You have probably heard that whole plant and whole grain foods are good for the health, but do you know exactly how and why?
Dietary fiber is the major reason for this. It is a carbohydrate which is part of the plant which is indigestible, and which travels through the digestive system and absorbs the water as it goes to promote bowel movements.
But there has been growing evidence that apart from aiding your digestion, fiber can be essential for the reduction of the risk of developing chronic disease, reduce your risk of heart disease, diabetes, as well as help you lose weight as well due to its effect on the gut flora microbiota.
Read on to find out what the different types of dietary fiber are, and what the scientific evidence for their benefits is.
What exactly is dietary fiber?
Dietary fiber is the part of your diet which is not actually digested by the enzymes in our GI tracts, but this non-digestible carb still plays a vital role for your digestive system and for your overall health.
Dietary fiber is usually found in vegetables, whole grains, fruits and legumes, and its intake on a regular basis is known to reduce the risk of developing diabetes and heart disease.
There are two main types of fiber:
- Soluble which can dissolve in water and which can be metabolized by the good gut bacteria
- Insoluble which cannot dissolve in water and passes through the digestive system intact
Another way to distinguish the two types of fiber is – fermentable and non-fermentable.
Understanding the difference between the two types is key because while some type of fiber has essential health benefits for the health, others are not so important.
But distinguishing the two is not so easy because there are insoluble fibers which can be digested, and there are foods which have both soluble and insoluble fibers but are richer in one type more than the other (1).
The daily recommended amount of fiber intake is 25g for women and 38g for men, and after the age of 50 – 21g for women and 30g for men (2). Preferably, the daily servings of fiber should be divided in at least five servings of fruit or vegetables, and one or more servings of whole-grain products.
Oatmeal, beans, Brussels sprouts, oranges, nuts, blueberries, and apples are rich in soluble fiber. Insoluble fiber is found in the skins and the seeds of fruits, as well as in brown rice and whole-wheat bread.
Oats, flaxseeds, and oat brans are rich in both types of fiber.
Foods like dairy and white bread have little or no fiber.
Fiber can help feed the beneficial gut bacteria
It may come as a shock to some, but bacteria which live in the human body usually outnumber the body’s cells by 10 times.
We have bacteria residing on our skin, in the nose, mouth, and elsewhere, but the majority live in the gut, mostly in the large intestine (3).
There are over 500 different species of bacteria residing in the intestine, totaling around 100 trillion cells. These bacteria and other microorganisms are referred to as gut flora or microbiome.
This isn’t something you should be alarmed about. In fact, the bacteria in the gut are essential for our digestive system and for the overall functionality and health of the body.
Here is where the fiber steps in. All organisms and microorganisms need to eat in order to get sufficient fuel to live and function, and so do the bacteria in the large intestine.
But because most of the nutrients from the carbs, fat, and proteins are absorbed along the way to the large intestine, the bacteria there have little left to eat.
Because we do not have enzymes to digest fiber, but these bacteria do, they feed on many of the fibers which reach the intestine.
This is why certain fibers are essential for our overall health and wellbeing because they act as prebiotics and feed the beneficial bacteria in the intestine (8).
The friendly bacteria are vital for the production of various nutrients for the body, including short-chain fatty acids like butyrate, acetate, and propionate (9).
These short-chain fatty acids feed the cells in the colon and thus reduce the risk of inflammation of the gut, as well as improve certain digestive problems like irritable bowel syndrome, ulcerative colitis and Crohn’s disease (10, 11, 12).
As the bacteria ferment the fibers, they produce gases, which is the reason why some people experience flatulence or stomach discomfort when eating high fiber diets.
These side effects will usually disappear as the body gets used to consuming and digesting higher quantities of fiber.
Certain types of fiber promote weight loss
Fiber has been found to promote weight loss, and adding just 30g of fiber to your diet per day can help you reduce your weight, lower your blood pressure and improve your response to insulin (13).
The soluble fibers which can absorb the water in the intestine can help slow down the absorption of the nutrients by the digestive tract, and can also promote the feeling of fullness for a longer time. This will reduce hunger, and can reduce the appetite (14).
Also, soluble fiber helps block the digestion and absorption of some of the fat, by spreading out around it as a thick gel.
But the resulting weight loss results largely depend on the type of fiber introduced to the diet.
One of the soluble dietary fibers with the highest water absorption ability is the popular glucomannan found in shirataki noodles and in the dietary supplement Lipozene. This natural fiber has the ability to absorb 50 times as much water than its size.
