MOCIÓN Exigir al Gobierno de la Comunidad de Madrid a:

Some of the most cherished myths about food and health involve carbohydrates. For example, a common myth is that sugar is poison to our body. While sugar can cause tooth decay (discussed in the next chapter), it’s hardly a poison. All carbo- hydrates are absorbed from the intestine as single sugars.

Let’s suppose that we’ve just taken a bite of Thanksgiving candied sweet potato. Like virtu- ally all foods, it has many components. It has a large number of chemical compounds, some of which play a role in nutrition and some of which do not. But since the chief nutrient substances in the dish are two classes of carbohydrates—starch in the potato, and sugar in both the potato and the candied topping—we can learn some principles by following a bite.

The starch and sugar in the sweet potato are digested to single sugars (monosaccharides) be- fore they’re absorbed into the bloodstream (details of digestion will be discussed in Chap. 10.) Our sweet potato is now quite unrecognizable. Its us- able carbohydrate is thoroughly broken apart into

the single sugars, like the blocks of a child’s build- ing set. For it’s only in very simple forms that nu- trients can actually enter the bloodstream to take part in life processes.

We use the example of sweet potatoes. But whether we begin with Fruit Loops, organical- ly-grown turnips, high-fructose corn syrup, or our sweet potato, what passes through our intes- tinal wall into our bloodstream is mainly glucose and fructose, with perhaps some galactose if milk is poured over the Fruit Loops.

Different foods release their sugars at different speeds, depending on particle size, fiber content, etc. Starch in brown rice, for example is digested slower than starch in white rice. Glycemic Index is a measure of how high a particular food raises your blood sugar. As you’d expect, jelly beans have a much higher Glycemic Index than pinto beans.

Once these sugars enter the bloodstream, their origin matters no more to the cells that will use them than do the origins of oxygen matter to the lung—whether from an ocean breeze, or a scuba tank. Glucose is glucose. Fructose is fructose.

Indeed, the next step is toward even greater simplicity. The blood coming from the intestine

Sugar Sucrose Corn Syrup High-fructose corn syrup Cost: $$$$ $ Taste: Sweet State: Solid

Sweeter (need less) Liquid (easier to add to soft drinks, other foods)

Glucose

Digested to single sugars

50% 50% Glucose 45% 55% Fructose Fructose

Figure 4-7: Sugar vs. High-Fructose Corn Syrup.

55

Chapter 4. The Trapping of the Sun

goes directly to the liver—and the final simplifi- cation of the sugars. Virtually all the single sugars which aren’t already glucose are converted by the liver into glucose.

If you’ve ever wondered why hospitals tend to provide caloric sup plementation to patients by us- ing only simple glucose (also called dextrose), the reason should now be clear. Ultimately, glucose is the sole carbohydrate used by most body cells for energy.

Alcohol

Alcohol is a fermentation product of carbo- hydrate. Yeast converts sugar to alcohol, using enzymes for this conversion. The first enzymes were, in fact, discovered in yeast, and the word

enzyme comes from the Greek words meaning in yeast. Alcohol has an energy value of about 200

calories per ounce (7 calories/gram).

Yeast use sugars—not starch—in fermentation. For this reason, sweet liquids, such as the juice of sweet fruits (including wine grapes) are good starters for making alcohol.

Starch must be first broken down to the sugar maltose or glucose before the yeast can use it. One way to do this is by a process appropriately called malting: Grain is allowed to germinate (sprout) for a few days; this produces enzymes that convert starch (the plant’s stored form of energy) to maltose and glucose (providing the fuel for the seedling).

There are other ways of converting starch to sugars for alcohol pro duction. One particularly

interesting method was used in Peru in the 16th century:3 _{Corn was ground and soaked in a pot}

of water. People then chewed this soaked corn, thereby breaking it into smaller pieces and mixing it with a digestive enzyme in saliva that breaks the cornstarch into maltose. Rather than swallow- ing the mixture, it was spit into a pot, where the action of the enzyme continued. Then, the entire mixture was boiled for several hours. This killed microbes from the saliva and concentrated the sugars by evaporating the water. The mixture was then filtered, providing a clear liquid rich in sug- ars, ready for fermentation.

