INDEX
• Diet: New Devts .. Non-Starch Polysaccharides & Resistant Starch.
• Diet: What We Now Know About Food Fiber, Prebiotin.
• Diet: Good Ways to Get Carbs Without Starches.
• Diet: The Nutrition Equation, "No Sugar, No Starch” Diet.
• Diet: Choosing Non-Starchy Vegetables.
• Diet: Why Starch is a Major Obstacle with Diabetes.
• Diet: Dietary Polysaccharides, VIVO Pathophysiology.
• .

• Insight: Selection of terms can result in confusion of meanings.
• Insight: Small intestine digestibility of starch is individually highly variable.
• Insight: No fiber is digested in the small intestine; fiber is not starch.
• Insight: Civilization has become synonymous with over-/under-nutrition.
• Insight: Resistant starches digest slowly & satisfy longer; unprocessed.
• Insight: Effective diet planning requires knowing starches from carbohydrates.
• Insight: Non starchy vegetables enable larger portions for fewer calories.
• Insight: Beware of deceptive labelling on processed foods & pharmaceuticals.
• Insight: Starch can be digested by vertebrates; fiber cannot, without fermentation.
• Insight: Starch is digested to glucose, a source of energy.
• Insight: With adequate fermentation fiber can become a major source of energy.

• -Focus-: Monographs on Toxins and Enhancers.

Diet: New Developments .. Non-Starch Polysaccharides & Resistant Starch. INDEX
https://link.springer.com/chapter/10.1007/978-1-4684-5784-1_20?no-access=true
New Developments in Dietary Fiber pp 205-225
Edited by I. Furda and C. J. Brine
Plenum Press, New York, 1990

NON-STARCH POLYSACCHARIDES (DIETARY FIBER) AND RESISTANT STARCH

INTRODUCTION
Hans N. Englyst and John H. Cummings MRC
Dunn Clinical Nutrition Centre
100 Tennis Court Road
Cambridge CB2 1QL, U.K.

Progress in dietary fiber research has been slow because of the lack of an agreed definition of fiber, and the development of different techniques for its measurement. Two main methods have emerged which, by adopting contrasting approaches, include different components of the diet as dietary fiber.

Enzymatic gravimetric methods measure dietary fiber as the residue remaining on a filter after treatment of the food with starch and protein degrading enzymes, and correction for ash and nitrogen content. The procedures of Asp et al. (1983), Schweizer and Wursch (1979) and Furda (1981) and their adaptations to an AOAC procedure (Prosky et al. (1984) are examples of this technique.

Enzymatic chemical methods aim to identify and measure dietary fiber as its chemical components.
The procedures of Southgate (1969), and Englyst et al. (1982) are examples of this technique. In the Englyst procedure starch is completely removed and dietary fiber measured as the non-starch (non -a-glucan) polysaccharides (NSP) by gas liquid chromatography of constituent sugars after acid hydrolysis. The residue measured as dietary fiber by the AOAC procedure consists of NSP, some retrograded starch, lignin, maillard reaction products and a number of unidentified components of plant and animal origin. The unpredictable nature of the residue of the AOAC method, and the inclusion of retrograded starch as dietary fiber has led to confusion as to the amount and physiological importance of fiber and starch in food.

DEFINITION OF DIETARY FIBER
The original concept of dietary fiber was based on an association between the intake of unrefined plant foods and the absence of some Western diseases in African peoples (Hipsley, 1953; Burkitt, Trowell, 1972). The refining of plant foods leads to the removal of cell-wall material and the term dietary fiber was introduced to describe this material. Southgate has pointed out (1980) that much confusion could have been avoided if the term cell wall material had not been replaced by the less descriptive and less precise term dietary fiber.

Hipsley's concept of dietary fiber was of material derived from the plant cell-wall which remained in feces (1953).
In 1972 Trowell defined dietary fiber as the skeletal remains of plant cells that are resistant to digestion by the enzymes of man. However such a definition, whilst focussing on the plant cell wall as the major component of fiber, does not form the basis for an analytical method because it includes the physiological concept of resistance to digestive enzymes in man. In order to give the analyst a proper objective therefore in 1978 we suggested that dietary fiber should be measured as the non-starch polysaccharides in plant foods (Cummings, 1980; Englyst, 1981).

