Table 1. Best Sources of Dietary Fiber

How Much Fiber is Enough?

Nutrition recommendations for daily needs are for 20-35 grams total of all types of dietary fiber per day.

Carbohydrates and Glucose

To understand the importance of carbohydrates in our diet, and how carbs differ from (say) protein and fats, remember two things:

• The human body runs on glucose. Therefore all foods need to be converted into glucose before they can provide energy.
• Carbohydrates are more readily converted into glucose than protein or fat, and may be considered the body's "preferred" source of energy.

Note: Carbs may be a very efficient source of energy, but this doesn't mean that carbs are more important than fats or protein. Indeed, both fat and protein are absolutely vital for good health, and without a balanced diet of carbs, fat and protein, the human body quickly becomes malnourished. Also, it's important to realize that nearly all foods (except for oils/fats) contain a mixture of carbs, protein and fat.

Effects of Simple or Complex Carbohydrates
on Blood Sugar

Due to their differing chemical structures, simple carbs and complex carbs affect the body in different ways.

Simple carbs (with the exception of fructose, fruit sugar) are basically sugars (glucose) so they are immediately absorbed into the bloodstream, causing a rise in blood-sugar levels. Because blood sugar-levels must be kept within a certain range, the body responds by telling the pancreas to secrete insulin into the digestive system. Why? Because insulin helps to "mop up" excess blood sugar and disperse it to other parts of the body. Unfortunately, the pancreatic gland typically "overreacts" to this sudden rise in blood sugar (thinking a huge amount of food has been eaten) and secretes too much insulin. Result? Within an hour or so, the insulin has mopped up too much blood sugar, so levels drop too far and this triggers hunger. This rapid rise and fall in blood sugar levels caused by excess production of insulin, is not good for our health or our eating habits. Over time, these "sugar spikes" can lead to impaired glucose tolerance, insulin insensitivity and type 2 diabetes.

By comparison, complex carbs need more time to be broken down into glucose. So they don't raise blood sugar levels as fast as simple carbs. This is why nutritionists recommend that we restrict our consumption of simple carbohydrates and eat complex carbohydrates instead.

Very complex carbohydrate (dietary fiber) has such a complicated chemical structure that the human body cannot metabolize it (break it down into glucose or other nutrients) at all. So it passes through the body mostly undigested. However, fiber remains very important for both health and weight control because it helps the body to process waste efficiently and helps us to feel fuller for longer. Fiber also helps protect us against some serious diseases, including various cancers.

Rating Carbohydrate Foods by the Glycemic Index

Recently, the Glycemic Index (GI) has become the benchmark for classifying carbohydrates. The glycemic index is a measure of how rapidly a particular food causes blood sugar to rise, compared with glucose. Foods are divided into high, medium or low glycemic index foods.

Although a valuable tool, especially for diabetics, the glycemic index confines itself to measuring a standard amount of carbs (50g). Since some foods contain only a small percentage of carbs, their glycemic index value may not be as relevant as their Glycemic Load, which takes into account portion size and carb content.

Fiber Ideas for Low Carb Dieters

The long list of dietary fiber sources means that it's still possible to get a certain amount of fiber from permitted low-carb foods, especially vegetables, nuts, and seeds.

Insoluble fiber may usually be obtained in sufficient quantities from wheat bran, although excessive wheat bran consumption may lead to some mineral deficiencies.

Soluble fiber is a bit more difficult to obtain in sufficient quantity from permitted low-carb foods, although you can obtain reasonable amounts from flax seed, seaweed, and avocados.

In practice, many dieters following a low carb weight loss plan are likely to need to use fiber supplements. Fortunately, many fiber supplements are no more than processed agricultural products and have been shown to be safe and quite effective. These include vegetable gums, pectins, seeds and brans.

Low Carb Diets Don't Need to Depend on Fiber Supplements

The weight loss and nutritional benefits of low carb diets don't really depend on excluding fiber. After all, fiber can't be digested and thus cannot contribute to the glucose/insulin problem. Furthermore, foods rich in soluble fiber (the more difficult fiber to obtain from permitted low carb foods) are probably worth the trouble. After all, healthy eating habits - whether low carb or high carb - rarely come from a bottle of processed supplements. In a nutshell, the issue of fiber-availability should not be allowed to obscure the merits (or otherwise) of low carb dieting.

Complex Carbohydrate

Dietary fiber, sometimes called roughage, is a group of very complex carbohydrates - found mostly in plants - whose chemical structure prevents them from being digested by humans. Although some metabolism of fiber (by certain bacteria) occurs in the intestines, we lack the digestive enzymes needed to break down the bonds that hold together fiber's sugar units. Therefore, fiber cannot be converted to glucose and contributes no calories to our diet. Most dietary fiber passes through the intestinal tract undigested.

Types of Fiber

There are two basic types of dietary fiber: soluble and insoluble fiber. The best sources of fiber include beans, wholegrain cereals, fruits, vegetables and nuts. Examples of fiber include: Cellulose, Lignin, Hemicellulose, Pectin, Beta-glucans and Arabinose. Although insoluble fiber and its health benefits have been known for some time, the benefits of soluble fiber have only recently appeared.

