Diet with less sodium and more potassium has slight slimming effect
If there is relatively less sodium and more potassium in your diet you'll automatically be a little slimmer. The link between slimness and the sodium-potassium ratio is not earth shatteringly strong, but it exists write epidemiologists at the University of Texas Southwestern Medical Center in the American Journal of Clinical Nutrition.Sodium & body fat
Some animal studies suggest that a diet containing large amounts of salt tends to facilitate the growth of fat deposits. [Obesity (Silver Spring). 2007 Sep;15(9):2200-8.] A few years ago Finnish epidemiologists also reported that people who consumed large amounts of salt were slightly fatter than people with a healthier salt intake.

So the discovery that Nishank Jain and his colleagues made is not so surprising. The researchers measured the amounts of sodium and potassium in the urine of nearly three thousand inhabitants of Dallas aged between 30 and 65. They also measured the subjects' body composition using DXA scans. They noticed that the participants with a higher sodium-potassium ratio in their urine also had more body fat.



Mechanism

The researchers didn't examine how the sodium-potassium ratio makes people fatter or thinner, but they do make a few suggestions."Salt intake is a major determinant of sugar-sweetened soft drink consumption, and soft drink consumption is associated with weight gain and incident diabetes mellitus", the Americans write. "A diet high in fat is generally high in Na+ and low in K+."
"Second, salt sensitivity may be related to insulin sensitivity through the interplay of an abnormal renin-angiotensin system. Thus, a diet high in Na+ and low in K+ may contribute to obesity."
Food sources
Salt is obviously the most important source of sodium in our diet. The food industry adds it to almost everything because salt is a powerful flavour enhancer, suppresses unpleasant aftertaste and on top of that it's dirt-cheap. The more pre-processed food you eat, the more salt you consume.

Potassium is found in nearly all vegetables and fruit. The more of these you eat, the more potassium you'll ingest.
Source:
Am J Clin Nutr. 2014 May;99(5):992-8.