Do you see any concern for elevated BUN and BUN-creatinine ratio of 36 in that semi-challenging, low-carb, high-fat diet intermittent fasting middle-aged female group when creatinine and UAs within normal limits?

No, I don’t. I’ve seen not for 10 years. Earlier on in my career I was chasing it down initially and never amounted to anything and when I learned just more about physiology and what BUN is reflecting, often if it’s mildly elevated it’s just a reflection of a higher protein intake. Remember that the ranges are calibrated based on averages of the general population. If someone’s eating a low-carb, high-fat diet, chances are it’s also a high-protein diet, and that’s why you’re seeing the BUN, which is nitrogen being a byproduct of protein digestion elevated, so usually not a consideration.