Why is fiber important?

Interview with a gastroenterologist

Fiber is good for digestion and digestive health. But what really makes fiber so great for our health and digestion? We sat down with Dr. Ken Brown, gastroenterologist, to get his input on the subject. The following interview sheds light on why fiber is just so good for our health: gut, microbiome, brain, immune, and really overall.

Is improving gut health the main reason we should eat enough fiber?

Yes, improving gut health is one of the most important reasons to ensure adequate fiber intake. Here are a few reasons why fiber is so crucial for digestive health:

• Digestion: Dietary fiber adds bulk to the stool, which helps the stool move more smoothly through the digestive tract. That helps prevent constipation and promotes regular bowel movements.
• Gut Microbiome: Dietary fiber serves as food for the beneficial bacteria that live in our guts. When these bacteria digest fiber, they produce short-chain fatty acids (SCFAs) like butyrate, propionate, and acetate. These fatty acids are important for gut health and might even protect against colorectal cancer.
• Weight Management: High-fiber foods tend to make you feel fuller, which can help prevent overeating. A healthy gut microbiome is associated with a lower risk of obesity, so this indirectly impacts your gut health.

The benefits of fiber extend beyond just gut health, too. Fiber can help regulate blood sugar levels, reduce cholesterol levels, and is associated with a lower risk of heart disease and type 2 diabetes.

Why is fiber the preferred food for the gut microbiome?

Some people think that fiber is the only fuel for the microbiome. In fact, prebiotic polyphenols are also important for microbial health. Some research has shown that polyphenols can improve microbial diversity and generate more metabolites like butyrate than fiber.

Fiber: Gut bacteria produce short-chain fatty acids (SCFAs) from dietary fiber. These SCFAs have various beneficial effects on human health, including promoting a healthy gut lining, regulating the immune system, and providing energy.

Polyphenols: Polyphenols are molecules that give many fruits and vegetables their color. They are well known for their antioxidant capabilities, but they also act as prebiotics for our microbiome. When our microbiome breaks them down, multiple anti-inflammatories, anti-aging, anti-viral, and anti-cancer molecules are produced in addition to short-chain fatty acids.

The gut microbiota can be said to “prefer” polyphenols in certain contexts because of these unique benefits. Moreover, some research suggests that polyphenols can enhance the growth of beneficial bacteria strains (like Bifidobacteria and Lactobacilli), while inhibiting the growth of pathogenic ones. This selective modulation of the gut microbiota can have profound effects on health overall.

Both fiber and polyphenols play a crucial and complementary role in supporting gut health.  

Why do gut bacteria prefer fiber?

Not all gut bacteria prefer prebiotics, (fiber and polyphenols) but many beneficial ones do. 

Beneficial bacteria like Bifidobacterium and Lactobacilli are particularly adept at breaking down prebiotics. Prebiotics are non-digestible by human enzymes, meaning they can make it to the large intestine (where most gut bacteria reside) intact. 

Once there, these beneficial bacteria can ferment these prebiotics and use them as a source of energy. This process of fermentation not only helps these beneficial bacteria multiply and thrive but also leads to the production of substances like SCFAs, which have various health benefits for the host including supporting gut health and reducing inflammation

What actually happens to the gut when people eat enough fiber? Are there physiological changes that happen, and if so, what are they?

First off, fiber adds bulk to your stool and helps it move smoothly through your digestive system, preventing constipation and promoting regular bowel movements. 

It also promotes the growth of beneficial bacteria, which can outcompete potentially harmful bacteria for resources. This balance is crucial for maintaining gut health and can influence overall health and disease risk.

So yes, there are indeed physiological changes that happen when you eat enough fiber – many of which contribute to improved gut health and overall well-being.

How does fiber benefit the body? 

A healthy digestive system is critical to your overall well-being, and it plays a key role in supporting both your immune system and brain function. Here is how:

How Fiber Helps Maintain a Healthy Immune System:

• Gut-Immune Connection: Your gut is like a training camp for your immune system. It’s where about 70-80% of your immune cells live. If harmful things, like bad bacteria or viruses, get into your gut, your immune cells start their work. They make antibodies to fight these invaders, and they also let the rest of your immune system know about the threat so it can be ready. Your gut and immune system talk to each other using chemical signals. So, taking care of your gut health is important for your immune system and your overall health.
• Gut Barrier Function: A healthy digestive system maintains a strong gut barrier that prevents harmful bacteria, toxins, and foreign substances from leaking out of your gut into your bloodstream. When this barrier becomes damaged (a phenomenon known as “leaky gut”), it can trigger chronic inflammation and other immune responses that weaken the immune system and increase the risk of various diseases.
• Microbiota and Immunity: The gut microbiota helps train and develop the immune system. A diverse and balanced gut microbiota reduces the risk of conditions like allergies, autoimmune disorders, and other immune-related diseases.

How Fiber Helps Maintain a Healthy Brain:

• Gut-Brain Axis: The gut and brain have an intricate connection called the gut-brain axis. Signals sent along this axis allow your gut bacteria to communicate with your brain and vice versa, which can influence mood, behavior, and brain function.
• Neurotransmitter Production: Certain types of gut bacteria can produce neurotransmitters that help to regulate mood, sleep, appetite, and other functions. For example, some gut bacteria can produce serotonin–a chemical messenger that carries signals between nerve cells in the brain.
• Reduced Inflammation: A healthy digestive system can help reduce inflammation in the body, including in the brain. Chronic inflammation has been linked to depression and neurodegenerative diseases like Alzheimer’s.

