We’ve all heard the advice that we should “eat more fiber,” but what is fiber, really? How does dietary fiber differ from prebiotics (another buzzword in the nutrition community) and starch? Read on to learn about the nuances of the different types of dietary fiber, starch, and prebiotics and how to incorporate more whole-food sources of these beneficial plant compounds into your diet.
You’ve probably heard the advice to “eat more fiber,” but what is fiber, and which types are most beneficial for your health? Check out this article from nutritionist Lindsay Christensen for a breakdown of the different types of fiber and their benefits. #nutrition #wellness
A Quick Introduction to Fiber, Prebiotics, and Starches
What Is Fiber?
Put simply, fiber is a type of non-digestible dietary carbohydrate found in plant foods. To picture where fiber is located in plants, think back to your high school biology class when you looked under the microscope at a cross-section of thinly sliced onion (or another plant). Under the microscope, you probably saw the onion’s cells arranged in a mosaic-like pattern. The outer edges of each cell, or the cell walls, are where dietary fiber is located. Whole, unprocessed foods are, thus, the best dietary fiber sources because they contain cells with intact, fiber-rich cell walls.
Dietary fibers are composed of chains of monosaccharides, the most basic units of carbohydrates. The monosaccharides in fiber include compounds you may be familiar with, such as glucose, fructose, and galactose. Other, less-familiar sounding monosaccharides found in dietary fiber include xylose and mannose. The monosaccharides in fiber are linked together such that the digestive enzymes produced by our pancreas and in our digestive tract cannot break them down. As a result, fiber passes through our digestive tracts mostly intact.
Fiber is found almost exclusively in fruits, vegetables, tubers, grains, and legumes. While there are a few animal-based fiber sources, including the exoskeletons of insects such as crickets, such foods don’t comprise a significant source of fiber in the typical Westerner’s diet! Consuming a variety of plant foods is, thus, the best way to ensure a sufficient dietary fiber intake. The Institute of Medicine (IOM) recommends that Americans consume 19 to 38 grams of fiber per day, depending on factors such as gender and age. However, most Americans fall short of these recommendations. (1)
An Evolutionary Perspective on Dietary Fiber Intake
Dietary fiber has played an essential role in human evolution. During the early days of hominid (a term used to describe primates, including humans and human ancestors) history, highly fibrous foods were considered “fallback foods,” or foods that hominids turned to when preferred foods, such as wild fruits, were scarce. Humans who could effectively digest and extract nutrition from fallback foods thus experienced a survival advantage when preferred foods were limited during times of famine. (2, 3)
When we look at traditional cultures worldwide, we see that most consume a diet rich in fibrous plant foods. The two exceptions may be the Inuit and Maasai, who consume almost exclusively animal products. Based on these observations, I think it is safe to say that fiber is a natural part of the ancestral human diet, and something that we should consume to optimize our diets in the present day.
Unfortunately, in the modernized Western world, dietary fiber intake is abysmally low compared to ancestral intakes. For example, in the United States, the average adult consumes only 12 to 18 grams of fiber per day, intakes that fall short of the recommended 19 to 38 grams of fiber per day recommended by the IOM. Conversely, in rural Africa, the average adult’s diet contains approximately 100 grams of fiber daily. (4)
What Are Prebiotics?
Prebiotics are naturally occurring compounds in food that promote the growth of beneficial gut bacteria, conferring beneficial physiological effects on the host (aka you!). (5) While fiber has long been considered the main dietary component with prebiotic activity, emerging research indicates that several other plant compounds, including phytochemicals called polyphenols, also exert prebiotic activity. By stimulating the growth of beneficial intestinal microorganisms, prebiotics offer a host of downstream health benefits, which I will discuss in more detail shortly.
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How about Starches?
The “starch” category shares some overlap with dietary fiber and prebiotics. Like fiber, starch consists of chains of monosaccharide units; in this case, the monosaccharide units are glucose. However, a crucial difference between starch and fiber is that our digestive enzymes can break down the glycosidic bonds between the glucose units of starch, making the glucose available to our bodies as energy.
Starch is the most common carbohydrate in the human diet and is contained in many staple foods globally, including wheat and rice. The quality and nutrient density of starchy foods vary widely. Many processed foods available to us at the grocery store, including bread, muffins, cookies, and snack foods, are quite starchy but essentially devoid of any nutritional value. Most of these starchy foods are also made with flour, the pulverized version of a previously whole food that has caused the starch molecules to be released from the plant cell walls, removing beneficial fiber.
