Corn, fresh or dried, is NOT safe for rabbits. The hull of kernels is made of a complex polysaccharide which rabbits can't digest.
Timothy-grass (Phleum pratense), is an abundant perennial grass native to most of Europe except for the Mediterranean region. It is also known simply as timothy, or as meadow cat's-tail or common cat's tail. It is one of the Phleum genus, consisting of about 15 species of annual and perennial grasses.
It is probably named after Timothy Hanson, a U.S. farmer and agriculturalist said to have introduced it from New England to the southern states in the early 18th century. Upon his recommendation it became a major source of hay and cattle fodder to British farmers in the mid-18th century.
Timothy-grass can be confused with Meadow Foxtail (Alopecurus pratensis) and Purple-stem Cat's-tail (Phleum phleoides).
It grows to 19–59 inches tall, with leaves up to 17 inches long and ½ inch broad. The leaves are hairless,rolled rather than folded, and the lower sheaths turn dark brown.
It has no stolons or rhizomes, and no auricles.
The flowerhead is 2¾–6 inches long and ¼–½ inches broad, with densely packed spikelets. It flowers from June until September. The stamen are pink.
The ligule is short and blunt.
It grows well in heavy soil, and is noted for its resistance to cold and drought, and thus ability to grow in dry upland or poor sandy soils. In pasture it tends to be overwhelmed by more competitive grasses. After cutting it grows slowly.
There are two subspecies:
Timothy-grass was unintentionally introduced to North America by early settlers, and was first described in 1711 by John Hurd from plants growing in New Hampshire. Hurd named the grass "hurd grass" but a farmer named Timothy Hanson began to promote cultivation of it as a hay about 1720, and the grass has been known by its present name since then. Timothy has now become naturalized throughout most of the US and Canada.
It is commonly grown for cattle feed and, in particular, as hay for horses. It is relatively high in fibre, especially when cut late. It is considered a harsh, coarse grass little relished by livestock if cut earlier. It is considered part of the standard mix for grass hay and provides quality nutrition for horses. Timothy hay is a staple food for domestic pet rabbits, guinea pigs, chinchillas, and degus, often making up the bulk of their diet. Timothy hay is rich in long fibre and its abrasive texture helps to grind down the teeth, keeping both the teeth and jaw in good order.
The caterpillars of some Lepidoptera use it as a foodplant, e.g. the Essex Skipper (Thymelicus lineola). It also grows in roadsides and abandoned fields but generally requires nutrient-rich soils.
Its pollen is a common allergen; it has recently been used in small amounts as part of a new hay fever vaccine Grazax, which is designed to recondition the body's immune system so it no longer responds to pollen.
Plants persist through the winter. Dead, straw-colored flowering stems may persist, but only for a short time, and are recognized by the distinctive spike-like inflorescence.
It is often confused with Meadow Foxtail (Alopecurus pratensis). Timothy flowers later, from June until August, whereas Meadow Foxtail flowers from April until June. The spikelets of Timothy are twin hornlike projections arranged in cylindrical panicles, whereas foxtail has a soft, single awn.
Purple-stem Cat's-tail (Phleum phleoides) prefers lighter soils and grows on chalk downland.
Mountain Timothy (Phleum alpinum) grows above 6,000 feet. A "wild Timothy" was found to grow in Yosemite at the time of its discovery but may have been a foxtail.
Timothy canary grass (Phalaris angusta), another species with a similar cylindrical panicle, is toxic to livestock.
Pepita (from Mexican Spanish: pepita de calabaza, "little seed of squash") is a Spanish culinary term for the pumpkin seed, the edible seed of a pumpkin or other cultivar of squash (genus Cucurbita). The seeds are typically rather flat and asymmetrically oval, and light green in color inside a white hull. The word can refer either to the hulled kernel or unhulled whole seed, and most commonly refers to the roasted end product.
Pepitas are a popular ingredient in Mexican cuisine and are also roasted and served as a snack. Marinated and roasted, they are an autumn seasonal snack in the United States, as well as a commercially produced and distributed packaged snack, like sunflower seeds, available year-round. Pepitas are known by their Spanish name (usually shortened), and typically salted and sometimes spiced after roasting (and today also available as a packaged product), in Mexico and other Latin American countries, in the American Southwest, and in speciality and Mexican food stores. In the Americas, they have been eaten since at least the time of the Aztecs][ and probably much earlier, since squash was one of the three earliest plant domesticates in the Western Hemisphere, along with maize (corn) and common beans (collectively the Native American agricultural "Three Sisters", originating in Mexico).
As an ingredient in mole dishes, they are known in Spanish as pipián. A Mexican snack using pepitas in an artisan fashion is referred to as Pepitoría.
Lightly roasted, salted, unhulled pumpkin seeds are popular in Greece with the descriptive Italian name, passatempo ("pastime").
The pressed oil of the roasted seeds of a specific pumpkin variety is also used in Central and Eastern European cuisine (see Pumpkin seed oil).][
The seeds are also good sources of protein, as well as iron, zinc, manganese, magnesium, phosphorus, copper, and potassium. 25 grams of pepitas can provide over 20 percent of the recommended daily iron intake. Furthermore, just one-fourth cup of pepitas provides approximately 185 mg of magnesium, nearly 50% of the Recommended Daily Intake.
