The microbiota of C-section children differ from their naturally born peers even a full seven years after birth. "The disappearance of microbes that play physiological roles early in life is particularly worrisome," says Blaser. "Perhaps they are missing in certain phases of the child's development."
What's more, a study of 1,255 mother-child pairs in Massachusetts indicated an increase in body weight. Of the children who were born in a natural manner, 7.5 percent were obese at the age of three -- compared to 16 percent of the C-section children.
Based on experiments with animals, Blaser has discovered that an abnormal bacterial colonization can cause excess weight. The New York physician fed mice a steady low dose of antibiotics for weeks, and then studied their colonization patterns. The drugs had changed the composition of the intestinal bacteria -- and thus also the animals' metabolism. The bacteria in treated mice activated more genes that transform sugar into fat.
Farmers are familiar with this phenomenon. They mix antibiotics into pig, cattle and chicken feed to promote growth and fatten up the animals more quickly -- a practice that is now banned in Germany. Blaser assumes that the drugs have the same effect on children. "Instead of the continuous, low-dose antibiotics that are administered on the farm, we are giving our children short, high-dose pulses," he warned in an article in Nature Reviews Microbiology in 2009.
A study of 11,000 children published in the International Journal of Obesity came to the same conclusion. According to the findings, children who were treated with antibiotics during the first six months of their lives have a 22 percent higher probability of being obese at the age of three.
In addition to increased body weight, a dysbiosis may also be connected with the susceptibility to allergic disorders and inflammation of the intestine. The immune system needs contact with intestinal bacteria in order to be able to differentiate between foreign cells and the body's own cells. If the diversity of bacteria is diminished, the immune system learns the wrong lessons. It classifies the body's own cells as foreign cells, which triggers allergic reactions.
Many people with autism have an abnormal digestive tract, as well. No one knows exactly why this is, but individuals with autism apparently have different intestinal bacteria than people without autism. For instance, they are missing the beneficial rod-shaped bacteria of the Bacteroides genus. Researchers at Columbia University, in New York, believe this allows harmful microbes to multiply. They examined the intestinal flora of 23 autistic children -- and discovered in 12 of the samples so-called Sutterella bacteria, which don't belong there.
Enriching Microbial Flora
There are now more than 25 different diseases and syndromes -- ranging from Alzheimer's and arteriosclerosis to depression and rheumatism -- that have been linked to an abnormal microflora.
This is good news for the food industry. It already sells so-called probiotic drinks and yogurts that contain lactic acid bacteria and allegedly improve the intestinal flora. But independent studies claim this is nonsense, saying that the bacteria ingested with the food usually don't even manage to colonize the intestinal tract. Experiments on humans have shown that, regardless of whether the test subjects ate probiotic yogurt every day or not, it had no influence on the composition of their microbiota.