Conversely, whole, unprocessed starches, such as sweet potatoes, plantains, cassava, and legumes, provide starch along with an array of micronutrients. These types of starches can absolutely be a part of a healthy diet, though individual tolerance for whole-food starch can vary from one person to the next for several reasons. We will cover starch in more depth shortly.
The Many Types of Fiber
The fiber “family” contains a mind-boggling array of compounds. In the nutrition community’s attempts to understand fiber, we’ve broken down the types of dietary fiber into several categories. However, please note that most foods contain several types of dietary fiber in one package.
Soluble Fiber versus Insoluble Fiber
You may have heard fiber described as either “soluble” or “insoluble.” The soluble versus insoluble distinction helps categorize types of dietary fiber.
Soluble fiber is a type of dietary fiber that dissolves in water and forms a gel-like material in the gastrointestinal tract. A critical feature of soluble fiber is that it slows the movement of food through the digestive tract; this effect is helpful for people who tend to have loose stools. Some types of soluble fiber can be fermented by bacteria in the large intestine, producing short-chain fatty acids (SCFAs) and other beneficial compounds that support gut health and whole-body health. However, not all types of soluble fiber are fermentable.
The major types of soluble fiber in the human diet include:
While most foods contain a combination of soluble and insoluble fiber, some foods that are especially rich in soluble fiber include:
- Sweet potatoes
- White potatoes
- Citrus fruits
On the other hand, insoluble fiber is a type of fiber that does not dissolve in water. It adds bulk to stool and tends to speed up the movement of food through the gastrointestinal tract. Certain types of insoluble fiber are fermentable. The major types of insoluble fiber present in the human diet include some kinds of hemicellulose and beta-glucan, cellulose, lignin, chitin, and resistant starch.
Fermentable versus Non-Fermentable Fibers
Fiber can also be classified as fermentable versus non-fermentable. The fermentable and non-fermentable fiber categories overlap with the soluble and insoluble fiber categories. For example, soluble fibers are usually fermentable. However, certain types of insoluble fiber are also fermentable. For our discussion, the most important thing to remember is that for a healthy gut, you want a balance of both soluble/insoluble and fermentable/non-fermentable fibers in your diet.
Next up, let’s talk about the main classes of dietary fiber and where these fibers can be found in the diet.
The Main Classes of Fiber
Cellulose is an insoluble fiber composed of long, straight chains of glucose molecules connected via beta-glycosidic bonds, a type of chemical bond that cannot be broken by human digestive enzymes. Cellulose is the main structural component of plant cell walls. It cannot be broken down at all by human digestive enzymes, so its primary function is to add bulk to stool, aiding with bowel movement regularity. (6) Cellulose is found in foods such as:
- Wheat and rice bran
- Root vegetables
- Apple skins
- Hearty leafy greens such as collard greens and kale
Like cellulose, hemicellulose is a fiber that serves as a structural component of plant cell walls. Unlike cellulose, it is composed of a variety of monosaccharides, including xylose, mannose, galactose, rhamnose, and arabinose. Unlike straight-chained cellulose, hemicellulose has complex side chains and branches. Depending on subtle variations in hemicellulose structure, hemicellulose can either be soluble or insoluble. Hemicellulose is found largely in cereal grains such as:
Pectin is a structural carbohydrate that acts like a “cement” within plants, holding plant cell walls together. The main component of pectin is galacturonic acid, a sugar acid derived from the monosaccharide galactose.
Pectin is highly soluble in water and has thickening effects that have long been employed in jam- and jelly-making. It is also fermentable by gut bacteria and has the potential to beneficially modify the gut microbiota. (7) Pectin is found in significant quantities in:
- Citrus fruits
Lignin is a complex fiber crucial for the formation of plant cell walls. It lends rigidity to wood and bark but is also found in edible plants such as root vegetables and leafy greens. It is insoluble and non-fermentable. Food sources of lignin include: (8, 9)
- Vegetables with an edible stem such as asparagus and broccoli
- Root vegetables such as parsnips and beets
Chitin is a unique fiber that is not commonly found in the Western diet. It is located primarily in fungi, such as edible mushrooms, and the exoskeletons of insects. Chitin is composed of a long-chain polymer of N-acetylglucosamine, a derivative of glucose, and is both insoluble and slightly fermentable. If you’re feeling adventurous, cricket flour is a rich source of chitin that you might consider incorporating into your diet!
