Fiber is a nondigestible type of carbohydrate found in plants, including fruits, vegetables, legumes, whole grains, nuts, and seeds. Fiber plays a key role in a healthy lifestyle. It helps you feel fuller longer, promotes healthy bowel movements, and aids in chronic disease prevention. You’ll naturally consume more fiber by eating whole plant-based foods, a habit that promotes overall health and supports longevity.
The recommended daily fiber goal is at least 21-25 grams per day for women and 30-38 grams per day for men, with around 10-15 grams of soluble fiber. However, an even higher fiber diet has been tied to a reduced death risk. That said, the average daily fiber intake in the United States is only 16 grams per day, so the goal for most Americans is to reach the minimum target.
Research suggests that a high-fiber diet can reduce chronic disease risk and have positive effects on gut and mental health. Here are four conditions fiber can help with and frequently asked questions about this important nutrient.
Obesity
Fiber is known to prevent obesity in several ways. First, many high-fiber foods are high in volume and low in calories. For example, a medium-sized pear provides over 5 grams of fiber and just 100 calories. That’s the same calorie level of just three Red Vine twists, which contain no fiber. High-fiber foods also take longer to chew, which slows eating pace. This allows the release of gut hormones that signal fullness.
Soluble fiber is a type of fiber that absorbs water and forms a gel-like texture inside the digestive tract. It’s found in found in foods like beans, avocado, apples, oats, and chia seeds. This type of fiber improves fullness, slows digestion, and increases satiation. Compared to insoluble fiber, soluble fiber has been shown to naturally decrease calorie intake by 39% and curb appetite by 45%. Fiber also reduces the number of calories you absorb from food.
In short, fiber allows you to eat more volume, feel fuller, remain fuller longer, and absorb fewer calories, all of which contribute to weight loss. Studies show that simply consuming an additional 14 grams of fiber per day over a 3.8-month period could lead to an average weight loss of 4.3 pounds.
Type 2 Diabetes
Fiber is beneficial for Type 2 Diabetes (T2DM) because it helps regulate blood sugar levels. Soluble fiber slows the movement of food through the digestive tract and causes carbohydrates to be absorbed from the gut into the bloodstream slower over a longer period of time. This prevents spikes in blood sugar and improves insulin sensitivity (how well insulin works to clear sugar from the blood).
A fiber intake of 25 grams per day for women and 38 grams per day for men is linked to a 20-30% reduced risk of developing T2DM.
Also, when fiber is fermented in the gut, healthy bacteria are produced, including two important probiotics called Lactobacillus and Bifidobacterium. Healthy levels of these “good” bacteria in the gut are associated with a reduced risk of both diabetes and obesity due to their anti-inflammatory effects. In contrast, a lack of fiber allows harmful bacteria to grow in the gut, which can lead to inflammation and promote the development of T2DM.
Heart Disease
A higher fiber intake is strongly associated with a reduced risk of heart disease, including hardening of the arteries. Consuming more than 22 grams of fiber per day reduces heart disease risk by 12%.
Soluble fiber helps to lower total cholesterol and “bad” LDL cholesterol. One study showed a 30% reduction in LDL cholesterol through a fiber-rich diet, which is comparable to the effects of common prescription medications. Fiber accomplishes this by binding to cholesterol and eliminating it in your stool, so it doesn’t circulate back into your bloodstream.
Due to its ability to regulate insulin, fiber prevents high concentrations of insulin in the blood. This effect may help reduce blood pressure, which helps reduce heart disease risk. A decrease in blood pressure also may be attributed to the generous amount of micronutrients found in fiber-rich foods, such as magnesium and potassium, as these minerals also help regulate blood pressure.
Fiber also increases the production of compounds in the gut called short-chain fatty acids (SCFAs), which are beneficial for heart health. In contrast, low-fiber diets can promote the production of a compound called trimethylamine-N-oxide (TMAO). TMAO has been shown to trigger the buildup of plaque inside arteries and raise blood clot risks.
Mental Health
Due to growing knowledge about the direct connection between the gut and the brain, known as the gut-brain axis, a fiber-rich diet has been linked to improved mental health. Studies show that diets low in fiber tend to be associated with a higher risk of depression, while more fiber is tied to overall better mental health.
Research has proven that too little fiber can lead to a poor variety of microbes in the gut. This lack of “gut biodiversity” can negatively impact the immune system, lead to inflammation, and decrease the strength of the gut wall, which may allow inflammatory toxins to be absorbed from the gut into the bloodstream. All of these outcomes can contribute to the development of mental health conditions. In addition, people who eat less fiber tend to have higher amounts of pro-inflammatory gut bacteria. This can lead to systemic or full-body inflammation, which is linked to depression and anxiety.
What is the difference between soluble and insoluble fiber?