It has been argued that dietary fiber be defined as the food components resisting digestion in the small intestine.

Such a definition would include

NSP,

lactose (in many ethnic groups),

raffinose,

stachyose and other oligosaccharides,

a small amount of lignin,

organic anions such as oxalate tartrate,

maillard reaction products,

some fat, hair, bone, grit and other insoluble materials and,

depending on food processing, a variable amount of protein.

Moreover, in the process of developing the Englyst method for measurement of dietary fiber as NSP a type of starch resistant to digestion in the small intestine of man was identified (Englyst et al., 1982). This led to the suggestion that some starch should be included as dietary fiber (Asp and Johansson, 1984). Subsequently it was shown that starch was the major carbohydrate to escape digestion for many foods (Englyst and Cummings, 1985,1986,1987).

In addition, lactulose, polydextrose, neosugar and similar synthetic products resistant to pancreatic amylase would be included as dietary fiber. Such a broad definition is in clear contrast to the original concept of dietary fiber. Resistance to digestion of foodstuffs in the small intestine depends not only on food processing and chemical structure and modification but on a number of highly variable factors not limited to the food itself. These include chewing, transit through the stomach and small intestine and the amount and type of other food components in the meal as a whole.

The extent of digestion in the small intestine is therefore highly variable for an individual and even bigger differences in digestibility are seen between individuals or between population groups. Large differences in small intestinal digestibility are also seen between man and animals. Defining dietary fiber as material resisting digestion in the small intestine is not analytically realistic or a scientifically meaningful alternative to defining dietary fiber as NSP.

Diet: What We Now Know About Food Fiber, Prebiotin. INDEX
https://www.prebiotin.com/prebiotin-academy/what-are-prebiotics/dietary-fiber/

... There are many types of fiber that have been discovered in plants, including various types of starches, lignins, cellulose, and others. These were of interest to plant chemists, but not to physicians. Then in the 1980s, it was discovered that fiber could broadly be separated into insoluble and soluble types. No fiber is digested by the small intestine. All of it arrives into the colon unchanged. Insoluble fiber does not dissolve in water, is not fermented or broken down by colon bacteria, but does retain lots of water in the colon and so provides a larger, softer stool. Soluble fiber, on the other hand, is broken down and fermented by colon bacteria. We really didn’t know too much more about these two types of fiber until the 1990s when better measuring methods were devised. In the last 15 years, the difference between these two fibers, insoluble and soluble, has become increasingly important, especially with the discovery of prebiotic soluble fibers.

The History of Fiber
At one time before farming occurred and animals were domesticated, our ancestors wandered around, eating berries, fruits, root vegetables and any plant that promised to have some nutrition. The diet contained 50-100 grams of fiber a day, all of it from plant material. Interestingly, one of the best-studied prebiotics fibers, inulin, has been found in over 36,000 plants, so these people were eating a lot of this beneficial fiber.

Then came villages with farming, growing grains, and raising livestock.
Fiber intake gradually diminished. Furthermore, in Westernized countries, fiber was removed from the grains as it was felt to be useless. We were left with white bread without fiber and many of the minerals and vitamins. The food industries also began boxing and packaging food products in ways that required further changes to basic foods. Many substances were added to prolong shelf life and enhance the taste but they did not contribute to health as far as we knew. High fructose corn syrup was found to be as sweet as sugar and replaced it in many drinks and foods, as it was much cheaper. This corn derivative and other sweeteners were used in many products and have resulted in or are associated with the epidemic of obesity we now see in our society. Food fiber was sidelined as an important factor in the diet.

... in the mid-1990’s, medical researchers and nutritionists began to discover something quite remarkable about some soluble fibers. They found that certain soluble fibers such as inulin, oligofructose and FOS (fructooligosaccharide) caused some remarkable changes in the bacterial mix of the colon. They had discovered prebiotics.

Prebiotic Fibers
Prebiotic fiber comes from plants such as the Jerusalem artichoke, chicory root, onions, whole grains, bananas, and garlic. These essential soluble fibers do more than help people who ingest them in adequate amounts stay regular; multiple studies demonstrate that prebiotic fiber can favorably change the bacterial mix in the lower gut.

