Developing a comprehensive database of nitrogen-to-protein conversion factors: the NiCE factors database

Summary

This European collaborative study addresses a fundamental limitation in food composition databases by developing the first comprehensive nitrogen-to-protein conversion factor (NCF) database. Empirical NCFs were systematically compiled, quality-assessed, and hierarchically aggregated using standardised computational methods, yielding food-specific k-values that vary substantially by food category—from 5.03 for starchy roots to 5.86 for dairy products. By providing evidence-based, food-specific alternatives to the universal NCF of 6.25, this database establishes an improved standard for accurate protein quantification across food composition databases and applied nutrition research.

Regional applicability

The NiCE database was developed through European collaboration and is aligned with FoodEx2 classification, which is the standard food classification system used by European food composition databases and regulatory bodies including the UK Food Standards Agency. The findings are directly applicable to UK food composition database development and nutrition labelling accuracy, and the database resource will support more precise protein quantification in UK dietary assessment studies and public health nutrition guidance.

Key measures

Nitrogen-to-protein conversion factors (k-values): purified-protein factor (k_A), food factor (k_P), and mean (k) across FoodEx2 food categories

Outcomes reported

The study developed the NiCE (Nitrogen Conversion Estimate) Factors Database, a comprehensive resource providing empirically-derived, food-specific nitrogen-to-protein conversion factors (NCFs) aligned with FoodEx2 classification. The database provides harmonized k-values ranging from 5.03 for starchy roots and tubers to 5.86 for milk and dairy products, replacing the universal NCF of 6.25 used for nearly 200 years.

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