Despite a number of studies questioning the usefulness of very low-salt diets in the last few years, most major medical organizations continue to recommend them. We would assume that they do so from a strong base of evidence.

But with respect to heart failure, there is a shockingly small amount of evidence.

Heart failure occurs when the heart can’t pump enough blood to the rest of the body. About 5.7 million people in the United States suffer from it. Chronic high blood pressure can force the heart to work too hard over time, weakening it and leading to heart failure. Treatment usually involves trying to strengthen the contractions of the heart muscle with drugs, or reducing the volume of blood with other drugs (like diuretics) or by restricting salt intake.

Recently, researchers searched for randomized controlled trials that evaluated the use of reduced sodium intake to treat heart failure. In all the literature, they found nine studies that involved 479 patients. One of them was published only in abstract form. None involved more than 100 patients. Over all, none were considered at low risk for bias.

There were no data that showed that salt restriction reduced mortality or cardiac disease; affected whether someone was admitted to the hospital; or influenced how long they had to stay if admitted. Of four outpatient studies, two showed no improvement in heart function, and two did.