The total number of microbes associated with our bodies exceeds the total number of our human cells by a factor of 10. In essence, we humans are one superorganism—one that's 90 percent microbial. The majority of the microbes within us exist in our GI tract. These microbes help us digest food, harvest nutrients, manufacture certain vitamins, kill germs, neutralize bacterial toxins, and modulate the immune system. Sickness, antibiotic therapy, and stress can disrupt the ecological balance amongst gut dwellers, diminishing their benefits. Other animals have evolved a similar symbiosis with—or even dependence on—gut microbes. For example, rodents born by cesarean section (so they get none of their moms' intestinal flora) and raised under germfree conditions end up smaller than normal despite eating about 30 percent more food than their microbe-laden counterparts. "Germfree" animals not only appear less efficient at harvesting calories, but also are prone to certain vitamin deficiencies" because gut microbes synthesize certain nutrients, such as vitamins B12 and K. Over-the-counter therapies exist to add microbes to our guts. Known as probiotics, these yogurts and other foods or dietary supplements introduce or replenish beneficial gut species in the digestive system. Probiotic microbes' role in fighting generic diarrheal disease is well established, but in the past decade other influences on human immunity and metabolism have emerged. Certain microbial supplements show the potential to reduce the severity of colds and other infections, temper body weight, and even help the elderly fight osteoporosis. Research is also showing that a probiotic's benefits can be very specific indeed. As such, it might be more appropriate to view these microbes as over-the-counter micro-pharmacists—each able to dispense only a few therapies or services. A few benefits have been shown in recent research. A study in 2005 showed that daily treatment with a trio of probiotics didn't reduce the incidence of colds, but did reduce the severity and duration of cold symptoms—including fever—compared with a group of people that did not receive probiotics; the authors of the study were not able to identify the mechanism for this benefit, however individuals given probiotics showed an increase in the number of activated helper T cells—white blood cells that fight infection. Over the past year, several research teams have reported some success with probiotics in treating inflammatory bowel disease. At least one study found they could help control exaggerated inflammation in intensive care patients at high risk for multiple organ dysfunction syndrome—a hyperinflammatory condition. Another study showed that probiotics administered to pregnant women and babies reduced the likelihood that high-risk infants developed food allergies. Another interesting aspect of recent studies is that it appears that probiotic microbes communicate with the microbes already established in the gut; this is not too surprising since it is well known that bacteria communicate and share genes in a wide variety of settings. It is thought that this communication causes the production and release of specific molecules, not only by the probiotic microbes, but by many of the other microbes present. Now, the complicated aspect. Each person's gut flora is to some extent unique. Thus, it will be a considerable challenge to determine what might work for a particular individual. To put this in context, there are roughly 5 thousand human genes that can be targeted with drug therapy, whereas there may be 100,000 genes that could be targeted amongst one's gut microbes. This is an interesting and exciting frontier of human health. However, as noted in a prior post, it is not all roses; some research has been poorly designed and lead to unnecessary suffering by and even death of patients. For more information, see http://jn.nutrition.org/cgi/content/full/137/3/781S, http://www.expert-reviews.com/doi/abs/10.1586/14787210.4.2.261, http://www.blackwell-synergy.com/doi/abs/10.1111/j.1440-1746.2006.04535.x, http://linkinghub.elsevier.com/retrieve/pii/S0140673603134903, http://linkinghub.elsevier.com/retrieve/pii/S0092867406001929, and http://www.blackwell-synergy.com/doi/abs/10.1111/j.1572-0241.2006.00465.x.