In press: Journal of Trace Elements in Experimental Medicine 1999

Food-Based Approaches to the Prevention of Trace Element Deficiencies

 

G.F. Combs, Jr. a*, R.M. Welch b,c and J.M. Duxbury b

Division of Nutritional Sciences(a) and Department of Crop and Soil Sciences(b), Cornell University, Ithaca, NY, USA; and U.S. Plant, Soil and Nutrition Laboratory, USDA, Ithaca, NY, USA(c)

 

*Correspondence to:

Gerald F. Combs, Jr., Ph.D

Division of Nutritional Sciences

122 Savage Hall

Cornell University, Ithaca, NY 14853 USA

Fax: +607-255-2140

e-mail: gfc2@cornell.edu

Abstract

Deficiencies of micronutrients including trace elements (e.g., iron, iodine, zinc, selenium) now affect half of the world's population. Although global food production has increased impressively in recent decades, this so-called "green revolution" has chiefly involved cereal grains which are important sources of calories and protein, but tend to provide only minimal amounts of the micronutrients. Further sustained efforts are needed to meet the increasing food demands of the world’s expanding population; but these must also increase supplies of bioavailable micronutrients. Approaches for such an effort, a "Greener Revolution", in which sustainability is an explicit goal, are outlined.

Introduction

Although the world now appears to produce enough total food to meet its current energy and protein needs (1,2), deficiencies of micronutrients including trace elements affect nearly half of the world's population (3) (Table I). Due to inadequate diets, a third of the world's children fail to reach their physical and mental potentials and many are made vulnerable to infectious diseases that account for half of all child deaths (3-5). Nutritional deficiencies decrease worker productivity and increase the rates of disease and death in adults. Many of these problems involve diets that provide insufficient amounts of iodine, iron, zinc, selenium and calcium.

That trace element deficiencies persist should be a cause of great concern, in view of the efforts and resources that have gone into agricultural development over the past two decades. These have more than doubled rice and wheat yields, while cutting their costs of production by a third. Coming over a period of time when the world was adding a billion people, this so-called "green revolution" averted the mass starvation that seemed to loom ahead in the 1960's. But the view of the green revolution was that malnutrition stemmed chiefly from insufficient and unaffordable supplies of total food and the "macronutrients", energy and protein, concentrated on the staple cereals rice, wheat and maize. The result was the growth in poor countries of food supplies that provided more food without providing more micronutrients that were already in short supply.

To meet the enormous challenge of feeding a world that continues to add 90 million people each year, a "Greener Revolution" is needed - one that will harness the latent power of food systems to prevent deficiencies of trace elements and other micronutrients. To do this, a greener revolution would employ food-based approaches: increasing the diversity of cropping systems, particularly with respect to indigenous fruits and vegetables and to pulses; developing "trace element-efficient" cultivars of staple crops to effect "field-fortification" of foods; finding more effective means of using the iron- and zinc-containing cereal brans; developing appropriate technologies for preserving and storing foods; developing models for integrated farming systems that maximize the production of trace element-rich crops and/or small-scale, low-input, environmentally sustainable, livestock enterprises on limited land spaces.

Values for a Greener Revolution

A Greener Revolution will demand that human food and nutrition needs be better linked to systems of food production and acquisition. This will require going beyond the traditional programs and interventions that have been targeted either to increasing the production of staple foods or to correcting specific nutrient deficiency diseases. Those approaches have been sectoral, conceived along either agricultural or medical lines, which by nature tend to be narrowly focused with limited objectives. Sectoral approaches have limited abilities to deal with truly complex issues; this can be seen in the limited success of such programs in addressing trace element malnutrition; most have not proven sustainable in developing countries.

In designing further agricultural expansion, it must be remembered that past gains in agricultural production have not been without costs. The high-yielding green revolution varieties of cereals require infrastructure for irrigation and costly inputs in the form of fertilizers, fuel and pesticides to realize their high yield potentials. Evidence is mounting that these high-input technologies may not be sustainable: as practiced in resource-poor countries, they have decreased soil quality, reduced the diversity of crop production and contributed to environmental vitiation from the improper use of agricultural chemicals. A Greener Revolution must, therefore, have strategies to reverse these trends.