Other health benefits of consuming dietary fiber
It can help stabilize blood sugar levels
Just like it slows down the absorption of fat, soluble fiber also slows down the digestion of the other nutrients in our food including carbohydrates.
This means that eating soluble fibers along with carbohydrates can prevent the sudden spikes in blood sugar levels which can occur after the consumption of high carb foods and meals.
High fiber foods do have lower glycemic indexes than refined carbs which have had most of their fiber removed.
This is essential, especially if you are on a high carb diet and want to prevent these harmful and dangerous spikes in the glucose levels in the blood.
So, if you have issues with blood sugar spikes or high blood sugar, you should cut out the carbs, especially refined, low fiber carbs like sugar or white flour, and add more soluble fiber to your diet.
Some studies have found that diabetics who eat more fiber need less insulin to manage their blood sugar levels (22).
Plus, fiber can help slow down the absorption of the sugar into the bloodstream and introduce it slowly to prevent spikes in its levels too.
It can help lower cholesterol and reduce the risk of heart disease
Soluble fiber can help prevent some of the dietary cholesterol being broken down and digested, and after regular intake, the fiber can help reduce the free cholesterol in the blood.
A review including 67 different studies has found that the consumption of 2-10g of soluble fiber on a daily basis leads to the reduction of the cholesterol by 1.7mg/dl and of the “bad” LDL cholesterol by 2.2mg/dl (23).
This correlation too depends on the viscosity of the soluble fiber.
It can help resolve constipation
This is one of the most common reasons why people resort to high fiber diets – resolving constipation problems.
Another study found the opposite – that people with constipation who were placed on high fiber diets saw no improvement while those on lower fiber diets reported that their bowel movements had improved (30).
Once again, the result depends on the type of fiber consumed.
The fiber which increases the content of water in the stool has a laxative effect while the fiber which adds more dryness to the dry stool has a constipating effect.
But in general, insoluble fiber does help add to the bulk and to the faster movement of the stool through the bowel and prevents constipation, slow bowel movements, and possible gastrointestinal blockage.
It also can help reduce the risk of hemorrhoids and the development of colon folds and even colorectal cancer.
Some soluble fibers absorb water and form a gel-like substance in the digestive tract. They are not fermented by the bacteria and help the bowel movements as well.
Overall, it is clear that certain types of fibers can help constipation while others can worsen it, so it is essential that you take the right type of fiber for your specific problem.
It can help reduce the risk of colorectal cancer
Colorectal cancer is the third leading cause of death by cancer worldwide (33).
There are numerous studies which have found a correlation between the high intake of fibers and a reduced risk of this type of cancer (34).
But then again, many of the high fiber foods, like fruits, vegetables, and whole grains also contain antioxidants and other healthy nutrients which can have an effect on the cancer risk as well.
So, it is not possible to single out the effect on fiber on lowering the risk of colorectal cancer, from all other potential benefits of eating a healthy whole-food diet.
There is still no strong evidence which proves that there is a definitive connection between the high fiber foods and the lowered cancer risk (35).
But while there is no firm evidence, it is clear from the other studies, that eating a healthy high-fiber diet with whole grains, fruits and veggies can play an important role for cancer prevention (36).
It helps feed the healthy bacteria in the gut
Fiber reaches the lower intestine undigested, and it provides the food which the good bacteria in the gut need to get fuel to properly absorb the nutrients and to keep the body healthy. It acts like a natural prebiotic (37).
Healthy gut flora is essential for a proper digestive system, as well as for the immune system, for fighting inflammations in the gastrointestinal tract and even for brain health.
So, dietary fiber is essential for keeping a well-balanced microbiome, and for encouraging the growth of the good bacteria in the gut (38).
Dietary fiber, soluble or insoluble, has a number of health benefits. It is, in fact, an essential nutrient for all humans, even though we don’t have the enzymes to digest and absorb it.
Dietary fiber helps feed the beneficial gut bacteria. It forms short-chain fatty acids which help nourish the wall of the colon.
Plus, it can help slow down the digestion and absorption of other nutrients like carbohydrates, proteins, and fats, and thus prevent blood sugar spikes.
It also gives a feeling of fullness and helps prevent the pangs of hunger for longer periods of time after eating. And it can slow down and limit the absorption of fat, and other high-calorie nutrients.
It can also help reduce the cholesterol levels and thus decrease the risk of stroke, heart attack and other heart and cardiovascular problems.
It is beneficial for diabetics, and people suffering from high blood sugar, and insulin resistance.
And it can help resolve problems like constipation, and according to some findings may even reduce the risk of developing colorectal cancer.