The Bellagio Declaration [3] on the nutrition transition in the developing world stressed on the need for initiatives that provide technical support in the programme evaluation and cost effective assessments of existing and new programs and interventions to control malnutrition at national and regional levels.

TABLE 2
Leading 10 selected risk factors as percentage causes
of Disease burden measured in DALYs in low
mortality countries (e.g. Latin America countries)

However, to be successful in the development and implementation of sustainable nutrition programs, a combination of relevant scientific knowledge and practical approaches are required to assure a reasonable level of success. Reviewing and evaluating nutrition intervention thus need reliable and cost effective tools. These allow the policy makers to adopt sound sustainable strategies.

The global nutrition community recognizes the usefulness of nuclear and isotopic techniques and especially stable isotopes for accurate measurements in key areas of human nutrition and health: assessment of nutritional status, nutrient uptake and bioavailability, nutrients requirements, micronutrient malnutrition, food analysis, etc. [4].

The objectives of this review are to highlight the role of isotopic techniques in nutritional studies in general and to review the role of the International Atomic Energy Agency in supporting nutrition interventions in Latin America in particular.

Nuclear and isotopic techniques applied to human nutrition: A brief overview
Stable isotopes do not emit radiation and hence can be safely utilized in human studies and are particularly useful in human nutrition. There are two forms of isotopic tracers: radioactive and stable.

Radioactive isotopes can be detected via radiation they emit. They have many important applications, such as measurements of body composition, uptake and bioavailability of nutrients and with ¹⁴C-urea breath test to examine bacterial colonization by Helicobacter pylori. However, the risk of radiation related health effects overtime has dampened the use of radiotracers in human subjects.

Stable isotopes on the other hand are invaluable since there are virtually no health risks associated with their use. Therefore they are preferred for work in humans, especially in infants, children and pregnant women. Many naturally occurring elements exist as a mixture of two or more stable non-radioactive isotopic forms. There are the heavy stable isotopes (e.g. ⁵⁴Fe, ⁵⁶Fe, ⁵⁷Fe, ⁵⁸Fe, ⁶⁴Zn, ⁶⁶Zn, ⁶⁸Zn, ⁷⁰Zn) and light stable isotopes (e.g. ¹H, ²H, ¹³C, ¹²C, ¹⁵N, ¹⁴N, ¹⁶O, ¹⁷O, ¹⁸O).

The main advantages and disadvantages of these two forms of isotopic tracers are summarized in Table 3.

TABLE 3
Advantages and disadvantages radioactive and stable isotopes

Some examples of the application of stable isotope applications in human nutritional studies are as follow:

Estimation of total energy expenditure
Energy expenditure data can be used to strengthen the base for public health policy. The doubly labeled water (DLW) method determines the caloric expenditure of people in their normal environment. It is accurate and can be applied under field conditions. After administration of a sample dose of double-labeled water 2H₂ ¹⁸O both isotopes equilibrate with total body water and are eliminated differentially in body fluids over a period of days. Deuterium (²H) leaves the body as water and ¹⁸O leaves it as water and CO₂. Thus, the difference rate of loss of the two isotopes ²H and ¹⁸O is used to calculate CO₂ production of the subject, which is in turn, is used to calculate energy expenditure (6).

Estimation of lean body mass (body composition)
There is a growing consensus among global nutrition experts that evaluating body composition in children and adults will help in designing strategies to improve national health profiles, which is an important step in targeting health and nutrition intervention. A trace dose of water labeled with ²H or ¹⁸O is administrated and allowed to equilibrate for 4-6 hours. Isotope enrichment in urine or saliva samples is measured to calculate body water volume. Total body water is used to quantify fat-free mass. Body composition is calculated from measured body water and the hydration coefficient of fat-free mass. The amount of fat (adipose) tissue is calculated as the difference between total body weight and lean body mass [7]. Exact measurements of lean mass and fat mass are very useful to assess under nutrition and obesity in populations at risk. In addition, lean body mass can be considered a valuable indicator to monitor body wasting in HIV/AIDS patient, which shows a decrease in lean body mass. An increased in energy expenditure also is seen when compared to HIV negative subjects (8).

