Fat and sugar can take a breather. There's a new public health enemy in town these days, and it's sitting in your salt shaker.

Concern about salt -- more specifically the sodium in salt -- isn't new, but as doctors, nutritionists and public health experts gear up for the release of the 2010 Dietary Guidelines for America this fall, much of the chatter has been about a renewed focus on limiting sodium.

Sodium in some amount is essential to healthy brain and body functions, but the medical community believes Americans are eating way too much of it and that helping the public cut back on salt will lower blood pressure and consequently reduce the incidence of heart attacks and strokes.

The dietary guidelines committee recently released its report, which pegged Americans' average sodium consumption at slightly more than 3,400 mg a day -- a full third more than the 2005 dietary guidelines and more than twice what they recommended for anyone at risk for high blood pressure.

The report concluded that a 1,200-mg reduction in daily sodium across the population could prevent up to 92,000 heart attacks, 59,000 strokes, and 81,000 deaths annually.

Despite the apparent consensus, some question whether lowering sodium intake will actually result in improved health outcomes.

Michael Alderman, a hypertension specialist at Albert Einstein College of Medicine in New York City, has been a leading voice of dissent, repeatedly calling for a randomized clinical trial to verify that sodium reduction has a meaningful impact on heart attacks, strokes and preventable deaths.

"There is good evidence that by reducing sodium by a fairly substantial amount you can lower the average blood pressure of a population by a few millimeters mercury. It's been demonstrated in more than 100 random clinical trials," said Dr. Alderman. "The problem is that reducing sodium by an amount necessary to lower blood pressure has a bunch of other [negative] effects that we know about."

Sodium, which leads the body to retain extra water, can cause blood pressure to rise in some people. The water can put stress on the heart and blood vessels.

Some effects of treatment, such as increased sympathetic nerve activity (such as speeded-up heart rate) and an increased resistance to insulin (where the body cannot properly use glucose for energy), actually increase the risk of heart attacks and strokes, he said. Without a randomized clinical trial -- in which some people would follow a reduced-sodium diet and others would not -- there is no way of knowing whether sodium reduction will have a positive effect, a negative effect, or no effect at all.

Those who favor reducing sodium have argued that such studies would cost too much money and take too much time.

German researchers Dieter Klaus, Joachim Hoyer and Martin Middeke wrote this year that randomized trials "are hardly possible because, in addition to exorbitant costs, several thousand participants would have to be recruited who, in the intervention group, would have to reduce their salt intake permanently for 10-15 years."

But Dr. Alderman countered that "we do trials that cost millions of dollars all the time on smaller issues that affect fewer people. It's a bogus argument and it's certainly not an argument for doing an experiment [in reducing salt] on 300 million Americans."

Dr. Alderman has been criticized for serving on a scientific advisory committee of the Salt Institute, an industry trade association, but said that other than a $700 honorarium 15 years ago, he has received no financial support from the institute, including no support for his research.

Dr. Alderman also has some allies.

In 2009, the Cochrane Collaboration, a nonprofit made up of thousands of volunteers from the global medical community who review randomized clinical trials, concluded that "intensive interventions" to reduce salt intake "provide only minimal reductions in blood pressure during long-term trials." The report also advocated clinical trials to test the salt-reduction theory.

One of the biggest efforts at reducing dietary salt has been spearheaded by New York City's National Salt Reduction Initiative.

Even though there has been no new evidence on the issue, "we reached the point where we realized that we were going to have continued needless deaths," said Sonia Angell, director of the Cardiovascular Disease Prevention and Control Program at the New York City Department of Health.

She believes that successful implementation of a salt-reduction program across the nation could result in up to 100,000 fewer deaths per year, and millions of dollars saved. "In terms of public health interventions [that] is about as good as it gets."

The question has moved from whether salt reduction would be medically helpful to how to achieve it.

When the New York City Department of Health looked at the problem, it quickly became apparent that for New Yorkers to eat less sodium, the whole country would need to eat less. "Almost 80 percent [of salt in the diet] is already in packaged and processed foods when you buy it," Dr. Angell said.

A traditional preservative, salt is still commonly used. Only about 16 percent of people's salt intake comes in the form of salt used in cooking or at the table. "We're targeting the salt that people have no control over," she said.

The Institute of Medicine, which offers advice to federal agencies on health issues, recently recommended that the federal government mandate the reductions, while New York City's initiative is asking the food industry to voluntarily reduce salt in packaged foods by 25 percent by 2015, which would translate to a 20 percent reduction in dietary salt.

For years, food companies have been fighting pressure to reduce salt by claiming that it isn't unhealthy and that consumers want it, but they seem to be sensing that the tide is turning against them. The new version of Heinz ketchup now being introduced has 15 percent less salt, dropping from 190 mg of sodium per serving to 160 mg.

The New York City group released final targets in April and now has commitments from 16 companies, including some of the country's largest food manufacturers, such as Kraft, Subway and Goya Foods. This reduction will only get the group about halfway to its goal, but it's an important first step.

"Salt didn't get there overnight and we recognize that it will take time for industry to take it out. If we adjust gradually people won't rebel as much," explained Dr. Angell.

Reducing salt doesn't simply make food taste less salty.

A recent article in the New York Times, "The Hard Sell on Salt," vividly described the numerous roles that salt plays in processed foods, from masking bitter flavors to "adding crunch" to enhancing other flavors. Removing salt requires a total re-engineering of the product.

Other dietary changes have had some surprising side effects.

Under pressure to reduce saturated fats, for instance, manufacturers reached to trans-fats, which turned out to be even worse for people. They also cut down on total fat by increasing carbohydrates -- a switch now implicated in the country's continually rising obesity and diabetes rates.

As these voluntary programs and new health advisories go into effect, there are several possible outcomes, including one in which Americans successfully reduce their sodium and tens of thousands of lives are saved. In the words of Dr. Alderman, "Either way, it's going to be an experiment."

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