Diet quality

Diet quality refers to both the amount of nutrients and the uptake of specific nutrients from foods to support body maintenance, growth, physiological status (for instance pregnancy and lactation), physical activity and protection against infection. Diet quality is also reflected in the variety (diversity) of food groups consumed. In resource-constrained settings, diets are majorly composed of plant-based foodstuffs which may be deficient in key nutrients such as proteins, vitamin A, iron and zinc.

Inadequate intake of high quality protein and micronutrients (especially zinc and iron) is associated with growth retardation, mortality and infections in infants and young children, reduced capacity for learning in children, and hence productivity in adults. Under improved economic conditions, diets change to include more animal food products, fats and oils, sugars and ultra-processed foods. This is called nutrition transition and can have longer-term health consequences, such as increasing the risk of becoming overweight or obese and developing non-communicable diseases later in life.

The IAEA supports the application of stable isotope techniques to assess diet quality and its impact on health with specific focus on:

• Absorption and retention of provitamin A, iron and zinc from fortified foods, or biofortified foods (accumulation of higher levels of minerals and vitamins during plant growth), or mixed diets. Stable isotope techniques are useful for the evaluation of food fortification programmes or dietary diversification strategies.
• Protein bioavailability from plant foods to maintain and optimize the protein quality in the diet.
• Body composition (fat and lean tissue) associated with changes in diet quality. Poor quality diet (deficient in nutrients or with elevated fat and sugar content) is more likely to promote body fat accumulation, which in turn may pre-dispose individuals to obesity and later risk of non-communicable diseases.
• Assessing vitamin A status. Changes in Vitamin A body stores reveal the success of interventions aimed at preventing vitamin A deficiency.

• A baseline blood sample is collected and a test meal (A), containing a known amount of a stable isotope of iron (⁵⁷Fe), is consumed.
• On the following day, a test meal (B) is consumed that contains a known amount of a second stable isotope of iron (⁵⁸Fe) and a potential enhancer or inhibitor of iron absorption.
• Half of the study participants receive the test meals in the reverse order.
• A second blood sample is collected two weeks later. After processing of the blood samples, the iron isotopes are analysed with an appropriate mass spectrometer.
• The ratios of stable iron isotopes before and after consumption of the test meals are used to determine the amount of iron absorbed from the meals and incorporated into the red blood cells, thus revealing the effect of enhancers or inhibitors present in the meal.