In 2007, Stevenson, et al., of the USDA's New Crops Products Research Unit searched the primary literature for information about the lipid content of pepitas, and then grew and analyzed pepitas from seven cultivars of C. maxima. They found the following ranges of fatty acid content in C. maxima pepitas (see pumpkin seed oil):
The reported concentration of myristate and palmitate (the cholestrogenic fatty acids) for the pepitas ranged from 1.6% to 4.9%. The total unsaturated fatty acid concentration ranged from 9% to 21% of the pepita. The total fat content ranged from 11% to 52%. Based on the quantity of alpha-tocopherol extracted in the oil, the vitamin E content of the twelve C. maxima cultivar seeds ranged from 4 to 19 mg/100 g of pepita.
The seeds (and seed oil, see below) of pumpkins, such as Cucurbita pepo varieties have been subject to a great deal of research, especially into the treatment of prostate ailments.
According to the USDA, one gram of roasted pepita contain 5.69 mg L-tryptophan and one gram of pepita protein contains 17.2 mg of L-tryptophan. One cup of milk contains 183 mg. This high tryptophan content makes pepita of interest to researchers studying the treatment of anxiety disorders. Some eat the seeds as preventative measure against onset of anxiety attacks, clinical depression and other mood disorders.
Some studies][ have also found pumpkin seeds to prevent arteriosclerosis (hardening of the arteries) and to regulate cholesterol levels in the body.
A 2011 Egyptian study found that in rats, pumpkin seed oil has anti-hypertensive and cardio-protective properties.
A 2009 double-blind, placebo-controlled Korean study found that in men suffering from benign prostatic hyperplasia (n=47), pumpkin seed oil is an effective treatment.
The oil of pumpkin seeds, a culinary speciality in (and important export commodity of) Central European cuisine as a salad oil and a cooking oil, is also used to treat irritable bowel syndrome and various other ailments, both in folk medicine and in modern medical practice and research.][
Long an Eastern European folk remedy for the prostate problems of men, the oil has in fact been shown to improve symptoms associated with an enlarged prostate due to benign prostatic hyperplasia.][ Components in pumpkin seed oil appear to interrupt the triggering of prostate cell multiplication by testosterone and DHT.][ However, it is questionable whether eating the seeds whole in snack quantities, rather than taking therapeutic doses of the concentrated oil, would provide any prostate benefit.
In German folk medicine, the oil is also used to quell parasitic infestations such as tapeworms.][
Cornmeal is a meal (coarse flour) ground from dried maize (corn). It is a common staple food, and is ground to fine, medium, and coarse consistencies, but not as fine as wheat flour. In the United States, very finely ground cornmeal is also referred to as cornflour. However, the word cornflour denotes cornstarch in the United Kingdom, where cornmeal is not widely available.
There are different types of cornmeal.
Steel ground yellow cornmeal, which is common mostly in the United States, has the husk and germ of the maize kernel almost completely removed. It is conserved for about a year if stored in an airtight container in a cool, dry place.
Stone-ground cornmeal retains some of the hull and germ, lending a little more flavor and nutrition to recipes. It is more perishable, but will store longer if refrigerated. However, it too can have a shelf life of many months if kept in a reasonably cool place.
White cornmeal (mielie-meal), made from white corn, is more common in parts of Africa. It is also popular in the Southern United States for making cornbread.
Blue cornmeal is light blue or violet in color. It is ground from whole blue corn and has a sweet flavor. The cornmeal consists of dried corn kernels that have been ground into a fine or medium texture.
Romaine or cos lettuce is a variety of lettuce (Lactuca sativa L. var. longifolia) which grows in a tall head of sturdy leaves with a firm rib down the center. Unlike most lettuces, it is tolerant of heat.
Many dictionaries trace the word cos to the name of the Greek island of Cos, from which the lettuce was presumably introduced. Other authorities trace it to the Arabic word for lettuce, خس khus ().
It apparently reached the West via Rome, as in Italian it is called lattuga romana and in French laitue romaine, both meaning 'Roman lettuce', hence the name 'romaine', the common term in American English.
The thick ribs, especially on the older outer leaves, should have a milky fluid which gives the romaine the typically fine-bitter herb taste. Romaine is the usual lettuce used in Caesar salad. Romaine lettuce is commonly used in Middle Eastern cuisine.
Romaine lettuce may be used in the Passover Seder as a type of bitter herb, to symbolise the bitterness inflicted by the Egyptians while the Israelites were slaves in Egypt.
As with other dark leafy greens, the antioxidants contained within romaine lettuce are believed to help prevent cancer. According to the 2011 edition of the Old Farmer's Almanac, the chlorophyll pigment in dark leafy greens, such as Romaine lettuce, may reduce levels of colon and liver cancer carcinogens.
The day of 22 Germinal in the French Republican Calendar is dedicated to this lettuce.
Nixtamalization typically refers to a process for the preparation of maize (corn), or other grain, in which the grain is soaked and cooked in an alkaline solution, usually limewater, and hulled.
