Writing in the journal Food Chemistry, Canadian researchers agree that extracts from cruciferous, dark green and Allium vegetables show the highest anti-cancer potential.
“Since the formation of tumours is a random event that occurs in a significant percentage of the adult population, the increased consumption of these vegetables with high anticancer properties could play a central role in preventing these tumours to reach a clinical stage and thus reduce the incidence of several types of cancers,” wrote lead author Dominique Boivin from Quebec University.
The anti-cancer properties of cruciferous vegetables, such as broccoli and cauliflower, are not new and previous studies have related these benefits to the high levels of active plant chemicals called glucosinolates. These are metabolised by the body into isothiocynates, and evidence suggests these are powerful anti-carcinogens. The main isothiocynate from broccoli, for example, is sulforaphane.
Other studies have proposed that the compound indole-3-carbinol (I3C), a phytochemical found naturally in cruciferous vegetables, could also have potential prevention activity against hormone-responsive tumours, such as breast, ovarian and prostate cancer.
Boivin and co-workers from Quebec’s Saint Justine Hospital and the Ministry of Agriculture, Fisheries and Food, evaluated how extracts from 34 vegetables may inhibit the growth of eight different tumour cell lines in the laboratory.
Significant inhibition of all the cancer cell lines tested – stomach, lung, breast, kidney, skin, pancreas, prostate, and brain – was observed for all the extracts from cruciferous vegetables, such as broccoli, kale, Brussels sprouts, and curly cabbage, and vegetables of the genus Allium, such as garlic.
“These chemopreventive effects are likely related to the formation of organosulfur compounds following mechanical disruption of these vegetables, namely isothiocyanates from cruciferous and a series of allyl sulfur molecules from Allium vegetables,” wrote Boivin.
On the other hand, vegetables such as potato, carrot, tomato and lettuce, were generally ineffective at providing cancer protection, said the researchers.
“The lack of inhibitory effect of these widely consumed vegetables is noteworthy since potatoes, carrots, tomatoes and leaf lettuces account for approximately 60 per cent of total per capita vegetable intake in the Unites States adult population,” they added .
More to come?
The researchers note that the vegetable juices studied do not contain many water-insoluble molecules such as lycopene and beta-carotene, despite containing many phytochemicals.
“It is thus possible that our results underestimate the whole antioxidant and anti-proliferative activities of specific vegetables containing water-insoluble bioactive phytochemicals,” they added.
The "five-a-day" message is well known, but applying this does not seem to be filtering down into everyday life. Recent studies have shown that consumers in both Europe and the US are failing to meet recommendations from the WHO to eat 400 grams of fruit and vegetables a day.
Source: Food ChemistryVolume 112, Issue 2, Pages 374-380 “Antiproliferative and antioxidant activities of common vegetables: A comparative study”Authors: D. Boivin, S. Lamy, S. Lord-Dufour, J. Jackson, E. Beaulieu, M. Cote, A. Moghrabi, S. Barrette, D. Gingras, R. Beliveau