Diet quality

 Diet quality

A good diet is a varied, balanced and healthy diet, which covers energy intake and all the nutrients necessary for growth, health and an active life. A person needs a variety of foods to meet their nutrient needs. Stable isotopes can be used to assess the quality of a diet and its effect on vitamin A stores and nutritional status.

The quality of a diet is determined by the amount of nutrients provided by it and the absorption of certain nutrients from foods that support the maintenance of good health, growth, certain physiological states (e.g. pregnancy and breastfeeding), physical activity and infection protection. The quality of a diet also depends on the variety (diversity) of food groups consumed. In resource-limited settings, diets consist mainly of plant-based foods, which sometimes lack essential nutrients, such as protein, vitamin A, iron and zinc.

Inadequate intake of quality protein and micronutrients (especially zinc and iron) can lead to stunted growth, increased mortality and infections in infants and young children. In addition, such deficiencies affect children's ability to learn and therefore their productivity in adulthood. As economic conditions become more favorable, diets begin to include more animal products, fats and oils, sugars, and heavily processed foods. This is called the “nutrition transition”. This transition can have long-term health consequences, including increasing the risk of becoming overweight or obese, and the risk of later contracting non-communicable diseases.

The IAEA supports the use of stable isotope techniques in the assessment of diet quality and health effects. Its activities focus in particular on:

• absorption and storage of provitamin A, iron and zinc from fortified foods, biofortified foods (through the accumulation of more minerals and vitamins during plant growth) or of mixed diets. Stable isotope techniques are useful for evaluating food fortification programs or dietary diversification strategies;
• the bioavailability of proteins in foods of plant origin for the maintenance and optimization of protein quality in diets;
• body composition (fatty tissue and lean tissue) in relation to changes in diet quality. A poor diet (lacking in nutrients or providing too much fat and sugar) often causes fat to accumulate in the body, which can predispose people to obesity and, later, to non-communicable diseases;
• assessment of vitamin A status. Changes in body stores of vitamin A are an indicator of the effectiveness of interventions to prevent vitamin A deficiency.

Measurement of iron absorption

• A reference blood sample is taken from the subject, then the subject consumes a test meal (A), containing a known quantity of a stable iron isotope (57Fe).
• The following day, the subject ingests a test meal (B), comprising a known amount of a second stable iron isotope (58Fe) as well as an agent that can promote or inhibit iron absorption.
• Half of the people in the study consumed the test meals in reverse order.
• A second blood sample is taken two weeks later. After processing the blood samples, the iron isotopes are analyzed with an appropriate mass spectrometer.
• The levels of stable iron isotopes are analyzed before and after the consumption of the test meals in order to determine the quantity of iron that the meals will have made it possible to absorb and which will have been assimilated by the erythrocytes. It is thus possible to measure the effect of the agents promoting or inhibiting the assimilation of iron which were contained in the meals.

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