Drinking Mountain Dew does NOT cause a man’s testicles to shrink.

This rumor is COMPLETELY unfounded. It has come in many different forms over the years: Mountain Dew will shrink your testicles, lower your sperm count, shrink your entire penis...none of which are at all true. This fantasy attributes its cause to Yellow No. 5, an FDA-approved dye which is frequently used to give foods a bright yellow coloring. Also known as tartrazine, Yellow No. 5 has been commonly used since 1916 so if there were any truth to this rumors we would definitely know it by now! The only stipulation with Yellow No. 5 is that all products that use it as an ingredient must clearly indicate this on their packaging. This is because the yellow dye has been shown to produce an allergic reaction in some people. We can’t say we’ve ever heard of any penis-shrinking allergies though...

Snopes breaks this rumor down...