Eating a high-fiber diet has numerous benefits, from promoting good digestive health to preventing a wide range of gastrointestinal and chronic diseases.
But most people don’t eat enough fiber.
This article will discuss what fiber is, why it’s good for us and what the best foods are for a high-fiber diet.
What is Fiber?
Fiber is a type of carbohydrate found in the cell walls of plant foods, and is indigestible.
Since it’s indigestible, our bodies do not absorb any calories from it (1).
High-fiber foods include:
- Fruits and vegetables
- Beans and legumes
- Whole grain cereals
- Nuts and seeds
Fiber is crucial for good digestive health. It bulks up and soften stools, allowing them to pass through the digestive tract more quickly, and preventing constipation.
A high-fiber diet can also keep your weight under control, prevent diverticulitis, and reduce your risk of diabetes, cardiovascular and coronary heart disease and colorectal cancer (2, 3, 4, 5, 6)
Unlike other types of carbohydrates—such as starch and sugar, which are digested in the small intestine—fiber passes through to the large intestine, where it’s fermented by healthy gut bacteria.
A healthy gut microbiome has several beneficial effects. It supports a healthy immune system, promotes good mental health, stabilizes blood sugar, regulates the appetite and helps lower cholesterol (7, 8, 9, 10, 11, 12).
In the US, the recommended daily amount of fiber for adults is 25 grams for women and 38 grams for men. In the UK, it’s 30 grams per day. However, average intakes are much lower than this, with most people eating just over half of the recommended daily amount (13, 14, 15).
Summary: Fiber is a type of carbohydrate found in the cell walls of plant foods. It’s important for maintaining good digestive health and can help reduce the risk of many chronic conditions, including diabetes and cardiovascular disease. The recommended daily amount of fiber for adults is 25 grams for women and 38 grams for men, but most people are only eating just over half of this.
Types of Dietary Fiber and Best Foods For a High-Fiber Diet
There are three main types of dietary fiber: soluble, insoluble and resistant starch.
Many plant-based foods contain a mix of these fibers, including whole grains, fruits, vegetables, legumes, nuts and seeds.
Insoluble fiber doesn’t dissolve in water, and refers to the plant components cellulose, hemicellulose and lignin, which all make up the plant’s cell wall.
It remains intact during its transit through the digestive tract. It adds bulk to our stools, absorbs fluids and sticks to other by-products of digestion, which helps to prevent constipation and diverticular disease (16).
Foods rich in insoluble fiber include:
- Whole grains (cereals, brown rice, granary bread, wholemeal pasta)
- Beans and legumes (lentils, chickpeas)
- Root vegetables (carrots, potatoes, beets)
- Nuts and seeds
Soluble fiber dissolves in water and gastrointestinal fluids, forming a gel-like substance in the intestine.
It refers to the plant components pectins, gums and mucilages.
Soluble fiber is partially digested by the gut bacteria, which releases gases and a small amount of energy (calories) for the body to use (17).
It also helps draw water into the intestines, delays the rate of gastric emptying, and softens stools, allowing them to move through the digestive tract more easily.
Foods rich in soluble fibers include:
- Beans (black, lima, pinto)
- Brussels sprouts
- Citrus fruits
Resistant starch is another type of fiber that “resists” normal digestion.
Instead of being digested in the small intestine, resistant starch is broken down in the large intestine, where it’s fermented by gut bacteria. This fermentation process produces gases and short-chain fatty acids (SCFAs), which are absorbed and used as an energy source (18).
Studies have shown that resistant starch can help with weight loss, blood sugar control and digestive health (19, 20, 21).
You can change the starch content of a food depending on how you cook and prepare it. Cooking or heating destroys most resistant starches, but if you cook and cool a starchy food, you can increase the resistant starch in it.
Foods high in resistant starch include:
- Cooked and cooled potatoes, pasta and rice
- Green bananas
Resistant starch can also be produced or modified commercially and added into food products, such as baked goods, dairy products, and pasta (22).
