Which of the following is a common technique advertisers use to mislead consumers into using "fad diets" to achieve optimal health and fitness?
a. promoting exercise
b. promoting vegetables
c. promoting fruits
d. promoting supplements

Explanation:

Since a while, fitness marketing has created some "fad diets" around supplements, because through this campaign they make people feel that they can have a really nice body just taken supplements, which most of the cases, are protein-base. But, what they don't tell is that a strict diet is necessary, because consuming to much proteins will be transformed in fat, making people even gain more weight than losing.

So, the most common misleading fitness ads is promoting supplements.