| Understanding Major
Nutrients by Janet Raloff Adults frequently refer to apples, fish, broccoli, and lean chicken as "nutritious." Brownies, soda pop, ice cream sundaes, and French fries, meanwhile, are often labeled "junk foods." What makes one group of foods good and the other bad? The answer lies mostly in the share of their energy-known as calories-that comes from particular sources. Everything in food doesn't have calories. For instance, most fiber doesn't. Vitamins are caloriefree, as are minerals, natural coloring chemicals, salt, and most natural flavorings. In fact, the only things that do have calories are carbohydrates, fats, proteins, and alcohol. That list may look short, but with the exception of water, these four nutrients account for most of what's in food and beverages-at least by weight. Carbohydrates, often called carbs, include sugars and starches. Each gram of carbs puts 4 calories into a food. It doesn't matter if the carb is table sugar or the starch in a potato-a gram of each provides the same amount of energy. The main function of carbohydrates, especially sugars, is the quick release of energy. That energy fuels a host of bodily processes, including those that allow you to run and grow. Starches tend to be more complicated molecules, made by combining sugars and other materials. They break down more slowly than sugars, so they release their energy more slowly. Proteins, made from combinations of building blocks known as amino acids, give energy. They also help build body tissues, such as muscle. Each gram of protein contributes 4 calories. Fats are energy dense. A gram of fat delivers more than twice as much energy-9 calories in all-as does an equal weight of carbs or protein. Although fats tend to get a bad name, they are very important. The body uses fats as building blocks to help make the walls of cells throughout the body. Many fats also turn on different processes and signals. Fats work in different ways. Some turn on signals that encourage the body to store them as body fat; others do just the opposite. Eating some types, such as saturated and trans fats, has been linked with an increased risk of heart disease. But other types, such as those known and omega-3's, have been linked with heart health. So it's too simple to just say fats are bad-or good. It all depends on the type and the amounts. Alcohol is not something kids should have to worry about, since it's illegal for Americans under 21 to drink it. However, it does show up in some foods and in medicines, such as many cough syrups not targeted at children. However, every gram consumed brings another 7 calories into the body. When a large share of a food is made from fats or sugars, they tend to acquire a bad rep-they're labeled junk foods. The reason: They give us energy but few other important micronutrients-such as vitamins. Or they encourage us to overeat. That's a special problem with fats and sugars, because our tongues have special receptors for both. It seems to be Mother Nature's way of encouraging us to eat sugars and fats when they're available. And that was a good strategy when people lived in clans of roaming hunter-gatherers several thousand years ago. Food was hard to come by, so the body encouraged us to eat foods rich in calories. Now that food is plentiful, easy to find, and inexpensive, our bodies may encourage us to eat much more than we need. The important thing to keep in mind is that neither carbs nor proteins nor fats are necessarily bad. The problem comes when we overeat-or undereat-any of them. |
Por ordem alfabética
Sites e publicações
ÍNDICE DE PLANOS
IMPRIMIR
ENVIAR
COMUNICAR ERRO
Fox 1.0 Pelo
Incrível: NotebookVárias marcas a partir de 
Roteador WirelessInternet sem fio a partir de
WebCamDiversos modelos