Eating plenty of onions, leeks and garlic dramatically slashes the risk of bowel cancer – one of Britain’s biggest killers, according to new research.
Each year 42,000 Britons are diagnosed with the cancer and it kills more than 16,000 but just one small onion a day is enough to prevent it.
A study of more than 1,600 men and women found those with the biggest intake were 79 per cent less likely to develop the disease than those with the least.
Allium vegetables – which also include chives and shallots – are rich in tumour-fighting compounds.
They are also known to protect against breast and prostate cancer.
Senior author Dr Zhi Li, of the First Hospital of China Medical University in Shenyang, said: “It’s worth noting that in our research there seems to be a trend – the greater the amount of allium vegetables, the better the protection.
“In general, the present findings shed light on the primary prevention of colorectal (bowel) cancer through lifestyle intervention, which deserves further in-depth exploration.”
Dr Li and colleagues worked out that consuming at least 35lbs a year of allium vegetables such as onions and leeks may effectively reduce an individual’s risk of the disease.
This would work out at around one-and-a-half ounces a day – equivalent to about one small onion.
The study published in the Asia Pacific Journal of Clinical Oncology compared 833 bowel cancer patients with the same number of healthy controls.
The Chinese participants were matched by age, sex and where they lived with demographic and dietary information collected via face-to-face interviews using a validated food frequency questionnaire.
Dr Li said bowel cancer is the third most common form of the disease worldwide – with about 1.23 million newly diagnosed cases annually. It’s the second biggest cancer killer in the UK.
Rates in China are lower than in Europe and the US. But they are growing because of an increasingly westernised diet.
Dr Li said: “Allium vegetables, including garlic, garlic stalks, leek, onion, and
spring onion, belong to the most commonly consumed vegetables in the world.
“Bioactive compounds in allium vegetables, particularly, flavanols and organosulphur compounds, have been shown to provide beneficial effects against cancer.
But although lab experiments have demonstrated this results from epidemiological studies have been inconsistent.
Dr Li said: “The present findings shed light on the reduced risk of colorectal cancer associated with diet, specifically the intake of allium vegetables.”
The questionnaire included 99 commonly consumed foods with frequency of
intake graded as never, monthly (2–3 times per month), weekly (2–3 or 4–5 times per week), and daily (2 or at leas 3 times per day).
Average annual intake of each allium vegetable (frequency of intake multiplied by the amount per meal) over the past 12 months was then computed to provide the most extensive analysis of its kind to date.
Allium vegetables are part of the customary diet in China making its population an appropriate model on which to assess their impact on bowel cancer incidence.
Dr Li said: “Based on the cohort of 1,666 participants in northeast China, we performed the hospital-based matched case-control study to explore the relationship of risk with allium vegetables intake.”
He pointed out cooking method could influence the bioactivity of allium vegetables. For example, slicing and crushing fresh garlic are important for the formation of
various organosulphur compounds.
On the other hand boiling onions lead to about 30 percent loss of the beneficial chemicals.
Dr Li said: “It had been reported the cooking methods for allium vegetables
are greatly different in the population from different areas, such as eastern and western countries, or the different parts of the same country.
“To our knowledge, this is the first epidemiological study to investigate the relationship between the intake of allium vegetables and the risk of colorectal cancer among the northeastern Chinese population.
“Moreover, the large sample size in the current study allowed for a more detailed
analysis for the potential association of specific allium vegetable type with colorectal cancer.”
It has been known for years that the humble flowering plants pack a mighty nutrient punch.
The wide array of sulphur compounds gives onions, garlic and other alliums their characteristic taste, smell, and tear-inducing pungency – as well as many health benefits.
These include cardiovascular protection, anti-cancer activity, lowering cholesterol and blood pressure and providing anti-clotting benefits.
Alliums also contain polyphenols, including the flavonoid quercetin, which along with many of the sulphur compounds have important anti-inflammatory effects.
To maximise the concentration of sulphur compounds experts advise allowing chopped onions, crushed or minced garlic, sliced leeks, or other alliums to sit for a few minutes.
This is before cooking them or adding to an acid – such as vinegar or lemon juice. This allows the enzymes released when the alliums’ cells are broken to more completely react with sulphur-containing molecules and convert them to beneficial forms.
Alliums – Latin for ‘garlic’ – evolved their pungent odours and tastes to deter hungry animals.
But humans, ironically, have singled them out specifically for those characteristics. They have become vital to every cuisine in the world.
Bowel cancer kills about 16,400 people in the UK each year. Lung cancer is the only form that claims more lives.