阅读理解
Calorie(卡路里)counts are everywhere. They appear on restaurant menus, milk boxes and bags of baby carrots. Grocery stores display lots of foods packaged with bright and colorful “low-calorie” claims.
A calorie is the measure of stored energy in something---energy that can be released as heat when burned. The term calorie on food labels is short for kilocalorie. A kilocalorie is the amount of energy it takes to raise the temperature of one kilogram of water by 1 degree Celsius. But what does boiling water have to do with your body's release of energy from food? After all, your body doesn't start boiling after eating. It does, however, chemically break down food into sugars. The body then releases the energy to fuel processes and activities throughout each hour of the day.
Food contains three main types of nutrients that deliver energy: fats, proteins and carbs(碳水化合物). A process called metabolism(新陈代谢) first cuts these into small pieces; Proteins break down into amino acids(氨基酸), fats into fatty acids and carbs into simple sugars. Then, the body uses oxygen to break down these materials to release heat.
Most of this energy goes toward powering the heart, lungs, brain and other vital processes. Exercise and other activities also use energy. If energy-rich nutrients aren't used right away, your body will hoard them---first in the liver(肝脏), and then later as body fat.
In general, someone should eat the same amount of energy each day as his or her body will use. If the balance is off, they will win lose or gain weight. It's very easy to eat more calories than the body needs. Having two 200-calorie donuts in addition to regular meals could easily put teens over their daily needs. At the same time, it's nearly impossible to balance overeating with extra exercise. Running a mile burns just 100 calories. Knowing how many calories are in the food we eat can help keep the energy in and out balanced.
