I think Gwilson is right it is usually a sign of loss of electrolytes like potassium, calcium and magnesium.

The higher protein low carb has a natural diuretic effect and promotes peeing as well as the extra water coming on board. You may want to try bottled mineral water instead, if you are using tap water, as these tend to be richer in the electrolytes.

I often think there are enough supplement tablets around and you perhaps do not want to rattle as well.