It followed a competitive pitch against three other agencies.
Rich Leigh & Co, the agency founded late last year by the founder of stunt and campaign website PRexamples, will operate a press office function for the brand, initially highlighting product news and promoting the range of products to journalists and bloggers.
Neil Kirwan of Monkey Nutrition said: "SEO is just as important to us as getting our name out there, and having been assured of its ability, although the agency is brand new, I sensed a team we could really grow with."
Leigh, who founded PRexamples in 2012, previously spent more than five years at Yetis PR. He was also a senior account director at Frank PR.