Health Benefits

However, although dietary fiber has no caloric or nutritional value, it does have significant health benefits and may assist weight control. Dietary fiber-deficiency in the average Western diet is now linked to a higher risk of digestive complaints (like constipation, diverticulosis), raised cholesterol levels and some intestinal cancers. Also, the presence of dietary fiber in carbohydrate foods helps to slow digestion thus reducing their glycemic index and their affect on blood glucose levels.

Modern Carbs are Less Nutritious

Concerning the health benefits of dietary fiber, it's worth noting that modern food processing techniques have gradually removed more and more of the natural fiber and other non-digestible parts of foods like wheat, rice and oats. For example, flour is now stripped of the fiber-containing shell or chafe, bleached and super-refined, in order to make lighter breads with a longer shelf-life. Result? These carbohydrate foods are now less natural, less filling, with a far higher glycemic index than the dense chewier breads we used to eat. Bad news for nutrition, eating habits and weight control.

Types of Dietary Fiber

There are several different kinds of dietary fiber, and with the exception of chitosan, a type of fiber synthesized from shrimp and crab shells, all dietary fiber comes from plants and whole grains. There is no fiber in animal foods, like meat, fish, poultry, milk products or eggs.

There are two basic types of dietary fiber: soluble and insoluble fiber, depending on whether it dissolves in water. Both soluble and insoluble fiber is indigestible by humans. Although insoluble fiber and its health benefits have been known for some time, the benefits of soluble fiber have only recently appeared.

Types of Insoluble Fiber

Insoluble dietary fiber is a natural laxative and includes cellulose and lignin which occur in whole grains (especially wheat bran), and hemicellulose (partly soluble) found in whole grains, nuts, seeds, fruits and vegetables.

Types of Soluble Fiber

Water soluble dietary fiber binds with and removes certain things in the gut. Types of soluble fiber include pectin, which occurs in fruits (apples, strawberries, citrus fruits); beta-glucans, found in oats, barley and rye; gums, found in beans, cereals (barley, oats, rice), seeds and seaweed; and arabinose, found in legumes/pulses. Soluble fiber can be further classified into fermentable and non-fermentable types. Fermentable soluble fiber helps to feed our intestinal bacteria - the "healthy" bacteria that helps us digest and absorb nutrition from our food.

Fiber-Rich Foods Contain Both Types of Fiber

Many fiber-rich foods, especially plant-foods, contain both soluble and insoluble fiber in varying proportions. But one type of fiber usually dominates.

Digesting Dietary Fiber

Although fiber is largely indigestible, the human digestive system does react with it. Bacteria in the digestive tract attack it, causing methane gas to be released in the process, which can cause bloating and flatulence. In addition, fiber - if eaten in excessive quantities - may interfere with the uptake of minerals and vitamins. Finally, excessive soluble fiber may attract too much water from the cells, thus impeding cell-function. For these reasons, it is best to increase your fiber intake gradually and avoid fiber supplements except in carefully measured doses.

Fiber & Weight Loss

In a nutshell, there are three main reasons why a diet rich in fiber can help you to regulate your eating habits and lose weight in the process.

Fiber Increases the Feeling of Fullness (Satiety)

Soluble fiber swells in the stomach when it comes into contact with water. This increased food-volume leads to a greater feeling of fullness. Result? We eat less.

Fiber Slows Down Digestion

The presence of fiber slows down the digestion of food in the stomach. This is especially helpful when we eat foods with a high glycemic index. Why? Because high glycemic index foods typically cause a rapid rise in our blood-sugar levels (often leading to a rapid fall in blood-sugar, after the release of insulin from the pancreas) which leads to a renewal of hunger pangs within a short time. In addition, rapid rises and falls in our blood-sugar levels may (it is believed) lead to insulin problems (like insulin resistance) as well as food cravings. Both these problems are associated with obesity and other weight-related health problems.

Fiber Increases the Feeling of Fullness (Satiety)

Soluble fiber swells in the stomach when it comes into contact with water. This increased food-volume leads to a greater feeling of fullness. Result? We eat less.

Fiber Slows Down Digestion

The presence of fiber slows down the digestion of food in the stomach. This is especially helpful when we eat foods with a high glycemic index. Why? Because high glycemic index foods typically cause a rapid rise in our blood-sugar levels (often leading to a rapid fall in blood-sugar, after the release of insulin from the pancreas) which leads to a renewal of hunger pangs within a short time. In addition, rapid rises and falls in our blood-sugar levels may (it is believed) lead to insulin problems (like insulin resistance) as well as food cravings. Both these problems are associated with obesity and other weight-related health problems.

Fiber is Found in Nutrient Rich Foods

A fiber-rich diet is more likely to be a healthy diet than a diet low in fiber. Why? Because fiber is found mainly in fruits, vegetables, whole grains, nuts and seeds - all of which are ideal for healthy weight loss. Therefore, by upping our fiber intake, we automatically increase our chances of reducing our weight and adopting healthier eating habits. Obviously this doesn't apply if you use fiber supplements: one reason why fiber-from-food is better for weight control.

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