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Bugs in Our Guts—Not All Bacteria Are Bad
How Probiotics Keep Us Healthy

(Released September 2006)

 
  by Leila Kiani  

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♦ Lactose Intolerance.

The inability of adults to digest lactose, or milk sugar, is prevalent worldwide. People of northern European descent are unique in retaining the ability to produce the lactose-digesting enzyme, lactase, into adulthood so they can continue to drink milk. Consumption of lactose by those lacking adequate levels of lactase produced in the small intestine can result in diarrhea, bloating, abdominal pain and flatulence. These symptoms are due to the undigested lactose reaching the large intestine and being fermented by the colonic microbes, which can produce gases and products that lead to watery stool (6).

The consumption of dairy products - important for supplying calcium and preventing osteoporosis - by people with lactose intolerance can be facilitated by probiotic bacteria (6).

It has been documented scientifically that many lactose intolerant individuals are better able to consume fermented dairy products, such as yogurt, with fewer symptoms than the same amount of unfermented milk, even though yogurt contains about the same amount of lactose as milk. Yogurt was found to aid digestion of lactose because the lactic acid bacteria used to make yogurt produce lactase and digest the lactose before it reaches the colon. In addition to yogurt starter bacteria, L. acidophilus and bifidobacteria have been shown by several studies to improve digestion of lactose, although generally to a lesser extent than the yogurt starter cultures, Lactobacillus bulgaricus and Streptococcus thermophilus (6).

♦ Hypertension.

About 50-60 million people in United States are estimated to have hypertension, or elevated blood pressure. Antihypertensive effects have been documented in animal models and in mildly hypertensive adults for three compounds derived from the growth of certain lactobacilli: i) fermented milk containing two tripeptides derived from the proteolytic action of L. helveticus on casein in milk; ii) bacterial cell wall components from cell extracts of lactobacilli; and iii) fermented milk containing fermentation-derived gamma amino butyric acid. Systolic blood pressure was decreased on the order of 10-20 mm Hg. These results suggest that consumption of certain lactobacilli, or products made from them, may reduce blood pressure in mildly hypertensive people. Viability of the lactobacillus is not required for the effect. Such fermentation-derived, but nonprobiotic, products have been developed (6).

♦ Antibiotic therapy disease

One group assessed for the impact of probiotics is people on antibiotic therapy. The purpose of antibiotics is to kill harmful bacteria. Unfortunately, they frequently kill normal bacteria as well, often resulting in disruption of the bacterial flora, leading to diarrhea and other intestinal disturbances. Replenishing the flora with normal bacteria during and after antibiotic therapy seems to minimize disruptive effects of antibiotic use. Studies show that probiotics can prevent antibiotic associated diarrhea, but that no strong effect on the ability of probiotics to treat diarrhea exists. Not all studies have shown positive results in the prevention of antibiotic associated diarrhea or other symptoms associated with antibiotic therapy (6).

♦ Vaginosis

The vagina and its microbiota form a finely balanced ecosystem. Disruption of this ecosystem can lead to a microbiological imbalance and symptoms of vaginosis. Vaginosis used to be considered a mere annoyance, but now is being examined for a role in serious conditions including pelvic inflammatory disease, pregnancy-related complications (low birth weight babies, etc.), and increased susceptibility to AIDS infection. Vaginosis can be caused by several different organisms, and in many cases, the causative agent may not be identified. What is known is that lactobacilli predominate in the healthy vagina, and a lack of lactobacilli (especially those producing hydrogen peroxide) is a risk factor for vaginosis. The lactobacilli are thought to maintain a favorable vaginal pH in the acidic range and to inhibit pathogens, possibly through the production of hydrogen peroxide and other antimicrobial factors. Intravaginal applications of lactobacilli have been somewhat effective in treating bacterial vaginosis. One study done with 13 women showed that consumption of yogurt containing L. acidophilus decreased the incidence of Candida yeast infections. Research suggests that lactobacilli may be helpful in controlling the incidence and duration of vaginal infections, but larger, controlled studies are needed (6).

♦ Small Bowel Bacterial Overgrowth.

Under certain conditions, such as during the production of low stomach acid or kidney dialysis, microbial populations in the small intestine can increase beyond normal levels. This is termed small bowel bacterial overgrowth. Growth of the misplaced microbes can produce potentially toxic byproducts. Researchers have found that feeding high levels of certain probiotic strains can control the toxic effects of these microbes. This is another example of the ability of probiotic strains fed in high numbers to modulate the activity of other intestinal bacteria (6).

♦ Helicobacter pylori.

Helicobacter pylori is a bacterium which colonizes the stomach. Its presence is associated with gastric ulcers and gastric cancer, although its role in the etiology of these diseases is still under investigation. The effect of probiotics on Helicobacter pylori has been studied. Most evaluations have been done either in laboratory assays or in animal models. These studies show that antibacterial substances including (but not limited to) organic acids produced by some lactobacilli inhibit the growth and survival of this pathogen. Results in animal models demonstrate that some lactobacilli inhibit H. pylori attachment and prevent colonization. Results in humans show that milk fermented by a Lactobacillus johnsonii strain can help control H. pylori gastric infections, but cannot eradicate H. pylori from the stomach. These results are preliminary, but suggest that probiotic growth in milk may yield anti-Helicobacter substances that may help control this infection (6).

♦ Kidney Stones.

A high oxalate level in the urine is a risk factor for the development of kidney stones. Use of oxalate by intestinal microbes limits its absorption. A probiotic preparation that contained bacteria able to degrade oxalate in vitro was shown to reduce oxalate fecal excretion in six patients. This study suggests that manipulation of the gut flora with the right probiotic bacteria may improve gastrointestinal tract oxalate levels and may decrease oxalate absorption. These results are intriguing, but preliminary (6).

♦ Elevated Blood Cholesterol.

Cholesterol is essential for many functions in the human body. It acts as a precursor to certain hormones and vitamins and is a component of cell membranes and nerve cells. However, elevated levels of total blood cholesterol or other blood lipids are considered risk factors for developing coronary heart disease. Although humans synthesize cholesterol to maintain minimum levels for biological functioning, diet also is known to play a role in serum cholesterol levels. The extent of influence varies significantly from person to person. Probiotic cultures have been evaluated for their effect on serum cholesterol levels. Clinical studies on the effect of lowering cholesterol or low-density lipid levels in humans have been inconclusive. Some human studies suggest that elevated blood cholesterol levels can be reduced by consumption of probiotic-containing dairy foods, but the evidence is not overwhelming. It is likely that some strains may demonstrate this property while others do not (6).

The dietary cholesterol absorption is reduced in three ways: assimilating, binding, or degradation. Probiotic strains assimilate the cholesterol for their own metabolism. Probiotic strains can get to the cholesterol molecule, and can degrade cholesterol to its catabolic products. The cholesterol level can be reduced indirectly by deconjugating the cholesterol to the bile acids, thereby reducing the total body pool (4).

Thanks to Deborah Whitman for all of her help, without which this Discovery Guide would never have been written

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