November 29th, 2016 / Claudia Canales, B4FA

This blog discusses the importance for health of iron in diets, and strategies for improving the nutritional status of target populations. Although not directly to do with plant genetics, it highlights many of the challenges facing plant scientists.

The common bean, Phaseolus vulgaris

Don’t spill your beans
The common bean, Phaseolus vulgaris, native to an area between central Mexico and Costa Rica and the Andean region of the American continent, is sometimes referred to as the “meat of the poor”. . Beans play an important role in providing essential vitamins and proteins to millions of people in Latin America and Africa, and in addition are also important for income generation for smallholder farmers. In the Great Lakes region of Central Africa, for example, one third of the cultivated land is dedicated to the production of beans, while per person consumption in Western Kenya and Rwanda can be as high as 66 kilograms a year, one of the highest in the world.

Beans are richer in iron, which is an essential nutrient, than wheat, maize and rice. About 70 per cent of the human body’s iron is in red blood cells in hemoglobin carrying oxygen from the lungs to all tissues, as well as in muscle cells in myoglobin. About 25 per cent is stored as ferritin in cells and 5 per cent is in proteins essential for respiration and energy metabolism while it is also needed for the body’s immune system to work properly. On average adult males have about 1,000 milligrams of stored iron whereas women have only about 300 milligrams.

People who rely mostly on a diet of beans and cereals, with no meat, often do not obtain enough iron. Its lack leads to anaemia and compromises the immune system, with significant consequences on health. According to the World Health Organization, the effects of iron deficiency are “stealthy but devastating, invisibly eroding the development potential of individuals, societies and national economies”.

While pregnant women and young children in resource-poor areas are most affected, anaemia is also widespread in developed countries. The numbers are astounding: 2 billon people, about 30 per cent of all people, are anaemic, and this makes iron deficiency not only the most common nutrient deficiency but also the most widespread human health condition globally, with about two thirds of all pre-school children and half of pregnant women in Africa affected. Iron deficiency is worsened by infectious diseases, such as HIV, tuberculosis and malaria as well as worm infections.

Most of the human requirement for iron is provided by plants that absorb it from the soil. Therefore, one obvious strategy to reduce the incidence of anaemia, in particular in resource-poor areas, is to increase either the concentration and/or the bioavailability of iron in key staple crops – a process is called biofortification. Beans show considerable natural genetic variation in iron concentrations that can be harnessed, and for the reasons outlined above, is a very good candidate.

Yet, while measuring the iron content of iron in crops is straightforward, determining how much of it will be taken up by the body is far from simple. The reason is that a proportion of the iron found in plants is not bioavailable, i.e. in a chemical form that cannot be absorbed by the small intestine. Phytate, the principal storage form of phosphorus in plants, has a strong binding affinity for iron and makes it unavailable to the body, while vitamin C has the opposite effect.

The availability of iron is also affected by food proteins. In animal foods (meat), but not in plants, iron is often attached to heme proteins, a small amount of meat in diets can significantly increase nonheme iron absorption – the “meat effect”– although the exact mechanisms by which this happens are not entirely clear. Supplementing vegetable-stew meals of Kenyan schoolchildren with meat, for example, increased the uptake of a number of micronutrients and vitamins and was also positively correlated with improved school performance. This of course does not mean that other, more varied and nutritious, vegetarian diets cannot provide sufficient iron.

The next blog will discuss some initiatives to develop iron-rich beans, and some of the challenges of these programmes.

Dr Claudia Canales Holzeis is a plant molecular biologist with a near-decade of experience in plant genetics research.  She previously worked as Senior Project Officer for the International Service for the Acquisition of Agri-Biotech Applications (ISAAA), based in the Philippines.  A graduate of the University of Reading in Environmental Biology, Dr.Canales gained a DPhil. in Plant Genetics at Oxford.