice, we encourage IBS patients to continue to trial foods with prebiotics, as they may find tolerance improves over time.” Help from a registered dietitian nutritionist with gut health expertise can make a big difference for people dealing with sensitivity. And I’d encourage Kate’s newest book, The Low-FODMAP Diet Step by Step.
Bottom Line on Food Choices with Prebiotics:
A limited range of foods provide what is technically defined as a prebiotic. Not all fiber functions as a prebiotic, nurturing the gut microbiota that seems to play an important role in health. But including an abundance and variety of whole plant foods in overall healthy eating choices provides an array of carbohydrates and polyphenol compounds that seem to support a healthy microbiota. The research here is still emerging, so stay tuned for the big picture.Choose plant foods with carbohydrates & phytochemicals that support a healthy microbiota. Click To Tweet
Want help exploring new, doable ways to include pulses at least three times a week? Sign up for the Half-Cup Habit 30-day challenge to target that goal. You’ll get free tips, menu ideas and recipes provided by U.S. and Canadian pulse growers.
(Once you master that, aim for pulses 5 to 7 days a week, as we discussed in a previous Smart Bytes®!)
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My sincere thanks to Patrice D. Cani, PhD; Johanna Lampe, PhD, RD; and Kate Scarlata, RDN; for graciously lending their expertise to this post through comments shared in personal interviews.
Information on Kate Scarlata’s book is provided for information only. I receive no compensation for mentioning it or for any resulting purchases.
Top photo credit: 123rf.com – 58544580_s – profile_marilyna