For these reasons a Greener Revolution must not be focused only on major staple crops but, rather, on entire cropping systems and their abilities to support balanced human nutrition in sustainable ways. This means going beyond the cereals, even though these crops will continue to be critical sources of food energy and protein. Cereals, however, provide only meager amounts of vitamins and essential trace elements, and their small amounts of these micronutrients are found mostly in the aleurone layer cells associated with the bran and germ, which are removed during milling. Therefore, cereal-based foods (e.g., wheat flour, polished rice) tend to be deficient in trace elements (6)(Table II). Deficient trace element yields of cropping systems can be overcome, however, by including pulses (grain legumes such as beans, peas, and lentils) and/or animal products along with vegetables and fruits all of which are richer in micronutrients (7) (Fig. I). A Geener Revolution must, therefore, emphasize the "re-diversification" of cropping systems. It must address the increasing need for total food and balanced nutrient output simultaneously, and it must do so in the context of environmental, economic and social sustainability. It must develop cropping systems that are optimized for the available physical resources of poor areas and that are sustainable in every sense of the word - Greener Revolution systems must be sustainable economically, but also environmentally and socially. Such systems must produce balanced nutrient output at least at region levels while striving to achieve as much balance as possible locally. This will require a new approach to agriculture - one that measures its success not only in bushels per acre yields or dollars per year, but also in terms of human health and overall sustainability.

Implementing a Greener Revolution

The core strategies for a Greener Revolution were laid out by an international expert consensus conference in 1995 (3). That report pointed out that, in general, these efforts will call for both biological and social science research to address several outstanding needs: better understandings of household decision-making related to food habits, agricultural practices, labor allocation and child care; simple, robust techniques for assessing the biological efficacies of trace elements from mixed diets; trace element contents of local foods in common database formats; creative new modalities by which the active participation of affected people (those operating within local food systems) can occur.

Eliminating trace element deficiencies will call for approaches that go beyond their diagnosis and description to deal seriously with their root causes. Such approaches must look broadly at food systems for the development of sustainable solutions. This can be achieved in several ways:

