One of the major worries on keto is whether it will impede, or even result in a loss of muscle strength and size. However, several studies determined that to be false. So, pick up the butter and the barbells! If you want to hear more on this topic, check out the WTF podcast episode 07, where @ryanplowery and @themusclephd talk about gaining muscle on a ketogenic diet.
Reference: Paoli, A., Grimaldi, K., D’Agostino, D. et al. Ketogenic diet does not affect strength performance in elite artistic gymnasts. J Int Soc Sports Nutr 9, 34 (2012). https://doi.org/10.1186/1550-2783-9-34.