The term can also refer to the removal via an alkali process of the pericarp from other grains such as sorghum. Maize subjected to the nixtamalization process has several benefits over unprocessed grain for food preparation: it is more easily ground; its nutritional value is increased; flavor and aroma are improved; and mycotoxins are reduced. These benefits make nixtamalization a crucial preliminary step for further processing of maize into food products, and the process is employed using both traditional and industrial methods, in the production of tortillas, tamales, corn chips, hominy and many other items.
In the Aztec language Nahuatl, the word for the product of this procedure is nixtamalli or nextamalli (pronounced or ), which in turn has yielded Mexican Spanish nixtamal (). The Nahuatl word is a compound of nextli "ashes" and tamalli "unformed corn dough, tamal." The term nixtamalization (spelled with the "t") can also be used to describe the removal of the pericarp from any grain by an alkali process, including maize, sorghum, and others. When the unaltered Spanish spelling nixtamalización is used in written English, however, it almost exclusively refers to maize.
The labels on packages of commercially-sold tortillas prepared with nixtamalized maize usually list corn treated with lime as an ingredient in English, while the Spanish versions list maíz nixtamalizado.
The ancient process of nixtamalization was first developed in Mesoamerica, where maize was originally cultivated. There is no precise date when the technology was developed, but the earliest evidence of nixtamalization is found in Guatemala's southern coast, with equipment dating from 1200–1500 BC][.
The ancient Aztec and Mayan civilizations developed nixtamalization using lime (calcium hydroxide, not the citrus fruit of the same name) and ash (potassium hydroxide) to create alkaline solutions. The Chibcha people to the north of the ancient Inca also used calcium hydroxide (also known as "cal"), while the tribes of North America used naturally occurring sodium carbonate or ash.
The nixtamalization process was very important in the early Mesoamerican diet, as unprocessed maize is deficient in free niacin. A population depending on untreated maize as a staple food risks malnourishment, and is more likely to develop deficiency diseases such as pellagra. Maize also is deficient in essential amino acids, which can result in kwashiorkor. Maize cooked with lime provided niacin in this diet. Beans, when consumed with the maize, provided the amino acids required to balance the diet for protein.
The spread of maize cultivation in the Americas was accompanied by the adoption of the nixtamalization process. Traditional and contemporary regional cuisines (including Maya Cuisine, Aztec cuisine, and Mexican cuisine) included, and still include, foods based on nixtamalized maize.
The process has not substantially declined in usage in the Mesoamerican region, though there has been a decline in North America. Many North American Native American tribes, such as the Huron, no longer use the process.][ In some Mesoamerican and North American regions, dishes are still made from nixtamalized maize prepared by traditional techniques. The Hopi obtain the necessary alkali from ashes of various native plants and trees. Some contemporary Maya use the ashes of burnt mussel shells.
In the United States, European settlers did not always adopt the nixtamalization process, except in the case of hominy grits, though maize became a staple among the poor of the southern states. This led to endemic pellagra in poor populations throughout the southern US in the early 20th century. Fortification of wheat flour, the other staple food, essentially has eliminated this deficiency.
Maize was introduced to Europe by Christopher Columbus in the 15th century, being grown in Spain as early as 1498. Due to its high yields, it quickly spread through Europe, and later to Africa and India. Portuguese colonists grew maize in the Congo as early as 1560, and maize became, and remains, a major food crop in parts of Africa.
Adoption of the nixtamalization process did not accompany the grain to Europe and beyond, perhaps because the Europeans already had more efficient milling processes for hulling grain mechanically. Without alkaline processing, maize is a much less beneficial foodstuff, and malnutrition struck many areas where it became a dominant food crop. In the nineteenth century, pellagra epidemics were recorded in France, Italy, and Egypt, and kwashiorkor hit parts of Africa where maize had become a dietary staple.
Health problems associated with maize-based diets in modern times have usually been remedied by means of vitamin supplements and economic improvement leading to a broader diet, rather than by adoption of nixtamalization. Though pellagra has vanished from Europe and the United States, it remains a major public health problem in lower Egypt, parts of South Africa, and southwestern India][.
The first step in nixtamalization, kernels of dried maize are cooked in an alkaline solution at or near the mixture's boiling point. After cooking, the maize is steeped in the cooking liquid for a period. The length of time for which the maize is boiled and soaked varies according to local traditions and the type of food being prepared, with cooking times ranging from a few minutes to an hour, and soaking times from a few minutes to about a day.
During cooking and soaking, a number of chemical changes take place in the grains of maize. Because plant cell wall components, including hemicellulose and pectin, are highly soluble in alkaline solutions, the kernels soften and their pericarps (hulls) loosen. The grain hydrates and absorbs calcium or potassium (depending on the alkali used) from the cooking solution. Starches swell and gelatinize, and some starches disperse into the liquid. Certain chemicals from the germ are released that allow the cooked grains to be ground more easily, yet make dough made from the grains less likely to tear and break down. Cooking changes the grain's protein matrix, which makes proteins and nutrients from the endosperm of the kernel more available to the human body.
