The McDougall Newsletter
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From July/Aug '99

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Gut And Its Microflora -- Our Unappreciated Vital Organ

 I’ll bet you never thought about the contents of your colon as something vital for your robust health. It is time to give some overdue appreciation to your intestines. Within our intestine lives trillions of organisms that are so important to our health and survival that they should be thought of as an organ of our body akin to our liver or kidneys. The bacteria and other organisms living in our intestine are known as the gut microflora. Their many functions include, completing the digestion of our foods through fermentation, protecting us against pathogenic (disease causing) bacteria, synthesizing water soluble vitamins, and stimulating development of our immune system. The health of the flora can become impaired by temperature, illnesses, antibiotics and other drug treatments, and changes in our diet. The effects of antibiotic therapy can be profound and persistent, even causing a life threatening infection with C. difficile bacteria when they overgrow and replace normal gut microflora -- a real testament to the vital nature of this organ.

Our Complex Intestine

Approximately 28 feet of digestive tube, known as the gut and intestine, processes our foods into life giving nutrients. The first 23 feet, which include the mouth, esophagus, stomach, and small intestine mechanically divide the foods we eat, mix them with digestive enzymes, and then break them into microscopic particles ready for absorption into the body. The last five feet, known as the large intestine, or colon, works as a microbial factory. More than 400 different species of bacteria have been identified living in a single person. These bacteria are not distributed randomly throughout the intestinal tract, but are found in different numbers and kinds in different regions of the gut. The stomach and small intestine contain low numbers, the last part of the small intestine contains many more organisms. Within the colon their concentration reaches 1,000,000,000,000 (a trillion) per milliliter of feces. On the typical American diet one-third of the dry weight of the feces is bacteria. (On a healthy diet, dietary fiber dilutes the concentration.) Although the bacteria are the predominant microflora, protozoans, yeast and other microorganisms are also present.

Our Diet Grows Friendly Flora

Dynamic balances exist between the microflora, our bodies, and our diet that directly influence the initial acquisition, development, and eventual stability of the gut ecosystem. The remnants of the foods we eat that are not digested by our small intestine become the foods for the microflora. Different bacteria live better on different sources of nutrients, similar to the way plants and animals do.

Undigestible complex carbohydrates, known as dietary fiber and undigestible (plant-derived) sugars, provide the bulk of the food for these bacteria. In general, people eating a vegetarian diet have higher counts of aerobic bacteria (bacteria that can live in the air) and lower counts of anaerobic bacteria (can live and grow in the absence of oxygen) than meat eaters (J Nutr 105:878, 1975). Most importantly, the gut microflora of meat-eaters contains greater amounts of "unfriendly" bacteria that do unhealthy things to the host (you). A vegetarian diet promotes the growth and activity of "friendly" bacteria.


The Newborn

The gastrointestinal tract of a normal fetus is sterile. During the birth process the newborn is inoculated primarily by organisms from the mother’s vagina and bowel, and to a lesser extent the surrounding environment. Newborns delivered by cesarean section do not get a healthy dose of mother’s bacteria and as a result are more likely to harbor more anaerobic forms of unhealthy bacteria. Furthermore, the hygienic conditions of the hospital may prevent the complete transfer of bacteria to the abdominally delivered infant. After birth, microbes are transferred by touching, suckling, kissing, and caressing.

Breast feeding encourages the growth of friendly bacteria known as Bifidobacterium, which protect the baby from gastrointestinal infections that can result in illnesses requiring hospitalization and sometimes death. By the fourth day of life, Bifidobacterium represent 48% of the bacteria in breast fed infants as opposed to 15% in bottle fed infants (J Perinat Med 26:186, 1998). Eventually, over 95% of the bacteria become Bifidobacterium bacteria in an exclusively breast fed baby (BMJ 3:338, 1973). This is because breast milk contains significant amounts of undigestible sugars that provide food for the "friendly," Bifidobacterium. Introduction of small amounts of formula to a breast fed baby will result in shifts from a breast-fed to a formula-fed pattern of the microflora. After weaning from breast milk after the age of 2 years, the child’s flora becomes similar to an adults.

Probiotics -- Adding Friendly Bacteria and Yeast

Probiotics are supplements sold as foods and pills that contain millions of friendly bacteria, and sometimes yeast. The best known and most popular probiotics are yogurts containing lactic acid-producing bacteria, called Lactobacillus. These organisms are non-toxic and survive passage through the intestine. However, since they do not colonize the colon they must be ingested regularly for any health promoting properties to persist. I do not recommend yogurt as a source of friendly bacteria because their beneficial effects have not been conclusively proven (Am J Clin Nutr 69:1035S, 1999). More importantly, yogurt has all the negative qualities of dairy products: high in fat and cholesterol, allergy producing dairy proteins, and it is often infected with harmful viruses and bacteria. You can buy supplement pills and liquids containing these bacteria and avoid the dairy products.