• Increasing the diversity of cropping systems, particularly with respect to indigenous fruits and vegetables and to pulses. This will call for the evaluation of available germ plasma and for the development of highly productive varieties that are rich in trace elements, are well suited to the local conditions, and offer such clear agronomic benefits to farmers as predictable yields and reduced perishability. Early maturing varieties of legumes are needed for inclusion in rotations of rice or rice-wheat cropping systems. Legumes can also returning nutrients to soils; such "green manures" offer the important benefit of reduced needs for chemical fertilizers.
• Developing "micronutrient-efficient" cultivars of staple crops. The techniques of molecular biology and plant breeding can be used to develop new high-yielding varieties with enhanced capacities to take up and retain trace elements from soils. That wheat cultivars have been identified that thrive on soils traditionally thought to be deficient in iron and zinc indicates that it should be possible to develop crops that are not limited by low soil mineral availabilities (8). Evidence indicates that such "field-fortified" crops not only have fewer needs for chemical fertilizers but also have richer contents of micronutrients in their edible tissues. This has been shown in the case of high-yielding varieties of rice containing twice the iron and zinc concentrations of varieties currently in the field (9). Importantly, the high grain iron trait seems to result in the deposition of the element in the endosperm where it is retained after polishing in a bioavailable form (9).
• Finding more effective means of using the iron- and zinc-containing cereal brans. Bran retention from wheat can be increased by producing higher extraction flours; but this will call for acceptance of coarser products by consumers. Promotion of unpolished rice will also call for finding ways to stabilize the highly unsaturated lipids contained in the bran fraction, perhaps by developing effective lipoxygenase inhibitors.
• Reducing phytates in staple grains. Low phytate (myo-inositol hexaphosphate) mutants have been isolated in maize and barley (10). It appears that the low-phytate trait has little effect on seed germination, plant growth or seed total phosphorus content; however, it reduces the phytate-bound phosphorus by at least half. Because the latter is not biologically available to humans or other monograstics, which lack intestinal phytases, low-phytate cultivars have increased amounts of bioavailable phosphorus (10). And, because phytate binds transition elements in biologically unavailable forms, the reduction of phytate in diets can be expected to increase the bioavailabilities of food iron, zinc and copper. While it is still not clear whether the low-phytate trait is actually free of all undesirable effects, no major ones have been identified and the trait has clear potential to improve trace element status in many populations if it can be incorporated widely into grain breeding programs.
• Development of heat-stable phytases. Recent applications of molecular techniques have produced recombinant phytases of at least moderate heat stability (11). Already it is clear that the use of phytase can significantly improve the utilization of plant phosphorus, iron and zinc in animals fed plant-based diets in which those nutrients are largely bound in or by phytates The incorporation of enhanced heat stability, which appears to relate to the glycosylation of the enzyme, will offer the prospect of phytase becoming useful in food processing and/or preparation to improve trace element bioavailabilities of human diets
• Developing simple, robust techniques for assessing the bioavailabilities of trace elements from foods in the context of the mixed diets in which they are consumed.
• Developing standardized food trace element composition data. The trace element compositions of most local foods have rarely been ascertained with the degree of accuracy necessary policy decisions. These data must be developed using standardized sampling and analytical methodologies, and they must be assembled into common database formats that can be used for diet formulation and analysis as well as for the evaluation of national food nutrient production.
• Developing models for integrated farming systems that maximize the production of trace element-rich crops and/or small-scale, low-input, environmentally sustainable, livestock enterprises on limited land spaces.

Conclusion

Sustainable solutions to the problems associated with deficiencies of trace elements and other micronutrients can be achieved. This will call for recognizing the critical roles of people as both participants and beneficiaries of their food systems, and actively involving local communities and households in both the development and implementation of solutions. For this, the "technology transfer" paradigm will not suffice. Instead, the Greener Revolution will need creative new modalities by which the active participation of affected people (those operating within local food systems) can occur. It will also require approaches that take comprehensive views of food production in both health and biophysical contexts. Accordingly, nutrition and health objectives must be incorporated into national agricultural plans; they must become targets of both agricultural interests and the health community. This will call for a new view of agriculture: as an enterprise inextricably linked to human health, with its output measured not merely in terms of quantity but also in terms of human health and welfare.

References

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2. United Nations Administrative Committee on Coordination-Subcommittee on Nutrition: Overview. In Second Report of the World Nutrition Situation, vol 1, Global and Regional Results. World Health Organization. Chapter 1, pp 4-16, 1992.
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Table I. The most prominent trace element-related problems of the developing world (5).

Problem	Trace element(s) problem involved*	People affected	Impacts
Low birth weight and stunting	Insufficient bioavailable Zn, Fe	35% of children 0-5 yrs	Impaired physical development; excess morbidity and mortality
Anemia	Insufficient bioavailable Fe	2.1 billion (including 42% of all women)	Lost work productivity; impaired Cognitive development; increased susceptibility to infections; excess morbidity; excess mortality during pregnancy and delivery
Goiter	Insufficient I and/or Se	200 million cases (1.6 billion at risk)	Lost work productivity; excess stillbirths, abortions and infant deaths
Cretinism	Insufficient I and/or Se	6 million births/yr	Severe neurological impairment
Cardiomyopathy	Insufficient Se	400 million at risk	Lost work productivity; excess morbidity and mortality

*Other deficiencies, notably those of energy, protein, calcium and at least some vitamins (e.g., vitamins A and C, riboflavin), also contribute to many of these and other less widespread problems of malnutrition.

Table II. Trace element contents (mg/kg, dry weight ) of whole cereal grains

and their milled fractions (6).