Wheat and dairy products are consumed daily by most people and are thought to be nourishing foods.

Although we've eaten them for thousands of years, we have never consumed them in such quantities and it is becoming apparent they may cause problems for some people.

I spoke to Umahro Cadogan, a nutrition consultant and lecturer from Denmark, who is an expert on the effects of opioids derived from food.

We usually associate opioids with morphine and heroin but the human body has the ability to make its own opiates as a normal response - for instance, to extreme pain. Cadogan says two common proteins in our diet may have opiate-like effects if not digested properly and absorbed into the bloodstream.

The culprits are protein fragments from gluten (from wheat, rye, barley and oats) and casein (from the milk of cows, sheep and goats).

If a person has incomplete digestion, combined with a "leaky gut", partially broken down proteins cross the blood-brain barrier and attach to opiate receptors in the brain.

The result is a signalling overload that interferes with sensory and cognitive function.

"Researchers have found very high levels of opiates in the blood and urine of schizophrenics and autistics," says Cadogan.

"The rate of schizophrenia is extremely low or non-existent in societies where no glutenous grains or dairy products are consumed. Yet the rate of schizophrenia rises to that of industrial societies when glutenous grains and milk are introduced among indigenous people."

Are our children being doped up on wheat and dairy products and does everyone need to avoid them? No, but Cadogan suggests those diagnosed with autism, schizophrenia, epilepsy, chronic fatigue syndrome and multiple sclerosis may benefit from a gluten and casein-free diet.

Such a diet is difficult and he stresses the importance of attempting it only under the guidance of a specially trained health professional.

This is because modern food processing makes gluten and casein difficult to detect and healthy alternatives need to be sourced. Plus, opiates are highly addictive and may cause initial withdrawal reactions.

So it's crucial to adopt the diet in stages and support digestive processes.

Cadogan emphasizes that, to be effective, a gluten and dairy-free diet must be followed 100 per cent because food-derived opiates are very strong-acting in low concentrations, but relatively weak in high concentrations. So a higher load of dairy and wheat may actually decrease symptoms slightly. An extremely low load could spark off strong reactions because every opiate-like molecule is more potent at low concentrations.

Are the rewards of such a regime worth it? "The diet is difficult at first but gets easier with time and experience," says Cadogan. "In many cases, it makes life more bearable for those with certain neurological, developmental or psychiatric conditions."

Cadogan is speaking on Foods as Opioids at the Children's Mental Health - Feeding The Next Generation conference in London on October 9.

For more details call, 0870 161 3505 or visit www.pavpub.com