Dietary intake assessment - Laboratory methods

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Back to: Matrix - Outcomes of Interest, Matrix - Practical Considerations, Matrix- Populations of Interest

Population of Interest (P=Parent, R=Researcher, C=Child)

  • Age: <1 yr (C); 1-10 yrs (C); 3-5 yrs (C); 10-12 yrs (C); 12 yrs+ (C)
  • Setting: Clinical
  • Administration Method: Face to Face

Laboratory methods

As most traditional diet assessment methods are subjective and associated with a large number of bias, it is becoming increasingly necessary to objectively measure dietary intakes. Assessment and analysis of nutritional biomarkers allows for this as measures are not affected by respondent error. Measurement of nutritional biomarkers and validation studies for diet assessment tools are more commonly carried out in adults however several studies exist in children.

Several common nutritional biomarkers exist which are known to reflect specific aspects of dietary intakes. These include:

Double labelled water (DLW): The gold standard for assessment of total energy expenditure. This method is not often carried out due to the expense, analysis and the limited facilities where such analysis can be undertaken. The DLW technique involves dosing individuals with a measured quantity of DLW at baseline and collecting urine samples over a designated period of time, usually 7-15 days which are then analysed to calculate an individual's total energy expenditure (TEE). The dose of DLW given to each individual is calculated by multiplying a certain quantity of DLW by an individual’s body weight or total body water however dosage varies depending on the age of the individual.

Plasma carotenoids: A common set of biomarkers of fruit and vegetable intake used for dietary intake validation studies. As a person increases their intake of fruit and vegetables, their carotenoid profile is altered similarly. Previous research has shown a dose-response relationship between intake and appearance in plasma, making carotenoids a reliable biomarker of fruit and vegetable intake. Carotenoids refer to a group of at least 600 compounds that naturally occur as plant pigments, providing yellow, orange and red colours seen in many fruits and vegetables. Only six occur in substantial quantities in human diets and serum/plasma. Individual variability in absorption, availability and metabolism are key considerations. The most commonly measured carotenoids in studies include the provitamin A compounds: α-carotene, ß-carotene, ß-cryptoxanthin and also lycopene, lutein and zeaxanthin.

Plasma fatty acids: Fatty acids are most commonly measured from plasma or red blood cell membranes and are nutritional biomarkers of dietary fat intake. Specific fatty acids can reflect dietary intake of individual and classes of fatty acids. This includes classes such as mono and polyunsaturated fats.

24-hr urine nitrogen: A well known biomarker of dietary assessments. The use of 24-hr urine nitrogen depends on the assumption that subjects are in nitrogen balance and there is no accumulation due to growth or repair or loss of muscle tissue or loss due to starvation and dieting. The 24-hr urine nitrogen collection can be used to validate estimates of protein intake and urine samples need to be collected from an individual over a period of 7-10 days.