Measurement of breast milk intake
Measurement of breast milk intake is fundamental for infant nutrition in developing countries since it is well known that early introduction of weaning foods is an important cause of child malnutrition. The isotope dilution method does not interfere with feeding behavior and is therefore suitable for nutritional studies in developing countries. The mother given dose of ²H or ¹⁸O labeled water, which mixes with the body water pool and is transferred to the baby via breast milk. By collecting samples of the mother's saliva or milk and the baby's saliva or urine, the breast milk intake of the baby can be calculated (9).

Trace element bioavailability
The uptake and metabolism of labeled micronutrients can be traced in vivo. In fact, stable isotopes provide the most acceptable way of measuring the uptake and bioavailability of trace elements in humans (10).

Analysis of food
Neutron activation analysis (NAA) is a highly sensitive method for the accurate determination of up to 60 elemental concentrations in material. Sensitivities are sufficient to measure certain elements at the nanogram level and below. The NAA method is based on the detection and measurement of characteristic gamma rays emitted from radioactive isotopes produced in the sample upon irradiation with neutrons. The technique requires only small amounts of sample material - 100 to 200 milligrams and it is also not necessary to do any sample preparation other than size reduction and (in some cases) drying, making the technique non-destructive. Application of NAA-related methods is particularly attractive for developing countries since many research reactors are available to provide the needed neutron source [11]. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) also offers multi-element determinations.

Osteoporosis
Measuring bone mass is essential to diagnosing and managing osteoporosis and related issues of bone metabolism. DEXA (Dual Energy X-ray Absorptiometry) is now the standard technique for measuring bone mass density. Low energy X-rays are passed through the bones to measure the mineral particularly calcium content of the bones. The precision of DEXA is very high and the data can be standardized for age, weight, height and ethnic status (12).

Detection of infection
The use of the stable isotope in 13C-urea breath test, instead of ¹⁴C-urea, has recently been applied to detect Helicobacter pylori infection in humans. Breath is collected for a base value before a ¹³C labeled urea is administered. The enzyme urease of H. pylori breaks down the urea into ammonium and labeled bicarbonate. The latter compound will be metabolized by the person into carbon dioxide and expired. After 20-30 minutes a second breath sample is collected and measured for ¹³C (13).

The role of the IAEA in supporting nutritional studies using nuclear and related techniques
The International Atomic Energy Agency (IAEA), as an independent intergovernmental, science and technology-based organization in the United Nations family, provides assistance in the use of nuclear science and technology for peaceful applications and facilitates the transfer of nuclear technology and knowledge in a sustainable manner to its Member States. One of its programmes focuses on human health, specifically for the use of isotopes or nuclear related techniques to evaluate human nutritional status and the nutritional quality of foods. Through this programme, the IAEA offers technical support via coordinated research projects (CRPs) and technical cooperation projects (TCP) (14) to evaluate the efficacy of fortified food supplementation initiatives and other interventions aimed at fighting many forms of malnutrition. It is a partner in addressing nutrition and health problems in more than 50 countries in collaboration with Member States, other United Nations organizations and donors.

Coordinated Research Projects (CRPs)
A Coordinated Research Project (CRP) is a mechanism by which group of countries are brought together to work on a well-defined research topic for an average duration of 3 years. Modest annual funding is made available to developing countries mainly for sample collection and analysis. As a crucial part of a CRP, collaboration between scientists from developing and developed countries is stimulated and exchanges of information are encouraged through participation at the research coordination meetings (RCM) funded by the IAEA.

Recently, the T-CRP (Thematic CRP or Doctorate CRP) a new type of CRP has been introduced that is dedicated to the support of PhD students. This increases the scope of a normal CRP for capacity building in developing countries. Pairs of countries (developed and developing countries) are stimulated to work together. The program promotes postgraduate training in the student's country of origin and supports the possibility of short training in a developed country. The T-CRP has a longer duration up to 4-5 years, and has an increased level of funding through traditional CRPs.

The Technical Cooperation Programme (TCP)
The Technical Cooperation Programme (TCP) support socio-economic goals to Member States based on their respective national development priorities and relevant nuclear applications. It promotes the transfer of known technology that has been used in the Agency and addresses priority problems identified by Member States and ensure its support through the TC programme is strategically planned for maximal impact generation. Unlike CRPs that focus on research for development of tools and techniques, the TCP covers projects relevant to proven nuclear techniques that are ready for practical applications and can contribute to the solutions of field or development problems.

