Dietary fiber

What is fiber? Fiber is made up of the indigestible parts or compounds of plants, which pass relatively unchanged through our stomach and intestines. Other terms for dietary fiber include ‘bulk’ and ‘roughage’, which can be misleading since some forms of fiber are water-soluble and aren’t bulky or rough at all.

In countries with traditionally high-fiber diets, diseases such as bowel cancer, diabetes and heart disease are much less common than in Western countries.

Research shows that many Americans are not getting enough dietary fiber. A diet low in fiber has been linked to: There are 2 categories of fiber – soluble and insoluble. Both are beneficial and we need to include them in our daily diets.

Most plant foods contain a mixture of both#

What is soluble fiber? Soluble fiber soaks up water like a sponge and helps to bulk out our poo (feces) so it can pass through the gut more easily. It acts to slow down the rate of digestion. Soluble fiber includes pectins, gums and mucilage, which are found mainly in plant cells.

One of its major roles is to lower LDL (bad) cholesterol levels.

It can also help with constipation#

Good sources of soluble fiber include:

• soy milk
• speeds up the time that food passes through the gut

Insoluble fiber includes cellulose, hemicelluloses and lignin, which make up the structural parts of plant cell walls. A major role of insoluble fiber is to add bulk to feces and to prevent constipation and associated problems (such as hemorrhoids). Good sources of insoluble fiber include: wholegrain foods.

Resistant starch, while not traditionally thought of as fiber, acts in a similar way. Resistant starch is the part of starchy food (approximately 10%) that resists normal digestion in the small intestine. Sources include:

• added to bread
• breakfast cereals

It can also be formed by cooking and manufacturing processes such as snap freezing.

Resistant starch is also important for gut health#

Bacteria in the large bowel ferment and change the resistant starch into short-chain fatty acids, which are important to bowel health and may protect against cancer. These fatty acids are also absorbed into the bloodstream and may play a role in lowering blood cholesterol levels. The digestive system is lined with muscles that massage food along the digestive tract – from the moment a mouthful is swallowed until the eventual waste is passed out of the bowel (a process called peristalsis).

It also important for other body functions, such as:

• reducing our risk of other conditions (such as heart disease
• some cancers). A high-fiber diet is protective against weight gain

High-fiber foods tend to have a lower energy density, which means they provide fewer kilojoules per gram of food.

As a result, a person on a high-fiber diet can consume the same amount of food, but with fewer Foods high in fiber are often bulky and, therefore, filling. Soluble fiber forms a gel that slows down the emptying of the stomach and the transit time of food through the digestive system.

This extends the time a person feels full#

Fiber also delays the absorption of sugars from the intestines. This helps to maintain lower blood sugar levels and prevent a rapid rise in blood insulin levels, which has been linked with obesity and an increased risk of diabetes.

If you have diabetes, eating a diet high in fiber slows glucose absorption from the small intestine into your blood.

This reduces the possibility of a surge of insulin – the hormone produced by to stabilize blood glucose levels. Increasing dietary fiber and wholegrain intake is likely to reduce the risk of cardiovascular disease, It is also very likely that these observed health benefits occur indirectly, through the protective effects of ‘phytochemicals’ (such as ) that are closely associated with the fiber components of fruits, vegetables and cereal foods.

There is good evidence that soluble fiber reduces total blood cholesterol levels and LDL (bad) cholesterol levels.

When blood cholesterol levels are high, fatty streaks and plaques are deposited along the walls of arteries. This can make them dangerously narrow and lead to an increased risk of coronary heart disease (which includes It is thought that soluble fiber lowers blood cholesterol by binding bile acids (which are made from cholesterol to digest dietary fats) and then excreting them.

Fiber is thought to decrease bowel cancer risk by increasing stool bulk, diluting possible carcinogens present in the diet and decreasing transit time through the colon.

Also, bacterial fermentation of fiber leads to the production of short-chain fatty acids, which are thought to have protective effects. Other research has found that a 10g per day intake of total dietary fiber equates to a 10% reduction in risk of bowel cancer. Research has shown that a high total fiber intake may reduce risk of breast cancer and a large-scale study also found that a higher fiber diet during adolescence and young adulthood may reduce women’s breast cancer risk.

