When it comes to eating fiber many of us know we should eat more, but why is fiber important?
Recently, I heard a talk by Brenda Davis, R.D and I was truly fascinated to learn about fiber and the role it plays in our diet.
I’ve always known fiber was important considering what we hear from many nutrition authorities—we need to consume more. But it wasn’t until I listened to Brenda Davis I realised just how little we’re consuming.
Why is Fiber Important?
The current Dietary Guidelines for Americans 1 recommend that adult men require about 34g of fiber depending on their age and adult women require about 28g depending on their age. However, on average we are consuming approximately 15 – 20g daily.
While this does indeed indicate a shortfall, it wasn’t until Brenda highlighted that the minimum health benefits from fiber were best achieved with intakes of 35 – 50g per day, that I became deeply concerned.
Why are we only been told to raise our intake to amounts less than this?
A long, long way from the past…
When Brenda went on to discuss Paleolithic intake, I was astonished. Fiber intakes as high as 70 – 150g per day were commonplace! And, before you start imagining people grazing grass all day long, these weren’t all plant-based eaters. Studies found the Paleolithics who consumed meat in their diet still averaged around 70g of fiber a day, while larger intakes were more closely related to those who consumed a more plant-based diet.
The 70g of fiber per day was reached by people who consumed 2/3’s of their calories from animal products like fish and meat. Only 1/3 of their calories came from plants. However, they still got a whopping 70g of fiber per day! This amazed me—what a long way from our 15g a day.
Brenda further highlighted the people who got 2/3’s of their calories from plants were eating 150g or more of fiber per day. This certainly raises some questions about our way of eating.
What happened between then and now that we struggle to meet even the minimum fiber requirement?
Why are we struggling to take in fiber?
It appears that wild plants contain up to 4 times the concentration of fiber than our conventional, or commercially grown, plants do today. In the past, they were just much more concentrated in fiber.
So the human, Davis believes, is designed to handle quite a lot of fiber and our gut microbiome gets messed up when we are not consuming a lot of fiber.
Fascinated by this, I set out on a mission to find our more about this nutrient, and just how important fiber is in our diet.
What is fiber?
Dietary fiber (DF), is a plant-based nutrient and a key component in healthy eating. It’s a complex saccharide-based molecule that binds potential nutrients, and nutrient precursors, to prevent their absorption.
Despite being a type of carbohydrate, it’s different to other carbs. Fiber will pass through the intestinal tract relatively intact as it can’t be broken down into digestible sugar molecules. This plant matter is not digested by the human digestive enzymes, however, some is digested or fermented by the gastrointestinal tract bacteria.
Fiber includes polysaccharides such as cellulose, hemicellulose, gums, mucilages and pectins, and non-polysaccharides such as lignins. Cellulose is the main constituent of plant cell walls and is found in foods like fruit, vegetables and legumes. Hemicellulose is the main part of cereal fibers. Pectins are naturally found in fruits and vegetables, but are also increasing found in manufactured food products as a stabiliser. Gums and mucilages are also used as an additive or stabiliser in processed food.
Lignins, which are the tough woody part of plants (for example the strings of celery) are known as roughage foods and primarily contain lignins.
Soluble and Insoluble fiber
Fiber is classified as either soluble or insoluble.
Soluble fiber will typically dissolve in water and can form gels or become viscous. It’s digested by our bacteria. Examples of these types of fibers include pectins, gums, and hemicelluloses. One of the major benefits of eating more soluble fibers is its ability to help us improve our heart health. These fibers have many benefits, but they are strongly associated with improved heart health. A good source of soluble fibers are oats, apples, and beans for example.
Soluble fiber has been associated with lowering our risk for cardiovascular disease, and modestly lowering LDL cholesterol, which is the “bad” cholesterol that we all tend to strive to keep low. The heart healthy benefits of a high soluble diet don’t occur independently. They occur alongside a diet that is low in saturated fat, trans fats and cholesterol. 2
Insoluble fibers, on the other hand, do not dissolve in water and cannot form gels. No gut bacteria activity occurs when we eat insoluble fibers. Examples of these types of fibers include cellulose and lignin. Insoluble fibers are best known for their ability to improve our gut health, however they also contribute to heart health. So, if you ever needed to take a supplement to help you with your bowel movement, it most likely contained insoluble fiber. You will find these types of fiber in rye bran, broccoli and celery for example.