After cooking, the alkaline liquid (known as nejayote), containing dissolved hull, starch, and other corn matter, is decanted and discarded (or sometimes used in producing amatl paper). The kernels are washed thoroughly of remaining nejayote, which has an unpleasant flavor. The pericarp is then removed, leaving the endosperm of the grain with or without the germ depending on the process. This hulling is performed by hand, in traditional or very small-scale preparation, or mechanically, in larger scale or industrial production.
The prepared grain is called nixtamal. Nixtamal has many uses, contemporary and historic. Whole nixtamal may be used fresh or dried for later use. Whole nixtamal is used in the preparation of pozole and menudo, and other foods. Ground fresh nixtamal is made into dough and used to make tortillas, tamales, and arepas. Dried and ground, it is called masa harina or instant masa flour, and is reconstituted and used like masa.
The term hominy may refer to whole, coarsely ground, or finely ground nixtamal, or to a cooked porridge (also called samp) prepared from any of these.
An alternative process for use in industrial settings has been developed known as enzymatic nixtamalization which uses protease enzymes to accelerate the changes that occur in traditional nixtamalization. In this process, corn or corn meal is first partially hydrated in hot water, so that enzymes can penetrate the grain, then soaked briefly (for approximately 30 minutes) at 50°-60°C in an alkaline solution containing protease enzymes. A secondary enzymatic digestion may follow to further dissolve the pericarp. The resulting nixtamal is ground with little or no washing or hulling.
By pre-soaking the maize, minimizing the alkali used to adjust the pH of the alkaline solution, reducing the cooking temperature, accelerating processing, and reusing excess processing liquids, enzymatic nixtamalization can reduce the use of energy and water, lower nejayote waste production, decrease maize lost in processing, and shorten the production time (to approximately four hours) compared to traditional nixtamalization.
Effects of enzymatic nixtamalization on flavor, aroma, nutritional value, and cost, compared to traditional methods, are not well documented.
The primary nutritional benefits of nixtamalization arise from the alkaline processing involved. These conditions convert corn's bound niacin to free niacin, making it available for absorption into the body, thus preventing pellagra.][ Alkalinity also reduces the amount of the protein zein available to the body, which improves the balance among essential amino acids, although the overall amount of protein is reduced.][
Secondary benefits can arise from the grain's absorption of minerals from the alkali used or from the vessels used in preparation. These effects can increase calcium (by 750%, with 85% available for absorption), iron, copper and zinc.][
Lastly, nixtamalization significantly reduces (by 90-94%) mycotoxins produced by Fusarium verticillioides and Fusarium proliferatum, molds that commonly infect maize and the toxins of which are putative carcinogens.][
Dietary fiber, dietary fibre, or sometimes roughage and ruffage is the indigestible portion of food derived from plants. There are two main components:
Dietary fibers can act by changing the nature of the contents of the gastrointestinal tract and by changing how other nutrients and chemicals are absorbed. Some types of soluble fiber absorb water to become a gelatinous, viscous substance and is fermented by bacteria in the digestive tract. Some types of insoluble fiber have bulking action and are not fermented. Lignin, a major dietary insoluble fiber source, may alter the rate and metabolism of soluble fibers. Other types of insoluble fiber, notably resistant starch, are fully fermented.
Chemically, dietary fiber consists of non-starch polysaccharides such as arabinoxylans, cellulose, and many other plant components such as resistant starch, resistant dextrins, inulin, lignin, waxes, chitins, pectins, beta-glucans, and oligosaccharides. A novel position has been adopted by the US Department of Agriculture to include functional fibers as isolated fiber sources that may be included in the diet. The term "fiber" is something of a misnomer, since many types of so-called dietary fiber are not actually fibrous.
Food sources of dietary fiber are often divided according to whether they provide (predominantly) soluble or insoluble fiber. Plant foods contain both types of fiber in varying degrees, according to the plant's characteristics.
Advantages of consuming fiber are the production of healthful compounds during the fermentation of soluble fiber, and insoluble fiber's ability (via its passive hygroscopic properties) to increase bulk, soften stool, and shorten transit time through the intestinal tract.
Disadvantages of a diet high in fiber is the potential for significant intestinal gas production and bloating. Constipation can occur if insufficient fluid is consumed with a high-fiber diet.
Originally, fiber was defined to be the components of plants that resist human digestive enzymes, a definition that includes lignin and polysaccharides. The definition was later changed to also include resistant starches, along with inulin and other oligosaccharides.
Official definition of dietary fiber differs a little among different institutions:
Dietary fiber is most found in vegetables and fruit. The exact amount of fiber contained in the food can be seen in the following table of expected fiber in USDA food groups/subgroups
Dietary fiber is found in plants. While all plants contain some fiber, plants with high fiber concentrations are generally the most practical source.
Fiber-rich plants can be eaten directly. Or, alternatively, they can be used to make supplements and fiber-rich processed foods.
The Academy of Nutrition and Dietetics (AND), formerly the American Dietetic Association, recommends consuming a variety of fiber-rich foods.
Some plants contain significant amounts of soluble and insoluble fiber. For example plums and prunes have a thick skin covering a juicy pulp. The skin is a source of insoluble fiber, whereas soluble fiber is in the pulp. Also, grapes have a fair amount of fiber in them.
