Harvesting nutrition: Grain legumes and nutritious diets in sub-Saharan Africa

Ilse de Jager

Research output: Thesisinternal PhD, WU


Low quality diets is the number one risk factor for the global burden of disease. Agriculture is one of the sectors with strong potential to enhance the quality of diets; especially among rural populations in low and middle income countries where malnutrition levels are highest and agriculture is often still the most important source of food and income. In sub-Saharan Africa the availability of nutrient-dense foods such as legumes, dairy, meat, fruits, nuts and seeds has declined while the availability of grains less-dense in protein and micronutrients has increased. The protein and micronutrient intake from sub-Saharan African diets is often estimated to be inadequate. Grain legumes are appreciated for their contribution to dietary protein and micronutrient intake in addition to their benefits in replenishing soil fertility. This thesis describes the research conducted to investigate the potential of grain legume cultivation for nutritious diets of smallholder farming households in sub-Saharan Africa. The research was conducted both at crop level (Chapters 2 and 3) and at whole diet level (Chapters 4 and 5). 

The current and potential role of grain legumes on protein, both quantity and quality, and micronutrient adequacy in the diet of rural Ghanaian infants and young children was studied (Chapter 2). Energy and nutrient (including amino acids) intakes of breastfed children of 6-8 months (n=97), 9-11 months (n=97), 12-23 months (n=114), and non-breastfed children of 12-23 months (n=29) were assessed using a repeated quantitative multi-pass 24-hour recall method. Food-based dietary guidelines that best cover nutrient adequacy within the constraints of the local current dietary patterns were modelled using the linear programming software Optifood (version 4.0.9, Optifood©). 60% of the children consumed legumes with an average portion size of 20 g per day contributing more than 10% of their total protein, folate, iron and niacin intake. The final food-based dietary guidelines included legumes and provided adequate protein and essential amino acids. Adding extra legumes to the food-based dietary guidelines, on top of the current dietary pattern, improved adequacy of calcium, iron, niacin and zinc but not reached sufficient amounts to meet requirements. Although legumes are often said to be the ‘meat of the poor’ and the current grain legume consumption among rural children does contribute to their protein intakes, the main nutritional benefit of increased legume consumption is improvement of micronutrient adequacy.

Within the framework of a large agricultural legume cultivation project (N2Africa), we studied (Chapter 3) the potential to improve children’s dietary diversity by comparing  N2Africa and non-N2Africa households in a cross-sectional quasi-experimental design, followed by structural equation modelling and focus group discussions in rural Ghana and Kenya. Participating in N2Africa was not associated with improved dietary diversity of children. However, for soybean in Kenya, structural equation modelling (combining data from N2Africa and non-N2Africa households) indicated that via production for own consumption the dietary diversity of children can be improved, but indicated no effect via income and food purchases and no effect for both pathways in Ghana. Results are possibly related to differences in the food environment between the two countries as was found in the focus group discussions. These findings confirm the importance of the food environment for translation of enhanced crop production into improved human nutrition. This study also showed that in a situation where rigorous study designs cannot be implemented, structural equation modelling is a useful option to analyse whether agriculture projects have the potential to improve nutrition and focus group discussions can provide valuable additional explanatory qualitative information.

For a high quality diet, legumes need to be consumed in combination with other foods from different food groups. Therefore in Chapters 4 and 5, a systems approach was used studying the potential of legumes as well as all other foods cultivated to cover the food needs of households based on the food-based dietary guidelines developed for this thesis. In Chapter 4, the current situation was examined among 329 rural Ghanaian households. The food production of about 60% of the households did not cover their required quantities of grains and legumes and none covered their required quantities of vegetables. At nutrient level, the food production of over half the households supplied insufficient calcium (75.7%), vitamin A (100%), vitamin B12 (100%) and vitamin C (77.5%) to cover their requirements. The diversity of the production of a household was positively related with their food and nutrient coverage, but not with children’s dietary diversity and nutrient adequacy. These findings suggest that the promotion of FBDGs alone is insufficient to lead to improvements in diets. Additional strategies are needed to increase the food availability and accessibility of the households, especially that of fruits and vegetables and also of grain legumes.

In Chapter 5, we used a farm-level systems approach to investigated the minimum farm size needed, the optimal crop combination to grow and the potential contribution of mainstream agricultural interventions to provide a nutritious diet and additional income in all seasons of the year for an average rural household in Northern Ghana. Linear programming was applied to model different scenarios and interventions. The food-based dietary guidelines developed for this thesis were used as well as data from other secondary sources for information on seasonal yields, waste factors, crop availability, crop land use and prices for all crops produced in Northern Ghana. Results indicate that 75% of the household had sufficient farm size (>1.43 ha) to produce their food needs for a nutritious diet. Agricultural interventions increasing the yields of grains and legumes decrease the farm size needed to about 1 ha (17% of households reported a farm size <1 ha). The vegetable and fruit needs cannot be covered by the food produced in the farm during the ‘hunger season’ unless irrigation is applied. Households need to produce a diversity of foods to cover their food needs from own production. When household do not  produce their own food needs, but need income from agriculture to purchase food, our analysis suggests that cultivating one or two of the most lucrative crops (onions and sweet potato), will result in the highest farm income. However, specialization also comes with increased risks, especially for small rural farming households. Using a farm-level system approach provided three major insights. First, considering seasonality is crucial in nutrition-sensitive farming. Ensuring a year-round nutritious diet requires enhanced availability of vegetables and fruits in the hunger season. Second, although staple crops are not nutrient-dense such as vegetables and fruits, increasing their yields may contribute to enhancing diets. It will decrease the farm size needed which enables households to produce sufficient to cover their food needs for a nutritious diet. Third, our approach confirms that smaller farms are unable to produce sufficient food to cover their needs and will depend on their income, both from agriculture and other sources, and the availability of foods on markets to meet their dietary needs.

Overall the results of this thesis show that the main contribution of grain legumes to nutritious diets is in terms of micronutrients intake and not protein intake. Whether a grain legumes cultivation project, such as N2Africa, will result in dietary improvements depends on the characteristics of the food environment, as well as whether a nutrition goal is set and activities such as nutrition behaviour change communication and women’s empowerment are included. This thesis also shows that a mixed method design including pathway analysis is a good approach to study nutrition impact of agriculture interventions when RCTs are not possible. Finally, the thesis results show that investigating the gaps in food availability and food needs using a systems approach at farm level provides useful insights to be able to better coordinate and integrate nutrition across agricultural interventions and investments. For future agriculture and nutrition research: specialists from both disciplines should be involved from the start and be able to think outside of their discipline; a shift from research at crop level to whole diet level research is needed using a systems approach; economic and market knowledge are necessary; and testing the practical feasibility of research findings need to be planned and incorporated from the beginning. Let’s harvest nutrition!

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • Giller, Ken, Promotor
  • Brouwer, Inge, Co-promotor
Award date18 Jun 2019
Place of PublicationWageningen
Print ISBNs9789463439350
Publication statusPublished - 18 Jun 2019


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