The TCP responds to project requests received from Members States by applying of appropriate criteria for project formulation and appraisal according to the TC strategy and Management Principles and by securing formal approval by the IAEA Board of Governors. These criteria include strong government support and patronage priority areas for national development. Requests must be linked directly to end-users, which in the case of nutrition projects are usually public health institutes that can implement recommendations that result from funded projects and use project results to modify interventions as needed. The TCP comprises of national, regional or inter-regional technical cooperation projects that are implemented for 2 to 4 years by one or more institutes in a country or various countries in a region.

As sources of technical co-operation, in kind contributions towards manpower development via training, fellowships, expert missions or scientific visits and equipment are provided to recipient Member States. Existing facilities relevant to the achievement of funded projects' objectives are supplemented with an end of sustaining the capabilities of Member States after project completion.

IAEA-supported nutrition studies in Latin America
Participation of the Latin America countries in the regular budget programme (CRPs)
Since early 1980's, Latin America countries have been involved actively in almost all IAEA's CRPs (Table 4). These have included studies on trace elements, amino acid and protein metabolism, osteoporosis, vitamin A, growth monitoring, osteoporosis and H. Pylori infection. Brazil, Jamaica, Mexico, Uruguay, Chile, Guatemala, Peru, Argentina and Venezuela have been among the participating countries.

The main outcomes of these CRPs and of the Latin America projects are described in the Nutrition and Health Related Environmental Studies (NAHRES) reports as indicated in (Table 5). In the last 20 years the total amount of the Agency' support to CRPs is about US$ 2.6 million, of which US$ 600,000 has been allocated to researches in Latin America countries.

Participation of Latin America countries in the Technical Cooperation Programme (TCP)
In the late 90s, the IAEA began its involvement in the evaluation of nutritional intervention programmes through the application of stable isotopes, primarily through initiatives of Member States with the support for national Technical Co-operation projects. By the decades end, Peru and Chile implemented and completed national TC Project in 1994 and 1997, respectively (Table 6).

TABLE 4
CRP list of IAEA Nutrition Studies during 1983 - 2004

TABLE 5
CRP list of IAEA Nutrition Studies during 1983 - 2004

The IAEA recognized the value of regional co-operation in facilitating transfer of know-how and capabilities, as well as integration of valuable results that provide regional if not global perspectives in dealing with common issues related to nutrition in some Latin America countries. Subsequently, some Latin American countries have become more involved in regional TC projects (Table 7). Through this realisation, a three-year regional Technical Co-operation project was initiated in 1999 on "Using Isotopes to Evaluate Nutrition Intervention Programmes (RLA/7/008)". This initially involved Argentina, Chile, Cuba, Brazil and Mexico but was completed in the latter four countries.

The regional nutrition project supported the evaluation of the effectiveness of some large nutrition supplementation programmes in place by the Latin America governments. These programs amounted US$ 300 million in Chile, US $ 2 billion per year in Mexico, US $ 56 million in Brazil and US$ 80 million per year in Cuba. These programs benefit millions of children and adults in those countries. The IAEA funded the application of isotopes activities through the Technical Co-operation Hard Core fund that subsequently was complemented by the U.S. extra-budgetary fund.

TABLE 6
List of IAEA supported National TC Projects on Nutrition Studies during 1994-2003

Implementation strategies
Investigations and measurements in the TC projects were carried-out on specific study areas. In keeping with the principle of Technical Cooperation in Developing Countries (TCDC) that recognizes diverse capabilities within regions, measurements of isotopes were made when possible in one of the participating institutes, e.g. in Chile when need laboratory capabilities are not available in another participating country. Each participating institute is expected to provide scientific, service or data to the other project participants. A Principal Co-coordinating Counterpart with expertise that is recognized globally provides advisory assistance that ensures adequate co-ordination of national and regional activities, and the integration of results in respective national plans and policy-making efforts. Scientific guidance provided through the implementation of national activities ensures moving towards the attainment of the objectives of regional initiatives.

