“TO YOUR HEALTH.” that traditional toast captures what we are only now beginning to learn—that what and how much you drink may be just as important as what and how much you eat.More than half of your body weight is made up of a briny ﬂuid that is much like the oceans that nurtured primordial life. This ﬂuid bathes, cushions, and lubricates cells, tissues, and organs. It gives cells their shape and provides their substance, and it forms the watery highways that transport nutrients, wastes, hormones, and other substances throughout the body.When it comes to ﬂuids, the constant struggle for survival can be reduced to this: You dry, you die. Your skin, kidneys, a number of hormones, and even your nasal passages work together to keep the ﬂuid part of you from drifting oﬀ into dry air. But preventing water loss isn’t enough. You need to take in enough ﬂuid to carry out a variety of critical metabolic tasks, things like making enough urine to ﬂush away toxic by-products of digestion and metabolism and other wastes, maintaining blood volume, preventing body salts from getting too concentrated, and replenishing whatever water you lose.
The average person needs about a milliliter of ﬂuid for every calorie burned. That’s about eight 8-ounce glasses for a 2,000-calorie-a-day diet. Exactly how much ﬂuid you need depends on you. An individual’s needs are partly genetically programmed and largely determined by diet, the environment, and activity.
• Diet. If you eat lots of fruits and vegetables, which are mostly water, you may not need to drink as much as someone who eats a lot of meat or bread. In western Tanzania, people drink much less water than they do elsewhere because they satisfy much of their daily ﬂuid needs from cooked bananas, which make up a large part of the diet.
• Environment/weather. When the temperature is perfectly comfortable, you lose about four pints of water a day through your skin, the moist air you exhale, and urine. When it’s “too darn hot,” as Ella Fitzgerald croons, you lose even more. You can also lose extra ﬂuid in the winter, when the relative humidity plummets and the dry air seems to draw water out of your skin.
learn more: EYE DISEASES
• Activity. The more active you are, the more ﬂuid you need. As your muscles burn glucose, they generate heat. As you sit and read these words, some of that waste heat helps keep your body temperature up near 100° F. Start scraping old wallpaper oﬀ a wall or running around a track and you quickly make more heat than you need. This extra heat must be vented or you literally risk cooking the temperature-sensitive proteins that make you you. That’s what sweat does. As sweat forms on your skin and evaporates, it carries heat away from your body.
When you are giving your body a real workout, you can lose up to a quart of ﬂuid an hour. Because your body doesn’t have an easy-to-read gauge that tells you when your ﬂuid level is low, several rules of thumb are often oﬀered: Drink when you are thirsty. Drink before you are thirsty. Drink enough so your urine is consistently clear or pale yellow rather than bright or dark yellow.
learn more: FIBER PRAISE FOR THE INDIGESTIBLE
Thirst, unfortunately, isn’t a very good guide—by the time you feel thirsty, your ﬂuid level can already be low. That’s especially true when you are working or playing hard and losing water quickly. In addition, aging tends to uncouple the sense of thirst from the body’s ﬂuid level, and many older people can become dehydrated without realizing it. Also, urine color by itself is not a perfect guide because it is also inﬂuenced by what you eat and some vitamin supplements. An easy guideline is to drink at least one glass of your beverage of choice with each meal and one in between meals. Boost your ﬂuid consumption if you are physically active or if you ﬁnd yourself urinating infrequently.
The consequences of not taking in enough ﬂuid each day range from the life-threatening to the merely irritating. Extreme dehydration, which can be deadly, is relatively uncommon, occurring mostly among children and older people during very hot weather and among endurance athletes. Minor dehydration can make you feel grumpy and tired and make it hard to concentrate. Chronic minor dehydration is a cause of constipation, especially among older people. It may also lead to the development of kidney stones and bladder cancer.
So far I have been deliberately general in talking about ﬂuid intake rather than specifying any speciﬁc beverage. Plenty of things ﬁt the bill, including water, juice, soda, milk, coﬀee, tea, and alcohol. Some are better than others, especially as routine thirst quenchers. Let’s take a look at each one. The “healthy” list might surprise you.