Soluble and Insoluble Fibers
Medical scientists and nutritionists categorize dietary fiber into two classifications.
Soluble fiber, as the name suggests, dissolves easily in water.
Plants such as beans, greens, and other complex carbohydrates contain soluble fiber; some foods, such as the potato, contain a mix of insoluble fiber (the peel) and soluble fiber (the flesh underneath). The human body breaks down these complex carbs into a gelatinous, viscous byproduct that the large intestine turns into gasses and acids that encourage the growth of beneficial bacteria in the lower gut. These bacteria positively affect several essential bodily functions and overall health.

Insoluble fiber won’t dissolve in water but is just as important to overall health and well-being as soluble fiber.
We can further classify insoluble fiber into two types: fermentable and non-fermentable. Non-fermentable insoluble fiber is known primarily as a bulking agent, and consuming adequate insoluble fiber keeps people regular. Fermentable insoluble fiber — such as resistant starch —produces the same healthy gasses and acids in the large intestine that soluble fiber does. One important difference between the two types of fibers is that soluble fiber tends to slow digestion while insoluble fiber speeds it up.

Resistant Starch
Entering the dietary fiber mix is resistant starch, considered a third type of fiber that provides the benefits of both insoluble and soluble fibers. The term “resistant” refers to this starch’s ability to resist digestion. Instead, it passes to the large intestine where it produces the same effects of soluble and insoluble fibers. Although the terms are complex, you probably eat resistant starch and other fibers in your diet every day — food such as seeds, unprocessed whole grains, legumes, and potatoes all contain resistant starch. People sometimes avoid eating starches because they fear weight gain; however, eating suitable amounts positively affects health in several ways.

Resistant Starch
These resistant starch foods help people stay fuller longer because they are not as easily digested.
That means people who eat resistant starches (even unknowingly) are more likely to consume fewer calories over the course of one day. Also, resistant starch helps people burn fat while avoiding fat storage, according to several studies; it also boosts metabolism. Natural resistant starch foods also help diabetics manage their condition by decreasing glycemic response and increasing insulin sensitivity. It increases the growth of healthy bacteria in the lower gut, just like its fermentable soluble and insoluble fiber cousins. Still, more research suggests that resistant starch contributes to digestive, brain, kidney and eye health. ...

Prebiotic supplements that contain fermentable insoluble fibers such as inulin and oligofructose contain enough plant fiber to make securing your daily intake much easier. Another added benefit? All-natural prebiotic supplements such as Prebiotin are low in calories, don’t impart an offensive taste or texture on foods and provide all the same benefits that whole food prebiotics do — without the planning, math and potential weight gain. ...

Diet: Good Ways to Get Carbs Without Starches. INDEX
http://healthyeating.sfgate.com/good-ways-carbs-starches-8673.html
Written by Serena Styles
Updated December 12, 2018

Even if your health care professional recommends you avoid or limit starch consumption, your body still needs a healthy amount of carbohydrates. MayoClinic.com recommends consuming between 45 and 65 percent of your daily calories from carbohydrates, and 1 gram of carbohydrates has 4 calories. If you eat a 2,000-calorie diet, aim for between 225 and 325 grams of carbohydrates each day. Include non-starchy carbohydrate sources in every meal to help meet your daily goals and stay healthy.

Dairy
Milk, yogurt and other dairy products contain lactose, a type of non-starchy carbohydrate.
Low-fat and fat-free dairy are low in calories, cholesterol and fat with a decent amount of protein and carbohydrates.
ChooseMyPlate.gov recommends consuming 3 servings of dairy each day. A one-cup serving of plain, fat-free yogurt has 137 calories and nearly 19 grams of carbohydrates. Other examples of dairy servings include 1 cup of milk, 2 cups of cottage cheese, 1/3 cup of shredded cheese and 1 cup of calcium-fortified soymilk. To include it in your diet, drink a glass of milk with breakfast, mix yogurt with a leafy green salad or eat cottage cheese with fruit as a snack.

