|In this issue of HEALTHbeat:
• The benefits of cooking veggies in the microwave
• Hydration for summer exercise
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|July 8, 2008|
Dear HEALTHbeat subscriber,
How you cook your vegetables may make a big difference in how much nutrition you get from them. And you might be surprised to learn that using a microwave may help retain the vitamins, minerals, and other compounds that make vegetables such a health boon to begin with. This issue of HEALTHbeat explains how microwave cooking affects the nutrient content of food and also gives tips for healthier microwave cooking. Also in this issue, Dr. Harvey Simon, editor in chief of the Harvard Men’s Health Watch, talks about getting hydrated properly during summer exercise.
Wishing you good health,
|The benefits of cooking veggies in the microwave|
The microwave oven is standard issue in today’s kitchen, from the home, to the workplace, to the dorm room. Their speed and convenience feel like nearly a necessity for today’s busy lifestyles. But does this method of cooking and heating meals and snacks compromise the nutritional value of foods we eat?
Microwave ovens use waves of oscillating electromagnetic energy to heat food. These waves are similar to radio waves but move back and forth at a much faster rate. They are also remarkably selective, primarily affecting polar molecules—molecules with a negatively charged end and a positively charged end. Water is a polar molecule, so a microwave oven cooks by energizing (heating) water molecules, and the water energizes its molecular neighbors. The reason glass, ceramics, and many types of plastic don’t get hot in a microwave oven is because they’re made up of nonpolar molecules.
Some nutrients break down when they’re exposed to heat, whether that heat comes from a microwave or a regular oven. Vitamin C is perhaps the clearest example. So, cooking with a microwave probably does a better job of preserving the nutrient content of foods because the cooking times are shorter.
Boiled, steamed or fried
Cooking vegetables in water causes some of the nutrients to leach out into that same water. For example, boiled broccoli loses glucosinolate, the compound that may be responsible for its cancer-fighting properties. However, you can incorporate the nutrient-rich water from boiled vegetables into sauces or soups. Steaming vegetables may help retain more nutrients. Steamed broccoli holds on to more glucosinolate than boiled or fried broccoli.
No matter how you slice it, vegetables are good for you pretty much any way you prepare them, and most of us don’t eat enough of them. And the microwave oven? A marvel of engineering, a miracle of convenience — and sometimes nutritionally advantageous to boot.
Healthy microwave-cooking tips
Here are some things to keep in mind when using the microwave:
For more information on food and your health, order our Special Health Report, Healthy Eating: A guide to the new nutrition, at www.health.harvard.edu/HE.
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|Hydration for summer exercise|
Q: I’ve always been told that it’s important to drink plenty of fluids during exercise, and it seems to work for me. But now I’ve read that too much water can be very dangerous. Which is right?
A. Both are right: good hydration is important, but overhydration can be hazardous, even lethal. Fortunately, common sense and moderation will protect you from both extremes.
Until the late 1970s, most athletes were advised not to drink before or during exercise. The idea was to avoid bloating and to improve performance. Some coaches may have also believed that withholding fluids would “build character.” It didn’t work. In fact, dehydration increases the risk of muscle cramps, heat exhaustion, and heat stroke during exercise in warm weather. And even in mild weather, dehydration can leave exercisers grumpy or groggy for hours afterward.
When the hazards of dehydration became apparent, experts began to encourage fluids during exercise. A common recommendation was to drink 20 to 40 ounces per hour of exercise. But these guidelines were formulated for elite male athletes whose high-intensity exercise produced lots of fluid loss in sweat. And they were intended to apply to exercise lasting two hours or less.
As a result of these guidelines, athletes began to drink. Spurred on, in part, by manufacturers of sports drinks and bottled water, they drank more and more. And some drank too much, producing water intoxication and hyponatremia (low blood sodium levels). Hundreds of cases and a number of deaths have been recorded in medical journals.
The tragic death of a female runner in the 2002 Boston Marathon called attention to the problem and has stimulated advice against drinking too much during exercise. The caution is justified and the advice is important, but it’s not easy to drink enough to get into trouble. The typical victim of water intoxication is a runner who is out on a marathon course for over four hours and who consumes enough fluids — often well over 3 quarts (96 ounces) — to gain weight during the race. That is way, way too much.
How much should you drink? In hot, humid weather, you can lose over a quart of sweat in an hour of moderate to intense exercise; in cool weather, much less. Plan to drink two to three cups of water an hour, but boost the amount if you are sweating heavily. If you drink a quart, or even two, during a long summer tennis game or hard workout, you won’t get into trouble. Extra salt is not required to prevent hyponatremia, and unless you get way behind in your fluid replacement, sports drinks won’t be any better than water. The trick is simply to avoid drinking too much fluid.
Best of all, evaluate your own needs. Drink when you feel dry or thirsty, but don’t arbitrarily force down huge amounts. To learn precisely what you need to stay in balance, weigh yourself before and after exercise, stripped down to avoid the effects of sweaty clothing. For each pound you lose, you’ll need a pint of fluids. You can also keep an eye on your urine output. If your urine is scant and concentrated, you’re dry, but if it’s clear and copious, you are fully hydrated. Remember, though, that if you gain weight, feel bloated, or experience nausea and vomiting, you’re on your way to hyponatremia and big trouble.
Medicine is a science, but its teachings often seem to swing like a pendulum. If you stay centered and use common sense in evaluating advice, you won’t be left high and dry — or, for that matter, all wet.— Harvey B. Simon, M.D.
Editor, Harvard Men’s Health Watch
This Question and Answer first appeared in the July 2008 Harvard Men's Health Watch, available at www.health.harvard.edu/men.
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