“Eat your porridge – it is good for you”
“Eat your fruits and vegetables – they are good for you.”
This is a common mantra given to people who want to eat a well balanced healthy diet. But, how often do we ask, “What does this really mean? Is there any science behind it or is it all hot air at the end of the tunnel?” You know what I mean.
Dietary fibre is found in plants. Fibre is composed of cellulose (a complex carbohydrate that is composed of glucose units, forms the main constituent of the cell wall in most plants), lignin (chief non-carbohydrate constituent of wood), pentosans (group of polysaccharides found with cellulose in many woody plants), pectin (water-soluble carbohydrate found in ripe fruits) and gums (viscid exudation from plants).
Fibre is divided into soluble and insoluble fibre.
Soluble fibre dissolves in water to form a gel-like substance. It is readily fermented by bacteria in the colon into gases and physiologically active byproducts. Sources of soluble fibre are oats, legumes (beans, peas, and soybeans), apples, bananas, berries, barley, some vegetables, and psyllium. More fibre you eat, more gas you produce. There is not much you can do about it except look over your shoulder and let it out.
Soluble fibre has now been shown to lower LDL (bad cholesterol) levels through a series of processes that alter cholesterol and glucose metabolism – reduces the absorption of sugar, reduces sugar response after eating, normalizes blood lipid levels and, once fermented in the colon, produces byproducts with wide-ranging physiological activities.
Insoluble fibre increases the movement of material through the digestive tract and increases stool bulk by absorbing water and easing defaecation, reduces transit time, thus preventing constipation which decreases the opportunity for both nutrients and fecal mutagens to interact with the intestinal lining. There is no fermentation by bacteria. Sources of insoluble fibre are whole wheat foods, bran, nuts, seeds and the skin of some fruits and vegetables.
Constipation leads to hemorrhoids and anal fissures. Although insoluble fibre is associated with reduced diabetes risk, the mechanism by which this occurs is unknown. Although many researchers believe that dietary fibre intake reduces risk of colon cancer, one study conducted by researchers at the Harvard School of Medicine of over 88,000 women did not show a statistically significant relationship between higher fibre consumption and lower rates of colorectal cancer or adenomas.
The five most fibre-rich plant foods, according to the Micronutrient Center of the Linus Pauling Institute, are legumes (15–19 grams of fibre per US cup serving, including several types of beans, lentils, and peas), bran (17 grams per cup), prunes (12 grams), Asian pear (10 grams each, 3.6% by weight), and quinoa (9 grams).
On average, North Americans consume less than 50 per cent of the dietary fibre levels required for good health. Current recommendations from the United States National Academy of Sciences, Institute of Medicine, suggest that adults should consume 20–35 grams of dietary fibre per day.
Although fibre falls under the category of carbohydrates, it is low in calories. Regardless of the type of fibre, the body absorbs fewer than 4 Calories (16.7 kilojoules) per gram of fibre. In some countries, fibre is not listed on nutrition labels, and is considered 0 Calories/gram when the food’s total Calories are computed.
For weight loss, a diet rich in fibre from cereals, not from fruit and vegetables, is more likely to help limit weight gain, says Dr. Khursheed Jeejeebhoy, a well known gastroenterologist in Toronto, writing in the Medical Post (March 9, 2010). High-fibre breakfast reduces subsequent intake of energy, delays digestion and slows absorption. A Dutch study found that an intake of 10 g of total fibre per day was associated with a loss of 39 g of body weight per year and a reduction in waist circumference of 0.08 cm per year.
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