Increase flow rate by increasing heart rate and more fluid goes thru the kidneys. Some of your weight loss may be stored water. HR of 40 is low. Can lead to fluid retention.
Just thoughts of issues I’ve seen in patients before.
My regular doc is focused on my kidneys as well. He keeps sending me for urine tests - Microalbumin value of less than 1.2. Creatinine of 156mg/dL. I'm told that's really good.
My bariatric doctor told me I actually showed signs of dehydration - we live in the high desert - and that I need to drink more water.
In answer to the other questions that come up...I don't smoke, I don't do drugs, I rarely drink alcohol, I don't drink sugar sodas though I will have a diet soda now and then. If I have a food weakness it is peanut butter. That tends to be my go to snack. I like the brands that are lower in sugar. My job is fairly physical. My relatives that didn't smoke lived long.