The salt equation taught to doctors for more than 200 years is not hard to understand.

The body relies on this essential mineral for a variety of functions, including blood pressure and the transmission of nerve impulses. Sodium levels in the blood must be carefully maintained.

If you eat a lot of salt — sodium chloride — you will become thirsty and drink water, diluting your blood enough to maintain the proper concentration of sodium. Ultimately you will excrete much of the excess salt and water in urine.

The theory is intuitive and simple. And it may be completely wrong.

New studies of Russian cosmonauts, held in isolation to simulate space travel, show that eating more salt made them less thirsty but somehow hungrier. Subsequent experiments found that mice burned more calories when they got more salt, eating 25 percent more just to maintain their weight.

The research, published recently in two dense papers in The Journal of Clinical Investigation, contradicts much of the conventional wisdom about how the body handles salt and suggests that high levels may play a role in weight loss.