##EXTREMELY PLAUSIBLE
At its simplest, what you're talking about is not radically different from the ethnic dietary requirements already found on earth. Ethnicities with longtime regional backgrounds in have adapted to the diet available in their region. Although radical dietary changes in real life tend to revolve around deficiencies, such as a Western European trying to get by on an Inuit diet, it's easy to see how such a change might be beneficial instead. Just make the effects are also plausible. People are unlikely to grow a foot if hair per day, for instance, whatever their diet.
