What are dietary biomarkers?
Biomarkers for dietary intake are objective biological characteristics measured in biological samples (like blood or urine) that indicate nutritional status, intake, or metabolism of dietary components. Unlike subjective methods such as food frequency questionnaires or 24-hour recalls, biomarkers are not prone to recall or social desirability bias, providing a more accurate representation of nutritional exposure. They are essential for validating self-reported dietary data, monitoring compliance in nutritional studies, and conducting more precise investigations into diet-disease associations.
Biomarkers can be obtained from various biological samples, each offering insights into different exposure timeframes. Blood, particularly serum or plasma, often reflects intake over days to a month, while red blood cells can indicate longer-term intake (up to 120 days). Urine is useful for assessing short-term intake and for recovery and predictive biomarkers. Adipose tissue provides information on long-term intake, especially for fat-soluble compounds. Hair and nails are also used for long-term exposure assessment and are easy to collect.
The main categories of dietary intake biomarkers
Dietary intake biomarkers are classified based on their relationship with dietary consumption.
Recovery biomarkers
Based on metabolic balance, these markers are excreted in proportion to intake over a specific period, making them suitable for measuring absolute intake. Examples include doubly-labelled water for energy expenditure, 24-hour urinary nitrogen for protein, and urinary potassium for potassium intake.
Concentration biomarkers
These biomarkers are correlated with intake but are also affected by metabolism, genetics, and lifestyle. They are useful for ranking individuals by intake rather than providing absolute amounts. Examples include plasma vitamin C and plasma carotenoids.
Predictive biomarkers
Predictive biomarkers show a dose-response relationship with intake, allowing for some prediction, though with lower recovery rates than recovery biomarkers. Urinary sucrose and fructose indicating sugar intake are examples.
Replacement biomarkers
Used as proxies when detailed food composition data is limited, these markers indicate exposure without providing quantitative intake measurements. Phytoestrogens, reflecting plant-based food consumption, are an example.
Examples of specific dietary biomarkers
Numerous specific biomarkers are used to assess the intake of different nutrients and food groups. Fatty acid concentrations in blood or adipose tissue reflect dietary fat intake over varying periods. Plasma phospholipid pentadecanoic acid can indicate dairy consumption. Total plasma alkylresorcinols are effective for assessing whole grain wheat and rye intake. Serum 25-hydroxyvitamin D is a reliable marker for overall vitamin D status. Serum retinol and retinol-binding protein are used for vitamin A assessment, particularly in deficient populations. Holotranscobalamin (holoTC) is a sensitive biomarker for vitamin B12 status. Urinary proline betaine is a good indicator of citrus consumption. Dihydrocaffeic acid derivatives can reflect coffee consumption.
Advantages and limitations of using dietary biomarkers
Biomarkers offer significant advantages but also present challenges in nutrition research.
| Aspect | Advantages | Limitations |
|---|---|---|
| Bias Reduction | Minimizes recall and social desirability biases inherent in self-reported methods. | Interpretation can be complicated by individual factors like genetics and health status. |
| Measurement Precision | Provides objective and reliable data on nutritional exposure. | Laboratory analysis, especially advanced techniques, can be expensive. |
| Validation | Useful for validating and calibrating subjective dietary assessment data. | Many potential biomarkers require further rigorous validation. |
| Sample Logistics | Some samples (e.g., hair, urine) are easy to collect non-invasively. | Other samples (e.g., blood, adipose tissue) require more invasive procedures. |
| Specificity | Can provide precise information about specific dietary components. | It can be challenging to link a biomarker definitively to a single food source. |
| Assessment Window | Different samples allow for assessing intake over various timeframes. | Results can be influenced by factors like time of day, fasting, and seasonality. |
The future of dietary intake biomarker research
The future of biomarker research focuses on overcoming current limitations and expanding capabilities. Metabolomics is a key area, helping to identify new biomarkers for specific foods and dietary patterns by analyzing the complete set of small-molecule metabolites in biological fluids. Developing multi-biomarker panels is also a priority to improve accuracy, as people consume complex diets, not isolated components. Advances in bioinformatics and larger food metabolome databases will speed up discovery and validation. Efforts are also directed towards developing less expensive and non-invasive methods to facilitate larger studies. Finally, improving methods to account for individual variability due to genetics and lifestyle is crucial for refining biomarker interpretation and enabling personalized nutrition.
Conclusion
Biomarkers for dietary intake are critical for objective nutritional assessment, providing a necessary alternative to subjective, error-prone self-reported methods. By measuring specific compounds in biological samples, they offer accurate data on nutrient intake and metabolism over different durations. While classified into types like recovery, concentration, and predictive, each having distinct strengths, they also present challenges regarding cost, invasiveness, and interpretation influenced by biological factors. Ongoing research, particularly in metabolomics and the development of multi-biomarker panels, promises to refine existing markers and uncover new ones. As the field progresses, biomarkers will enhance the precision of nutritional science, offering improved insights into diet-disease relationships and supporting evidence-based health policies and personalized nutrition strategies.