Both soluble and insoluble fiber have positive impacts on health. Soluble fiber absorbs water to form a gel-like consistency. This helps promote fullness and controls blood sugar by slowing digestion. Soluble fiber can also be fermented in the gut, which leads to beneficial heart effects, such as reduced blood pressure and cholesterol. Insoluble fiber is a type of fiber that doesn’t absorb water. It adds bulk to your stool and promotes regular bowel movements to help maintain overall gut health.
Soluble fiber is found in oats, peaches, bananas, potatoes, and mushrooms.
Insoluble fiber is found in broccoli, brussels sprouts, nuts, carrots, berries, and whole grains.
Some foods contain both types of fiber.
How do fiber, pre-, and probiotics affect my health?
Probiotics are beneficial microbes in the gut linked to health benefits, including digestive and immune support, and improvements in mood and sleep. Probiotics exist naturally in your body. You can also consume some types of probiotics in the form of supplements and in certain foods. Probiotics may be found in non-pasteurized fermented foods, like fermented vegetables, kefir, kombucha, and miso.
Prebiotics are non-digestible compounds found in foods like asparagus, garlic, onions, and underripe bananas. Prebiotics stimulate the growth or activity of “good” or friendly bacteria in the gut. In other words, prebiotics are food for probiotic bacteria.
When fiber-rich foods are fermented in the gut, anti-inflammatory compounds called SCFAs are produced. Without fiber to aid in the production of SCFA, other compounds get fermented, such as proteins or amino acids (the building blocks of protein). Rather than producing beneficial SCFAs, this interaction creates inflammatory metabolites that increase chronic disease risk.
In addition to their anti-inflammatory properties, SCFAs promote the release of hormones that properly regulate satiety and hunger cues, insulin response, and the health of the intestinal wall.
Prebiotics and probiotics also may help lower “bad” LDL-cholesterol and inflammatory markers, which improve heart health and reduce inflammation. This is accomplished by promoting the growth of healthy gut bacteria and curbing harmful or pathogenic bacteria, which improves immune function. Some fiber rich foods also provide antioxidants called polyphenols, which reduce inflammation and counter damage caused by compounds called free radicals, which harm cells and promote disease.
When should I have a low-fiber diet? What plant-based whole foods are low in fiber?
A low-fiber diet may be required in times of gastrointestinal distress, specifically when there is a narrowing or blockage inside the intestines or if you’ve been told to reduce your fiber intake prior to a colonoscopy or other GI procedure. If this is the case, both high-fiber foods and fiber supplements should be avoided.
Eating a low-fiber plant-based diet can be a challenge. Cooking vegetables thoroughly helps break down their fibrous structures. You should also avoid the skins and edible seeds of fruits and vegetables and choose canned produce over fresh. Generally speaking, aim for soft foods. Other examples of plant-based low-fiber foods include applesauce, grits, smooth nut butters, and plant-based milks or yogurts.
Can I get too much fiber?
Yes. Reaching close to 70 grams of fiber per day from supplemental forms can negatively impact the body’s ability to absorb vitamins and minerals, which can lead to nutrient deficiencies.
How do I incorporate more fiber into my diet?
If fiber is a new part of your diet, it’s best to incorporate it into your daily routine slowly and gradually. If your body isn’t used to a large amount of fiber, a big increase at once can overwhelm your digestive system and cause bloating, gas, or abnormal bowel movements. To avoid these symptoms, add fiber-rich foods to your diet slowly over time to allow your system to adjust. Continue to add high-fiber foods as you tolerate them and hold off on increasing your fiber intake if you experience any irregular symptoms. Work your way up to a high-fiber diet at your own pace.
Does fiber help with constipation or with diarrhea?
Fiber helps with both constipation and diarrhea. Fiber adds bulk to stool, which promotes formed bowel movements as opposed to diarrhea. It also promotes regular bowel movements to prevent constipation. Therefore, fiber assists in promoting healthy bowel movements overall.
When you experience constipation, eat vegetables, fruits with edible peels, beans, lentils, skin-on potatoes, nuts, and whole grains. And be sure to drink plenty of water to help your body properly utilize fiber.
When you experience diarrhea, eat bland, starchy foods, such as bananas, rice, applesauce, oatmeal, sweet potatoes, or toast, and stay well hydrated.
Should I take a fiber supplement?
You can meet your body’s fiber by eating whole plant-based foods. Fiber supplements may offer positive benefits that come with an increased fiber intake, such as blood sugar regulation. However, fiber supplements can also decrease the absorption of certain medications. If you choose to take a fiber supplement, be sure to talk to your healthcare provider about possible medication interactions. If you meet the recommended fiber intake by eating fiber-rich plant foods, you shouldn’t need to take a fiber supplement.