β-Carotene-rich orange sweet potato (OSP) has been shown to improve vitamin A status of infants and young children in controlled efficacy trials and in a small-scale effectiveness study with intensive exposure to project inputs. However, the potential of this important food crop to reduce the risk of vitamin A deficiency in deficient populations will depend on the ability to distribute OSP vines and promote its household production and consumption on a large scale. In rural Mozambique, we conducted a randomised, controlled effectiveness study of a large-scale intervention to promote household-level OSP production and consumption using integrated agricultural, demand creation/behaviour change and marketing components. The following two intervention models were compared: a low-intensity (1 year) and a high-intensity (nearly 3 years) training model. The primary nutrition outcomes were OSP and vitamin A intakes by children 6–35 months and 3–5·5 years of age, and women. The intervention resulted in significant net increases in OSP intakes (model 1: 46, 48 and 97 g/d) and vitamin A intakes (model 1: 263, 254 and 492 μg retinol activity equivalents/d) among the younger children, older children and women, respectively. OSP accounted for 47–60 % of all sweet potato consumed and, among reference children, provided 80 % of total vitamin A intakes. A similar magnitude of impact was observed for both models, suggesting that group-level trainings in nutrition and agriculture could be limited to the first project year without compromising impact. Introduction of OSP to rural, sweet potato-producing communities in Mozambique is an effective way to improve vitamin A intakes.

The role of zinc deficiency as an important cause of morbidity and impaired linear growth has prompted the need to identify indicators of population zinc status. Three indicators have been recommended – prevalence of zinc intakes below the estimated average requirement (EAR), percentage with low serum zinc concentrations, and percentage of children aged < 5 years who are stunted. This review outlines steps to estimate the prevalence of inadequate intakes, and confirm their validity based on the EARs set by International Zinc Nutrition Collaborative Group. Next, the appropriateness of serum zinc as a biochemical marker for population zinc status is confirmed by a summary of: (a) the response of serum zinc concentrations to zinc intakes; (b) usefulness of serum zinc concentrations to predict functional responses to zinc interventions; (c) relationship between initial serum zinc and change in serum zinc in response to interventions. Height- or length-for-age was chosen as the best functional outcome after considering the responses of growth, infectious diseases (diarrhoea, pneumonia), and developmental outcomes in zinc supplementation trials and correlation studies. The potential of other zinc biomarkers such as zinc concentrations in hair, cells, zinc-metalloenzymes, and zinc-binding proteins, such as metallothionein, is also discussed. Molecular techniques employing reverse transcriptase (RT)-polymerase chain reaction to measure mRNA in metallothionein and ZIP1 transporter hold promise, as do kinetic markers such as exchangeable zinc pools (EZP) and plasma zinc turnover rates. More research is needed to establish the validity, specificity, sensitivity, and feasibility of these new biomarkers, especially in community-settings.

Plant foods are the major staples of diets in developing countries, in which the consumption of animal-source foods is often low because of economic and/or religious concerns. However, such plant-based diets are often associated with micronutrient deficits, exacerbated in part by poor micronutrient bioavailability. Diet-related factors in plant foods that affect bioavailability include: the chemical form of the nutrient in food and/or nature of the food matrix; interactions between nutrients and other organic components (e.g. phytate, polyphenols, dietary fibre, oxalic acid, protein, fat, ascorbic acid); pretreatment of food as a result of processing and/or preparation practices. Consequently, household strategies that reduce the content or counteract the inhibiting effects of these factors on micronutrient bioavailability are urgently needed in developing-country settings. Examples of such strategies include: germination, microbial fermentation or soaking to reduce the phytate and polyphenol content of unrefined cereal porridges used for young child feeding; addition of ascorbic acid-containing fruits to enhance non-haem-Fe absorption; heating to destroy heat-labile anti-nutritional factors (e.g. goitrogens, thiaminases) or disrupt carotenoid–protein complexes. Such strategies have been employed in both experimental isotope-absorption and community-based studies. Increases in Fe, Zn and Ca absorption have been reported in adults fed dephytinized cereals compared with cereals containing their native phytate. In community-based studies in rural Malawi improvements in dietary quality and arm-muscle area and reductions in the incidence of anaemia and common infections in young children have been observed.

Both cereal staples and household diets can be manipulated to enhance the content of micronutrients and/or alter the levels of absorption modifiers to improve micronutrient bioavailability. Strategies described range from plant breeding, use of fertilizers and genetic engineering to changes in food preparation and processing methods at the household level involving soaking, fermentation and germination. The impact of five household strategies designed to enhance the content and bioavailability of iron, zinc and calcium in a representative daily menu for rural Malawian preschool children has been calculated using food composition data. In the five strategies, relishes based on small dried fish replaced plant-based relishes, maize-based porridges prepared with maize flour soaked to reduce its hexa (IP-6)- and penta (IP-5)-inositol phosphate content replaced conventional porridges; and a pumpkin-leaf relish replaced sweet potato to increase the retinol content of the daily menu. Comparison of the calculated energy, nutrient, and phytate content, and [phytate]:[zinc] molar ratios of the five modified menus compared with the unmodified menu emphasizes that to ensure that the estimated requirements for iron and zinc are met, the optimal strategy includes dried fish relish twice daily together with porridges prepared using soaked (or fermented) maize flour to reduce their hexa- and penta-inositol phosphate content. Implementation of these household strategies has the potential to increase the bioavailability of iron and zinc in rural Malawian diets from low to high.