Summary: There are three types of dietary fiber, which offer numerous health benefits: soluble, insoluble and resistant starch. Many plant-based foods contain a mix of these fibers, including whole grains, fruits, vegetables, legumes, nuts and seeds.
High-Fiber Diet Benefits
High-fiber diets are associated with numerous health benefits, including supporting your gut microbiome, promoting weight management, and reducing the risk of chronic conditions like diabetes, cardiovascular disease, colorectal cancer and diverticular disease.
There are approximately 100 trillion microbes living in the gastrointestinal (GI) tract, mostly within the large intestine.
These microbes are collectively referred to as the gut microbiome, and can be thought of as a separate, multi-functional organ within the body (23).
They are responsible for the digestion of soluble fibers and resistant starch through bacteria fermentation. This produces short-chain fatty acids (SCFAs), which are associated with health-promoting processes, including:
- Appetite regulation
- Immune system protection
- Blood sugar stabilization
- Cholesterol-lowering effects (24, 25, 26, 27).
Eating a diet high in fiber is one of the best ways to look after your gut microbiome.
Summary: You can beneficially influence the composition and diversity of your gut microbiome by eating a diverse, balanced diet that is high in fiber.
Type 2 Diabetes
A high-fiber diet may help reduce the risk of developing type 2 diabetes.
For example, a recent randomized controlled trial found that a high-fiber diet improved blood sugar control, enabled weight loss and improved lipid profiles in people with type 2 diabetes compared with a control group who ate a normal diet (28).
Consuming soluble fiber in particular has been shown to reduce high blood sugar responses after carbohydrate-rich meals. This could be due to its ability to slow gastric emptying and subsequent absorption of sugar (glucose) from the gut into the bloodstream (29 , 30).
Large-scale studies have shown that eating cereal fibers may have the greatest effects on reducing diabetes risk. Cereal fibers are those found in wholegrains, such as wheat, rice, barley, quinoa, or oats.
A study of 25,000 adults found that over an 11-year period, people with a high cereal fiber intake had a 28% reduced risk of developing type 2 diabetes compared to those with a low cereal fiber intake (31).
This has been confirmed in a more recent and large-scale review, which found that people who consumed a high-fiber diet, especially cereal fiber, reduced their risk of type 2 diabetes by a third (32).
Summary: A high-fiber diet may reduce your risk of developing type 2 diabetes. In particular, eating foods rich in soluble fiber, like whole grains and cereals, have been shown to reduce high blood sugar responses after eating carbohydrate-rich meals.
A high-fiber diet may help reduce the risk of cardiovascular disease, perhaps by lowering blood cholesterol levels.
Having high levels of bad cholesterol (LDL) is a known risk factor for cardiovascular disease. Soluble fiber in foods such as oats and whole grains forms a gel-like substance in the gut that acts like a sponge, soaking up bad cholesterol in the blood (33).
One study found that consuming 3 grams of soluble fiber per day (equivalent to 84 grams of oatmeal, or about 3 servings) lowered LDL cholesterol by 0.13 mmol/L over a number of weeks. While this is a significant change, statins (cholesterol-lowering drugs) are likely to have a bigger impact in the long term (34).
The SCFAs produced during the fermentation of dietary fiber in the large intestine also have cholesterol-lowering effects (35).
A study of over 40,000 men 75 years and older found that a high-fiber intake reduced incidences of heart attacks, even when other factors like smoking were accounted for. For every 10 grams of fiber eaten, risk of heart attacks reduced by nearly one-fifth (19%) (36).
Another study of 300,000 participants with similar findings concluded that fruit and cereal fiber (as opposed to vegetable fiber) had the greatest effect on risk reduction (37) .
Summary: A high-fiber diet may help reduce the risk of cardiovascular disease, possibly by reducing blood cholesterol levels. In particular, soluble fiber found in fruits, cereals and whole grains has been shown to help lower LDL (or bad cholesterol).
There is strong evidence to suggest that a high-fiber diet reduces risk of colorectal cancer.
