Ishikawa H et al. (2005) Randomized trial of dietary fibers and Lactobacillus casei administration for prevention of colorectal tumors. Int J Cancer [10.1002/ijc.21115]

The rising incidence of colon cancer in Japan has been blamed on changes in diet, which correspond to the increasingly Westernized lifestyle. Since dietary fiber is thought to help prevent colorectal cancer, Ishikawa et al. carried out a clinical trial to examine the association between dietary fiber and colorectal cancer incidence among Japanese individuals. In addition, they asked whether the risk of developing these tumors was reduced by Lactobacillus casei, which reduces the level of mutagens in stool.

The investigators recruited 398 subjects aged 40–65 years who had had at least two colorectal tumors removed within the previous 3 months. All received dietary instruction, and were randomly assigned to a regular intake of wheat bran biscuits, L. casei preparation, or both. A control group received dietary instruction only.

Colonoscopic examination at 2 years and 4 years follow-up showed no significant difference between the groups in the occurrence of new colorectal tumors. Large tumors, however, were significantly more frequent after 4 years among subjects who received wheat bran than among those who did not (3.7% vs 0.0%, P <0.01). Interestingly, L. casei administration was associated with a significant decrease in the development of tumors with moderate or severe atypia after 4 years.

In summary, the study does not support the use of dietary fiber supplements to prevent colorectal cancer. The possible mechanism by which L. casei suppresses the development of tumors with moderate or severe atypia is the subject of ongoing studies.