Fiber is part of the carbohydrate group and is present to one degree or another in all grains, fruits, vegetables, pulses, legumes and nuts. Technically a non-starch polysaccharide or NSP for short, our digestive systems lack the necessary enzymes to break fiber down and so, as far as we are concerned, fiber is a calorie-free food. Animals that can extract energy from fiber have more than one stomach or have the ability to produce specialised enzymes so they can digest this tough plant-derived starch. For humans, although fiber does not contribute any energy to your daily diet, it provides numerous other health-related benefits.
Types of Fiber
Fiber can be classified as soluble or insoluble. This refers to its interaction with water. Soluble fiber forms a gel-like substance as it passes through your digestive track. Like a dry sponge, it soaks up liquid as it passes though your intestines and absorbs small but significant amounts of bile acid, cholesterol, fats and other such nastiness in your digestive system. Soluble fibre is found in the soft flesh of fruits, vegetables and grains. Think of soluble fiber as your friendly digestive-tract cleaner!
Insoluble fiber, sometimes called roughage, is found in the tough outer husk of grains as well as the skins of vegetables and fruit. Insoluble fiber passes through your digestive system like an old-fashioned bottle brush and gives it a good internal scrubbing. This helps keep your innards nice and clean!
Despite being calorie and nutrient-free, fiber offers a wide range of health benefits. The RDA (recommended daily allowance) for fiber is around 35 grams per day, split evenly between soluble and insoluble varieties. Your total daily fiber requirement varies according to your age, weight and the amount of food you are eating which is why you may often see a recommended range for fiber consumption of 24 to 35 grams. As fiber is calorie free, there is little harm in making sure you hit the upper ranges of this scale. If you are currently eating too little fibre and decide, as the result of reading this article to eat more, increase your daily fiber intake gradually. Going from a low fiber diet to a high fibre diet overnight is like trying to run a marathon on the first day you take up jogging. Increase your fiber intake slowly and gradually over a few weeks to minimize your chances of suffering digestive discomfort.
Weight Control – as previously discussed, fiber is calorie free. This means that foods that contain a lot of fibre such as whole grains, fruits and vegetables are generally lower in calories than less fibrously-dense foods. To put this in perspective, an apple and a typical biscuit both contain around 60 calories. Because much of the mass of the apple is made up from calorie-free fiber and water, compared to sugar and fat in the biscuit, the apple is bigger, far more filling and much more satisfying to eat. Most of us can eat a few biscuits in a single serving but it’s pretty unlikely you’ll eat the same number of apples!
Filling up on fiber is a great way to prevent overeating. Stretch receptors in your stomach send signals to your brain when it is full so you know when to stop eating. This message can take as long as 30 minutes to be sent and delivered. Fibrous foods cause greater gastric distension than non-fibrous foods. Simply put, this means you feel fuller, quicker which results in your brain getting the “stop eating” signal sooner than usual. This limits your potential for overeating.
In addition to being low in calories, fibrous foods generally take longer to chew and eat and keep you feeling fuller for longer. Fiber is a major gastric inhibitor. This simply means that fibre delays the emptying of your stomachs contents into your small intestine. The longer food stays in your stomach, the longer you feel full. A real-world example of this phenomenon is Chinese food. It’s an old truism that after eating a Chinese meal, 20 minutes later you are hungry again. Why? White rice! White rice is mostly devoid of fiber and subsequently passes out your stomach and into your small intestine very rapidly. This means you can go from feeling full to feeling empty very quickly.
By delaying gastric emptying, fiber also helps to control your blood glucose levels. Large fluctuations in blood glucose can trigger corresponding fluctuations in insulin levels. Roller coasting blood glucose levels play havoc with your hunger. A rapid drop in blood glucose can often result in cravings for carbohydrate (one reason never to go grocery shopping on an empty stomach!) so by ensuring that your stomach empties slowly, fibre helps ensure that your blood glucose levels remain relatively stable.
The hollow tubes of your intestines are made of smooth muscle and like the muscles of your chest, arms and legs, benefit from a regular workout. Fibre provides the means to exercise your digestive system. A diet devoid of fiber will result in poor intestinal health in the same way that a lack of exercise will result in a flabby, weak body.
To push food though your digestive system, the smooth muscular tubes that make up your digestive tract must squeeze inward in an action called peristalsis. Picture a snake swallowing an egg and the wave-like undulations as the snake squeezes the egg down the length of its body – that’s peristalsis.
Low fiber foods do not travel though your hollow digestive tubes very easily. A large amount of pressure is required to push food along. Imagine trying to get the very last bit of toothpaste out of the tube – it’s a real challenge! Fiber adds bulk to your food and, consequently, it passes though your digestive system much more easily and with far less pressure. Easy food passage and reduced food transit time (the time it takes from ingestion to elimination) has a major impact on digestive health and is strongly linked to a lower incidence of diverticular disease, also known as diverticulitis. This is a painful and serious medical condition where bacteria-filled bulges develop in the walls of your intestines. By consuming adequate fibre, intestinal pressure is kept to a minimum and there is much less likelihood of developing this unpleasant disease.
While getting enough fiber is very important, supplementation is seldom the best way. Fiber supplements such as bran and psyllium husks do indeed provide fiber but they do not provide any of the other nutritious benefits associated with eating fibrous fruits, vegetables and whole grains; specifically vitamins and minerals. An overreliance on fiber supplements may actually result in a vitamin and mineral deficiency. The best way to get enough fiber in your diet is to eat a wide variety of fruit, vegetables, grains and other natural food. Refined foods such as white bread, white rice, white pasta and processed meals contain very little fibre so, wherever possible, seek out foods in their most natural and unprocessed state. Simply following the old advice of eating an apple a day is one way to make sure you are on your way to getting enough essential fibre in your diet.