by YING WANG, BSC, BSPHARM, RPH
“You need to eat more fibre.” There’s a good chance that you’ve heard this piece of advice before. But why, exactly, is dietary fibre so important? And how, realistically, can we manage to get enough of it?
What is fibre?
Before we dive into the numerous health benefits of fibre, we must understand what fibre is, and where it comes from.
Fibre is a type of carbohydrate that our bodies cannot readily break down into sugar molecules to use as fuel. Instead, fibre passes through the stomach, small intestine, and colon, and is expelled relatively intact – imparting its many health benefits along the way.
Dietary fibre is found in fruits and vegetables, legumes, and whole grains. It comes in two forms, soluble fibre and insoluble fibre, and most plant foods contain a combination of both forms.
Soluble fibre dissolves in water to form a sticky, viscous gel. In doing so, this type of fibre can help to slow the digestion of food, thereby helping to regulate blood sugar and cholesterol levels.
Additionally, some types of soluble fibre, such as inulin, pectin, and beta-glucan, act as prebiotics that feed the good bacteria in the gut.
These friendly bacteria, in turn, produce nutrients that promote a healthy gut and robust metabolism.
Soluble fibre is found in grains like oat and psyllium, legumes like beans and peas, seeds and nuts, and some fruits and vegetables like citrus fruit and carrots.
Insoluble fibre does not dissolve in water. Rather, it passes through the digestive tract unchanged, adding bulk to the stool to promote healthy movement of the digestive tract.
By adding volume in the gut, insoluble fibre can help to enhance the feeling of satiety, reducing the risk of overeating leading to obesity.
Insoluble fibre is found in foods like corn and wheat bran, whole grain cereals, and many vegetables like cauliflower and green beans.
The amount of soluble and insoluble fibre varies between different plant foods. Thus, to maximize the health benefits of a high-fibre diet, it is important to eat a wide variety of these foods.
Health benefits of a high-fibre diet
Fifteen to thirty percent of Canadians suffer from chronic constipation, particularly young children and the elderly.
The mechanism by which fibre helps to resolve constipation is two-fold: soluble fibre draws in water to soften the stool, while insoluble fibre stimulates gut motility to promote healthy, regular bowel movements.
Conversely, fibre helps to resolve diarrhea by absorbing the excess water in loose stools. By regulating bowel movements, fibre reduces the risk of various gastrointestinal diseases.
For example, fibre prevents hemorrhoids by reducing the need to strain during bowel movements.
Dietary fibre also helps to reduce the risk of diseases of gut inflammation. Diverticulitis, a highly prevalent disease of gastrointestinal inflammation, was found to be 40% less likely in people who ate a high-fibre diet.
Moreover, dietary intake of fibre from whole grains has been associated with a lower risk of colorectal cancer. A 2005 study showed a 16% lower risk of colorectal cancer in people with a high-fibre diet compared to people with a low-fibre diet.
Irritable bowel syndrome
The relationship between dietary fibre and irritable bowel syndrome (IBS) is complex.
In addition to soluble and insoluble fibre, we can further categorize fibre based on how easily our gut microbiome ferments the fibre.
Soluble fibres that are easily fermentable, known as “fermentable oligosaccharides, disaccharides, monosaccharides and polyols,” or FODMAPs, tend to result in rapid gas production that worsens abdominal discomfort, bloating, and flatulence in people with IBS.
Similarly, insoluble fibre may exacerbate IBS-related abdominal pain and bloating. In contrast, soluble and poorly fermentable fibre, such as psyllium, has been shown in numerous studies to improve global IBS symptoms.
In fact, the American College of Gastroenterology recommends psyllium fibre for overall symptom improvement in all patients with IBS.
Metabolic syndrome is a cluster of co-existing conditions: high cholesterol, high blood sugar, high blood pressure, and excess body fat around the waist.
This syndrome is associated with an increased risk of heart attack, stroke, and type-2 diabetes.
Fibre helps to combat metabolic syndrome by a variety of mechanisms. Fibre binds to cholesterol in the small intestine and reduces its absorption—particularly LDL-C, the “bad cholesterol.”
Fibre slows gut digestion and absorption of sugar, thereby preventing spikes in blood sugar and improving insulin sensitivity. A high-fibre diet facilitates weight loss by improving satiety and, thus, reducing the risk of overeating.
Fibre has also been associated with reducing the risk of high blood pressure. These benefits have translated to disease reduction in numerous studies.
A 6-year study of over 40,000 men showed that high dietary fibre intake was associated with a 40% decrease in risk for heart attack.
Many other studies have found similar benefits of fibre, for reducing the risk of stroke, heart disease, and cardiovascular death.
Dietary fibre has been shown to reduce the risk of developing type-2 diabetes mellitus. Fibre is effective, not only in diabetes prevention, but also in diabetes treatment.
A 2012 study showed that in diabetic patients, increasing dietary fibre significantly reduced fasting blood glucose and A1C, a measure of average blood sugar levels in the previous three months.
A 2020 study showed that high dietary fibre may reduce the risk of breast cancer by 8%. The study found similar effects of both soluble and insoluble fibre, and these protective effects were consistent among both pre- and post-menopausal breast cancers.
This protective effect is thought to be mediated by fibre’s effect on modulating blood sugar levels, which subsequently decreases estrogen levels.
Fibre from foods and supplements
The recommended dietary fibre intake is around 38 g per day for men and 25 g per day for women. However, the Western diet achieves a daily fibre intake around half of what is recommended.
Thus, it is important to make a conscientious effort to increase fibre intake by eating a variety of high-fibre foods. Fibre supplements are also readily available to help bridge the gap between actual and recommended intake.
High-fibre foods include:
- Whole-grain products: oats, bran cereal, psyllium
- Fruits: apples, pears, strawberries
- Vegetables: avocados, skin-on potatoes, Brussels sprouts
- Beans, peas, and other legumes: lentils, kidney beans, chickpeas
- Nuts and seeds: almonds, chia seeds, pistachios
Fibre supplements include:
- Psyllium, husk or powder
- Flax seed, ground or whole
When increasing fibre intake, it is important to take it slow–no more than 5 g per week–and to ensure that you are drinking more fluids.
This will help to maximize the health benefits of fibre while reducing the risk of side effects like bloating and discomfort.
If you are taking a fibre supplement, it is important to consult with your healthcare provider to ensure that the supplement is safe for you and does not interfere with the absorption of any other medications.