Gum is a complex type of fiber that can be either soluble, partly soluble, or insoluble. Gums are naturally found in several foods, including the konjac plant (used to make those zero-calorie “Miracle Noodles”) and carob beans. However, synthetic gums have also been invented for use in industrial food processing; some examples of synthetic gums include xanthan gum and carrageenan. Carrageenan, in particular, appears to have undesirable pro-inflammatory effects on the gut and should be avoided as much as possible. (10)
Beta-glucans are a class of fibers found in the cell walls of certain types of yeast, fungi, bacteria, and plant foods such as oats, barley, rye, and mushrooms. Beta-glucans are soluble fibers, and some demonstrate beneficial effects on metabolic health, including blood sugar control. (11)
Mucilage is a viscous, soluble fiber that readily absorbs water in the gastrointestinal tract, swelling up in size and forming a gelatinous substance that adds bulk to stool. While it is soluble, it is not very fermentable.
Mucilage is found in several time-honored medicinal herbs, including:
- Licorice root
- Slippery elm bark
- Psyllium seed
It is also found in many foods, including:
- Chia seeds
- Aloe vera gel
Fructans are soluble and highly fermentable carbohydrates consisting of chains of fructose molecules joined together with a glucose molecule at the terminal end. Fructans are found in inulin, a popular prebiotic fiber included in certain prebiotic/probiotic combination supplements, as well as:
- Jerusalem artichoke
What about FODMAPs?
The acronym “FODMAP” stands for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols,” a group of short-chain carbohydrates in a variety of plant foods. FODMAPs tend to be poorly absorbed by individuals with gut dysbiosis and can trigger symptoms such as gas, bloating, and diarrhea. In some individuals, temporarily limiting FODMAP-containing foods in the diet can alleviate symptoms while the underlying causes of the dysbiosis are being treated. However, a low-FODMAP diet is not necessarily a low-fiber diet; it is possible to maintain a healthy fiber intake while limiting FODMAPs. On the low-FODMAP diet, you’ll want to avoid a specific type of dietary fiber, the fructans, which are a type of oligosaccharide. To maintain a robust fiber intake on a low-FODMAP diet, focus on low-fructan plant foods such as:
- Bok choy
- Ripe plantains
Please note that people can be sensitive to certain FODMAP foods but tolerate others just fine, so a bit of dietary experimentation may be required. Working with a nutritionist can be immensely helpful in this situation. A nutrition professional can help design a diet for you that limits the problematic FODMAP foods while retaining sufficient FODMAPs to support a healthy gut microbiome.
What about Starch?
How does starch differ from fiber? While our bodies lack digestive enzymes capable of breaking down the bonds between monosaccharides in fiber, we do have digestive enzymes capable of breaking down starch. Unlike fiber, starch can, thus, be used directly as a source of caloric fuel for our bodies. The exception to this rule is resistant starch, a special type of starch that can be broken down only by our gut bacteria. The roots of plants frequently serve as energy storage sites and are, thus, rich in starch. Examples of edible starchy roots include:
- Sweet potatoes
Starch is also found in the endosperm of cereal grains such as wheat, corn, and rice.
There are three main types of starch in food: amylose, amylopectin, and resistant starch. Let’s discuss each in turn.
