Reaching for the anti-salt

(This article was first printed in the March 2007 issue of the Harvard Health Letter. For more information or to order, please go to http://www.health.harvard.edu/health.)

Potassium is an important nutrient because it helps offset all the sodium that we get from salt, which, chemically, is sodium chloride. Potassium blunts sodium’s tendency to increase blood pressure.

Potassium is important for another reason. We now eat much more meat, dairy-based food, and grains than evolution has equipped our bodies to handle. As a result, we end up in a mildly acidic state that’s bad for our bones. Potassium in the form found in food is metabolized so it generates bicarbonate, which neutralizes this diet-induced acidity.

The Institute of Medicine (IOM) recommends that we consume 4.7 grams (4,700 milligrams) of potassium a day. The Daily Value, set by the FDA and the basis for the Nutrition Facts label you see on packaged food, is 3.5 grams.

Can’t get enough?

We’ve heard from readers who are daunted by the 4.7-gram goal. Bananas deserve their reputation as a good source of potassium: A medium-size banana contains 422 milligrams (mg) of the nutrient. But even if you ate 11 bananas a day, you’d still be 58 mg shy of the IOM recommendation.

But relax — for two reasons. First, don’t get hung up on the 4.7-gram mark. Dr. Walter Willett, chair of the Harvard School of Public Health’s nutrition department, says the IOM recommendation is shaky and based on one small study of African American men who were put on high-salt diets. His bottom line is that while, yes, most of us should get more potassium in our diets by eating more fruits and vegetables, we should also be cutting back on salt, which is so often “hidden” in prepared foods. Second, potassium is not an esoteric nutrient. There’s some in almost every plant-based food you can think of. Even a cup of coffee contains 171 mg. So a reasonably well-balanced diet, perhaps one with a vegetarian slant, will give you a pretty good supply.

Diuretics and salt substitutes

An interesting side issue — one which readers have also written to us about — is whether diuretics cause potassium deficits and if so, how they should be corrected. Diuretics (particularly the thiazides) are the first-line treatment for high blood pressure. They work by interfering with sodium absorption in the kidneys, which may lead to extra excretion of potassium and also chloride.

People with high blood pressure are often on low-salt diets. So if a diuretic that increases chloride excretion is added, a chloride shortfall is possible. Chloride is important for fluid and electrolyte balance in the body.

Salt substitutes, which are often made of potassium chloride, are helpful because they provide chloride — and make up for the loss of potassium. Potassium from food doesn’t come as potassium chloride, so while it would help with the potassium, it doesn’t bring any chloride to the table. But even if you are short on chloride, using a salt substitute may not be necessary. Dialing back the diuretic dose just a little will often correct the problem without compromising blood pressure control.

(This article was first printed in the March 2007 issue of the Harvard Health Letter. For more information or to order, please go to http://www.health.harvard.edu/health.)

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