When it come to which type of fiber we need more, according to Katie Ferraro, MPH, RD, CDE, it’s not necessary to split hairs over. Katie’s advice is to just eat more fiber in general. By doing so we will naturally consume more soluble as well as insoluble fiber.
The perfect example of this is an apple. If we consume an apple, skin included, it will contain approximately 4g of fiber, which is typically made up of 2g soluble and 2g insoluble.
The Obesity Epidemic
Before we look at some of the main benefits of including more fiber in our diet, let’s take a look at what some of our main problems regarding nutrition are today. According to the World Health Oragnisation, (Oct, 2017)….
“Obesity has reached epidemic proportions globally, with at least 2.8 million people dying each year as a result of being overweight or obese. Once associated with high-income countries, obesity is now also prevalent in low- and middle-income countries.”
“In 2016, more than 1.9 billion adults were overweight and 650 million were obese. “
“Globally, 41 million preschool children were overweight in 2016. Childhood obesity is one of the most serious public health challenges of the 21st century. Overweight children are likely to become obese adults. They are more likely than non-overweight children to develop diabetes and cardiovascular diseases at a younger age, which in turn are associated with a higher chance of premature death and disability.”
“Overweight and obesity are linked to more deaths worldwide than underweight. Most of the world’s population live in a country where there are more people overweight and obese than underweight. This includes all high-income and middle-income countries. Diabetes, ischaemic heart disease and certain cancers are attributable to overweight and obesity.”
“Children’s diet and physical activity habits are influenced by their surrounding environment. Social and economic development as well as policies in the areas of agriculture, transport, urban planning, environment, education, food processing, distribution and marketing influence children’s dietary habits and preferences as well as their physical activity patterns. Increasingly, these influences are promoting unhealthy weight gain leading to a steady rise in the prevalence of childhood obesity.”
The importance of being underweight and malnourished is definitely not to be disregarded. It is certainly an extremely important issue. However, what I think a lot of us forget, or perhaps fail to recognise, is malnutrition linked to poor nutritional habits.
The food choices that we make daily have a tremendous impact on our health. While many of consume more calories than we need, these calories are often not very nutrient dense. This is where malnourishment can arise. Low-quality calories mean we have to consume more calories to meet our nutritional needs.
To achieve optimal health, it’s recommended we consume a proper diet combined with a positive lifestyle that includes physical activities, socialising, avoiding smoking and excess alcohol consumption.
And, this is where fiber comes in. When we are striving for the proper diet, fiber without a doubt is of great assistance in improving our gut bacteria and overall health.
Benefits of fiber
The benefits of fiber in a healthy diet are numerous. To help with the prevention and mitigation of type 2 diabetes, as well as cardiovascular disease, we need to eat more fiber rich foods! By modulating food ingestion, digestion, absorption and metabolism, DFs reduce the risk of hyperlipidemia, hypercholesterolemia and hyperglycemia. They may also help infection prevention and the improvement of mood and memory. 3
Much research has been carried out on fiber and it’s many positive effects. These studies have shown that;
- Fiber can help improve our heart health as it lowers LDL, total cholesterol and reduces triglycerides 4
- It helps stabilise blood sugar regulation which can help with diabetes
- Including fiber in the diet has been shown to have a positive effect on gut health for example constipation, haemorrhoids and diverticular disease. 5
- Fiber promotes satiety which can help with weight management and weight loss. 6
- Promotes regularity in bowel movements
- Improves gut flora
- Reduces cravings which can help assist with weight loss.
