Mostly, CRC carcinogenesis or other neoplasms mainly occurs due to epigenetics such as change in food habits. Though, western life style foods is an main cause of CRC.
It is mostly depends from what kind of food you call western lyfe style food. Because many American, European and Eurasian national kitchens have big value of dishes containg plants. But for my opinion higher role in CRC plays increase of eating such things as semi-finished products, procceed meat and fast food.
you should have a look in the implication of genetics in this disease and therefore the repartition of disease genes among populations. there are a lot of papers and reviews, just read this one: http://www.jcancer.org/v10p0643.htm. but it's sure that environmental factors as microbiome and foods have real impacts on gene behavior (Article The effects of dietary polyunsaturated fatty acids on miR-12...