Fruits and Berries
Fruits and berries get their carbohydrates from fiber and fructose, both of which are non-starchy.
The exceptions include bananas, plantains and breadfruit, all of which are high in starches.
Aim for around two servings of fruit or berries each day. A serving of raspberries is 1 cup and it has 64 calories and 15 grams of carbohydrates. Other fruit and berry servings include a small apple, 1 cup of grapes, eight large strawberries or half-cup of unsweetened, dried fruit. Fruit and berries make energizing snacks, and they work well as a side dish or dessert.

Non-Starchy Vegetables
Non-starchy vegetables do not yield as many carbohydrates as their starchy counterparts, but you can eat large portions for minimal calories. Aim for around three servings of vegetables each day. A 1-cup serving of broccoli has 31 calories and 6 grams of carbohydrates.

Other non-starchy vegetables to add to your carbohydrate intake include butterhead lettuce, arugula, onions, mushrooms and asparagus.

Vegetables that contain starches include potatoes, yams, carrots, beans, beets, taro root, corn, peas, parsnips and squash.

Diet: The Nutrition Equation, "No Sugar, No Starch” Diet. INDEX
http://www.nutritionequation.org/how-to/no-sugar-no-starch-diet-getting-started/

THE PRIMARY RESTRICTION: CARBOHYDRATES
On this diet, no sugars (simple carbohydrates) and no starches (complex carbohydrates) are eaten.
The only carbohydrates encouraged are the nutritionally dense, fiber-rich vegetables listed.
Sugars are simple carbohydrates.
Avoid these kinds of foods: white sugar, brown sugar, honey, maple syrup, molasses, corn syrup, beer (contains barley malt), milk (contains lactose), flavored yogurts, fruit juice, and fruit.

Starches are complex carbohydrates.
Avoid these kinds of foods: grains (even “whole” grains), rice, cereals, flour, cornstarch, breads, pastas, muffins, bagels, crackers, and “starchy” vegetables such as slow-cooked beans (pinto, lima, black beans), carrots, parsnips, corn, peas, potatoes, French fries, potato chips.

FATS AND OILS
All fats and oils, even butter, are allowed.
Olive oil and peanut oil are especially healthy oils and are encouraged in cooking.
Avoid margarine and other hydrogenated oils that contain trans fats.

For salad dressings, the ideal dressing is a homemade oil-and-vinegar dressing, with lemon juice and spices as needed.
Blue-cheese, ranch, Caesar, and Italian are also acceptable if the label says 1 to 2 grams of carbohydrate per serving or less. Avoid “lite” dressings, because these commonly have more carbohydrate. Chopped eggs, bacon, and/or grated cheese may also be included in salads.

Fats, in general, are important to include, because they taste good and make you feel full.
You are therefore permitted the fat or skin that is served with the meat or poultry that you eat, as long as there is no breading on the skin. Do not attempt to follow a low-fat diet!

WHEN YOU ARE HUNGRY,
EAT YOUR CHOICE OF THE FOLLOWING FOODS:

Meat: Beef (including hamburger and steak), pork, ham (unglazed), bacon, lamb, veal, or other meats.
For processed meats (sausage, pepperoni, hot dogs), check the label carbohydrate count should be about 1 gram per serving (and be organic if able and nitrate free).

Poultry: Chicken, turkey, duck, or other fowl.

Fish and Shellfish: Any fish, including tuna, salmon, catfish, bass, trout, shrimp, scallops, crab, and lobster
(no farmed seafood, there are to many toxins in them).

Eggs: Whole eggs are permitted without restrictions.

You do not have to avoid the fat that comes with the above foods.
You do not have to limit quantities deliberately, but you should stop eating when you feel full.

FOODS THAT MUST BE EATEN EVERY DAY:
Salad Greens: 2 cups a day.
Includes arugula, bok choy, cabbage (all varieties), chard, chives, endive, greens (all varieties, including beet, collards, mustard, and turnip), kale, lettuce (all varieties), parsley, spinach, radicchio, radishes, scallions, and watercress. (If it is a leaf, you may eat it.)

