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by Joanne Slavin, Ph.D., R.D.
The Prebiotic Benefits of Arabinogalactan
Next to tobacco, dietary factors are now considered to be one of the most important risk factors for cancer and heart disease. Chronic disease is now the leading killer of Americans. Of these chronic diseases, heart disease is the number one cause of deaths, killing about three-quarters of a million people annually. Cancer is the next leader, killing about one-half million U.S. citizens annually. In women, colorectal cancer is third, behind lung and breast cancers. In men colorectal cancer is third behind lung and prostate cancers. Since these are chronic diseases, lifestyle changes could potentially have an impact on these health outcomes.
Lower blood cholesterol levels protect against heart disease. Increased fiber consumption can decrease blood cholesterol levels. Because of the complexity of the human diet and the types of dietary fibers consumed, it is likely that a variety of mechanisms are involved in cholesterol lowering. Leading research has indicated that several factors can play a role in fiber-related cholesterol lowering.
Ingesting a high-fiber diet can increase satiety and decrease intake of fatty foods. The reduction of fatty food intake may reduce cholesterol levels. Other mechanisms involving the consumption of soluble dietary fibers and the lowering of blood cholesterol have been proposed. These mechanisms involve short-chain fatty acid production and probiotic microflora.
One mechanism for the blood lowering effects of dietary fiber is elevated short-chain fatty acids (SCFA). When dietary fibers are fermented in the colon (or large intestine), SCFA are produced. High SCFAs decrease blood lipid levels. For example, some research supports that the SCFA propionate may be cholesterol lowering. Diets supplemented with propionate lowered blood cholesterol in rats.
The colon is involved in many disease states. Potentially harmful colonic microflora, or pathogenic overgrowth, is thought to contribute to colon cancer. Carcinoma of the colon is among the most common cancers in humans. Epidemiological data suggest that diets low in fat and high in complex carbohydrates may protect against large bowel cancer. Production of SCFA may be involved in the protection against colon cancer by reduced ammonia levels and decreased pH.
Many dietary fibers such as arabinogalactan (AG) provide energy to friendly colonic bacteria for their growth and metabolism. This results in the release of SCFA into the colon lumen (cavity) and often reduces the concentration of ammonia by increasing its utilization of ammonia by the bacteria.
Fermentation of dietary fiber and production of short-chain fatty acids, particularly butyrate, may protect against colorectal cancer. Diets high in dietary fiber may elevate butyrate levels. Butyrate is an important fuel for normal colonic epithelial cells. Decreased butyrate levels have been found in feces of patients with colonic cancers. Some research supports the theory that increased SCFAs produce decreases in colonic pH, which in turn, protects against colon cancer.
Fermentation of dietary fiber to SCFA and lactic acid is associated with health benefits in addition to providing nutrition for the mucosal lining of the colon and the cells of important organs, such as the liver. SCFAs improve health of the colonic environment, by providing energy to friendly bacteria that reduce the levels of toxic waste products such as ammonia and urea.
Ammonia is produced in the colon by bacterial degradation of nitrogenous substrates such as protein, nucleic acids and urea. The concentration of ammonia in the colon can reach 60 mmol/kg of colonic contents in humans. Ammonia is potentially toxic to cells; it shortens cell life span and alters DNA synthesis in various tissues, including the ileum and colon. Ammonia is also thought to promote colon carcinogenesis.
Both animal and human studies have shown a reduction in ammonia and in the numbers of pathogenic bacteria in the colon when AG was consumed. In a poultry study numbers of clostridia, as a percentage of total anaerobes, trended lower when various levels of AG were fed. This pattern occurred in both the presence and absence of antibiotics. Likewise, numbers of E.coli in various sections of weaning pig gut were reduced when AG was included in the diet. In human clinical studies at the University of Minnesota, AG consumption reduced the level of pathogens and the amount of ammonia in the colon.
In addition to increased SCFA and decreased pH, many researchers believe that the proliferation of beneficial bacteria within the colon may be protective. These beneficial bacteria include Bacteroides, Bifidobacterium and Lactobacillus. Proliferation of beneficial colonic bacteria has been associated with improved host health. Some intestinal pathogenic bacteria may be involved in the onset of colon cancer. Epidemiological studies and laboratory research indicate a link between the metabolic activity of pathogenic intestinal microflora and colon cancer. Some colonic bacteria have been found to produce tumor-promoting compounds during their metabolism. Some bacteria enzymes are thought to act as procarcinogens. Dietary fiber is thought to inhibit the production of potentially harmful enzymes, while dietary fat is believed to increase the enzymes. Animal studies have shown a decrease in potentially harmful beta-glucuronidase enzyme activity when AG has been included in the diet.