The root of the konjac plant, or glucomannan, produces results similar to fiber and may also be used to relieve constipation. Glucomannan is sold in various forms, and while safe in some forms, it can be unsafe in others, possibly leading to throat or intestinal blockage.
Soluble fiber is found in varying quantities in all plant foods, including:
Sources of insoluble fiber include:
These are a few example forms of fiber that have been sold as supplements or food additives. These may be marketed to consumers for nutritional purposes, treatment of various gastrointestinal disorders, and for such possible health benefits as lowering cholesterol levels, reducing risk of colon cancer, and losing weight.
Soluble fiber supplements may be beneficial for alleviating symptoms of irritable bowel syndrome, such as diarrhea and/or constipation and abdominal discomfort. Prebiotic soluble fiber products, like those containing inulin or oligosaccharides, may contribute to relief from inflammatory bowel disease, as in Crohn's disease, ulcerative colitis, and Clostridium difficile, due in part to the short-chain fatty acids produced with subsequent anti-inflammatory actions upon the bowel. Fiber supplements may be effective in an overall dietary plan for managing irritable bowel syndrome by modification of food choices.
The insoluble fiber, resistant starch from high amylose corn, has been used as a supplement and may contribute to improving insulin sensitivity and glycemic management as well as promoting regularity and possibly relief of diarrhea. One preliminary finding indicates that resistant corn starch may reduce symptoms of ulcerative colitis.
Chemically defined as oligosaccharides occurring naturally in most plants, inulins have nutritional value as carbohydrates, or more specifically as fructans, a polymer of the natural plant sugar, fructose. Inulin is typically extracted by manufacturers from enriched plant sources such as chicory roots or Jerusalem artichokes for use in prepared foods. Subtly sweet, it can be used to replace sugar, fat, and flour, is often used to improve the flow and mixing qualities of powdered nutritional supplements, and has significant potential health value as a prebiotic fermentable fiber.
Inulin is advantageous because it contains 25–30% the food energy of sugar or other carbohydrates and 10–15% the food energy of fat. As a prebiotic fermentable fiber, its metabolism by gut flora yields short-chain fatty acids (see below) which increase absorption of calcium, magnesium, and iron, resulting from upregulation of mineral-transporting genes and their membrane transport proteins within the colon wall. Among other potential beneficial effects noted above, inulin promotes an increase in the mass and health of intestinal Lactobacillus and Bifidobacterium populations.
Vegetable gum fiber supplements are relatively new to the market. Often sold as a powder, vegetable gum fibers dissolve easily with no aftertaste. In preliminary clinical trials, they have proven effective for the treatment of irritable bowel syndrome. Examples of vegetable gum fibers are guar gum and acacia Senegal gum.
Dietary fibers have three primary mechanisms: bulking, viscosity and fermentation. Dietary fibers can change the nature of the contents of the gastrointestinal tract, and to change how other nutrients and chemicals are absorbed through bulking and viscosity. Some types of soluble fibers bind to bile acids in the small intestine, making them less likely to enter the body; this in turn lowers cholesterol levels in the blood. Viscous soluble fibers may also attenuate the absorption of sugar, reduce sugar response after eating, normalize blood lipid levels and, once fermented in the colon, produce short-chain fatty acids as byproducts with wide-ranging physiological activities (discussion below). Insoluble fiber is associated with reduced diabetes risk, but the mechanism by which this occurs is unknown. One type of insoluble dietary fiber, resistant starch has been shown to directly increase insulin sensitivity in healthy people, in type 2 diabetics, and in individuals with insulin resistance, possibly contributing to reduced risk of type 2 diabetes.
Not yet formally proposed as an essential macro-nutrient, dietary fiber is nevertheless regarded as important for the diet, with regulatory authorities in many developed countries recommending increases in fiber intake.
Dietary fiber has distinct physicochemical properties. Most semi-solid foods, fiber and fat are a combination of gel matrices which are hydrated or collapsed with microstructural elements, globules, solutions or encapsulating walls. Fresh fruit and vegetables are cellular materials.
A slowly eaten meal will enter the absorptive phase of the gastrointestinal tract more slowly than a rapidly eaten meal of similar composition. Many of the differences between low and high glycemic foods would disappear if a meal was eaten slowly.
The chemical and physico-chemical nature (lipid, protein, carbohydrate) of the meal will also influence the gastric emptying of the food multiphase system. Fatty foods and hypertonic solutions empty slowly. The movement of food, i.e., chyme, along the gastrointestinal tract is typical of flow in a disperse system. As chyme moves along the gastrointestinal tract, polymer flow and diffusion becomes important.
Following a meal, the stomach and upper gastrointestinal contents consist of
Micelles are colloid-sized clusters of molecules which form in conditions as those above, similar to the critical micelle concentration of detergents. In the upper gastrointestinal tract, these detergents consist of bile acids and di- and monoacyl glycerols which solubilize triacylglycerols and cholesterol.
Two mechanisms bring nutrients into contact with the epithelium:
The multiple physical phases in the intestinal tract slow the rate of absorption compared to that of the suspension solvent alone.
