12.7: Water in Food and Drink

Even if we knew exactly how much water we needed on a given day, it would be hard to know how much water we actually took in. This is because, for most of us, drinks can play a relatively small part in meeting our water needs—“solid” food is a big source.

Roughly half of the food we eat is water. If this sounds incredible, think of how much water you add to uncooked rice, and how the water “disappears” into the rice when cooked. Or how the thin package of dry spaghetti becomes a potful when cooked. Or how raw mushrooms shrink and seep as we sauté them in a bit of butter. Even when we eat low-moisture foods, we typically have something watery at the same time, whether we drink beer with our pretzels, pour milk over our cornflakes, or sip a soft drink between mouthfuls of movie popcorn.

We have a clear notion of which foods are solid and which are liquid. For example, we think of milk as a liquid, and of oranges or apples as solid. But the chemical truth is that milk, oranges, and apples all have about the same relative amount of water—about 85%.

Even solid-seeming meat is usually more than half water. And many vegetables, such as lettuce and asparagus, which appear to be more solid than milk, are actually less so, being about 95% water. Why would such “solid” foods have so much water?

Water and the Structure of Food

Whether vegetable or animal, the processes of life hinge on water-based chemistry and must take place in a watery medium. This suggests that the solid structures of life, even though they serve important purposes, could, in large amounts, hinder life’s chemistry. So nature keeps “real solids” to a minimum in living systems.

Since our foods are taken from one life form or another (either “animals” or “plants”), they follow this same rule of minimal solid matter. For example, the structural framework of plants, with the roots that hold them in the soil and the stems that lift their leaves to the sun, are very fibrous. To maximize structural integrity with a minimum of solid material, the fibrous structures of plants (and the bony structures of animals) are built in a honeycomb-like way—a lattice-work of supporting solid matter. It’s this construction that deceives us into seeing as solid even the most watery of foods.

Watch raw spinach cook. When raw, the spinach fills the pot. Within a minute or two of cooking, the fibrous structure goes limp, and the spinach shrinks to a thin layer at the bottom of the pot. Yet even with this loss in structural integrity, the water content of the spinach changes little. So even in its seemingly condensed form, cooked spinach, like the raw spinach leaves, is still more than 90% water.

Figure 12-4: Percent Water in Various Foods.

To get a more graphic image of the water-to-solid ratio of a “solid” food such as asparagus or lettuce, imagine a cup of water with about 2 spoonfuls of sugar dissolved into it. The relative amounts of water and sugar represents the water-to-solid ratio of these vegetables.

In other words, if it weren’t for the cleverness of nature’s structural arrangements, we could very well say that we live on “liquid” diets.

“Juicy” Fat and Sugar

Even if we took all our food as liquids, we can still be deceived as to how watery they are. Foods that are high in fat or sugar are particularly deceptive. The moisture illusion created by fat is easy to understand, as when we “moisten” our baked potato, rice, pasta, vegetables, bread, or popcorn with butter.

The moisture illusion of high-sugar foods is caused by their stimulation of saliva. So most people find hard candies (including cough drops) quite moist. But they aren’t. This illusion can be counterproductive for athletic competitors like runners or cyclists who are dehydrating and suck on candies for an illusion of quenching thirst.

When the candy contains fat as well, this compounds the illusion. For example, most forms of chocolate are only 1-2% water, being mostly sugar and fat. It’s not surprising that eating much moist-seeming candy is often followed by thirst.

Water and Deception in Food Choices

Comparisons of foods, whether for pricing or nutrient evaluation, can be distorted by water content. In pricing, a clear example is when companies inject broth into the carcass of the Thanksgiving turkey for a “juicier” turkey. Since we pay for turkey by the pound, we pay turkey prices for the added water. Different amounts of water in different brands of the same product make it hard to make cost comparisons.

In trying to compare the fat content of foods, water can distort the comparison. To repeat the example given in Chapter 9, milk is mainly water, so its fat content, by weight, appears deceivingly low.

By weight, whole milk is only about 3.5% fat, lower-fat milks 1-2% fat, and fat-free milk is almost fat-free. These are very low percentages. But about 50% of the calories in whole milk comes from fat, while 35% of the calories in reduced-fat (2%) milk, 15% of the calories in lowfat (1% fat) milk, and 5% of the calories in non-fat milk comes from fat. By expressing fat content in terms of calories from fat, as opposed to percentages of total food weight, comparisons of the fat content become realistic—the comparisons aren’t distorted by water content.

Categorizing foods as liquids or solids can also be deceptive, especially for the dieter. For example, the perception is that a glass of clear apple juice has fewer calories than an apple. True, the apple is more filling and takes longer to eat. But it’s the apple’s non-caloric fiber that makes it so. A cup of apple juice is about 115 calories, whereas a medium sized apple is about 80 calories. In many ways, the dieter is better off eating whole fruits rather than drinking their juices.

In thinking of meeting our water needs, we also tend to categorize foods as liquids or solids. But as we’ve seen, “solid” foods often have as much water as liquids. Even “real solids” can provide some water. Recall that the complete metabolism of the energy-providing nutrients provides water as a breakdown product. We can meet our water needs with a wide variety of beverages and foods. Plain tap water is, however, calorie-free and the least expensive.