Probiotics can be purchased in the natural foods stores -- they are usually found in the refrigerated section. Probiotics contain various combinations of "friendly" bacteria, from species of Lactobacilli, Streptococci, and Bifidobacterium. Some are labeled as "newborn formulas" and others are sold for improving the flora of a child or adult.

Prebiotics and Synbiotics

Prebiotics are nondigestible food ingredients that stimulate the growth and activity of "friendly" bacteria already present in your intestine. They are the preferred foods of "friendly" bacteria. The most effective prebiotics identified are FOS (fructooligosaccharides). Other effective growth enhancers are GOS (galactooligosaccharides), inulin (not insulin), lactulose, and lactitol. These are small carbohydrates that are found naturally in artichokes, onions, chicory, garlic, leeks, and to a lesser extent, cereals. These simple prebiotic molecules are also produced industrially and a number of commercial products are sold on the market. They have no toxic effects. They can act as a mild laxative in small amounts, and may produce flatulence when consumed in large amounts. Prebiotics of FOS are already increasing the number of Bifidobacterium at a dose of 2.75 grams/day and the effect lasts for 7 days (Br J Nutr 80:S197, 1998) In studies of people, 15 grams/day of FOS increased Bifidobacterium 10-fold while reducing "unfriendly" bacteria, such as clostridia (Bifidobacteria and Microflora 5:37, 1986). Beans, peas, and lentils also contain nondigestible sugars, raffinose and stachyose, that feed bacteria. Their digestion by bowel bacteria produces the notorious flatus.

Combining probiotics (bacteria) with prebiotics (the bacteria’s food) results in a logical partnership, called synbiotics. You will most often find synbiotic products sold as mixtures of bacteria with FOS.

Benefits of a Healthy Gut Microflora

Controlling Intestinal Infections

The microflora normally presents a barrier to invading organisms, but disease-causing pathogens can become established when the integrity of the microflora is impaired. Manipulating the microflora with probiotics and prebiotics will cause "friendly" bacteria to grow and crowd out pathogens that cause illness. Many "friendly" bacteria secrete antibiotic substances that are active against harmful organisms. Lactobacillus acidophilus supplements given to bottle fed babies were found to improve their weight gain (J Pediatr 41:395, 1952). Better and faster recovery from acute diarrheal diseases has been seen with the addition of various species of Lactobacillus (Pediatrics 88:90, 1991; J Pediatr Gastroenterol Nutr 21:125, 1995; J Pediatr 84:261, 1974). Feeding probiotics to children has been shown to reduce the episodes of diarrhea during hospitalization (Lancet 344:1046, 1994).

Preventing Cancer:

"Friendly" bacteria protect us from cancer in many ways. They have the ability to bind and deactivate cancer-causing substances in our foods. For example, living or dead Lactobacilli absorb cancer causing chemicals known as pyrolysates that are produced by cooking meat at a high temperature. These chemicals are deactivated when absorbed into the bacteria’s cell walls (J Dairy Sci 73:2702, 1990). "Friendly" bacteria also actively degrade cancer causing substances, like N-nitrosamines (Appl Microbiol 29:7, 1975). Bifidobacteria produce antitumor substances that cause the human white cells (macrophages) to destroy growing tumor cells (Bifidobacteria and Microflora 13:65, 1994). A vegetarian diet decreases excretion of bile acids and the intestinal bacterial metabolism of these acids into cancer causing substances. A meat based diet causes bacteria to grow that make animal proteins into neutral sterols that are associated with an increased risk of colorectal cancer (Scand J Gastroenterol 23:277, 1988). Research shows that a change from a mixed diet to a vegetarian diet leads to a decrease in certain enzyme (beta-glucuronidase, beta-glucosidase, and sulphatase) activity known to increase the risk for colon cancer in three months (Nutr Cancer 14:239. 1990). Overall, by many mechanisms, a healthy gut microflora from a vegetarian diet, prebiotic and/or probiotics reduce your risk of cancer (Am J Clin Nutr 63:709, 1996, Br J Nutr 80:S219, 1998).

Reducing Excess Sex Hormones

A high-fat, low-fiber diet, causes overgrowth of bacteria in the gut microflora that have the ability to convert bile acids into sex hormones, which are then absorbed through the gut wall and into the blood stream (Lancet 2:472, 1971). Bile acids are produced by the liver for the purpose of digesting fats. The more fat consumed, the more bile acids flow into the intestine to be converted to sex hormones. Thus a low-fat, vegetarian diet will reduce sex hormones.

