British researchers believe that most of the produce we eat is low in important cancer-fighting compounds called salvestrols. A typical five-a-day diet would give you only 10 per cent of the beneficial compounds you need to keep cancer at bay.

In research published in the British Naturopathic Journal, Gerry Potter, Professor of Medicinal Chemistry, and Dan Burke, Emeritus Professor of Pharmaceutical Metabolism, explain how salvestrols work.

How salvestrols work

It seems that human cells affected by diseases such as cancer contain an enzyme protein called CYP1B1. Triggering this protein halts the progress of the disease — and salve-strols provide the trigger.

"CYP1B1 is a kind of Trojan horse inside the cancer cells," says Prof Burke. "Provide it with salvestrols in the diet and it will unleash a stream of chemical agents that are deadly to the cancer cells."

Scientists generally believe that cancer cells are forming in the body continually, but most are destroyed before they develop into malignant tumours. The research team now believe that salvestrols play a key role in this process.

One of the first salvestrols to be identified was resveratrol, a chemical from grapes, present in red wine. Other, more powerful salvestrols have now been found in a variety of fruits including tangerines, strawberries and cranberries.

Woefully low levels

But the new research has also found that salvestrol levels vary in even the healthiest diet. Profs Burke and Potter have discovered woefully low levels in many of the fruit and vegetables we had thought were doing us good in the fight against disease. "We believe have rediscovered one of nature's defences against cancer and certain other diseases," says Prof Burke.

"In previous times salvestrols would have formed an important part of a traditional fruit and vegetable-containing diet, their levels now depleted in our food due modern farming and food processing practices." Fungicides may be partly to blame. "A ripening fruit or vegetable is prone to attack by fungal mould," says Prof Burke.

"Fruit and vegetable plants have evolved over the years to fight off the fungi by generating salvestrol compounds. When we eat the plants we also ingest the salve-strols and derive health benefits.

"But when crops are regularly treated with agrochemical fungicides the plants are rarely exposed to fungus, so they are never stimulated to make salve-strols and the fruit and vegetable harvest lacks these compounds."

The research also suggests that levels of salvestrols are up to 30 times higher in organic produce, but almost absent in some commercially grown varieties. Some varieties of fruit have 40 or 50 times higher levels than others.

Another reason our salvestrol intake is so low is our taste for sweeter flavours.

Modern varieties of fruit and vegetables are selected for sweetness, which has led to older and more robustly flavoured hybrids being overlooked. For instance, the scientists found that small, organically grown alpine strawberries have 100 times the level of salvestrols of commercially grown (non-organic) strawberries. The tart English Cox ranks significantly higher on the cancer-fighting front than a sweet apple such as the French Golden Delicious.

Salvestrols tend to lurk in the bitter flavours, and much food processing removes this bitterness to make 'unsweetened' products.

Salvestrols also tend to be found more in the skins, pulp and stones of fruit rather than in the pure juice, so when juices are clarified much of their salvestrol content is lost. Real cranberry juice, for instance, is darker and more bitter than the juice you buy in the supermarket, and more potent.

Stone ground, unfiltered olive oil (which is cloudy) will also do more good than the clear variety. And, traditional wine-making techniques, which allow the grapes to ferment in their skins, produce more salvestrols.