Amid all the brouhaha surrounding the publication of the paper “A large-scale intervention to introduce orange sweet potato in rural Mozambique increases vitamin A intakes among children and women” in the British Journal of Nutrition, it is worth reminding ourselves what the study did and did not find.
Adoption of 6 orange-fleshed sweet potato (OSP) varieties and their displacement of white and yellow varieties in the diet of the people in the study area led to significant, important change in vitamin A intake in vulnerable groups:
…the net change in mean vitamin A intakes of the intervention groups relative to the control represented increases by 63, 169 and 42% among reference children, young children and women, respectively. These net increases were equivalent to approximately 74, 118 and 55% of the corresponding EAR for vitamin A(26) for the same groups, representing a substantial increase in dietary vitamin A.
The study also found that “estimated prevalences of inadequate vitamin A intakes by these groups commensurately decreased.” All of which is of course great. But the authors cannot be said to have found any change in the vitamin A status of people. That’s because this wasn’t measured. As the authors themselves admit:
…it is not possible to predict the impact of these increases in vitamin A intake on change in vitamin A status.
But they were not guessing wildly, of course:
One of the main reasons for not including vitamin A status indicators in the present study was that a similar but smaller-scale study in the same area serving as a precursor to the present one had already demonstrated a positive impact on children’s serum retinol concentrations following increased intake of vitamin A from OSP and other vitamin A sources.
So the argument is not entirely tied up, though it does seem pretty solid. Evaluation of nutritional and health impacts is hard.
Just a final word about diversity. Six OSP varieties were introduced and adopted, and as we’ve seen seem likely to be having a significant health impact. But are they also having an impact on the diversity of the local production systems? The authors suggest that they might: “OSP is an acceptable, local food source of vitamin A that can easily replace currently grown white or yellow sweet potato varieties.” And in fact it does seem they did:
OSP accounted for 47–60% of all sweet potatoes consumed in the … [study] groups across ages, indicating a moderately high degree of substitution for other varieties. In the control groups, 20–24% of all sweet potatoes consumed were OSP.
Again, paralleling the vitamin A story, this is replacement in the diet, not necessarily substitution in the fields. But it is an alarm bell nonetheless to a conservationist. Genesys shows a worrying situation for sweet potato conservation in Africa, though that’s because it does not yet pick up some very significant national and regional collections, including Mozambique’s own. Hopefully that will change. But as we’ve mentioned here before, it is important for such projects to survey the local diversity before they introduce their own new, no doubt “better” diversity, and make sure the local stuff is placed in genebanks, if it is not there already. I don’t know if that was done in this case. I hope so. Those “currently grown white or yellow sweet potato varieties” may not be much good for vitamin A intake this year in Mozambique, but they may well be very good for something else, next year, somewhere else. And maybe even in the very farms in which they have been replaced.