Adding viscous polysaccharides to carbohydrate meals can reduce post-prandial blood glucose concentrations. Wheat and maize but not oats modify glucose absorption, the rate being dependent upon the particle size. The reduction in absorption rate with guar gum may be due to the increased resistance by viscous solutions to the convective flows created by intestinal contractions. Dietary fiber interacts with pancreatic and enteric enzymes and their substrates. Human pancreatic enzyme activity is reduced when incubated with most fiber sources. Fiber may affect amylase activity and hence the rate of hydrolysis of starch. The more viscous polysaccharides extend the mouth-to-cecum transit time; guar, tragacanth and pectin being slower than wheat bran.
The colon may be regarded as two organs,
The presence of bacteria in the colon produces an ‘organ’ of intense, mainly reductive, metabolic activity, whereas the liver is oxidative. The substrates utilized by the cecal have either passed along the entire intestine or are biliary excretion products . The effects of dietary fiber in the colon are on
Enlargement of the cecum is a common finding when some dietary fibers are fed and this is now believed to be normal physiological adjustment. Such an increase may be due to a number of factors, prolonged cecal residence of the fiber, increased bacterial mass, or increased bacterial end-products. Some non-absorbed carbohydrates, e.g. pectin, gum arabic, oligosaccharides and resistant starch, are fermented to short-chain fatty acids (chiefly acetic, propionic and n-butyric), and carbon dioxide, hydrogen and methane. The cecal fermentation of 40–50 g of complex polysaccharides will yield 400–500 mmol total short-chain fatty acids, 240–300 mmol acetate, and 80–100 mmol of both propionate and butyrate. Almost all of these short-chain fatty acids will be absorbed from the colon. This means that fecal short-chain fatty acid estimations do not reflect cecal and colonic fermentation, only the efficiency of absorption, the ability of the fiber residue to sequestrate short-chain fatty acids, and the continued fermentation of fiber around the colon, which presumably will continue until the substrate is exhausted. The production of short-chain fatty acids has several possible actions on the gut mucosa. All of the short-chain fatty acids are readily absorbed by the colonic mucosa, but only acetic acid reaches the systemic circulation in appreciable amounts. Butyric acid appears to be used as a fuel by the colonic mucosa as the preferred energy source for colonic cells.
Dietary fiber may act on each phase of ingestion, digestion, absorption and excretion to affect cholesterol metabolism, such as the following:
An important action of some fibers is to reduce the reabsorption of bile acids in the ileum and hence the amount and type of bile acid and fats reaching the colon. A reduction in the reabsorption of bile acid from the ileum has several direct effects.
The fibers that are most effective in influencing sterol metabolism (e.g. pectin) are fermented in the colon. It is therefore unlikely that the reduction in body cholesterol is due to adsorption to this fermented fiber in the colon.
Feces consist of plasticine-like material, made up of water, bacteria, lipids, sterols, mucus and fiber.
Water is distributed in the colon in three ways:
Fecal weight is dictated by:
Wheat bran is minimally fermented and binds water and when added to the diet increases fecal weight in a predictable linear manner and decreases intestinal transit time. The particle size of the fiber is all-important, coarse wheat bran being more effective than fine wheat bran. The greater the water-holding capacity of the bran, the greater the effect on fecal weight. For most healthy individuals, an increase in wet fecal weight, depending on the particle size of the bran, is generally of the order of 3–5 g/g fiber. The fermentation of some fibers results in an increase in the bacterial content and possibly fecal weight. Other fibers, e.g. pectin, are fermented and have no effect on stool weight.
Research has shown that fiber may benefit health in several different ways. Lignin and probably related materials that are resistant to enzymatic degradation, diminish the nutritional value of foods.
Color coding of table entries:
Fiber does not bind to minerals and vitamins and therefore does not restrict their absorption, but rather evidence exists that fermentable fiber sources improve absorption of minerals, especially calcium. Some plant foods can reduce the absorption of minerals and vitamins like calcium, zinc, vitamin C, and magnesium, but this is caused by the presence of phytate (which is also thought to have important health benefits), not by fiber.
An experiment designed with a large sample and conducted by NIH-AARP Diet and Health Study studied the correlation between fiber intake and colorectal cancer. The analytic cohort consisted of 291 988 men and 197 623 women aged 50–71 y. Diet was assessed with a self-administered food-frequency qustionnaire at baseline in 1995-1996; 2974 incident colorectal cancer cases were identified during 5 y of follow-up. The result was that total fiber intake was not associated with colorectal cancer. But on the other hand, the analyses of fiber from different food sources showed that fiber from grains was associated with a lower risk of colorectal cancer.
Although many researchers believe that dietary fiber 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 fiber consumption and lower rates of colorectal cancer or adenomas. Similarly, a 2010 study of 58,279 men found no relationship between dietary fiber and colorectal cancer.
Dietary fiber has many functions in diet, one of which may be to aid in energy intake control and reduced risk for development of obesity. The role of dietary fiber in energy intake regulation and obesity development is related to its unique physical and chemical properties that aid in early signals of satiation and enhanced or prolonged signals of satiety. Early signals of satiation may be induced through cephalic- and gastric-phase responses related to the bulking effects of dietary fiber on energy density and palatability, whereas the viscosity-producing effects of certain fibers may enhance satiety through intestinal-phase events related to modified gastrointestinal function and subsequent delay in fat absorption.
