Updated: May 30, 2019
Dietary Fibre is a class of food that is not digested by enzymes in the gut but rather, they are substantially fermented by bacterial flora of the large intestine. There are two classes of dietary fibre: Insoluble fibre, and Soluble fibre.
Insoluble fibre does not absorb water and is mainly comprised of cellulose. A good list of foods that contain insoluble fibre includes; vegetables (celery, zucchini, cauliflower, avo, broccoli), the skin of fruits, nuts, legumes, wheat bran, whole grains and seeds. Historically, insoluble fibre has been used to “bulk out” stool.
Soluble fibre absorbs water to form a gel like substance. You may have noticed this with chia pudding, or runny oats. This substance binds bile and slows down the process of digestion through the intestines. A good list of foods that contain soluble fibre includes; oats, oat bran, rice bran, barley, citrus fruits, apples, berries, psyllium husks, flaxseed, peas, and potatoes.
Over the past few decades an increased respect for the role of fibre in the diet has developed. Fibre has been said to increase the feeling of fullness (satiety), lower blood cholesterol, stabilize blood sugar and reduce constipation. According to the Dietary Guidelines for Americans, 2010, all adults should consume 14grams of total fibre for every 1000 calories.
But is this amount truly necessary?
Some of the attributes of fibre have recently been under attack, and so, I will take us through the most current research and the “ins and outs” of dietary fibre. But first, I always like to look back at the history of a medical theory or discovery.
It seems the advocation of dietary fibre is down to an Irish surgeon and physician called Denis Burkitt. Denis Burkitt (1911 to 1993) was a medical missionary in Africa. There he observed a disease pattern that would eventually give him the nickname ‘fibreman’. While in Uganda, he observed that Africans produced several times more feces than westernized people did. In addition, the stool was more easily produced with minimal discomfort. He stated from his epidemiological studies:
“In Africa, treating people who live largely off the land on vegetables they grow, I hardly ever saw cases of many of the most common diseases in the United States and England – including coronary heart disease, adult-onset diabetes, varicose veins, obesity, diverticulitis, appendicitis, gallstones, dental cavities, hemorrhoids, hiatal hernias and constipation. Western diets are so low on bulk and so dense in calories, that our intestines just don’t pass enough volume to remain healthy.”
He led a life-long crusade to encourage Americans to eat more fibre and published a book “Don’t forget Fibre in your Diet”, which was an international best seller. Only in current years has his work begun to be severely questioned.
According to Ho Hoang et al in an extensive systematic review, β-glucans from the fibre in oats has a lowering effect on LDL-cholesterol,VLDL-cholesterol and apoβ.
What does that mean?
LDL-Cholesterol is often labelled “Bad Cholesterol” because it may cause a build up of cholesterol in arteries. Apoβ is the main protein constituent of VLDL and LDL-Cholesterol. Therefore, by lowering these, there are reduced risk factors for cardiovascular diseases associated with cholesterol build up.
A second systemic review was conducted on the use of Psyllium husks to reduce overall cholesterol. The findings of Javanovski et al stated that “Psyllium fiber effectively improves conventional and alternative lipids markers, potentially delaying the process of atherosclerosis-associated CVD risk in those with or without hypercholesterolemia”.
There is also research to suggest that the viscosity of the fibre you use is more important that the quantity. Vladimir et al suggests that the higher the viscosity of fibre, the more reduced your cholesterol levels become.
To lower cholesterol, choose psyllium husks over wheat bran when buying fibre from the health shop.
These types of fibre are examples of soluble fibres that form a gel. While I have only quoted two systemic reviews, there are many more papers online to suggest that soluble fibres are beneficial for lowering cholesterol and reducing risks associated with cardiovascular disease.
β-glucans may improve insulin sensitivity due to its ability to form a thick gel, which delays the emptying of the stomach and absorption of glucose into the blood. β-glucan may also promote the release of peptide YY (PYY), a hormone produced in the gut in response to eating. This satiety hormone has been shown to lead to reduced calorie intake and may decrease your risk of obesity.
Another systemic review by Andade E et al., found that β-glucans was efficient in reducing glucose levels in diabetic patients. Continual doses of β-glucans over a long period of time yielded the best results.
β-glucans is found in oats, barley, certain types of mushrooms (eg, reishi, shiitake, maitake), yeasts, seaweed, and algae. Again, these are examples of soluble fibre.
I saved the most controversial topic for last. It has recently been debated as to whether fibre helps with constipation at all. Here we are assessing the efficacy of insoluble fibre.
One issue that was raised with Burkitt’s hypothesis was the fact that the Western diet is usually unhealthy. It was proposed that it might not be the lack of fibre in the diet, but rather the large amounts of dairy-fat, sweets, refined grains and processed meat that were causing the higher rates of disease in the West than in Africa. This extends to his hypothesis that increased fibre would decrease reduce risk of colorectal cancer. Again, if whole grains are replacing refined grains and sugars there will be a decreased chance of hyperinsulinemia. Hyperinsulinemia may act as a growth factor and tumour promoter. To back this up, I found a recent pooled analysis of 13 prospective cohort studies that found that dietary fibre was not associated with a reduced risk of colorectal cancer after adjusting for other dietary risk factors.
The results from the following study suggests that the less fibre we eat the less symptoms of bloating and constipation we will have:
At 6 months, 41 patients remained on a no fiber diet, 16 on a reduced fiber diet, and 6 resumed their high fiber diet for religious or personal reasons. Patients who stopped or reduced dietary fiber had significant improvement in their symptoms while those who continued on a high fiber diet had no change. Of those who stopped fiber completely, the bowel frequency increased from one motion in 3.75 d (± 1.59 d) to one motion in 1.0 d (± 0.0 d) (P < 0.001); those with reduced fiber intake had increased bowel frequency from a mean of one motion per 4.19 d (± 2.09 d) to one motion per 1.9 d (± 1.21 d) on a reduced fiber diet (P < 0.001); those who remained on a high fiber diet continued to have a mean of one motion per 6.83 d (± 1.03 d) before and after consultation. For no fiber, reduced fiber and high fiber groups, respectively, symptoms of bloating were present in 0%, 31.3% and 100% (P < 0.001) and straining to pass stools occurred in 0%, 43.8% and 100% (P < 0.001).
For anyone who studied in the health sector this seems shocking. We were all taught that increased fibre is the “gold standard” for reducing constipation. Yet the research is stating that this concept is due to one man’s observations and not down to replicable research.
While I believe that fibre is a very important aspect of our diet, it is important to be clear about the reasons we are using it. There is enough evidence to support the use of soluble fibre for reducing cholesterol and increasing insulin sensitivity. However, there is not enough evidence to support the use of insoluble fibre for constipation. But before we enter an “anti-insoluble-fibre fad” always remember that food groups are intertwined within one food source. The "Western world" loves to assess topics in isolation, yet this is not how it works in reality. Within one food source you might find insoluble and soluble fibre along with fructose, sucrose and a host of other nutrients. This natural blend works synergistically towards your dietary needs and general health. The holistic view of Phytotherapy always supports a balanced and plant-dominant diet. For more queries about the phytotherapeutic consultation feel free to email me.
Those with inflammatory bowel diseases like ulcerative colitis or Crohn’s disease may need to monitor their fibre intake and limit chia seeds during flare-ups. Caution is advised for those on blood pressure medication and those with diabetes.