- Reduces the risk of cardiovascular disease (CVD)
- Slows digestion and stabilises blood sugar levels
- It reduces your risk of gastrointestinal (GI) disorders
- Improves your immune function
- Lessens hormonal imbalances
- It’s further thought fiber may help reduce the risks of developing colon cancer.
Interestingly enough, studies have also shown that dietary fiber may also help pre-diabetes people prevent progressing to full-blown diabetes 7. While there is still very little known definitely about the role between diet and cancer, they are pretty confident that a diet high in fruits and vegetables, which will automatically be high in fiber, helps protect against certain types of cancer and most notably colorectal cancer. 8
After reading these benefits you might be quite tempted to run out and grab as many high fiber foods as possible, but do keep in mind when increasing your fiber we need to do it gradually, over time.
When increasing your fiber intake, take it slow and be sure to consume adequate fluid. You’ll need the extra moisture to help move that extra bulk through your digestive tract.
Remember! Your body needs to time adjust to the extra fiber, so increase your intake gradually over a couple weeks.
THE BENEFITS OF FIBER IN YOUR DIET
1) HEART DISEASE
Studies suggest that adequate fiber intake consistently lowers the risk of cardiovascular disease (CVD) and coronary heart disease (CHD). 9 This happens primarily through a reduction in low density lipoprotein (LDL) levels. Fiber is thought to help with the prevention of heart disease by helping lower your cholesterol.
Individuals with high intakes of dietary fiber appear to be at significantly lower risk for developing coronary heart disease, stroke, hypertension, diabetes, obesity, and certain gastrointestinal diseases.
Soluble fiber improves hyperlipidemia. This is abnormally elevated levels of any or all lipids or lipoproteins in the blood. Soluble fiber can help improve hyperlipidemia through the combined effects of delaying gastric emptying, increasing the excretion of bile acids and reducing our liver’s production of cholesterol. 10
Food containing soluble fiber take longer to digest than fiber free foods. This in itself helps to play a role on satiety and weight control. But this of course does not mean people at a healthy weight don’t develop heart disease. Unfortunately it’s not as simple as that. We just know that being overweight or obese increases the risk of developing certain types of heart disease. It is also believed that delaying gastric emptying may also play a role, or have a beneficial effect, on insulin sensitivity.
As Ferraro explains, soluble fiber is like a sponge. It soaks up the bad cholesterol and takes it out of our body. It essentially reduces the rate of bile acid recycling. This loss of bile acids in our stool stimulates the liver to increase the uptake from circulation to replenish supply. This results in serum total and LDL cholesterol being reduced.
Furthermore when we consume soluble fiber our body’s gut bacteria can ferment it and produce a byproduct, short-chain fatty acids (SCFA), which travel to our liver and tell it to stop making so much cholesterol.
So this is what soluble fiber does to benefit our heart, but what about insoluble fiber?
Insoluble fiber promotes motility in the gut – you want heavy bulky stools that travel easy through the lower part of your digestive tract, so you can have regular bowel movements.
Consuming fiber promotes satiety which is linked to healthy weight. It may also help lower blood pressure and the risk of clots while also having a positive impact on inflammation.
Regularly consuming the recommended amount of fiber helps to reduce glucose absorption rates, prevent weight gain, and increase the load of beneficial nutrients and antioxidants in the diet, all of which may help prevent diabetes.
One particular large-scale study followed 75,000 people for 14 years. The research found people who ate more than 15 g of fiber per day had significantly lower diabetes risk than people who consumed smaller amounts. 11
Studies have also shown time and again that fiber helps to control blood sugar levels for people with diabetes. Increasing fiber intake lowers blood pressure and serum cholesterol levels. An increased intake of soluble fiber also improves glycemia and insulin sensitivity in non-diabetic and diabetic individuals.
Fiber slows the absorption of carbohydrates which leads to a less marked increase in blood sugar and less demand for insulin. Fiber, therefore, plays a crucial role in diabetes because of this. Whether or not we have diabetes, we all need to steady blood sugar control. It’s not a good feeling to peak then crash, peak then crash…
Fiber also promotes the feeling of fullness. It’s not the case all people who have diabetes are overweight. However, a large percentage of people with type 2 diabetes are overweight or obese. Therefore, promoting a high fiber diet that helps you feel fuller for longer is important for helping individuals achieve and maintain a healthy weight in order to reduce the really negative side effects of uncontrolled diabetes.