Vegetables: 1 cup (measured uncooked) a day.
Includes artichokes, asparagus, broccoli, Brussels sprouts, cauliflower, celery, cucumber, eggplant, green beans (string beans), jicama, leeks, mushrooms, okra, onions, pepper pumpkin, shallots, snow peas, sprouts (bean and alfalfa) sugar snap peas, summer squash, tomatoes, rhubarb, wax beans, zucchini.

Bouillon: 2 cups daily --- as needed for sodium replenishment.
Clear broth (consommé) is strongly recommended, unless you are on a sodium-restricted diet for hypertension or heart failure.

FOODS ALLOWED IN LIMITED QUANTITIES:
Cheese: up to 4 ounces a day.
Includes hard, aged cheeses such as Swiss and Cheddar, as well as Brie, Camembert blue, mozzarella, Gruyere, cream cheese, goat cheeses. Avoid processed cheeses, such as Velveeta. Check the label; carbohydrate count should be less than 1 gram per serving.

Cream: up to 4 tablespoonfuls a day.
Includes heavy, light, or sour cream (not half and half).
Mayonnaise: up to 4 tablespoons a day. Duke’s and Hellmann’s are low-carb. Check the labels of other ...

IMPORTANT TIPS AND REMINDERS
The following items are NOT on the diet: sugar, bread, cereal, flour-containing items, fruits, juices, honey, whole or skimmed water, milk, yogurt, canned soups, dairy substitutes, ketchup, sweet condiments and relishes.

Avoid these common mistakes:
Beware of “fat-free” or “lite” diet products, and foods containing “hidden” sugars and starches (such as coleslaw or sugar-free cookies and cakes). Check the labels of liquid medications, cough syrups, cough drops, and or other over-the-counter medications that may contain sugar. Avoid products that are labeled “Great for Low-Carb Diets!” ...

Sugar by any other name is still sugar!
All of these are forms of sugar: sucrose, dextrose, fructose, maltose, lactose, glucose, honey, agave syrup, high-fructose corn syrup, maple syrup, brown-rice syrup, molasses, evaporated cane juice, cane juice, fruit- juice concentrate, corn sweetener.

Diet: Choosing Non-Starchy Vegetables. INDEX
http://www.diabetes.org/food-and-fitness/food/
what-can-i-eat/making-healthy-food-choices/non-starchy-vegetables.html
Last Reviewed: August 24, 2017 --- Last Edited: August 25, 2017

Choose fresh, frozen and canned vegetables and vegetable juices without added sodium, fat or sugar.

If using canned or frozen vegetables, look for ones that say no salt added on the label.
As a general rule, frozen or canned vegetables in sauces are higher in both fat and sodium.
If using canned vegetables with sodium, drain the vegetables and rinse with water to decrease how much sodium is left on the vegetables.

For good health, try to eat at least 3-5 servings of vegetables a day.
This is a minimum and more is better! A serving of vegetables is:

    ½ cup of cooked vegetables 
    1 cup of raw vegetables

    Amaranth or Chinese spinach
    Artichoke
    Artichoke hearts
    Asparagus        
    Baby corn
    Bamboo shoots
    Beans (green, wax, Italian)
    Bean sprouts
    Beets
    Brussels sprouts
    Broccoli
    Cabbage (green, bok choy, Chinese)
    Carrots
    Cauliflower
    Celery
    Chayote
    Coleslaw (packaged, no dressing)
    Cucumber
    Daikon
    Eggplant
 Greens (collard, kale, mustard, turnip)
    Hearts of palm
    Jicama

    Kohlrabi
    Leeks
    Mushrooms
    Okra
    Onions
    Pea pods
    Peppers
    Radishes
    Rutabaga
    Salad greens 
 (chicory, endive, escarole, lettuce, 
    romaine, spinach, arugula, 
      radicchio, watercress)
    Sprouts
    Squash 
      (cushaw, summer, crookneck, 
       spaghetti, zucchini)
    Sugar snap peas
    Swiss chard
    Tomato
    Turnips
    Water chestnuts
    Yard-long beans

Diet: Why Starch is a Major Obstacle with Diabetes. INDEX
https://diabetesmealplans.com/10562/starch-and-diabetes/
By Elizabeth: Dietitian (MS, RD, CDE)
May, 2017 ?