This notion was first proposed in the 1970s, when scientists observed low rates of colorectal cancer among rural African populations who consumed a high-fiber diet (38).
Later, in 2015, the UK government agreed with this conclusion after their own review. As a result, they increased the daily recommended amount of dietary fiber from 18 grams to 30 grams for adults. (39).
Another meta-analysis found that high intakes of cereal fiber and whole grains (but not fiber from fruit, vegetables or legumes) reduce the risk of colorectal cancer (40).
This is likely because fiber increases the bulkiness of our stools, which is thought to:
- Reduce stool transit time (the time taken for the stool to pass through your digestive system)
- Dilute carcinogenic (cancer-causing) substances in the stool
- Reduce the amount of time that the carcinogenic substances are in contact with the intestinal walls of the digestive tract (41).
Summary: Evidence suggests that a high-fiber diet reduces the risk of colorectal cancer risk due to its ability to reduce stool transit time and dilute cancer-causing substances in the stool. These findings have led some countries like the UK to increase their recommended daily amount of dietary fiber for adults.
Diverticular disease is a digestive condition that affects the large intestine.
Small bulges or pockets called diverticula can develop in the lining of the intestine. When diverticula cause symptoms, such as pain in the lower tummy, it’s called diverticular disease.
When they get inflamed or infected, it’s known as diverticulitis, which can cause more severe symptoms such as rectal bleeding, fever and vomiting.
A low-fiber diet is associated with increased risk of diverticular disease and diverticulitis. This is thought to be due to a narrowing of the intestine, which puts pressure on the walls of the intestine, forming diverticula (42).
A high-fiber diet may help prevent and manage diverticular disease. If you experience a flare-up of diverticulitis, you will need to stick to a low-fiber diet while your digestive system recovers. However, once you are better, you can typically return to eating a high-fiber diet (43).
A study of over 47,000 adults found that people who ate at least 25.5 grams of fiber per day had a 41% lower risk of developing diverticular disease than those who ate less than 14 grams per day (44).
Research shows that the type of fiber eaten may also impact disease risk, with wholegrain cereals such as oats, wheat, rice and barley, appearing to have the most effect, but the reasons for this remain unclear (45).
Summary: A high-fiber diet is important for maintaining a healthy digestive system and may also help prevent diverticular disease. During episodes of diverticulitis, you may need to follow a low-fiber diet while your symptoms resolve, but you should adopt a higher fiber diet once you are better.
High-fiber diets may also help with satiety and maintenance of body weight.
Observational studies have shown that people with a higher body mass index (BMI) and higher body fat percentage have significantly lower dietary fiber intakes than people of a healthy weight (46, 47).
Meanwhile, a 10-year study of 3,000 healthy young adults found that high-fiber diets may protect against obesity and CVD by lowering insulin levels. They also found that low-fiber intake was a predictor of obesity (48).
High-fiber diets are thought to affect body weight in several ways:
- Increases feelings of satiety (fullness): One small study of obese and overweight women found that supplementing diets with 20 grams of dietary fiber significantly reduced self-reported hunger while following a low-calorie (under 1,000 calories) diet (49).
- Reduces caloric intake: A review concluded that even when calorie intake is not restricted, eating an additional 14 grams of fiber per day is associated with a 10% reduction in calorie intake, resulting in an average weight loss of 1.9 kg over 3.8 months in healthy weight adults. In obese individuals, this effect was even greater with a 2.4kg weight loss. (50).
- Delays gastric emptying: Soluble fiber is thought to contribute to increased and prolonged satiety, decreasing hunger and therefore preventing subsequent food intake (51).
- Changes in the gut microbiome: A 9-year follow-up study of 1,632 women found that those with higher fiber intakes had greater gut microbial diversity and gained less weight over time compared to those with lower fiber intakes (52).
It’s important to mention that foods that are commonly consumed on a high-fiber diet (such as fruits, vegetables, whole grains, pulses and beans) tend to also be low in saturated fat, added sugars and calories—all of which also support weight loss and management.