3) DIGESTIVE PROBLEMS
Fiber is important when it comes to digestion and regularity. Meeting the recommended amount of fiber intake from foods can also help to prevent constipation and hemorrhoids.
Fiber assists the digestion process and helps to maintain good gastrointestinal health. The benefits of fiber when it comes to gastrointestinal disorders actively helps those who suffer from gastroesophageal reflux disease, duodenal ulcers, diverticulitis, constipation, and hemorrhoids.
Individuals with high intakes of dietary fiber appear to be at significantly lower risk for developing certain gastrointestinal diseases in the first place. 12
Dietary fiber plays an important role in our colon or large intestine. It helps to lower the rates of diverticulosis which is the presence of having diverticula. These diverticula are essentially pouchings on the side of the walls of the large intestine. Ferraro explains that if we don’t exercise our colon with a high fiber diet it will get lazy and the walls get lazy and will easily sag outwards forming these diverticula.
While many people may have diverticulosis, it is when these diverticula become inflamed and we develop diverticulitis that we become more concerned. When you have diverticulosis, studies have shown a high fiber diet to be beneficial as you are essentially exercising the colon wall which has been shown to reduce the likelihood of developing those outpouches. However, if you have diverticulitis you’re likely to be on a low fiber diet.
4) WEIGHT MANAGEMENT
Fiber can help with weight management. A high-fiber eating plan is lower in calories and tends to make you feel fuller, faster. Research shows that Higher intakes of fiber are linked to lower body weight. 13
One particular study, carried out for just under 2 years on women and fiber intake, found that those who reduced fiber intake had a much greater risk for weight gain. On the other hand, women who increased fiber intake, increased their likelihood of losing weight. Further studies have shown that whole-grain cereals can protect against obesity.
Another study found that people who ate 3+ servings of whole-grains per day had lower body and abdominal fatness overtime. So switching to foods like fruits, vegetables, whole-grains, legumes, nuts and seeds are great when trying to shed a few pounds and keep it off.
It’s an important part of your intestinal health and waste elimination process. Studies have pointed to the fact that increased fiber intake decreases the risk of colorectal cancer 14. There are many theories as to why this is. Many point to fibers tendency to add bulk to the digestive system which shorten the time waste travels through the colon.
This is helpful as this waste often contains carcinogens which intestinal cells require as little exposure to as possible in order to remain healthy. On top of this, a substance called ‘butyrate’, is produced when the intestine breaks down fiber. This particular substance is associated with inhibiting the growth of tumors in both the colon and rectum.
Research has indicated that a diet that is high in fruits and vegetables, thereby high in fiber, is protective against many types of cancer. However, this is about as far as researchers will go in linking diet and cancer because there is just too many unknowns about what causes or exasperates cancer or promotes cancer.
When it comes to prevention of cancer, the World Cancer Research Fund recommend:
- be a healthy weight
- be physically active
- eat whole-grains, vegetables, fruit and beans
- limit fast foods and other processed foods
- limit red and processed meats
- don’t rely on supplements
- limit sugar sweetened drinks
- limit alcohol consumption
The World Cancer Research Fund further recommends that 2/3’s of our dinner plate to be vegetables, fruits, whole-grains and beans while 1/3 or less to be animal protein or plant-based protein. You can read more about their recommendations at World Cancer Research Fund
6) IMMUNE SYSTEM
Prebiotic fibers appear to enhance immune function. This is because almost 70% of your immune system is located in your GI tract.
Prebiotic fibers promote digestive health and are clinically proven to naturally activate your immune system.
