Which of the following statements is true about incomplete proteins?

Incomplete proteins are defined by their amino acid profile. They do contain amino acids, which is why the statement claiming they contain none is inaccurate. Furthermore, while animal sources typically provide complete proteins that contain all essential amino acids, incomplete proteins can also be found in plant sources. This distinction highlights that the assertion limiting them to animal sources is incorrect.

When it comes to essential amino acids, incomplete proteins are recognized for lacking one or more of these vital components necessary for various bodily functions, which makes option C the correct statement. Regarding the idea that proteins serve as the primary fuel for the body, this is misleading; carbohydrates are generally utilized as the main energy source. Thus, emphasizing the characteristics of incomplete proteins as those lacking essential amino acids clarifies why this particular statement holds true.