TABLE 7
List of IAEA supported Regional TC Projects on Nutrition Studies during 1994-2003

The TC regional projects in Latin America likewise have supported the regional co-ordination of activities that result in the exchange of scientific results and assess progress and future directions. Transfer of know-how has been facilitated through workshops and training courses conducted for young scientists from each participating country.

Main outcomes from the regional project on nutrition in Latin America RLA/7/008
Prior to the regional project on nutrition (RLA/7/008), worldwide data on energy expenditures were based on surveys in developed countries. No data existed from Latin America to provide a scientific basis to formulate food programmes suited to local conditions. A comparison of recently obtained project data indicates that existing references values overestimate energy needs of children below 7 years old [14]. Results from the Cuban study designed to evaluate the Cuban nutrition program's capacity to cover the energy requirements of children were obtained by applying the doubly labeled water technique. This study concluded that the energy requirement of well-nourished children is 8.6% lower than the 1985 FAO/WHO/UNU recommendations.

Through the initiatives under the regional project, Chile carried out a national effort to investigate energy balance, physical activity pattern, dietary intake and body composition in preschool children. As a result, the Chilean government recognized the necessity to reduce the energy intake of children to prevent obesity, an increasing problem in countries considered to be in "nutrition transition" (15). Scientific papers were published and presented during the International Congress on Nutrition (16).

In addition, other specific results also had other significant impacts on national programmes. Policies related to food fortified with iron and zinc in pre-school food programmes of the National Supplementary Feeding Programme (coverage of ~1.3 million) of Chile were modified based on this projects scientific results. As a result, anemia has been reduced from 28.8% to less than 8% within a year in a sample of 300 children after the program increase its foods fortified with use of iron and zinc. This generates impact on the enhancement of educational performance and decrease infections among children.

In Mexico the Social Security System in recognition of the importance of isotopic studies to their nutrition programme purchased two mass spectrometers to sustain the assessment of the effect of food supplementation to pregnant and lactating mothers and to monitor the effect of iron and zinc fortification.

In Brazil, US $40,000 equivalent was allocated by the government for the first large-scale epidemiological study employing isotopes to measure the body composition of 200 under-nourished children after 6 months of participation in a specific intervention.

The results of investigations of energy expenditure of young children in Cuba and Chile based on doubly labeled water [14,15] were used for the first time by the FAO/WHO/UNU expert committee convened in 2001 to establish new energy recommendations. The IAEA has the opportunity to partner with other UN agencies in promoting isotope based research relevant to energy and protein requirements, mainly in developing countries.

Financial resources in support of NAHRES nutritional projects
In the last 20 years, the IAEA invested about US $2.6 million for research activities through CRPs. Over 20% of the financing was allocated for Latin American countries. In the ten-year period, regional and national TC projects amounted to over US$ 7.6 million, more than double of what was invested in research in the previous 20 years. About 40% of this total amount was invested in TC projects supporting the use of isotopic techniques in nutrition research programmes in Latin American countries, and enhancing capabilities and laboratory facilities relevant to those studies. It is notable that Latin American countries are more active in TC projects than in work through the CRPs. This reflects the region's interest in applications of techniques that can yield information relevant to existing socio-development programmes.


CONCLUSION
Since the 90s Latin America countries have developed and planned designed to meet nutritional priorities in each country. However, the rate of progress of nutrition programs effectiveness remains slow in many Latin America countries. To reach millennium goals, countries must build cost effective by strategies using accurate tools for evaluation and monitoring.

It is clear that through their participation to the IAEA program in nutrition, Latin America countries have recognized the significance of nuclear and stable isotopic techniques to help secure accurate assessments of nutritional status of population and the effectiveness nutrition interventions in improving health. Indeed, some countries such as Chile, Mexico and Cuba focused nutrition intervention programmes according to local population needs that were informed by results enabled by isotopic investigations.

Although Latin America countries are represented in all the IAEA nutrition activities (CRPs and TC projects), some countries in the region have yet to incorporate isotopic techniques in tackling nutritional issues.

In addition, good technical capabilities and scientific infrastructures are now available in some countries in the region e.g. Chile and Mexico. These can be used as regional expertise centers and serve to build capacities in the region.


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