page-23-What-are-calories.doc

Page23 what are calories? Page 3 of 3What are calories? Human beings(人类) need energy to survive(生存) to breathe（呼吸）, move, pump（输送） blood and they obtain（获得） this energy（能量） from food. The number of calories（卡洛里） in food is a measure of how much potential energy that food has. Foods are a combination of these three nutrients: carbohudrates, protein, and fat. If you know how much of these three nutrients are in any given food, you can find out how many calories, or how much energy that food contains. If you look at the nutrition label on the back of a granola bar, you find that it has 148 calories. This means that if you were to put this granola bar into a dish, set it on fire, and get it to burn completely, the reaction would produce 148 kilocalories, which is enough energy to raise the temperature of 148 grams of water by 1. If we look closer at the nutrition label, we see that the granola bar has 25 grams (g) of carbohydrates，3 grams of protein, and 4 grams of fat, for a total of 148 calories. Of these 148 calories, 100 come from carbohydrates (4 calories 25g), 12 come from protein (4 calories 3g) , and 36 come from fat (9 calories 4g). Our bodies burn the calories in the granola bar through a metabolic process by which enzymes break the carbohydrates into glucose and other sugars, the fats into glycerol and fatty acids, and the protians into amino acids. These molecules are then transported through the bloodstream to the cells. Sue nutrition labels to find out the calories in food. What happens when you take in more calories than your body burns? If you eat more or fewer calories than your body burns, you either gain or lose fat. For example, if you eat 3,500 more calories than your body burns, then that extra 3,500 calories are stored in your body, some as fat. Fat is the bodys way of saving energy. If, on the other hand, you burn 3,500 more calories than you eat, whether by exercising more or eating less, your body converts some of its stored fat into energy to make up for the fewer calories. Exercise is important for your health. Your body burns an increased number of calories when you exercise. In fact, it keeps burning extra calories for a number of hours after youve stopped exercising. Its very important to eat healthy food to replenish your calories. Carbohydrates and proteins are healthier sources of calories than fats. But our bodies need a certain amount of fat to function properly. An adequate supply of fat allows the body to absorb vitamins. However, an excess of fat can be unhealthy and result in extra body weight. Many doctors and nutritionists now set the maximum n