Amylose is a form of starch consisting of long, linear chains of glucose. It is insoluble in water. Amylose is found in:
- Whole grains
Amylose is fairly resistant to digestion and may exacerbate gastrointestinal discomfort in individuals with small intestinal bacterial overgrowth, or SIBO, by triggering bacterial fermentation in the gut. There are also significant genetic differences in people’s ability to digest amylose due to variations in the genes that code for amylase, the digestive enzyme that breaks down amylose. These variants lead some people to produce more amylase than others. Those with a genetic predisposition toward higher amylase production may better tolerate starchy foods than people with lower amylase production. (12)
Unlike linear-chain amylose, amylopectin consists of long, branched chains of glucose molecules. The branched structure of amylopectin makes it easier to digest. Amylopectin is found in:
- Jasmine rice
- Russet potatoes
- Ripe plantains
Resistant starch is a form of starch that cannot be broken down by the amylase enzyme. Instead, resistant starch feeds bacteria in the large intestine. It is insoluble but highly fermentable, making it unique among the various types of fiber and starch in the human diet. Food sources of resistant starch include:
- Raw white potatoes (13)
- Cooked and cooled white potatoes
- Cooked and cooled white rice
- Green banana flour
- Purple sweet potatoes (14)
Most foods contain a complex mixture of the dietary fibers and starches I’ve discussed here. However, there may be some fibers and starches that you tolerate better than others, based on your current gut health, digestive capacity, metabolic health, and inflammation levels. A certified nutrition specialist or registered dietitian can help you determine which dietary fibers and starches work best for your body.
Together with nutritionists and practitioners, health coaches are essential members of an effective Functional Medicine healthcare team. Health coaches work with clients to tackle behavior change. Whether that means adding healthy, whole-food sources of fiber to the diet or taking other steps to support the gut, a health coach is there each step of the way to offer support and accountability—crucial components to successful, long-lasting change.
Want to learn more about what health coaches do and how they’re uniquely qualified to offer support? Check out the ADAPT Health Coach Training Program.
Prebiotics are compounds that support the growth of beneficial gut bacteria. Dietary fibers and starches can act as prebiotics, but so can other plant-derived molecules such as polyphenols and microRNA, small bits of non-coding genetic material that play essential roles in cellular processes in plants. (15, 16) By improving the gut microbiota composition, prebiotics have downstream beneficial effects on many aspects of health, including bone health and brain function.
Examples of prebiotic foods include:
- Inulin (found in chicory and dandelion roots)
- Green tea
- Cacao and dark chocolate
- Raw honey
The Health Properties of Fiber, Prebiotics, and Starches
Now that we’ve discussed the compositional differences between fiber, starch, and prebiotics, let’s talk about health benefits. Fiber, starch, and prebiotics offer a fascinating array of health benefits that start (but definitely don’t stop) in the gut.
Fiber is well-known for its effects on bowel movement regularity. Dietary fiber supports gastrointestinal peristalsis or the muscular contractions that move food through the gut, by altering the stool viscosity. Increased stool viscosity provides visceral feedback to the enteric nervous system, increasing muscular contractions, and accelerating stool movement. (17)
However, not all types of fiber aid bowel regularity; research indicates that some fibers, such as wheat dextrin (an insoluble fiber found in supplements such as Benefiber) and wheat bran particles, can actually exacerbate constipation. (18) If you need additional fiber, beyond the fiber-containing foods in your diet, to help with constipation, you may be better off consuming a high-viscosity soluble fiber such as acacia fiber, also known as “gum arabic.”
Promote Gut Health
Dietary fibers, starches, and prebiotics work together to support a healthy gut ecosystem. Fructans and resistant starch are readily metabolized by intestinal bacteria to create SCFAs. SCFAs, in turn, support a resilient intestinal barrier and regulate the immune system of the gut. (19, 20) Dietary fiber also promotes a healthy gut microbiome by slowing the release of carbohydrates from ingested foods; this effect facilitates the growth of beneficial gut bacteria while limiting the growth of pro-inflammatory bacterial species.