In general, fiber-rich diets, whether achieved through fiber supplementation or incorporation of high fiber foods into meals, have a reduced energy density compared with high fat diets. This is related to fiber’s ability to add bulk and weight to the diet.
However, the subsequent effect of fiber on food intake has been more variable because in some cases, food intake at a test meal was reduced, in other cases, it was not. Although much of the discrepancy in results may be ascribed to differences among studies, different responses related to gender and body weight status (i.e., obese vs. normal weight) may also be responsible. With regard to gender, work in our][ laboratory indicates that women may be more sensitive to dietary manipulation with fiber than men, which is consistent with a previous report by Burley et al. (1993). Moreover, we][ have found that the subjective satiety response to dietary manipulation in men and women is supported by differences in the CCK response, suggesting that signals for satiety differ between genders (Burton-Freeman et al. 1998 and personal communication). The relationship of body weight status and fiber effect on energy intake suggests that obese individuals may be more likely to reduce food intake (Evans and Miller 1975, Porikos and Hagamen 1986) with dietary fiber inclusion.
Current recommendations from the United States National Academy of Sciences, Institute of Medicine, suggest that adults should consume 20–35 grams of dietary fiber per day, but the average American's daily intake of dietary fiber is only 12–18 grams.
The AND (Academy of Nutrition and Dietetics, previously ADA) recommends a minimum of 20–35 g/day for a healthy adult depending on calorie intake (e.g., a 2000 Cal/8400 kJ diet should include 25 g of fiber per day). The AND's recommendation for children is that intake should equal age in years plus 5 g/day (e.g., a 4 year old should consume 9 g/day). No guidelines have yet been established for the elderly or very ill. Patients with current constipation, vomiting, and abdominal pain should see a physician. Certain bulking agents are not commonly recommended with the prescription of opioids because the slow transit time mixed with larger stools may lead to severe constipation, pain, or obstruction.
The British Nutrition Foundation has recommended a minimum fiber intake of 18 g/day for healthy adults.
On average, North Americans consume less than 50% of the dietary fiber levels recommended for good health. In the preferred food choices of today's youth, this value may be as low as 20%, a factor considered by experts as contributing to the obesity levels seen in many developed countries.
The actual fiber intake gaps of different age groups of Americans are shown in the graph from USDA:
Recognizing the growing scientific evidence for physiological benefits of increased fiber intake, regulatory agencies such as the Food and Drug Administration (FDA) of the United States have given approvals to food products making health claims for fiber.
In clinical trials to date, these fiber sources were shown to significantly reduce blood cholesterol levels, an important factor for general cardiovascular health, and to lower risk of onset for some types of cancer.
Soluble (fermentable) fiber sources gaining FDA approval are:
Other examples of fermentable fiber sources (from plant foods or biotechnology) used in functional foods and supplements include inulin, resistant dextrins, fructans, xanthan gum, cellulose, guar gum, fructooligosaccharides (FOS), and oligo- or polysaccharides.
Consistent intake of fermentable fiber through foods like berries and other fresh fruit, vegetables, whole grains, seeds, and nuts is now known to reduce risk of some of the world’s most prevalent diseases—obesity, diabetes, high blood cholesterol, cardiovascular disease, and numerous gastrointestinal disorders. In this last category are constipation, inflammatory bowel disease, ulcerative colitis, hemorrhoids, Crohn's disease, diverticulitis, and colon cancer—all disorders of the intestinal tract where fermentable fiber can provide healthful benefits.
Insufficient fiber in the diet can complicate defecation. Low-fiber feces are dehydrated and hardened, making them difficult to evacuate—defining constipation and possibly leading to development of hemorrhoids or anal fissures.
In June 2007, the British Nutrition Foundation issued a statement to define dietary fiber more concisely and list the potential health benefits established to date:
‘Dietary fibre’ has been used as a collective term for a complex mixture of substances with different chemical and physical properties which exert different types of physiological effects. The use of certain analytical methods to quantify dietary fiber by nature of its indigestibility results in many other indigestible components being isolated along with the carbohydrate components of dietary fiber. These components include resistant starches and oligosaccharides along with other substances that exist within the plant cell structure and contribute to the material that passes through the digestive tract. Such components are likely to have physiological effects. Yet, some differentiation has to be made between these indigestible plant components and other partially digested material, such as protein, that appears in the large bowel. Thus, it is better to classify fiber as a group of compounds with different physiological characteristics, rather than to be constrained by defining it chemically. Diets naturally high in fiber can be considered to bring about several main physiological consequences:
Fiber contributes less energy (measured in Calories or kilojoules) than sugars and starches because it cannot be fully absorbed by the body. Sugars and starches provide 4 Calories per gram, and the human body has specific enzymes to break them down into glucose, fructose, and galactose, which can then be absorbed by the body. The human body lacks enzymes to break down fiber. Insoluble fiber does not change inside the body, so the body cannot absorb it and nutritionists say that it contributes 0 Calories per gram. Soluble fiber is partially fermented, with the degree of fermentability varying with the type of fiber, and contributes some energy when broken down and absorbed by the body. Dietitians have not reached a consensus on how much energy is actually absorbed, but some approximate around 2 Calories (8.36 joules) per gram of soluble fiber. Regardless of the type of fiber, the body absorbs fewer than 4 Calories (16.7 kilojoules) per gram of fiber, which can create inconsistencies for actual product nutrition labels. In some countries, fiber is not listed on nutrition labels, and is considered 0 Calories/gram when the food's total Calories are computed. In other countries all fiber must be listed, and is considered 4 Calories per gram when the food's total Calories are computed (because chemically fiber is a type of carbohydrate and other carbohydrates contribute 4 Calories per gram). In the US, soluble fiber must be counted as 4 Calories per gram, but insoluble fiber may be (and usually is) treated as 0 Calories per gram and not mentioned on the label.
