The correct answer is: E. No error.
The sentence “How you eat is as important as what you eat” is grammatically correct. The word “as” is used to compare two things, and in this case, it is comparing the importance of how you eat to the importance of what you eat. The sentence is also clear and concise, and it conveys the intended meaning effectively.
The other options are incorrect because they either contain grammatical errors or they do not make sense in the context of the sentence. For example, option A, “How you eat,” is missing a subject. Option B, “is as important,” is missing a verb. Option C, “as what,” is missing a subject and a verb. Option D, “you eat,” is missing a comma.
Overall, the sentence “How you eat is as important as what you eat” is grammatically correct, clear, and concise. It conveys the intended meaning effectively.