Critically evaluate the statement: 'Because existing observational studies link high protein with improved weight loss, no further research is needed on long-term health tradeoffs.' Which rebuttal is most defensible?

• A. The observational evidence is sufficient to declare that all populations should adopt very high protein diets without studying effects on other nutrients or long-term outcomes.
• B. The statement is correct because short-term weight loss guarantees long-term health benefits and therefore no further study can alter current understanding.
• C. Only animal studies are necessary now because human diets are too variable; therefore, human cohort or RCT data are redundant.
• D. Observational links to weight loss do not address long-term consequences such as kidney function, bone health, and displacement of micronutrients; randomized or well-controlled prospective studies are still needed to clarify causality and tradeoffs.

Answer: (D)