I was skimming "The High Blood Pressure Solution" by Richard D. Moore
MD, PhD 2nd edition 2001.

The following caught my eye.

"..... Insulin is also one of the most potent sodium-retaining hormones...."

The author goes on to remark that insulin stimulates the
sodium-potassium pump. A twice normal blood level of insulin can cause
almost total reabsorption of sodium from the prefiltrate? urine back
into the blood inside the kidney.

He adds that high insulin seems to be why obese people tend to retain
sodium and frequently have high blood pressure.

The thrust of the book was to strongly encourage diet, exercise,
nutrition and weight loss as a means to control hypertension, with
classical medication being adopted when these lifestyle changes aren't
sufficient.

He also commented that if you have been on a pretty restrictive calorie
diet [he didn't discuss low carb at all], and then suddenly hit the
cookies, the blood sugar excursion raises the insulin and leads to
significant water retention.

There are nice parts with good sounding physiological explanations
towards the end, for those who like these sorts of details. Even some
drawings, for the visually inclined.