In the body of a healthy adult, microbial cells are estimated to outnumber human cells by a factor of ten to one. The Human Microbiome Project is an NIH project exploring the bacterial flora that live in all of us, with the mission of generating resources to characterize human microbiota and analyze their role in health and disease.

  One exciting implication of this research will be improved understanding of a large category of natural products called probiotics, which may affect health by altering the microbial environment in the body. The World Health Organization and the Food and Agriculture Organization of the United Nations define probiotics as "live microorganisms which, when administered in adequate amounts, confer a health benefit on the host."

  Probiotic foods and supplements are becoming increasingly popular in the United States. The most common types of probiotics used in food and dietary supplements are Lactobacilli and Bifidobacteria. Yogurt and other fermented foods are the main sources of naturally occurring probiotic bacteria.

  Researchers supported by the NIH National Center for Complementary and Alternative Medicine (NCCAM) are examining whether there are potential benefits of probiotics through studies that seek to alter the gut microbial environment. Investigators are looking at several conditions, including Crohn's disease, ulcerative colitis, and antibiotic-associated diarrhea.

  NCCAM is collaborating with the NIH Office of Dietary Supplements and the U.S. Food and Drug Administration's Center for Food Safety and Nutrition to conduct an evidence-based review on probiotic safety. The analysis will catalog what is known about the safety of probiotics being used; assess the quality and completeness of information; and provide recommendations, tools, and other resources for research.

  "We're in the infancy of trying to understand the human microbiome," says Patricia L. Hibberd, M.D., Ph.D., chief, Division of Global Health, Massachusetts General Hospital for Children. "One of the things that has made my research more interesting and relevant is that NCCAM [funding] is allowing me to study the effects of probiotics on the microbiome."

--Source: Excerpted from "The Art and Science of Natural Products," Complementary and Alternative Medicine: Focus on Research and Care, newsletter of NIH Center for Complementary and Alternative Medicine, May 2010