Kale is a slightly tough but highly nutritious member of the brassica family. It's rich in vitamin C, vitamin A, beta carotene, calcium and folates. It also makes an excellent source of dietary potassium, with one of the highest potassium concentrations of any vegetable, particularly in its raw form. Potassium is a crucial electrolyte in the body, meaning it helps to transmit impulses through nerves and muscles. It also plays a role in healthy blood pressure.
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A 100 gram serving of boiled, drained and lightly salted kale contains 228 milligrams of potassium, according to the USDA National Nutrient Database. The same amount of raw kale contains 447 milligrams per 100 grams. Much of the potassium is lost to the cooking water during the boiling process. Unfortunately, raw kale often tastes tough and chewy. Steaming or stir-frying kale helps to retain more potassium in the leaves and softens the leaf for eating.
The average healthy adult should aim for 4,700 milligrams, or 4.7 grams, of potassium from food each day, according to Colorado State University Extension. So, a small serving of kale provides between 5 and 10 percent of your daily potassium needs. As a comparison, 100 grams of roasted chicken breast with the skin left on contains 245 milligrams of potassium, significantly less than raw kale, though slightly more than boiled kale.
Potassium is a crucial mineral for proper function of the nervous system, and it also appears to help to maintain a stable blood pressure. In fact, if your diet is high in potassium, you may be helping to lower your blood pressure, according to an analysis by Jane Higdon, Ph.D., at the Linus Pauling Institute. This may in part be because of potassium's role in stabilizing water levels in the body. The more potassium you consume, the more sodium it triggers for excretion through urine. Sodium is directly connected with increased blood pressure and hypertension.
Kale's potassium content isn't its only nutritional benefit. Though it consists of more than 90 percent water and contains only 36 calories per cup, it is rich in essential nutrients. As the Harvard Medical School Center for Health and The Global Environment points out, it can provide six times more than your daily requirements for vitamin K, twice your beta-carotene needs and an entire day's worth of vitamin C in one cup.