Eating greens reduces the cases of cancer of the colon?

Source: Van Guelpen B et al. Low folate levels may protect against colorectal cancer. Gut 2006; 000:1

According to Swedish research, in an article published in a journal of gastroenterology (Gut), a diet poor in folates prevents cancer of the colon. Folates are vitamins contained in vegetables (greens, cauliflower, cabbage, Swedes, carrots, oranges, pulses, corn, barley) brewers’ yeast, liver, and kidney.
In the past, studies showed that a diet rich in folates could actually be considered as preventive of cancer, The Nurses’ health study, one of the most detailed on this topic, asserts on the contrary, that a diet rich in folates is associated to the reduction of the risk of colorectal cancer, but only after an intake of 15 years and in individuals who are genetically prone to colorectal cancer. It is assumed that folates work in the early years of life when critical events can be altered at a molecular level.
The assumptions of the Swedish study contradict what has been asserted so far, the authors of the research assert that folates could prevent the formation of tumours but could also accelerate the progression of developed tumours, or could transform a benign tumour into a malign one.
However the study published in GUT concludes without commitment “We can not exclude the possibility that high levels of folates have a protective effect, although our studies suggest that low levels may reduce the risk of cancer of the colon”; which leaves the question unresolved and open to further study.