Dolphins come closest, with a brain to body weight ratio just below ours and just above chimpanzees. (sciencemag.org)
Using the various estimated brain size, one gets brain / body weight ratios of: (archaeologyinfo.com)
So assuming the same 2100 - 2600 calories, 13 % -17 % protein results in protein / lean body weight ratios range from 0.91 g / kg to 1.47 g / kg. (nutritionfacts.org)