You can argue the pros and cons of a ketogenic or a vegan diet on end, but there are only upsides to a high-fiber diet. If you had a diet matchmaker, it’s likely a high-fiber diet is “the one” — with zero reservations or stipulations. Yes, fiber is that good.
“Research has shown that diets low in fat and high in fiber reduce the risk of heart disease, diabetes, irritable bowel syndrome and even some cancers,” says Robert Graham, a board-certified integrative-medicine doctor and co-founder of FRESH Med. “So start eating your fiber!”
Read on to learn more about fiber, and the best food sources to get your fill.
The Facts on Fiber: Soluble vs. Insoluble
Dietary fiber is the indigestible parts of plant-based foods, such as fruits, vegetables, beans and whole grains, that travel through the gut and help manage digestion and waste. This essential nutrient falls into the carbohydrate category, but unlike most carbs that break down into sugar, dietary fiber remains untouched as it passes through the body.
“Fiber is like a sponge, so without water, it won’t work.”
There are two types of fiber: soluble and insoluble. Soluble fiber comes from structures within the cells of the plant. Once it enters the digestive tract, it mixes with water to form a gel in the digestive tract that binds to fatty acids. This slows down digestion and the rate of sugar absorption. As a result, blood-sugar levels stabilize and cholesterol levels go down, which in turn helps prevent heart disease.
On the other hand, insoluble fiber comes from the hard, structural part of plants, such as bran, seed husks and the skins of fruits and vegetables. Insoluble fiber makes its way through the digestive system relatively intact, bulking up stools and acting as an intestinal broom that sweeps waste out through the colon.
Both types of fiber are necessary, but neither one can function on its own. “Both types of fiber are completely dependent on the amount of hydration in your system,” says Graham. “Fiber is like a sponge, so even an adequate amount of fiber won’t work without enough water.”
The Health Benefits of a High-Fiber Diet
In addition to regulating bowel functions, a high-fiber diet has been linked to a lower risk of heart disease and lower risk of breast cancer. Fiber can also contribute to weight loss because it makes you feel full without the extra calories (insoluble fiber has no calories). Some studies even link a high fiber diet to fewer and less severe food allergies. Got digestive issues, like constipation or an upset stomach? Fill up on fiber.
“When there isn’t enough fiber in the diet, bad bacteria can take over.”
Fiber helps power the gastrointestinal system, which plays an important role in boosting your immune system, says Andrea Arikawa, PhD, a professor of nutrition and dietetics at the University of North Florida. “Once undigested fibers arrive in the large intestine, they serve as prebiotic fuel for the friendly bacteria living there,” she says. “When there isn’t enough fiber in the diet, there will be a shift in the microbiome to favor growth of bacteria that can survive on fat and protein (aka the bad guys).”
Arikawa explains that gut microorganisms produce compounds that are circulated throughout the entire body. An overgrowth of bad bacteria can produce inflammatory compounds or compounds that cause plaque in the veins. “Therefore, a lack of fiber has implications for cardiovascular disease, diabetes and obesity,” she says. “It goes way beyond gut health.”
Are You Getting Enough Fiber?
The recommended daily amount of fiber is 25 grams for women and 38 grams for men. But it’s worth noting that these numbers are just the minimum requirement. “That is where we should be starting,” says Graham. “A high-fiber diet is considered to be anything over that minimum.”
Currently, Americans only eat about 16 grams of fiber per day, which is alarming since fiber is essential for healthy bowels and regularity. “We’re a fiber-deficient society,” says Graham, “which means we’re a constipated society.”
On the other end of the spectrum, it’s also possible to overdo it. Arikawa says going above your maximum tolerable amount (40 to 50 grams for most people) can result in gas, bloating, cramping and, ironically, constipation. “The important thing is that if you want to increase your fiber intake, do it gradually and drink lots of fluids along with it,” says Arikawa.
Those on low-carb diets (we’re looking at you keto) are at more risk of fiber deficiency because a lot of fiber is found in grains and fruits. “The diet itself is fine, but the problem is people sacrifice fruits and vegetables for too much meat,” says Graham. “Instead, they should focus on low-carb, plant-based foods.” Avocados, for example, could meet both high-fiber and high-fat needs.
Fiber Supplements: Friend or Faux?
So, can we just take fiber supplements to boost our intake? Yes and no. Fiber pills and powders can help get you there, but they’re not a one-to-one substitute for natural fiber-rich foods. Graham says fiber supplements should only be used to complement a well-balanced diet, but never as a primary source. “The whole is greater than the sum of its parts,” he explains, “and these products don’t provide the vitamins, minerals and micronutrients that fibrous foods have.”
If you need supplements to fill in gaps, be wary of synthetic sources of the fiber, such as methylcellulose, calcium polycarbophil and wheat dextrin. “They’re chemicals and we’re not robots,” says Graham. “We’re humans and we need to process food.” He recommends food-based supplements, like psyllium and inulin, which is also a prebiotic.
The best sources of fiber are always going to be whole foods, most of which contain the two types of fiber. But Arikawa says it’s not necessary to calculate them separately. The focus should be on overall fiber intake, rather than the specific type of fiber.