If you’re looking to lose weight, try switching out more calorie-dense foods like pizza, pastries and cakes with these higher fiber options.
Summary: Observational studies have found that people who follow a high-fiber diet are less likely to be overweight or obese. This may be because high-fiber foods improve satiety, delay gastric emptying, reduce calorie intake, and have beneficial effects on the gut microbiome.
Tips for Increasing Fiber Intake
Here are some tips for ways to increase your own dietary fiber intake:
- Choose whole grain foods (such as bread, cereals and pasta) rather than white or refined versions.
- Eat whole fruits instead of fruit juices
- Add pulses, beans, legumes or extra vegetables to stews, curries and salads.
- When eating potatoes, keep the skin on.
- Have fruit, nuts and seeds for snacks.
If you don’t usually eat a high-fiber diet, build up your fiber intake gradually over a few days or weeks. Switching from a low-fiber diet to a high-fiber one too quickly may cause gastrointestinal symptoms such as bloating and gas. Increasing your intake slowly over time, allows time for your gut to adjust.
We are all different and our bodies respond to fiber in different ways, so try to find a level that is right for you.
In addition to a high-fiber diet, you can also prevent constipation by drinking enough water every day and getting regular exercise (53).
Summary: A high-fiber diet should include plenty of whole grains, fruits, vegetables, beans, pulses and nuts and seeds. If you don’t usually follow a high-fiber diet, increase your fiber intake slowly and be sure to drink plenty of water and get regular exercise to avoid constipation.
High-Fiber Diet Plan
Here are two example daily menus that provide at least 30 grams of fiber per day (the recommended daily amount for most adults).
- Breakfast: ¾ cup bran flakes (8 g fiber), ¾ cup milk, 1 medium banana (1.5 g fiber)
- Snack: 1 apple (2.4 g fiber)
- Lunch: 2 slices wholemeal toast (4.7 g fiber), 150 g baked beans (6.8 g fiber), ¼ cup grated cheddar cheese
- Dinner: Medium baked potato with skin on (6.5 g fiber), tuna mayonnaise filling (½ cup), 1 cup of side salad of lettuce, tomato and cucumber (1.7 g fiber)
- Dessert: ½ cup yogurt with ¾ cup strawberries (1.5 g fiber), 1/10 cup almonds (1.3g fibre)
Total Fiber Intake = 34.4g
- Breakfast: 1¼ cup wholewheat cereal (3.8 g fiber), ¾ cup milk, 1 apple (2.4 g fiber)
- Snack: Small bag of popcorn (1.3 g fiber)
- Lunch: Sandwich with 2 slices of oatmeal bread and egg salad filling (3.9 g fiber), small handful mixed nuts (2.2 g fiber), ¾ cup raspberries (5.2 g fiber)
- Dinner: 1 cup whole grain pasta (3.8 g fiber), tomato and basil sauce (1.6 g fiber), 1 ½ cup red pepper, sliced (1.5 g fiber)
- Dessert:⅓ cup dried mango (2.8 g fiber)
Total fiber intake = 32.4g
Why You Should Be Eating a High-Fiber Diet
Fiber is a type of carbohydrate found in plant foods such as whole grains, fruit and vegetables, pulses and legumes, and nuts and seeds.
The different types of fiber, including soluble, insoluble, and resistant starch each function in a slightly different way and offer their own unique health benefits.
A high-fiber diet has been shown to promote good digestive health and reduce the risk of many chronic conditions such as type 2 diabetes, cardiovascular disease, colorectal cancer and diverticulitis.
Eating enough fiber can also help with weight loss and management.
The recommended daily amount of fiber is 30 grams per day.
However, most Americans are only eating just over half this amount.
Simply by increasing your fruit and vegetable intake, opting for whole grain foods over white or refined versions, and making an effort to replace high sugar and fat snacks with more nutritious, plant-based options, you can easily meet the daily fibre recommendations.
This can go a long way in promoting good health and preventing disease.