Model Answer
0 min readIntroduction
The Protein Efficiency Ratio (PER) is a historical nutritional measurement used to evaluate the quality of protein in food. Developed by Wilbur Buehler in 1930, it gained prominence as a tool to compare the protein content of different food sources, particularly during periods of food scarcity and rationing. While largely superseded by more sophisticated methods today, understanding PER remains relevant for comprehending the evolution of nutritional science and its impact on dietary guidelines. It essentially assesses how effectively a protein source promotes body weight gain in a test animal fed a controlled diet.
What is the Protein Efficiency Ratio (PER)?
The Protein Efficiency Ratio (PER) is a measure of how efficiently a protein source is used by the body to promote growth. It is calculated by dividing the weight gain of an animal (typically a rat) fed a specific protein source by the amount of protein consumed.
Calculation Methodology
The calculation involves a standardized procedure:
- Animal Selection: Young, growing rats are used, ensuring they are of similar age and weight.
- Controlled Diet: Rats are fed a controlled diet deficient in protein, except for the protein source being tested.
- Weight Gain Measurement: Over a specific period (typically 7-14 days), the weight gain of the rats is meticulously recorded.
- Protein Intake Calculation: The total protein consumed by the rats during the experimental period is calculated.
- PER Calculation: PER = Weight Gain (grams) / Protein Intake (grams).
Historical Significance and Limitations
PER was widely used in the early to mid-20th century to assess the nutritional value of various protein sources, like casein, soybean, and wheat gluten. However, PER has significant limitations:
- Species-Specific: Results are highly dependent on the animal species used. Rat protein metabolism may not perfectly reflect human protein utilization.
- Metabolic Variability: Individual animal variation in metabolism can skew results.
- Ignores Amino Acid Profile: PER doesn’t account for the amino acid composition of the protein. A protein with a low PER might still be valuable if it contains essential amino acids.
- Ethical Concerns: Animal testing raises ethical concerns, prompting a shift towards alternative methods.
Modern Alternatives to PER
Due to the limitations of PER, more sophisticated methods are now preferred:
- Amino Acid Scoring (DIAAS): Digestible indispensable amino acid score (DIAAS) considers the digestibility and bioavailability of each essential amino acid individually. This provides a more precise assessment of protein quality.
- Net Protein Utilization (NPU): NPU assesses both the digestibility and biological value of protein.
- PDCAAS: Protein Digestibility-Corrected Amino Acid Score – Used by the FDA in the US.
Example: PER Values for Different Proteins
| Protein Source | PER Value (Approximate) |
|---|---|
| Casein | 2.5 |
| Egg White | 2.0 |
| Soybean | 1.4 |
| Wheat Gluten | 0.8 |
Conclusion
The Protein Efficiency Ratio, while a historically important tool for assessing protein quality, has been largely superseded by more refined methods like DIAAS and NPU due to its limitations concerning species-specificity and failure to consider amino acid profiles. Understanding PER's evolution provides valuable insight into the progress of nutritional science and the ongoing efforts to develop more accurate and ethical methods for evaluating food quality and human health. The focus now is on methods that provide a more nuanced understanding of protein utilization.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.