Prebiotics also enhance bacterial SCFA production. Non-fiber prebiotic molecules, including microRNAs, improve gut health through different mechanisms, including direct modulation of the intestinal inflammatory milieu. (21) Cricket flour, a rich source of chitin, supports the growth of beneficial Bifidobacterium animalis, an anti-inflammatory and immune-modulating microbe. (22)
Improve Blood Sugar Control
One of the main benefits of fiber, beyond its effects on the gut microbiota, is its impact on blood sugar control. Soluble fiber slows the absorption of carbohydrates from foods and can, therefore, help support healthy blood sugar levels. (23) Resistant starch also lowers blood sugar after meals and may improve insulin sensitivity by altering the activity of adipokines, cell signaling molecules secreted by adipose tissue. (24, 25, 26, 27)
Reduce Hunger and Promote Satiety
Dietary fiber may enhance satiety and reduce hunger by stimulating neuroendocrine pathways that regulate food intake. This effect may be attributable, in part, to the water-absorbing, bulking effect fiber has on the gastrointestinal tract. (28)
Bind to Toxins in the Gastrointestinal Tract
Interestingly, fiber may serve as a binding agent for excess hormones and environmental toxins in the gastrointestinal tract, limiting their reabsorption in the gut and recirculation via the enterohepatic circulation. For example, fiber binds estrogen in the gut, increasing fecal excretion of the hormone. (29) This is why nutritionists often recommend that women increase their dietary fiber intake if they are dealing with estrogen excess. Dietary fiber also binds with certain heavy metals, such as lead, facilitating metal excretion from the body. (30)
Soluble fiber is excellent at binding up bile acids, substances found in bile, a critical digestive fluid necessary for fat emulsification and absorption in the gut. Bile acids grab on to cholesterol molecules, and soluble fiber grabs on to bile acids, facilitating the excretion of excess cholesterol from the body in the stool. This effect explains why soluble fiber-rich foods, such as oats, have long been touted as a cholesterol-lowering superfood. (31)
Support Bone Health
Dietary fiber may support bone health by reducing gut inflammation, which contributes to bone degeneration when left unchecked, and by improving the intestinal absorption of bone-building minerals such as calcium. (32) Prebiotics and probiotic bacteria work together to regulate bone health. (33)
Influence Brain Health and Mood
The gut–brain axis is a bidirectional network of neurons and signaling molecules that connects the enteric nervous system of the gut and the gut microbiome with the central nervous system. As Chris has discussed at length in several articles, including “Heal Your Gut, Heal Your Brain,” the goings-on of the gut significantly impact brain health, mood, and behavior via this axis. Emerging research indicates that dietary fiber, starches, and prebiotics influence brain function and mood via the gut–brain axis by altering the gut’s microbial ecosystem and the signaling molecules produced by gut bacteria.
Soluble fiber may support healthy brain function during the aging process by enhancing the production of butyrate, an SCFA. Butyrate exerts anti-inflammatory effects both locally in the gut and distally in the brain via the gut–brain axis. (34) A high-fiber diet may also promote healthy gene expression in the brain, protecting against neurodegenerative disease processes and promoting regenerative processes. (35) Fascinating research also suggests that resistant starch alters the gut–brain axis, at least in non-human animals. (36)
Aid in Body Composition and Weight Management
Last but not least, higher dietary fiber intakes are associated with a healthier body composition and lower body fat levels. (37) When adhered to over the long term, a high fiber intake may promote a healthier body composition by reducing caloric intake.
Resistant starch has also been hailed as a weight loss aid. Research indicates that resistant starch consumption inhibits body fat accumulation, potentially by improving satiety and glucose and insulin metabolism. (38)
Impact Nutrient Accessibility with Both Positive and Negative Effects
The fiber content of edible plants significantly impacts the bioaccessibility of the nutrients contained within those plants. (39) This characteristic offers both benefits and drawbacks. In terms of benefits, eating starches rich in fiber, such as sweet potatoes, slows the absorption of the carbohydrates found in the food; this has beneficial effects on blood sugar control and the gut microbiota. Chris has previously discussed this topic in the context of cellular versus acellular carbohydrates. However, the fiber in foods also has a drawback in that it can inhibit the absorption of certain micronutrients, such as iron, when consumed in large quantities. Antinutrients, such as phytic acid and oxalates, can also impact the bioaccessibility of nutrients in foods; however, that is another whole topic that requires its own article!
Striking a balance between raw plant food intake and the consumption of plants that have been fermented, soaked, sprouted, and cooked will ensure that you get plenty of dietary fiber and micronutrients.
Fiber-Rich Foods, Prebiotics, and Starches to Add to Your Diet
When most people think of fiber, they think about whole grains. However, there is an entire world of fiber-rich foods out there beyond just whole grains. Here’s a sampling of some fiber-rich foods to consider adding to your diet.
Many medicinal herbs contain dietary fibers and prebiotics with health-supportive properties. Licorice root, slippery elm bark, Triphala, garlic, and ginger are a few botanicals that are particularly rich in dietary fibers and prebiotics.