Fiber is even more important for older people#

The digestive system slows down with age, so a high-fiber diet becomes even more important. Some very high-fiber breakfast cereals may have around 10g of fiber per serve.

If this cereal is not accompanied by enough fluid, it may cause abdominal discomfort or constipation.

How much fiber do we need? Many adults do not consume enough fiber – on average, most Americans consume 20–25g of fiber daily.

The recommended daily fiber intake is: women = 25g of fiber each day#

Boys (14 to 18 years) = 28g.

Most Americans do not eat enough fruit and vegetables, beans/legumes, or whole grain cereals - all of which are great sources of fiber. Simple suggestions for increasing your daily fiber intake include:

• Eat breakfast cereals that contain barley
• wheat or oats. Switch to wholemeal or multigrain breads
• brown rice

Add an extra vegetable to every evening meal#

Snack on fruit, dried fruit, nuts or wholemeal crackers. A daily intake of more than 30g can be easily achieved if you eat: nuts or seeds instead of low-fiber cakes and biscuits. You do not need to eat many more kilojoules to increase your fiber intake.

Make sure you stick to the recommended intake and slowly introduce fiber into the diet to avoid any negative outcomes. A sudden switch from a low-fiber diet to a high-fiber diet may lead to some abdominal pain and increased ). This occurs when fiber binds these minerals and forms insoluble salts, which are then excreted.

This could result in an increased risk of developing deficiencies of these minerals in susceptible people. Also, it is better to get fiber from food sources rather than from fiber supplements, as these can aggravate constipation, especially if you do not increase the amount of water you drink daily. Dietary fiber is found in wholegrain cereals and fruit and vegetables Fiber is mainly a carbohydrate.

The main role of fiber is to keep the digestive system Conditions linked to low-fiber diets constipation hemorrhoids diverticulitis irritable bowel syndrome (IBS) overweight and obesity heart disease diabetes bowel cancer breast cancer Types of dietary fiber fruit and vegetables oat bran, barley, seed husks, flaxseed, psyllium legumes – dried beans, lentils, peas bran – wheat bran, corn bran, rice bran the skins of fruits and vegetables nuts and seeds dried beans Resistant starch acts like fiber many unprocessed cereals and grains unripe bananas potatoes lentils Health benefits of dietary fiber As dietary fiber is relatively indigestible, it adds bulk to our feces (poo) and lowering blood cholesterol keeping our weight under control stabilizing glucose – which is important if you have diabetes Dietary fiber and weight control kilojoules (calories) Dietary fiber and diabetes the pancreas Dietary fiber, cancer and heart disease type 2 diabetes, weight gain and obesity, and may lower blood

• pressure antioxidants Dietary fiber blood cholesterol angina heart attack Fiber
• bowel cancer risk Studies have shown that dietary fiber
• cereal fiber
• wholegrains are protective against some forms of cancer Fiber
• breast cancer risk Dietary fiber
• legumes Higher fiber food choices Fiber (g) (approx.) Lower fiber food choices Fiber (g) (approx.) 2 wholewheat cereal biscuits (e.g

Weetbix or Vita Brits) 2 1 cup puffed rice cereal 4 4 slices wholegrain bread 7 4 slices white bread 0 2 pieces of fruit (such as an apple and pear) 9 1 piece of fruit (apple) 1/2 cup canned fruit, undrained 7 4 1 cup frozen mixed vegetables 6 1/2 cup frozen mixed vegetables 3 1 small, boiled potato (with skin on) 8 1 cup of mashed potato 7 1 cup brown rice 7 1 cup white cooked rice 0 2 wholemeal dry biscuits 5 2 plain dry biscuits 4 25 almonds 0 1 slice plain cake 6 Total 4 5 A sudden increase in dietary fiber flatulence (wind) Also, very high-fiber diets (more than 40g daily) are linked with decreased absorption of some important minerals (such as iron, zinc and calcium

Where to get help#

Key Points#

• Soluble fiber includes pectins, gums and mucilage, which are found mainly in plant cells
• Resistant starch is also important for gut health
• Fiber is even more important for older people
• digestive system slows down with age, so a high-fiber diet becomes even more important
• If this cereal is not accompanied by enough fluid, it may cause abdominal discomfort or constipation