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A low-sodium diet has a shaky foundation in heart failure, a systematic review showed.

Out of more than 2,600 studies on sodium restriction in heart failure, only nine small trials with a total sample of 479 -- none of which were free from bias -- made it into an analysis by a group led by Kamal Mahtani, PhD, of the University of Oxford, England.

In the end, the investigators found "no clinically relevant data on whether reduced dietary salt intake affected outcomes such as cardiovascular-associated or all-cause mortality, cardiovascular-associated events, hospitalization, or length of hospital stay," they reported online in .

Three studies showed a trend toward limited improvement in chronic stable heart failure outpatients who consumed less salt. And with no solid evidence on harms of cutting dietary salt intake either, they stopped short of calling for a change to current practice for outpatients.

In contrast, the literature was wholly inconclusive for inpatients admitted with acutely decompensated heart failure, the researchers found.

"Overall, a paucity of robust high-quality evidence to support or refute current guidance was available. This review suggests that well-designed, adequately powered studies are needed to reduce uncertainty about the use of this intervention," Mahtani and colleagues said.

"We have long treated the dictum to restrict sodium intake in heart failure as a pillar of best practices and a sacrosanct edict that populates the core database for all physicians treating cardiovascular disease," according to Clyde Yancy, MD, MSc, of Northwestern University Feinberg School of Medicine in Chicago.

It's time for a critical reevaluation of sodium restriction in heart failure, Yancy wrote in an . "There is simply too much uncertainty for a conviction we hold as truth."

The ongoing SODIUM-HF trial will be helpful, but it's not enough, he suggested.

"The first step is not a call for more trials but a retreat from an unbridled and potentially harmful insistence on rigorous sodium restriction in those with symptomatic heart failure. To state that we can do better is an understatement; to acknowledge our embarrassment for acting upon uncertain logic is closer to the truth," the editorialist emphasized.

Sodium restriction in heart failure was a Class I recommendation based on expert consensus in the 2009 guidelines. The 2013 guideline revision downgraded that to a Class IIa (reasonable) recommendation, also based on expert consensus.

Challenges for researchers include how to gather high-quality evidence in the face of the ubiquity of sodium in westernized diets and the uncertainty that sodium is really "the villain" and not just a surrogate for a more significant nutritional concern, according to Yancy.

"Emerging data may be expanding our nutritional concerns to include potassium-deficient diets, intake of inorganic phosphates, and lack of dietary fiber, all of which are highly associated with excess sodium intake but less well recognized," he wrote.

Rather than focusing on sodium alone, a whole-diet approach might make more sense, shifting heart failure patients to a Dietary Approaches to Stop Hypertension (DASH) or Mediterranean diet, Yancy suggested.