A systematic review of agricultural interventions that aim to improve nutritional status of children.
This report is a systematic review of the impact of potential 'win-win' agricultural interventions that aim to improve children's nutritional status by improving the incomes and the diet of the rural poor. Previous reviews on the same subject found mixed results or no impact of agricultural interventions on nutritional status. The differences in results across these reviews are the result of the different timeframes and methodologies adopted, and of the different types of agricultural interventions reviewed. We build on and expand previous reviews by covering the period 1990-2010 and we find results similar to those of previous reviews, but we attribute the lack of impact of agricultural interventions on child nutrition to methodological weaknesses of the studies reviewed rather than to specific characteristics of these interventions.
The review is based on a systematic search of the published and unpublished literature. The search was broken down by interventions of the following types: bio-fortification interventions; home gardens; aquaculture and small fisheries; dairy development and animal source food promotion. During the search we found more than 7,000 studies, but only 23 qualified for final inclusion based on the exclusion criteria set.
We outlined a programme theory of the interventions and we assessed the efficacy of the interventions on five outcome indicators: programme participation; income; diet composition; micronutrients intake and children’s nutritional status. Of all the studies we reviewed, 23 met our criteria for establishing a credible counterfactual. We found little information on participation rates and characteristics of programme participants. We found that the agricultural interventions considered have a positive impact on the production of agricultural goods promoted by the interventions, but poor evidence of impact on total households’ income. We found only one study that tested for impact on total household income. This study found a positive effect of the intervention.
We found that the interventions were successful in promoting consumption of specific foods but very little evidence was available on changes in the diet of the poor. We found no evidence of impact on the absorption of iron and some evidence of the impact on absorption of vitamin A. Nineteen studies attempted to assess the impact of the interventions on diet composition. Two of these studies undertook no statistical test on diet change, four found no statistically significant impact and 13 found a significant and positive impact on the consumption of food targeted by the intervention. None of the studies assessed whether the interventions improved the quality of the whole diet. Five studies undertook tests for impacts on iron intake. Four tests showed no statistically significant difference at the 5% level and one showed a positive impact at the 5% level. Nine studies tested for programme impact on vitamin A intake, but only four reported data to be able to verify whether there was indeed an impact. The summary effect, assessed by meta-analysis, of these four studies reveals a positive difference in vitamin A intake between project and control groups.
We found no evidence of impact on prevalence rates of stunting, wasting and underweight among children under five. Eight studies examined the impact on children nutritional status. Of these, only one found a positive and significant impact on stunting prevalence, three found a positive and significant impact on underweight and two found a positive and significant impact on wasting. Five of the eight studies showed no impact on any of the three indicators.
We performed ex-post calculations of the statistical power of the selected studies in detecting differences in nutritional status between the programme and the control groups. We found that none of the studies reviewed would have been able to detect a ‘small’ impact on prevalence rates of malnutrition; few would have detected a ‘medium’ impact; and only 50% of the studies would have detected a ‘large impact’. Based on this analysis, we concluded that the absence of any reported statistically significant impact of agricultural interventions on children nutritional status found by this review, as well as by other reviews that preceded this one, should not be attributed to the inefficacy of these interventions. Rather it is the lack of power of the studies reviewed that could have prevented the identification of such impact, if any.
We also conducted a validity assessment of the methodologies adopted by the studies reviewed. Few studies performed a rigorous counterfactual analysis of the impact of the interventions. Most studies neglected the analysis of the characteristics of programme participants. Sample sizes were often inadequate and power calculations for determining sample size were rarely performed or presented. Most studies were based on good conceptual framework and analysed intermediate outcomes, but often relied on inappropriate outcome indicators. Finally, all studies neglected the analysis of heterogeneity of impact and were unable to extrapolate results outside the area of interventions considered.
We also conducted a separate assessment of the existing evidence on the impact of bio-fortification interventions. We built a programme theory of these interventions and reviewed the existing evidence along five intermediate outcomes: successful plant breeding; farmers’ response; consumers’ response; bioavalability and nutritional status. We found that consumers’ acceptance of bio-foritified staple food is good and that micronutrients in staple food are successfully absorbed by the body. Seven of the studies reviewed found that consumers are willing to pay a premium for food with higher micronutrient contents and only one study found that a discount was needed for consumers to accept bio-fortified staple food. We found little evidence of farmers’ acceptance of bio-fortified crops, with only one study reporting farmers’ adoption rates. We found little evidence of any impact of these interventions on nutritional status. Only find two studies assessed the impact of bio-fortification interventions on nutritional status and found a positive impact.
NB. Full report, subject to copychecking and publication edits. Final formatted report to follow shortly.
Masset, E.; Haddad, L.; Cornelius, A.; Isaza-Castro, J. A systematic review of agricultural interventions that aim to improve nutritional status of children. EPPI-Centre, Social Science Research Unit, Institute of Education, University of London, London, UK (2011) 65 pp. ISBN 978-1-907345-09-8