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  • Nonetheless previous studies on the

    2019-08-16

    Nonetheless, previous studies on the effect of diet in sub-Saharan Africa focussed on the putative protective role of individual constituents [10]. Another limitation of earlier studies was the absence of individuals with colorectal cancer as the comparator. The studies invariably recruited healthy people only, who were all assumed to have a uniformly low risk. There is need to evaluate the role of dietary patterns on the risk of colorectal cancer in sub-Saharan Africa using neoplasia as the end-point. This is particularly relevant now, given the on-going changes in dietary practices in the region. There is rising intake of meat, processed animal products and high SC 560 foods, and decreasing intake of traditional grains and plants [14]. Therefore, we sought to establish whether there is an association between dietary patterns and colorectal cancer risk in an African population in Zimbabwe.
    Materials and methods
    Results
    Discussion This study confirms that a traditional African dietary pattern, which is predominantly plant and grain based, is associated with a reduced risk of colorectal cancer. While ecological studies suggested that African diets are protective as far back as the 1960s [19], this has never been assessed in a case-control or cohort study [10]. In our study, the traditional African diet was associated with living in rural areas and a low income. The other two dietary patterns, termed urbanised and processed, had no significant effect on colorectal cancer risk, despite high loadings of red meat, and processed meat. This implies that loss of the protective effect of the traditional diets is a more critical determinant of colorectal cancer risk in our population than adoption of potentially adverse ones. It can be speculated that maintaining some components of the traditional African diet may ameliorate the increased risk inherent in adopting modern style diets. Thus differences in the degree of retention of traditional diets may partly explain the variation in colorectal cancer risk described across different countries in sub-Saharan Africa [10]. To an extent, our findings are consistent with previous studies on the effect of dietary patterns on colorectal cancer risk described in other populations. A meta-analysis of these studies concluded that dietary patterns with a high consumption of fruits and vegetables are associated with a reduced risk of colorectal cancer [20]. However, unlike our findings, dietary patterns with a high loading of red meat were associated with an increased risk of colorectal cancer in this meta-analysis. In our study, the traditional dietary pattern is associated with living in rural areas, and a low income. It can be anticipated that dietary transitions will continue with increasing urbanisation, and rising incomes, with a resultant loss of the protective benefits of the traditional African diet. Thus the rising incidence of colorectal cancer can be expected to accelerate in the coming decades, worsening the epidemic of non-communicable diseases in sub-Saharan Africa. It has been proposed that traditional African diets affect colorectal cancer risk through changing the composition and function of the gut microbiota [21,22]. In an elegant study, swapping the diets of rural South Africans and African-Americans resulted in rapid reciprocal changes in the composition and function of the gut microbiota, and in markers of colonic mucosal proliferation [21]. There was a reduction in butyrate production, with increases in secondary bile acids and colonic mucosal proliferation in Africans commenced on a high fat, low fibre American diet. In contrast, African-Americans commenced on a high fibre, low fat African diet had a rapid increase in butyrate production, with reduction in secondary bile acids and epithelial proliferation. This suggests that the traditional African diets changes gut microbiota function and composition towards production of metabolites favourable to colonic health whilst suppressing potentially carcinogenic ones. A major limitation of this particular study was the use of epithelial proliferation rather than colorectal neoplasia as the study end-point. Our study provides complementary evidence that traditional African diets may be protective of colorectal cancer.