The intestinal microflora play a key role in circulating estrogens in a woman’s body by deconjugating (freeing up) bound estrogens that appear in the bile, thereby permitting the free hormones to be reabsorbed by the intestine, back into the woman’s body, causing elevated hormone levels. (Rev Infect Dis 6(suppl 1):S85, 1984; N Engl J Med 307:1542, 1982). The same effects occur in men, raising testosterone levels. Problems from excess sex hormones include: precocious puberty, fibrocystic breast disease, PMS, uterine fibroids, prostate enlargement, and breast, uterine, and prostate cancer. By changing the microflora with a low-fat, high-fiber diet and/or probiotics and prebiotics, more estrogen is excreted in the feces, resulting in less estrogen in the body and sex-hormone related problems are prevented and improved (often cured) (See the McDougall Program for Women for more details.)

A high-fiber, plant-based diet promotes the growth and/or the activity of bacterial populations in the microflora responsible for equol production (Proc Soc Exp Biol Med 217:335, 1998). Probiotic and prebiotics would be expected to have the same effects on the microflora. Equol is a phytoestrogen produced from the soy isoflavone daidzein by gut microflora. As a weak estrogen, it decreases the adverse effects of stronger estrogens made by a woman’s body, and later in life it may provide estrogen-like benefits, such as a reduced risk for osteoporosis (Eur J Clin Nutr 52:850, 1998).

Enhancing Immunity:

Probiotic organisms interact with the immune system at many levels, including enhancing the production of antibodies, activating the white blood cells (macrophages) to eat bacteria and cancer cells, and preventing adherence of pathogenic bacteria to our cells. Inflammation of the colon has been decreased by probiotics given to elderly people and they have shown improvement in the function of their immune system (Immunopharmacol Immunotoxicol 14:331, 1992). Cow’s milk allergy and eczema have been improved in children taking probiotics (J Allergy Clin Immunol 99:179, 1997). A pure vegetarian (vegan) diet has been shown to change the fecal microflora in patients with rheumatoid arthritis, and these changes are associated with improvement in the disease activity (Br J Rheumatol 1997 36:64, 1997).

Lowering Cholesterol:

The fermentation products made by the gut microflora reduce the synthesis of cholesterol and triglycerides by the liver and thereby can reduce their blood levels (Adv Exp Med Biol 427:211, 1997; Br J Nutr 80:S225, 1998). The evidence for these benefits is so far confined to animal studies.

Evidence indicates that the use of probiotics can:

* Reduce symptoms of lactose malabsorption

* Increase the natural resistance of infections from bacteria, yeast, and viruses

* Prevent traveler’s diarrhea

* Speed healing from diarrheal diseases and relapsing colitis

* Improve digestion

* Relieve constipation

* Stimulate the immune system of the gastrointestinal tract

* Benefit inflammatory arthritis

* Suppress cancer development and growth

* Reduce sex hormones

* Reduce cholesterol and triglycerides

* Restore the intestinal flora after antibiotic use

(J Appl Bacteriol 66:365, 1989; Biotherapy 8:126, 1995; Lancet 2:1519, 1987; J Pediatr Gastroenterol Nutr 21:125, 1995; J Pediatr 84:261, 1974; J Nutr 125:1401, 1995; BMJ 318:999, 1999; J Dairy Sci 78:1597, 1995).

Who Should Alter Gut Bacteria?

Everyone should foster the growth of a healthy microflora by eating right and avoiding antibiotics, whenever possible. A breast milk diet for infants, and a healthy vegetarian diet for children and adults are the foundation for acquiring and maintaining a healthy gut microflora by providing the correct remnants of undigested food for "friendly" helpful bacteria. Newborns who were delivered by cesarean section, as well as bottle-fed babies, need to have their microflora properly established and maintained shortly after birth. You will find probiotics specifically designed for infant use in the refrigerated section of your natural foods stores.

Use of antibiotics is a clear indication for the use of microflora replacements and enhancers -- probiotics and prebiotics. You also should consider their use if there are areas of your health that still need improvement even though you are eating a healthy diet, such as bowel dysfunction (constipation or diarrhea), indigestion, or elevated cholesterol or triglycerides. This is an easy decision to make, since there are no adverse effects from the use of probiotics, prebiotics, and synbiotics. Be a careful observer; look for real benefits, and continue them only if they really work for you, because they are costly. The claims that probiotics have cholesterol-lowering and anti-tumour actions are based on animal experiments and require further investigation. Some of the proposed benefits, such as improvement in the immune system and reduction is risk of infection are hard to evaluate. Many of the claims for health benefits you might hear in the health food store are understudied and still unproven, even though the theories have some scientific research support and their use sounds reasonable.

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From July/Aug '99

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Back Issues of Newsletter

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