Connection with the brain
But asthma and allergies are just the tip of the iceberg. There is a raft of childhood problems that may be due to a malfunctioning gut-which also affects the brain. Learning difficulties, poor coordination and even autism have been linked with 'gut dysbiosis', an imbalance of intestinal bacterial species. One clue is that autistic children have more digestive problems than normal children, as recently confirmed in an in-depth study led by Dr Andrew Wakefield at London's prestigious Royal Free Hospital, which showed "a consistent profile of . . . increased pro-inflammatory and decreased regulatory activities" in the intestines of autistic children (J Clin Immunol, 2004; 24: 664-73).

How does what happens in the gut affect the brain? The most obvious answer is simple malnutrition. With-out the proper balance within the gut flora, food may be poorly digested and absorbed, leading to nutritional deficiency. Too many 'bad' bacteria can also mop up nutrients or, worse, an overgrowth of, say, Candida or Clostridium can produce toxins and create a 'Catch-22' vicious circle. The original gut dysbiosis leads to a so-called 'leaky gut', where intestinal walls are damaged, thus allowing toxins to pass through into the bloodstream, from where they may then penetrate the blood-brain barrier.

Chief among these toxins are acetaldehyde, alcohol and opiate-like substances from undigested foods. "The theory is that autism is the result of a metabolic disorder," says Paul Shattock, of the Autism Research Unit at the University of Sunderland. "Peptides with opioid activity derived from . . . foods that contain gluten and casein, pass through an abnormally permeable intestinal membrane and enter the central nervous system to exert an effect on neurotransmission" (Expert Opin Ther Targets, 2002; 6: 175-83).

To test this theory, Professor Glenn Gibson, director of the University of Reading's Department of Food Biosciences, analyzed the feces of young autistic children, and found abnormally high levels of Clostridium species, confirming Dr Wakefield's earlier findings.

Gibson then wondered whether giving the children 'good', probiotic bacteria would reverse the dysbiosis and reduce their autism. He randomly selected 20 of these children to receive a probiotic capsule containing Lacto-bacillus plantarum, and gave another 20 children an identical placebo capsule. After a few weeks, the chil-dren switched to the other capsule, but neither group knew when they were receiving the real probiotics.

Sadly, the trial soon collapsed. "The effect of the probiotic bacteria was so great that many of the parents realized their children were taking something other than a placebo, and refused to allow the switch to take place," says Professor Gibson. "Parents told me how the probiotics had made such improvements in their children's concentration and behaviour that, as one parent said, it would have been heartbreaking to force the children to stop taking them. But it meant I couldn't draw any firm scientific conclusions from the trial because of the high drop-out rate."

Nevertheless, Gibson's 'results-too-good-to-be-scientific' trial will be a landmark in probiotic therapy, paving the way for more studies of not only autism, but of the more widespread autistic-spectrum disorders such as Asperger's syndrome, hyperactivity and learning difficulties in general. Indeed, gut problems similar to those in autism have been seen in children with these related conditions (Am J Gastroenterol, 2000; 95: 2285-95).