The American Association of Cereal Chemists has defined soluble fiber this way: "the edible parts of plants or similar carbohydrates resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine." In this definition:
As an example of fermentation, shorter-chain carbohydrates (a type of fiber found in legumes) cannot be digested, but are changed via fermentation in the colon into short-chain fatty acids and gases (which are typically expelled as flatulence).
According to a 2002 journal article, fibers compounds with partial or low fermentability include:
fiber compounds with high fermentability include:
When soluble fiber is fermented, short-chain fatty acids (SCFA) are produced. SCFAs are involved in numerous physiological processes promoting health, including:
SCFAs that are absorbed by the colonic mucosa pass through the colonic wall into the portal circulation (supplying the liver), and the liver transports them into the general circulatory system.
Overall, SCFAs affect major regulatory systems, such as blood glucose and lipid levels, the colonic environment, and intestinal immune functions.
The major SCFAs in humans are butyrate, propionate, and acetate, where butyrate is the major energy source for colonocytes, propionate is destined for uptake by the liver, and acetate enters the peripheral circulation to be metabolized by peripheral tissues.
The FDA allows producers of foods containing 1.7g per serving of psyllium husk soluble fiber or 0.75g of oat or barley soluble fiber as beta-glucans to claim that reduced risk of heart disease can result from their regular consumption.
The FDA statement template for making this claim is: Soluble fiber from foods such as [name of soluble fiber source, and, if desired, name of food product], as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of [name of food product] supplies __ grams of the [necessary daily dietary intake for the benefit] soluble fiber from [name of soluble fiber source] necessary per day to have this effect.
Eligible sources of soluble fiber providing beta-glucan include:
The allowed label may state that diets low in saturated fat and cholesterol and that include soluble fiber from certain of the above foods "may" or "might" reduce the risk of heart disease.
As discussed in FDA regulation 21 CFR 101.81, the daily dietary intake levels of soluble fiber from sources listed above associated with reduced risk of coronary heart disease are:
Soluble fiber from consuming grains is included in other allowed health claims for lowering risk of some types of cancer and heart disease by consuming fruit and vegetables (21 CFR 101.76, 101.77, and 101.78).
A study of 388,000 adults ages 50 to 71 for nine years found that the highest consumers of fiber were 22% less likely to die over this period. In addition to lower risk of death from heart disease, adequate consumption of fiber-containing foods, especially grains, was also associated with reduced incidence of infectious and respiratory illnesses, and, particularly among males, reduced risk of cancer-related death.
16 sp., see text
Cottontail rabbits are among the 16 lagomorph species in the genus Sylvilagus, found in the Americas.
In appearance, most cottontail rabbits closely resemble the wild European rabbit (Oryctolagus cuniculus). Most Sylvilagus species have stub tails with white undersides that show when they retreat; giving them their name, "cottontails". This feature is not present in some cottontails (for example, the underside of the brush rabbit's tail is gray), nor is it unique to the genus (for example, the European rabbit also has a white scut).
The genus is widely distributed across North America, Central America, and northern and central South America, though most species are confined to particular regions. Most (though not all) species live in nests called forms, and all have altricial young.
Cottontail rabbits show a greater resistance to myxomatosis than European rabbits.
Unlike squirrels and chipmunks that eat sitting up on their hind legs, and can hold food with their front paws while spinning it in circles to devour it quickly, a cottontail eats on all fours; and can only use its nose to move and adjust the position of the food that it places directly in front of its front paws on the ground. A cottontail will turn the food with its nose to find the cleanest part of the vegetation (free of sand and inedible parts) to begin its meal. The only time a cottontail uses its front paws to enable eating, is when vegetation is above its head on a living plant. The cottontail will lift its paw to bend the branch to bring the food within reach.
Cottontails are rarely found out of their burrows looking for food on windy days. This phenomena is due to the fact that the wind interferes with their hearing capabilities. Hearing an oncoming predator approaching is their primary defense mechanism.
Desert Cottontail (Sylvilagus audubonii) in submissive posture anticipating food
From behind with white tail easily visible
California high Desert Cottontail resting on a full stomach
Mother and Juvenile Cottontail enjoying a carrot dinner