What is a common effect of protein deficiency?

Protein is an essential macronutrient that plays a critical role in the body, particularly when it comes to building and repairing tissues, including muscle. When a person experiences protein deficiency, the body does not receive enough of this vital nutrient to maintain its normal functions, which can lead to a decrease in muscle mass. This occurs because the body starts to break down muscle tissue to obtain the necessary amino acids it needs for vital processes, effectively using muscle as an alternative protein source. This is especially important for individuals who engage in regular physical activity or who are of growing age since adequate protein intake is crucial for development and recovery.

The other options, while they may seem plausible in other contexts, do not accurately reflect the common effects associated with protein deficiency. Increased energy would generally be associated with adequate protein intake, as protein contributes to overall energy levels. Weight gain typically occurs when there is a caloric surplus, not necessarily linked to protein deficiency. Lastly, better immune function is not a characteristic of protein deficiency; in fact, protein is important for a robust immune system, and its absence may lead to impaired immune responses.