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Body Fat



To supply the calories our bodies need for energy, we must eat food. As food passes through our digestive systems, it is mechanically and chemically broken down into nutrients (amino acids, simple sugars, fatty acids, and monoglycerides) that our bodies use for growth, maintenance, and repair. When these simplified nutrients -- especially the simple sugars and fats -- reach the cells, they are metabolized as fuel. This releases heat, which is measured in calories. With calories, the body works on a supply-and-demand system. If the daily calorie supply from food you've eaten meets the daily demand, all the calories from fats, proteins, and carbohydrates are converted to energy. If the daily supply exceeds the demand, the excess calories are stored in fat cells. These fat cells serve as energy warehouses for fat molecules, allowing your body to draw upon the stored fat when your demand for calories exceeds the daily supply from the food you consume. Despite the recent negative publicity about fatty foods, we all need some fat in our diets. It's a good source of the calories we require to fuel our bodies and to keep us going when our energy demands suddenly increase. One gram of fat provides nine calories of energy, while one gram of protein or carbohydrate offers only four. Fat also gives texture and flavor to foods. It helps us feel full and satisfied after we eat. In addition, it protects our organs, aids in the development of cell membranes and hormones, and insulates our bodies. However, we should eat fat sparingly -- it should make up no more than 30 percent of our daily caloric intake. Excess fat in our bodies is linked to health problems such as hardening of the arteries and heart disease, to name just two. Throughout a day, a month, a year, and even a lifetime, the body's supply of and demand for fat changes. Demand increases with activity and decreases in sedentary times. We can modify our caloric intake to meet these changing conditions. We can also manage the body' s fat supply through exercise, which uses fat as fuel. So, to maintain a healthy balance in our bodies, we need to monitor our food intake and energy demands and add a daily dose of exercise.


Want to get away from it all? Go mountain hiking? Now's your opportunity. Plan a three-day backpacking trip to the Rocky Mountains in Colorado. Your trip will involve climbing, carrying, eating, cooking, and sleeping. All these activities will challenge your body's supply of and demand for calories. Plan what you'll pack for your trip as if your life depended on it. Materials
  • scale
  • food already in plastic bags
  • metric conversion charts
  • Food Guide Pyramid and servings chart
1. As a class, discuss what items you should include in your gear. Write these on the chalkboard. Discuss how important each one is for a safe trip. 2. For this trip your gear is limited to 40 pounds (18 kilograms), of which 15 pounds (6.75 kilograms) can be food. Plan for your nonfood gear to weigh 25 pounds (11.25 kilograms). 3. Estimate how many calories you'll need to consume each day. Keep in mind that your activity level will be higher than normal during this three-day hike so you'll burn more calories than you do normally. 4. Knowing your total calorie needs, figure how you can meet your daily nutritional needs in each of the five USDA food groups. What percentage of your total daily calories should come from each group? 5. Next, think of foods you can carry that will meet both your caloric and nutritional needs for three days, yet allow you to remain within your food weight limit. Discuss your food list with your classmates and your family. 6. Gather your food choices and weigh them. Add or subtract items as necessary, keeping in mind your daily food needs as well as water consumption needs. Questions
  1. What effect did vigorous activity have on your menu?
  2. Why did you choose the foods you chose? How close were you to your weight limit?
  3. How are you planning to meet your water needs?
  4. What percentage of the calories were from fat?
  5. What kinds of foods were light in weight but high in nutrition and calorie needs?


    Are you eating right? (1992, Oct) Consumer Reports, pp. 644 - 655.
    Lambourne, M. (1992) Down the hatch. Brookfield, CT: The Millbrook Press, Inc.
    Munoz, W. (1992) Nutrition: What's in the food we eat? New York: Holiday House.
    Choose a diet low in fat, saturated fat, and cholesterol:

    Surgeon General's Report of Physical Activity and Health. For a copy, call
    (888) 232-4674, or request a summary sheet at:

    United States Department of Agriculture
    Nutrient Data Laboratory
    4700 River Rd
    Riverdale, MD 20737
    (301) 734-8491
    Request Home and Garden Bulletin #72: Nutrient value of food.