Low dietary cyanogen exposure from frequent consumption of potentially toxic cassava in Malawi

In a cassava-growing area in Malawi, where roots are processed by soaking a nd water is available throughout the year, we interviewed 176 women farmers regarding their preferences for cassava cultivars and frequency of cassava consumption. Dietary cyanogen exposure was estimated from urinary levels o f linamarin, the cyanogenic glycoside in cassava, and urinary thiocyanate, the main cyanide metabolite, Protection against unplanned harvest by family members, theft and animal spoilage were stated to be very important reason s for growing bitter cassava cultivars by 91%, 90% and 74% of the women, re spectively. The mean (+/-SD) number of cultivars grown by each woman was 4. 6 (+/-2.4). The correlation between mean taste and mean danger scores for t he 25 most grown cultivars was strong (r > 0.98). The scoring indicated tha t cultivars belonged to two distinct groups, eight to a group referred to a s 'cool' and 17 to a group termed 'bitter'. The dumpling-like porridge (kon dowole) made from cassava flour from bitter roots was eaten twice daily by 51% and at least weekly by 81%. The mean (+/-SEM) urinary linamarin was 14 (+/-1) mu mol/L and thiocyanate was 50 (+/-4) mu mol/L, less than a tenth o f levels reported from populations eating insufficiently processed bitter c assava roots, and in the same range as in a non-smoking Swedish reference p opulation. We conclude that cyanogenesis is a preferred characteristic of c assava by the studied farmers because it enhances food security. The availa bility of water and their knowledge about toxicity and processing enables t hese women farmers to provide a safe staple food from bitter cassava roots.