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The basics:

Food opioids are indigestible peptides that can cause constipation and may be the main cause of constipation for IBS-C (opioid-induced bowel dysfunction). The two most troublesome food opioids are from wheat and milk. Opioids bind to receptors and have sedative, satiating and addictive effects (although not as pronounced as for opiates).

The opioid system in general controls food reward processing and also regulates gastrointestinal transit.

Opiates are well known for their constipating effect. Adenosine, an inhibitory neurotransmitter derived from wheat gluten has been proven to depress the peristaltic reflex in rats.

Studies have proven the link between bioactive food opioids and gastrointestinal motility.

Peptides are pieces of protein. Dietary opioid peptides are small chains of amino acids that bind to opioid receptors in the brain. These are smaller (lengths of 4 to 8 amino acids) than the body's naturally occurring endorphins (40 or more).

Opiates and Opioids:

Opiates are drugs derived from the poppy plant. Opiates include heroin, opium, morphine and codeine. Opioids are substances that bind to opioid receptor sites, and this includes opiates and opioids. All opiates are opioids, but not all opioids are opiates.

Endorphins - the body's naturally occurring opioid peptide, and exorphins - dietary opioid peptides - are not opiates. However both opiates and opioids bind to opioid receptors in the brain. When these receptors are activated, the brain interprets these messages as euphoria, sleepiness, numbness, as well as a reduction in pain sensation.

Endorphins aren't considered to be neurotransmitters, however they modify their action.

Generally, food opioids mimic opiate behaviour, albeit in a milder fashion. They play a major role in food cravings, satiety and addiction. They stimulate the "hedonic and reward" pathway in the brain. This is why it's so hard giving up foods that we know are bad for us. Chemical dependency is involved as with any other drug addiction.

The two main food opioids are gluten exorphin (wheat) and casomorphin (milk).

Rice, spinach, coffee, red meat, chocolate and sugar also have food opioids.

Our liking for food opioids might be pre-programmed. Human breast milk contains morphine-like peptides and this could be part of nature's design to strengthen the maternal bond.

The peptides in dairy milk, casomorphins, are derived from the milk protein, casein which is 209 amino acids long. There are 2 types of casein, A1 and A2. These 2 milks are almost exactly identical except for no. 67 amino acid link. All cows used to have A2 milk, which was safe for consumption. Roughly a thousand years ago a natural mutation occurred which switched the 67th amino acid link in A2 milk, proline, to histidine. Histidine allows digestive enzymes to create a breakaway amino acid called beta-casomorphin-7 (BCM 7). This exogenous morphine-like opioid interacts with the digestive system and can cross the blood/brain barrier.

Black and white Friesian cows produce A1 type milk, which contains beta-casomorphin-7 (BCM 7) whereas Guernsey and Jersey cows (brown cows) produce the safer A2 type milk.

There is a threshold at which opioid peptides may become a problem and produce IBS symptoms. This is highly individual and differs from person to person.


Ligands bind to receptors. In this case, the ligand is the exorphin (food) peptide. The peptide binds to the opioid receptor. However there needs to be a certain number of these interactions before symptoms are produced. For example, one molecule of morphine won't alleviate pain, however 5 mg might. The threshold depends on a great many variables including individual physiology.

Suppose that 100 gut opiate receptors are needed to trigger constipation from the wheat exorphin. If 10 ligand binding sites are filled, that is only 10% - and not enough to cause problems as it is below the threshold of available receptors. The more receptors that are filled, the more likely constipation will occur. Toxicity depends on dose.

One of the biggest side effects of opioid analgesics is constipation. These medications block pain but also anaesthetize the colon and retard peristalsis.

Three main opioid receptors exist in the intestine: delta, kappa and mu.

There's a fair bit to wade through but it's all interesting. Basically we'd all be better off giving up wheat. Rice cakes might be safer to fill up on, but not too many. If you have milk in tea and cereal, try the A2 milk.

Most studies supporting the theory of exogenous opioids having a direct relation to colonic motility involve animals. I'm not aware of any human studies so would appreciate if anyone can provide any links for these.
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