Growing needs

Edward Joy
March 27, 2013

The question of how to feed a future world of 9 billion people is often pondered. Supplying the energy needs of such a massive population will be challenging enough. An even greater task will be meeting all of its micronutrient (vitamin and mineral) needs - and ensuring equitable and sustainable access.

Humans require at least 22 different minerals for healthy living. Examples include calcium for bone formation, iron for oxygen binding in haemoglobin and zinc for DNA and RNA synthesis. Inadequate intake or absorption of these minerals is a major cause of disease burden around the world.

Buying ants in Mzuzu market, northern Malawi

In few countries is the challenge of meeting micronutrient needs greater than in Malawi. A small, landlocked country in Southern Africa, Malawi’s population of 16 million is likely to reach 45 million by 2050. The country has suffered famine in recent times, and there is increasing evidence that micronutrient malnutrition is widespread and chronic.

Farming is the main livelihood activity for most Malawians. Even when you meet an urban professional, whether a taxi driver, teacher, civil servant or lawyer, they can tell you about their plot at home. Most grow maize, often rotated with a legume such as groundnuts, and intercropped with beans and pumpkins.

A number of wild indigenous vegetables and fruits are collected and eaten, such as bonongwe (Amaranthus spinosus) and chisoso (Bidens pilosa). Highly nutritious (and tasty) flying ants are also collected at this time of year (March); these are best served roasted and salted. Tropical fruits such as mangoes, guavas, bananas and avocadoes are widely grown, with availability highest in the rainy season.

With the variety of fresh fruits and vegetables available in farmers’ fields and in the markets, it’s not immediately clear why micronutrient malnutrition is so prevalent. But we are gaining a better understanding through analysis of locally-collected food composition data and dietary surveys.

Usipa market stall                     

In a recently-published, ESPA funded paper, we show that selenium deficiency is likely to be widespread in Malawi. Most Malawian soils are highly acidic and high in iron oxides, meaning that selenium is held in a form unavailable to plant roots. Whether it’s maize, leafy vegetables or fruits, products from these soils will have a low selenium concentration, relative to those grown on more alkaline soils.

Dietary composition data and serum samples show that women living in areas with acidic soils are consuming selenium well-below required intakes, whilst women from areas with alkaline soils, such as in the Shire Valley, are generally consuming adequate amounts.

We also estimate that calcium deficiency is a widespread problem, partly because calcium concentration in maize grain is low due to plant physiological constraints - calcium is not readily transported from leaves to grains, and the average Malawian diet is grain-based. Moreover, every day an adult male would need to eat close to the unlikely amount of 1 kg of calcium-rich leaves, such as pumpkin, in order to meet their requirements.

In Western diets, the majority of calcium comes from animal products, including meat and dairy sources. Animal products in Malawi are expensive compared to household income and consumption is low. However, fish caught in Lake Malawi are commonly consumed, in particular usipa (Engraulicypris sardella). Usipa is dried at the lakeshore and can be transported inland and stored for weeks, where it is subsequently eaten whole (including bones) as a relish.

Living in northern Malawi, I now view usipa as an essential part of my diet: an efficiently-packaged source of calcium, selenium and other minerals. Disseminating information about mineral requirements and food concentrations will allow people to make informed decisions regarding their diets. This will also apply for other micronutrients such as vitamin A and iron. Households on most of Malawi’s soils will need either to import selenium rich foods such as usipa, or apply selenium-enriched fertiliser to their crops. The lack of health infrastructure and prohibitive costs make a supplement scheme unrealistic.

For some nutrients, breeding crops high in mineral concentration or low in anti-nutrients (particularly phytate in grains), holds promise. Malawians can also adapt their crop choices. The staple crop, maize, is low in most micronutrients, especially after processing stages such as de-germing. Households might also improve their nutrition by growing millet, which used to be the staple prior to the introduction of maize in the 20th century: millet is generally more nutritious, particularly as a source of calcium. A more diverse food supply will provide a more diverse dietary intake of micronutrients.

Research is helping us to understand the nutritional problems in Malawi and, although major data gaps remain, the benefits of investing in nutrition for agriculture are becoming clearer.  Research is also helping us to develop solutions, further adapting our environment to meet our growing needs.

Edward Joy’s PhD research is funded by the University of Nottingham and the British Geological Survey, and carried out with assistance from the Ministry of Agriculture and Food Security, Malawi. The funding for this research was made possible by this initial ESPA Partnership and Project Development grant to Dr Martin Broadley.