Eating a balanced, fiber-rich diet and staying hydrated can therefore support both a healthy immune system and a healthy brain.

What else happens when people get enough fiber? 

Increasing fiber intake can result in regular bowel movements. This helps remove waste and toxins from the body, although if you have constipation, it can lead to discomfort, bloating, and other digestive issues. 

How many healthy bowel movements a day will vary from person to person. Some people might be fine with 3 times a week, while others might be normal once or twice per day. Regularity is most important. A sudden change in bowel habits – such as constipation or diarrhea – may indicate a problem, and you should see a healthcare provider.

Beyond supporting gut health and promoting a healthy immune system and brain, dietary fiber can help with:

• Weight Management: High-fiber foods tend to be more filling, so they can help prevent overeating and indirectly impact gut health by reducing the risk of obesity.
• Blood Sugar Control: Fiber, particularly soluble fiber, can slow the absorption of sugar into your bloodstream and reduce blood glucose levels, helping you to manage or prevent type 2 diabetes.
• Heart Health: Eating enough fiber can help lower general levels of LDL cholesterol, blood pressure, and inflammation, all of which contribute to heart health.

What happens when people don’t get enough fiber? What physical consequences might they suffer as a result?

Not getting enough fiber in your diet can have a negative effect on your health. 

It can cause constipation, hemorrhoids, and diverticular disease. 

It also increases the risk of heart disease and type 2 diabetes because fiber helps regulate blood sugar levels and reduces LDL (bad) cholesterol levels.

 A lack of fiber can lead to weight gain because high-fiber foods tend to be more filling. 

Fiber plays a key role in maintaining a healthy gut microbiome by promoting the growth of beneficial bacteria that support a healthy immune system and mental health. 

In addition, several studies suggest that a low-fiber diet is linked with an increased risk of certain types of cancer, particularly colorectal cancer.

How much fiber do you recommend daily? 

Should we follow recommended dietary guidelines (25 grams for women, 38 for men) or would we benefit by getting more? Why or why not?

The amount of dietary fiber you need depends on several factors, including your age and sex. 

People who increase their fiber intake too quickly may experience bloating, gas, or other digestive symptoms. 

While there is some evidence that consuming more than the recommended amount of fiber could provide additional health benefits such as further reductions in heart disease risk, this is still an area of ongoing research. 

It’s also important to remember that consuming extremely high amounts of fiber can potentially interfere with the absorption of certain minerals such as iron and calcium; however, this is usually only a concern for those consuming large amounts of fiber (over 50 grams per day) from supplements rather than food.

For most people, the best way to meet the recommended dietary guidelines for fiber is to focus on a variety of fiber-rich foods–such as fruits, vegetables, whole grains, legumes, nuts, and seeds–to ensure they are getting a mix of different types of fiber.

Insoluble vs Soluble: What type of fiber is best? 

Soluble and insoluble fibers have different properties and health benefits. Soluble fiber dissolves in water to form a gel-like substance that can help lower blood cholesterol and glucose levels.

Insoluble fiber promotes the movement of material through your digestive system and increases stool bulk, so it can be beneficial to those who struggle with constipation or irregular stools. Whole-wheat flour, wheat bran, nuts, beans, and vegetables such as cauliflower, green beans, and potatoes are good sources of insoluble fiber. 

A well-balanced diet that includes a variety of fruits, vegetables, whole grains, and legumes will typically provide a good mix of both types of fiber.

How many servings of plant-based foods should we aim for to get more fiber?

The Dietary Guidelines for Americans recommend that adults eat at least five servings of fruits and vegetables daily. A serving is typically defined as one medium-sized piece of fruit, half a cup of cooked or canned fruit or vegetables, or one cup of raw leafy vegetables. 

However, individual dietary needs can vary based on:

• Age
• Sex
• Activity level
• Overall health. 

When increasing fiber intake gradually over time and water intake, it supports fiber’s role in the digestive system.

What 2 or 3 tips might you suggest for how readers can meet their daily fiber needs?

• Start Your Day with Fiber: For a healthy start to the day, consider a high-fiber breakfast. This could be a bowl of oatmeal topped with nuts and berries or whole-grain toast with avocado. Many breakfast cereals are also high in fiber but check their sugar content.
• Choose Whole Grains: Whole grains are a great source of fiber and they can be included in your diet in many ways. For example, you could choose whole grain bread over white bread, or brown rice over white rice. Other whole grains to include in your diet could be barley, quinoa, or farro.
• Snack Smart: Snacking on fiber-rich foods throughout the day is a good way to keep your digestive system running smoothly. Fresh fruits and vegetables are high in fiber, as are nuts and seeds. An apple or pear can be a quick snack, and carrot sticks with hummus can satisfy your hunger if you need an afternoon pick-me-up. A handful of almonds or a small serving of popcorn can also give you a dose of fiber.
• Incorporate More Legumes: High in fiber, beans, lentils, and peas can be a helpful addition to your diet. Try adding them to salads, soups, stews, or even as a side dish. Chickpeas or black beans can also be a great addition to a stir-fry.

Fiber is so important to our gut health and overall well-being. And we greatly appreciate Dr. Brown for giving us so much great information!

Do you have any questions for Dr. Ken Brown to answer? We’d love to do more articles like this that contain questions that our readers want answered. Drop your questions in the comments section below and we will put them in our article queue for future topics.