In wine, grape juice typically provides the sugar that’s converted to alcohol; in beer, malted barley commonly provides the sugar. Such wine and beer thus have some of the nutrients that are in grapes and barley.

Wine and beer also have a limited alcohol con- tent because yeast can’t grow once the alcohol reaches about 15-20% by volume. Wine is about 12% alcohol, beer about 4%.

In order to make high-alcohol liquors (hard li- quor), the alcohol must be distilled (vaporized and condensed). Alcohol vaporizes at a lower temper- ature than water, so when a mixture of alcohol and water is heated, the alcohol will vaporize first, separating and concentrating it.

Alcohol content of distilled liquors is designated by proof. Doubling the % alcohol in the liquor gives its proof, e.g., liquor designated as 100 proof is 50% alcohol by volume. Brandy (~80 proof) is distilled from wine; whiskey (~90 proof) from beer; and rum (~90 proof) from fermented molasses.

Distilled liquors are not only a concentrated source of calories because of their high alcohol content, but are essentially devoid of nutrients. The small amount of nutrients in the original fer- mented product is left behind in the distillation process. For some people, more than half their ca- loric intake comes from alcohol. It isn’t surprising that people who drink a lot of alcohol are suscep- tible to nutrient-deficiency diseases, as well as the toxic effects of alcohol itself.

Part of our corn crop is being used to produce ethanol to partially replace gasoline (see Fig.

Beef Pork Poultry Ethanol Soft drinks Candy Pastries Corn oil High fructose corn syrup Corn meal Corn bread Corn flakes Corn tortillas Corn chips Animal feed Popcorn

56 Part 2. Carbohydrates and the Foundations of Food

4-8). The U.S. is the world’s leading producer of ethanol. Brazil is second, and uses sugar cane to produce most of its alcohol. Making alcohol from sugar cane is much more energy-efficient (uses less energy) than making it from corn.

There’s much interest in developing efficient methods of making ethanol from cellulose, e.g., from corn cobs and husks. A big advantage is that it uses inedible crops (e.g., switchgrass), but the process is much harder and not yet commercially viable.

Summary

Carbohydrates are created by photosynthesis: The energy of the sun is captured by the green chlorophyll in plants to create hydrated carbons— carbohydrates—from carbon dioxide and water. In fact, plant life and animal life provide a natural balance—plants produce food and oxygen, and animals take in that food and oxygen and turn it back into carbon dioxide and water.

The simplest carbohydrates are single sugars (monosaccharides). The most common single sugars in food are glucose, fructose, and galactose. When two sugars are linked together, they are called double sugars (disaccharides). The most common ones are sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

When many sugars are linked together, they are called polysaccharides or complex carbohydrates. We can digest only some of them, depending on whether we have the proper digestive enzymes. (Enzymes are biological catalysts that enable life’s chemical reactions to take place.) The digestible complex carbohydrates include starch and

glycogen. Starch is the storage form of glucose in plants; glycogen is the storage form of glucose in animals.

There are various indigestible complex carbo- hydrates, which are collectively called fiber. In fact, the definition of fiber is simply the edible but indigestible parts of plants, since fibers aren’t nec- essarily complex carbohydrates. But most fibers, are chains of sugar or sugar-like substances. Fibers include a wide variety of substances, broadly clas- sified according to whether they dissolve in water —soluble fibers and insoluble fibers.

Insoluble fibers include cellulose, lignin, and some hemicellulose. These form the structural components of plants and add bulk and softness to stools. Soluble fibers include pectin, gums, and some hemicellulose. Many of these impart gel-like qualities to food, and can bind to bile products in the intestine. All plants contain an in timate mixture of various fibers which vary in their physical properties, health effects, and how well they are fermented by bacteria in the colon.

Carbohydrate-rich foods—plant foods—are the staple food for most of the world’s population. The typical American diet—a high-fat, low-fiber diet—can be improved by including more of these plant foods.

Carbohydrates have a caloric value of 4 calo- ries per gram, and must be broken down to sin- gle sugars (monosaccharides) before they are ab- sorbed from the digestive tract. Practically speak- ing, fiber, indigestible as it is, has no caloric value (though short-chain fatty acids produced from some fibers by bacterial in the colon do). Alcohol, a fermentation product of carbohydrate, has 7 cal- ories per gram.

57

Chapter 5

Of Carbohydrates