More MS news articles for July 2002

Rogue peptide theories

01 July 2002
Volume 1, Number 3
John McCrone

Here is a shocking little factoid of which the neurologist might want to take note. Meat, fat, and sugar made up ten percent of our diet a century ago. Now that figure has soared to 60 percent.

Why should this second great change in human eating habits (the first being the agricultural revolution 10 000 years ago) be of any particular interest to neurologists? Well, have you seen the headlines screaming: “Tenfold rise in autism in ten years”, “Six percent of US children now on drugs for hyperactivity”, “Dyslexia triples to affect one-in-five”?

Although official confirmation remains hard to come by, many in the frontline of child care feel we are facing a modern plague of developmental brain disorders. They say it's not just a matter of better diagnosis, or the creation of new borderline classifications like PDD-NOS (pervasive developmental disorder not otherwise specified!). Something really is up. And perhaps not just with kids; adult complaints, such as migraines and chronic fatigue syndrome, and even outright psychiatric conditions like postnatal psychosis, obsessive–compulsive disorders, and depression, all seem to be on the rise.

What could be the reason? One X-Files style answer is that our changed diet is largely to blame. Not to put too fine a point on it, our brains are being poisoned by undigested milk and wheat. The plague is the terrible result of a clash between our evolutionary past and our polluted, disrupted, junk food present.

This “opioid excess” theory has been doing the rounds since at least the 1970s. But recently people have begun to find it more credible. The hypothesis is that the human digestive system evolved for a stone age diet—tubers, berries, and lots of lean meat. At the end of the last ice age we settled down to be farmers. Suddenly, grain and milk products became the new staples and hurriedly we had to develop a matching set of digestive enzymes. The consequence of this rushed evolution is a wide genetic variation in how well people can cope with the proteins in these foods. An incomplete breakdown can leave the gut awash in opioid-like peptide fragments such as casomorphine and gliadomorphine.

The second part of the story is that these peptides fragments float through to the brain where their close resemblance to neuropeptides and nerve growth factors creates all kinds of neurological mayhem. In a mature adult brain, the effects may range from mild immune system disruption to serious psychiatric disturbance. In the infant brain, autism and other developmental syndromes may result.

Now here is the rub. Believers in the rogue peptide theory have to explain how these largish molecules manage to penetrate the body's natural defences—the three barriers of the gut lining, the immune system, and then the particularly tight protection of the blood-brain barrier itself. Many have dismissed the opioid excess story on these grounds alone. Then, even those willing to grant the theory a basic plausibility find themselves balking because such a confusing range of penetration mechanisms have been suggested.

Is it organophosphate pollution from our environment eroding the membranes of the gut and brain, causing them to spring leaks? Or perhaps a genetic incompetence of some key protective mechanism, such as the sulphate transferase system? Or maybe an overgrowth of thrush (the yeast, Candida) creating holes in the intestine? Or a lack of essential fatty acids and trace elements like zinc and selenium doing the same to the choroid plexus? Or—most notoriously—the measles, mumps, and rubella triple vaccine inflaming the gut and perhaps brain membranes? All these and more have their proponents.

When this maze of suggested causal pathways is then being linked to an equally various range of neurological and immunological disorders—did I remember to mention schizophrenia, multiple sclerosis, Gulf War syndrome and allergy-proneness?—you can see the problem. The rogue peptide story is an aetiological mess and no serious medical practitioner would touch it with a barge pole.

And yet something does seem to be going on here. It is hard to deny the increase in autism and other allied complaints. Or that our kids are eating a heck of a lot of junk food these days (yes, and their busy parents too). If indeed peptides are poisoning our brains, then it is going to take some pretty committed scientific detective work to untangle all the strands of the tale. However, this does seem to be one wacky theory that deserves a proper hearing.