Licorice root is an herb with an extensive history of use in traditional Chinese medicine and Western herbalism. In recent years, its health-supportive constituents have been more thoroughly explained. Licorice root contains a variety of fibers, including mucilage, which enhances the growth of beneficial gut bacteria such as Bifidobacterium spp., Lactobacillus spp., and Bacteroides spp., while reducing the abundance of the opportunistic pathogen Klebsiella pneumoniae. (40)
Slippery elm bark also contains beneficial dietary fibers with gut-soothing and prebiotic properties. It contains mucilage, gums, and pectin, which soothe the gut mucosa and increase the production of SCFA-producing gut bacteria. (41)
Triphala, a combination of three herbs (Emblica officinalis, Terminalia bellerica, and Terminalia chebula) used in traditional Indian Ayurvedic medicine, also offers prebiotic properties that enhance the growth of beneficial gut bacteria. (42)
Garlic contains fructans that selectively stimulate the growth of Bifidobacterium spp., while ginger contains microRNAs that reduce intestinal inflammation and enhance the gut microbiome. (43, 44, 45)
Honey isn’t just a delicious sweetener; it also contains carbohydrate molecules called oligosaccharides that have prebiotic properties, promoting the growth of Lactobacillus and Bifidobacterium. (46) Be sure to choose raw, organic honey; this will ensure that you’re not purchasing honey that has been adulterated with corn syrup or other unsavory additives.
Green Banana Flour and Green Plantains
Green, unripe bananas and green plantains are excellent sources of resistant starch. Research indicates that supplementation with green banana flour can improve gastrointestinal symptoms, improve glucose metabolism, and support a healthy body weight. (47) You can find organic green banana flour on Amazon or make your own resistant starch-rich green plantain chips at home in an oven or dehydrator. For more on adding plantains to your diet, see this article.
The fermentation process used to create fermented vegetable foods like sauerkraut and kimchi breaks down certain dietary fibers, particularly fibers in the fructan family, and can render the fermented vegetables easier to digest than their unfermented counterparts. Sourdough fermentation of wheat flour breaks down fructans in wheat, reducing the bread’s FODMAP content and making it easier to digest. (48)
Berries, Apples, and Citrus Fruits
Berries, apples, and citrus fruits contain substantial amounts of pectin, a fiber that is readily fermented by gut bacteria. (49) Blueberries also offer a nice dose of polyphenols, small phytochemicals with prebiotic properties. (50)
Green tea doesn’t contain fiber, but it does contain polyphenols with prebiotic properties. In fact, green tea polyphenols have been found to exert prebiotic properties on the gut microbiota, at least in animal studies. (51)
Tigernuts are small tubers (with a funny name!), also known as “chufa” or yellow nutsedge. Tigernuts contain resistant starch and are a great Paleo-friendly, autoimmune-protocol-friendly way to get more resistant starch into your diet. (52) Tigernuts can be ground into a flour with a slightly sweet, nutty flavor that is great for baking. (53)
Legumes, such as lentils and chickpeas, are an excellent source of resistant starch. (54) I recommend that you soak, sprout, or ferment legumes before cooking and eating them; these preparation processes reduce antinutrients in legumes that can be irritating to the digestive tract and maximize digestibility.
Oats are rich in soluble beta-glucan fibers, which offer several health-promoting properties. The soluble fiber in oats can help normalize bowel movement frequency and consistency, increase intestinal bacterial production of SCFAs, and help reduce blood cholesterol levels, if high cholesterol is a concern. (55, 56)
This source of dietary fiber is for the adventurous souls out there! While insects such as crickets are a part of many traditional diets around the world, they are foreign territory for most of us here in the United States. However, research on the health benefits of edible insect consumption is growing. If you are interested in adding edible insects to your diet, cricket flour is a great place to start. It is rich in the dietary fiber chitin, which has been found to improve the gut microbiota composition. The cricket flour trend is growing; you can now find cricket flour recipes on the Food & Wine website, try cricket flour protein bars from an up-and-coming company called Exo, and even buy a bag of edible insects from Amazon!
However, please note that if you have an allergy to dust mites, you may want to avoid cricket flour. The allergic response to dust mites may be driven by an immune reaction to chitin, and cricket flour could potentially cause a cross-reaction.
Dietary fiber, prebiotics, and starches are essential elements of a nutrient-dense, ancestral-template diet. Incorporating more of these plant compounds into your diet may support your beneficial gut bacteria and improve overall gut health, support a healthy metabolism and body weight, and even influence your brain and bone health.