Starch is produced by plants through photosynthesis and stored as granules as a source of nutrition for the plant to grow and stay healthy. It might be in the seed (as in the case of corn) or tuber (in the case of a potato). When we eat foods with starch, we are consuming this nutrition in the form of carbohydrates. Carbohydrates consist of sugars, starches and fiber.

When you look at a nutrition label, sugars and fiber are listed.
The remaining carbohydrates are various forms of starch.
Unlike sugars that tastes very sweet, starches are long complex molecules and do not generally taste sweet.
Unlike fiber, which passes through digestion to promote healthy bowel function, starches are broken down, digested and absorbed into the bloodstream and do not promote healthy digestive function

Starch is a type of carbohydrate formed by long strings of glucose units bonded together–also known as a “polysaccharide (poly=many; saccharide=sugars).” By contrast, simple sugars (or simple carbs) are individual sugars (monosaccharides such as fructose) or 2 sugar units held together by a single bond (such as lactose, which is glucose and galactose, also known as disaccharides).

What Foods Contain Starch?
Starch is the most common form of carbohydrate consumed in modern diets. To us, we all know these foods as ‘staples.'

It's found in large amounts in
rice, potatoes, wheat (including ‘white’ versions of wheat such as bread, pancakes, biscuits, pasta, tortillas), corn (including chips) and tapioca.

There are also moderately starchy foods, which include: bananas, oats, rye, taro, beans and peas.

Here is a table of foods high starch foods compared with low starch alternatives:

*Note: Starch contents listed above are estimates, as USDA’s official database does not list starch specifically but can be estimated based on calculations by elimination of sugar and fibers.

Starch has historically been a significant part of our diets as it provides a large amount of calories and is relatively inexpensive to produce.

On top of this, many starchy foods taste great and tend to be very shelf stable compared with their non-starchy counterparts.

Starch provides a thickened texture giving certain foods a viscosity that is difficult to replicate without it. And starches are often used in pudding, salad dressings, sauces, and pie fillings, as thickeners and stabilizers.

When we eat cooked starch (the body is unable to digest raw starch well), therefore the long straight or branched compounds are broken down into individual glucose molecules.

These glucose molecules are then absorbed through the small intestine into the bloodstream where they can be utilized to fuel cells. Or if the body has enough glucose stores, the excess will be stored as fat – if there is sufficient insulin to process them and the cells are responsive to insulin. If not, as in the case of diabetes, the glucose stays in the bloodstream.

What is Resistant Starch?
Resistant starch is digested differently to other starches.
It passes through the small intestine undigested – similar to soluble fiber.
It makes its way to the colon where it is then fermented by microbes that produce byproducts called short chain fatty acids – butyrate, acetate and propionate. These unique fatty acids feed healthy gut bacteria, along with playing important roles in lipid, glucose, and cholesterol metabolism.

Very little energy is extracted from resistant starch, which results in minimal impact on blood glucose levels.
Resistant starch has been shown to improve insulin sensitivity, increase satiety/fullness, increase calories burned and improve colon health by reducing inflammation in the colon, thereby helping reduce/prevent cancer. Resistant starches are often destroyed in cooking, so most foods need to be eaten in their raw form or cooked, then cooled.

Resistant Starch Food Sources
Foods high in resistant starch include:

    Green bananas
    Raw potato starch
    Oats
    Beans and legumes
    Cooked, then cooled potatoes

Keep in mind that all of these foods are still high in carbohydrates, and generally these are not the types of carbs we recommend you eat. The exception being beans and legumes, in small portions only. The point is, resistant starches are better for you than non-resistant starches, but certainly not as healthy as non-starchy high fiber foods like our low carb vegetables. Even though resistant starch is considered “healthy” for the general population, it is likely they will still have an impact on blood glucose, to varying degrees depending on the person.

Grey Area Starches
There are some ‘grey area’ starches.
These are what some people refer to as “healthy carbs,” which include:

whole grains, oats, sweet potatoes, beans, lentils etc

Some diabetics can include these in small controlled amounts, whereas others aren’t able to eat any of them due to their impact on blood sugar.