Many researchers are currently focusing their attention on developing ways to enhance the proliferation of beneficial colonic microbiota. The bacterial groups Bifidobacterium and Lactobacillus are thought to have properties that promote the health of the host. Evaluating the effects of introducing these beneficial bacteria directly into the system has been extensively studied. When these bacteria are fed directly to humans, survive digestion and become active upon reaching the colon, they are called “probiotics.” Many studies have been conducted with specific probiotic strains of bacteria. Some of these strains are now believed to exert beneficial effects on the colon health of the host. A food source is classified as a “prebiotic” if when it is fed, it escapes digestion and reaches the colon, allowing beneficial resident bacteria to feed on it and therefore proliferate.
It remains unclear whether indigenous bacterial strains are as effective as probiotic strains in the promotion of colonic health. Upon ingestion, probiotics encounter conditions that may compromise their survival en route to the large intestine, while prebiotics grow and proliferate within the colon itself. A combination of probiotics and prebiotics might best contribute to the promotion of colonic health and when fed together are classified as “synbiotics.” Larch AG has demonstrated consistent increases in numbers of probiotic and lactic acid bacteria across numerous animal and human clinical studies, including two human studies at the University of Minnesota. In those studies preliminary blood cholesterol reduction in hyperlipidemics may be the result of this alteration in friendly gut microflora.
The American Dietetic Association recommends 25–35 grams of total dietary fiber per day. Historically this has been a difficult problem for Americans. Fiber is found not only in fruits and vegetables, but also in whole grain products and legumes. Americans do not eat enough of these products. Some reasons have been provided as to why Americans don’t consume enough fiber in foods:
• Dislike of certain foods
• No time due to a fast paced lifestyle
• Fruits and vegetables don’t last long, therefore they are added expenses.
Larch AG (Western larch) is a fermentable, non-starch polysaccharide that has been approved as a dietary fiber by the Food and Drug Administration. It is classified as a prebiotic dietary fiber since it resists digestion by enzymes of the saliva and small intestine and enters the large bowel intact, where it is fermented. Many common plants contain arabinogalactan and arabinogalactan proteins. The carbohydrate component is the primary constituent of arabinogalactan proteins and is generally composed of arabinose and galactose sugars. Humans consume arabinogalactan in such foods as carrots, tomatoes, radishes, pears, maize, wheat and red wine. In addition, several herbs have also been found to contain significant amounts of AG, including Echinacea purpurea, Angelico acutiloba and Curcuma longa.
A commercially available, concentrated AG that is free of bound protein has been extracted from larch trees (of the genus Larix).
Larch AG is a unique product that is easily extractable by water in a pure form from the lower portions of debarked larch. Larch chips from logs are steam-heated and pressed to reveal a purified form of arabinogalactan. This procedure is unique because harsh chemicals are not needed to release the polysaccharide from the plant matrix and therefore the product remains pure and structurally unaltered.
Appreciation for AG as a rich source of dietary fiber is coming from clinical research studies out of American universities. However, even before scientific studies were able to elucidate larch fiber benefits, Native Americans in this country used larch resin, leaves and bark for medicinal food and cosmetic applications. The bark was used as an infusion for colds and tuberculosis. Bark tea traditionally was used as a laxative, tonic and diuretic. The decoction of leaves and plant was used to soak arthritic limbs and as a strengthening wash for infants. Along with Oregon grapes it had blood purification benefit. The AG-rich gum resin was used by the Thompson Indians for sores, cuts and burns. The sap was considered valuable as a bonesetter for broken bones that would not heal, for tuberculosis, respiratory disease and sore throat. Today trees are sometimes tapped for the sap that can be dried down into syrup then mixed with sweeteners.
There is a relatively new admission in the healthcare profession that health begins in the colon. Many human diseases can be tracked back to conditions in the colon. The gastrointestinal tract is residence of two-thirds of the active cells of the immune system. An active immune system is regarded by most as our best defense against the ravages of disease. AG is a unique material. It has been approved as a direct food additive by the FDA and can be used for many of its technical effects in food items. It is a dietary fiber that is easy to work with. It is a prebiotic fiber that supports gastrointestinal health. It is non-toxic with no known oral toxicity limits. It is perhaps the newest commercially available water-soluble polysaccharide on the market.
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