Probiotics
The bacteria that reside in the intestinal tract generally have a symbiotic relationship with their host. Beneficial bacteria produce natural antibiotics to keep pathogenic bugs in check (preventing diarrhea and infections) and produce some B vitamins in the small intestine where they can be utilized. Beneficial bacteria help with food digestion by providing extra enzymes, such as lactase, in the small intestine. Beneficial bacteria help strengthen the immune system right in the gut where much of the interaction between the outside world and the body goes on. Beneficial bacteria can help prevent food allergies. They can help prevent cancer at various stages of development. These good bacteria can improve mineral absorption, maximizing food utilization.
However, the balance of beneficial and potentially pathogenic bacteria in the gut is dependent on the diet. Vegetable fiber encourages the growth of beneficial bacteria. A group of Adventist vegetarians was found to have a higher amount of beneficial bacteria and lower amount of potentially pathogenic bacteria compared to non-vegetarians on a conventional American diet [159]. Differences in bacterial populations were seen between patients who recently had a colon polyp removed, Japanese-Hawaiians, North American Caucasians, native rural Japanese, and rural native Africans. Lactobacillus species and Eubacterium aerofaciens, both producers of lactic acid, were associated with the populations with the lower risk of colon cancer, while Bacteroides and Bifidobacterium species were associated with higher risk of colon cancer [160]
There is a solid theoretical basis for why probiotics should help prevent cancer, especially colon cancer, and even reverse cancer. Probiotics produce short chain fatty acids in the colon, which acidify the environment. Lower colon pH is associated with lower incidence of colon cancer. Probiotic bacteria reduce the level of procarcinogenic enzymes such as beta-glucuronidase, nitroreductase, and azoreductase [161].
L. casei was used in two trials of patients with superficial bladder cancer. In the first trial, the probiotic group had a 50% disease free time of 350 days, compared to 195 days for the control group [162]. The second trial also showed that the probiotics worked better than the placebo, except for multiple recurring tumors [163].
Except for the two studies noted above, most of the research of probiotics and cancer has been done in animals. Studies have looked at markers of tumor growth or at animals with chemically induced tumors.
Studies in rats have shown that probiotics can inhibit the formation of aberrant crypt foci, thought to be a pre-cancerous lesion in the colon. Some of the best results were obtained with a probiotic strain consumed with inulin, a type of fructooligosaccharide. Total aberrant crypt foci, chemically induced, were reduced 74% by the treatment of rats with inulin and B. longum, but only 29 and 21% by B. longum and inulin alone, respectively [164]. There was a synergistic effect in using both products together. Similar synergy was seen in rats with azoxymethane-induced colon cancer in another study. Rats fed Raftilose, a mixture of inulin and oligofructose, or Raftilose with Lactobacilli rhamnosus (LGG) and Bifidobacterium lactis (Bb12) had a significantly lower number of tumors compared to the control group [165]. A probiotic mixture, without any prebiotic, given to rats fed azoxymethane reduced colon tumors compared to the control (50% vs 90%), and also reduced the number of tumors per tumor-bearing rat [166].
In lab mice bred to be susceptible to colitis and colon cancer, a probiotic supplement, Lactobacillus salivarium ssp. Salivarius UCC118, reduced fecal coliform levels, the number of potentially pathogenic Clostridium perfringens, and reduced intestinal inflammation. In this small study two mice died of fulminant colitis and 5 mice developed adenocarcinoma in the control group of 10 mice, while there was no colitis and only 1 mouse with adenocarcinoma in the probiotic test group [167].
The research on probiotics and disease is still an emerging field. There is a high degree of variation of health benefits between different strains of bacteria. As new methods for selecting and screening probiotics become available, the field will be able to advance more rapidly.