Which of the following statements regarding protein-quality is true?

• A. Plant-based proteins tend to be higher-quality than animal based proteins because they're more digestible.
• B. A protein that contains all 20 amino acids is always considered high-quality.
• C. A protein that contains all 9 essential amino acids & easily digestible is considered high quality.
• D. A protein that is easily digestible & contains at least 9 different amino acids is considered complete.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of protein quality. Protein quality is determined by two main factors: the presence of all 9 essential amino acids (which the body cannot produce on its own) and the protein's digestibility (how efficiently the body can break it down and use it).
2. Step 2: Clarify the difference between essential and non-essential amino acids. Essential amino acids must be obtained through the diet, while non-essential amino acids can be synthesized by the body.
3. Step 3: Evaluate the first statement: 'Plant-based proteins tend to be higher-quality than animal-based proteins because they're more digestible.' This is incorrect because plant-based proteins are generally less digestible and often lack one or more essential amino acids, making them lower in quality compared to animal-based proteins.
4. Step 4: Evaluate the second statement: 'A protein that contains all 20 amino acids is always considered high-quality.' This is incorrect because not all 20 amino acids are essential. A high-quality protein must contain all 9 essential amino acids and be easily digestible.
5. Step 5: Evaluate the correct answer: 'A protein that contains all 9 essential amino acids & easily digestible is considered high quality.' This is correct because it aligns with the definition of high-quality protein. Additionally, the last statement about 'complete proteins' is also correct, as complete proteins contain all 9 essential amino acids but may not necessarily be high-quality if they are not easily digestible.