Accurate protein measurement could reshape nutrition and agriculture, say University of Pretoria researchers

A team of researchers at the University of Pretoria (UP) is calling for a re-evaluation of how protein is measured in food, warning that longstanding calculation methods may be inaccurately influencing food labeling, nutrition policy, and even agricultural choices. Their findings suggest that updated and more precise protein measurement could help tackle global malnutrition and drive interest in underutilized plant-based protein sources.

The research was conducted by academics from UP’s Department of Animal Science and School of Health Systems and Public Health. The team examined the limitations of the commonly used nitrogen-to-protein conversion method – known as the Jones conversion method – which assumes that protein contains 16% nitrogen and uses this to estimate total protein content in food. While widely used, this approach can misrepresent the actual amount of protein in food, sometimes significantly.

“Traditionally, scientists have used the proximate system to measure protein content,” said Dr Beulah Pretorius, one of the study’s co-authors. “This method assumes that most of the nitrogen in food comes from amino acids, which are the building blocks of protein. However, our research shows that these assumptions can lead to over- or underestimation of protein content.”

The researchers collected amino acid data from various animal-source foods and calculated both crude protein (based on nitrogen content) and 'true protein', measured as the sum of amino acid residues. For meat samples, nitrogen was measured using the Dumas method, while dairy products were assessed using the Kjeldahl method. These values were then compared to the standard Jones conversion factors – 6.25 for meat and 6.38 for dairy.

“The findings were concerning,” said Professor Hettie Schönfeldt, another key contributor to the study. “For all animal products, the protein content was over-reported. The assumed nitrogen content of protein isn’t consistent – it varies significantly depending on the source.”

This discrepancy matters. Inaccurate protein estimates can skew food composition tables, misinform consumers, and complicate efforts to address malnutrition – particularly in lower-income countries where accurate nutrient profiling is essential for designing affordable, nutritious diets.

But there is also a broader opportunity, the researchers argue. By improving the accuracy of protein measurement, the food industry and policymakers can unlock the potential of lesser-known plant-based protein sources. This, in turn, could support biodiversity, climate resilience, and food security.

“Accurately determining protein content could help shift agricultural and dietary focus to a wider variety of crops,” Prof Schönfeldt said. “We’re talking about moving beyond the staples and encouraging the cultivation of often-overlooked protein-rich plants. That would benefit both the environment and people’s diets.”

However, implementing new methods isn’t straightforward. Amino acid profiling is more accurate but also complex and expensive, limiting its feasibility in many regions. Still, the researchers believe that improvements to current conversion factors – tailored to specific food sources – could be a practical first step.

“These changes will affect virtually all sectors in the food chain,” said Dr Pretorius. “Agriculture, food manufacturing, preservation, labeling, and regulation would all need to adapt. But perhaps the biggest hurdle will be convincing the public to embrace new dietary norms.”

While changing consumer habits will be a long-term effort, the team sees this as an urgent challenge. With millions of people still lacking access to adequate protein and climate pressures intensifying, the researchers argue that the food system must evolve – and that better science could help lead the way.