THE EXORPHIN PUZZLE: HOOKED ON FOOD?
The endorphins are all peptides – short chains made up of amino acids. Proteins also consist of amino acid chains (see p23), but in proteins the chains are much longer. When foods are broken down in the gut, the proteins are split into shorter lengths – in other words, into peptides. By chance, some of those peptides consist of a very similar sequence of amino acid to the natural endorphins. Such peptides are therefore called exorphins (exogenous mor-phine-hke molecules). In the laboratory, these exorphins have been produced from milk, wheat, maize and barley, using human digestive enzymes. Other foods have yet to be investigated.
Further laboratory experiments show that exorphins can bind to the natural receptors for endorphins – but whether they actually do so in the body is another matter. First they would have to get through the gut wall and into the bloodstream. They would also have to evade protein-cracking enzymes in the liver: endorphins have a special chemical structure at the end of the molecule which prevents such enzymes from attacking them, but exorphins do not.
So can the exorphins have any effect on the body? One experiment suggests that they can. A partially digested sample of wheat protein was fed to human ‘guinea-pigs’, and produced certain measurable changes in bodily function. The experiment was then repeated, with a drug called naloxone being given before the wheat. This drug is known to block endorphin receptors, and prevents peptides from binding to them. When naloxone was given first, the wheat protein had no effect.
Many more experiments are needed before we can reach any firm conclusions about exorphins, but the results so far suggest that they might influence our mood. There is certainly no question of anyone getting ‘high’ on a glass of milk or a slice of bread – the amounts involved are too small for that -but these foods might induce a sense of comfort and well-being, as food-intolerant patients often say they do. There are also other hormone-like peptides in partial digests of food, which might have other effects on the body.
If foods can produce these peptides, then why do they only affect certain people? It is possible that the leakiness of the gut wall is important here – if more peptides get through, more are likely to get to the receptors before they are broken down by enzymes. Any deficiency in those enzymes would also increase the person’s vulnerability to exorphins.
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