One particular study from the University of Illinois explores this further, concluding fiber reduces the inflammation associated with obesity-related diseases and strengthens the immune system. 15
“Soluble fiber changes the personality of immune cells — they go from being pro-inflammatory, angry cells to anti-inflammatory, healing cells that help us recover faster from infection,” said Gregory Freund, a professor involved in the study.
This happens because soluble fiber causes increased production of an anti-inflammatory protein called interleukin-4.
WHAT’S THE RECOMMENDED INTAKE FOR FIBER?
The Institute of Medicine recommends a daily amount (RDA) of 20g-35g for fiber intake.
Many Americans don’t eat enough fiber, typically consuming only half the recommended amounts each day. Furthermore, average fiber intakes for US children are less than half of the recommended levels. Dietary fiber provides similar benefits for children as for adults.
The most commonly consumed foods are low in dietary fiber, with generally accepted servings of food containing 1-to-3g of fiber per serving.
Foods such as whole grain cereals, legumes, vegetables and fruits, have a high fiber content. Aim to eat 2 cups of fruit and 2 ½ cups of vegetables every day. Include beans and whole grains in your diet to help meet your daily fiber intake. Other fiber sources include fiber supplements, and fiber-fortified foods.
Nutritional labels on foods will show dietary fiber amount. 2.5g of fiber means it’s a good source of fiber, while 5.0g of fiber is an excellent source to include.
Hopefully this has answered your questions regarding Why is Fiber Important? For more information on what fiber rich foods you can eat, check out our High Fiber Food List.
- Schneeman, B. O. (1987). Soluble vs insoluble fiber: different physiological responses. Food Technology.
- Kaczmarczyk, M. M., Miller, M. J., & Freund, G. G. (2012). The health benefits of dietary fiber: beyond the usual suspects of type 2 diabetes mellitus, cardiovascular disease and colon cancer. Metabolism, 61(8), 1058-1066.
- Anderson, J. W., et al (2009). Health benefits of dietary fiber. Nutrition reviews, 67(4), 188-205.
- Slavin, J. (2013). Fiber and prebiotics: mechanisms and health benefits. Nutrients, 5(4), 1417-1435.
- Slavin, J. L. (2005). Dietary fiber and body weight. Nutrition, 21(3), 411-418.
- Leahy, J. L. (2005). Pathogenesis of type 2 diabetes mellitus. Archives of medical research, 36(3), 197-209.
- Van Duyn, M. A. S., & Pivonka, E. (2000). Overview of the health benefits of fruit and vegetable consumption for the dietetics professional: selected literature. Journal of the American Dietetic Association, 100(12), 1511-1521.
- Mellen, P. B., Walsh, T. F., & Herrington, D. M. (2008). Whole grain intake and cardiovascular disease: a meta-analysis. Nutrition, Metabolism and Cardiovascular Diseases, 18(4), 283-290.
- Mcintosh, M., & Miller, C. (2001). A diet containing food rich in soluble and insoluble fiber improves glycemic control and reduces hyperlipidemia among patients with type 2 diabetes mellitus. Nutrition Reviews, 59(2), 52-55.
- Slavin, J. (2013). Fiber and prebiotics: mechanisms and health benefits. Nutrients, 5(4), 1417-1435.
- Marlett, J. A., McBurney, M. I., & Slavin, J. L. (2002). Position of the American Dietetic Association: health implications of dietary fiber. Journal of the American Dietetic Association, 102(7), 993-1000.
- Slavin, J. L. (2005). Dietary fiber and body weight. Nutrition, 21(3), 411-418.
- Howe, G. R., Benito, E., Castelleto, R., Cornée, J., Estève, J., Gallagher, R. P., … & Kune, S. (1992). Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. JNCI: Journal of the National Cancer Institute, 84(24), 1887-1896.
- Sherry, C. L., Kim, S. S., Dilger, R. N., Bauer, L. L., Moon, M. L., Tapping, R. I., … & Freund, G. G. (2010). Sickness behavior induced by endotoxin mitigated by the dietary soluble fiber, pectin, through up-regulation of IL-4 and Th2 polarization. Brain, behavior, and immunity, 24(4), 631-640.