Diet: Dietary Polysaccharides, VIVO Pathophysiology. INDEX
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/basics/polysac.html
Send comments to Richard.Bowen@colostate.edu
Richard Bowen

Dietary Polysaccharides
Polysaccharides, particularly of plant origin, are prominent components in the diets are herbivores and omnivores.
This complex set of molecules has been categorized in several ways, depending on whether the focus is chemistry or nutrition. From the standpoint of digestive physiology and nutrition, perhaps the most relevant classification is based on whether or not animals synthesize enzymes that allow the polysaccharide in question to be digested into absorbable monosaccharides. In this view, we have starch, which can be digested by vertebrate enzymes, versus fiber, which cannot.

Starch: Amylose and Amylopectin
Starch is the principle carbohydrate found in plant seeds and tubers; important sources of starch include maize (corn), potato and rice. Starch exists in the form of granules, each of which consist of several million amylopectin molecules together with an even larger number of amylose molecules. Since amylopectin is a much larger molecule than amylose, the mass of amylopectin is typically 4 to 5 times that of amylose in starch.

Amylose consists of a linear, helical chains of roughly 500 to 20,000 alpha-D-glucose monomers linked together through alpha glycosidic bonds.

Starch is digested to glucose in two basic steps:

First amylose and amylopectin are hydrolyzed into small fragments through the action of alpha-amylase, secreted by salivary glands in some species, and from the pancreas in all. Amylase cleaves only internal alpha glycosidic bonds, thereby reducing starch to three different oligosaccharides:

maltose (disaccharide),
maltotriose (trisaccharide), and a group of
alpha-limit dextrins which contain branch points from amylopectin.

Second, maltose, maltotriose and limit dextrins are hydrolyzed on the lumenal surface of the small intestine by a brush border enzyme complex called sucrose-isomaltase (also often referred to as maltase). This step ultimately yields glucose monomers that are then transported into the small intestinal enterocyte by co-transport with sodium ions.

Dietary Fiber: Cellulose and Hemicellulose
Several definitions have been proposed for "fiber".
An early definition, still quite appropriate, basically states that fiber is the portion of food derived from plant cell walls that is poorly digested by mammals." To put it another way, mammals often consume fiber, but do not themselves secrete the enzymes necessary to digest it into a form that can be absorbed. Another common definition for fiber is the non-starch polysaccharide component of foodstuffs.

The chief components of dietary fiber are cellulose and hemicellulose, both of plant origin.
Pectin and pectic acid are other plant polysaccharides often present in diets.

Cellulose is a linear polymer of between 1000 and 10,000 beta-D-glucose molecules in which adjacent glucose molecules are joined covalently through beta glycosidic bonds. The beta bonds cause the polymer to assume a non-helical, straight structure, which is different from the helical structure imposed on starch molecules by the alpha bonding. The non-helical structure of cellulose also promotes hydrogen bonding between cellulose molecules.

Cellulose polymers associate with one another through a huge number of hydrogen bonds to form microfibers.
Microfibers interact to form cellulose fibers. A typical fiber contains roughly 500,000 cellulose molecules.
The high tensile strength of cellulose fibers reflects the massive number of hydrogen bonds involved in its structure.

Hemicellulose is a heteropolymer composed of a variety of sugars, including xylose, arabinose and mannose in a branched structure. In contrast to the highly ordered structure of cellulose, hemicellulose assumes an amorphose structure and becomes highly hydrated to form a gel.

No vertebrate cell has been identified that produces an enzyme that hydrolyzes celluloses or hemicelluloses.
Certainly, amylase will not cleave these two polysaccharides. Dietary fiber therefore is indigestable and passes through the small intestine essentially unchanged.

Within the large intestine (or the forestomaches of ruminants), fiber is digested by enzymes - cellulases and hemecellulases - of microbial origin, a process referred to as fermentation. Fermentation does not yield monosaccharides that can be absorbed. Rather, its chief products are short chain volatile fatty acids, which are readily absorbed and utilized for energy and lipid synthesis. Thus, if the fermentation vat is of sufficient size (i.e. herbivores), dietary fiber can be a major source of energy.

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