Obesity is a growing problem in all western countries including New Zealnad.The government should intervene in the free market and take steps to influence the type of food children eat in order to avoid overweight adults.

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INTRODUCTION
Obesity, medical condition characterized by storage of excess body fat. The human body naturally stores fat tissue under the skin and around organs and joints. Fat is critical for good health because it is a source of energy when the body lacks the energy necessary to sustain life processes, and it provides insulation and protection for internal organs. But the accumulation of too much fat in the body is associated with a variety of health problems. Studies show that individuals who are overweight or obese run a greater risk of developing diabetes mellitus, hypertension, coronary heart disease, stroke, arthritis, and some forms of cancer.
Body Mass Index
Body Mass Index (BMI) is used to estimate healthy weight of average people. A BMI of 20 to 24 is desirable for most adults. A person with a BMI of 25 to 29.9 is considered overweight, and a person with a BMI of 30 or above is considered obese. Obesity is associated with an increased risk for heart disease, diabetes, and other life-threatening diseases.
According to the Centers for Disease Control and Prevention (CDC), in the United States nearly 31 percent of the population is obese, up from 13 percent in 1960. From 1980 to 2000 obesity among American adults doubled, and the number of obese children and teenagers nearly tripled. Public health officials are concerned that obesity is reaching epidemic proportions. The health problems resulting from obesity could reverse many of the health gains achieved in the United States in recent decades.
II.
MEASURING OBESITY
The body mass index (BMI) is commonly used to determine desirable body weights. BMI is a measure of an adult’s weight in relation to height, and it is calculated metrically as weight divided by height squared (kg/m2). People with a BMI of 25.0 to 29.9 are considered overweight and people with a BMI of 30 or above are considered obese.
Body mass index only provides a rough estimate of desirable weight, however. Physicians recognize that many other factors besides height affect weight. Weight alone may not be an indicator of fat, as in the case of a bodybuilder who may have a high BMI because of a high percentage of muscle tissue, which weighs more than fat. Likewise, a person with a sedentary lifestyle may be within a desirable weight range but have excess fat tissue. In general, however, the higher the BMI, the greater the risk for developing serious medical conditions.
III.
COMPLICATIONS OF OBESITY
Obesity increases the risk of developing disease. According to the National Institute of Diabetes and Digestive and Kidney Diseases, almost 70 percent of heart disease cases in the United States are linked to excess body fat, and obese people are more than twice as likely to develop hypertension. The risk of medical complications, particularly heart disease, increases when body fat is distributed around the waist, especially in the abdomen. This type of upper body fat distribution is more common in men than in women.
Obese women are at nearly twice the risk for developing breast cancer, and all obese people have a 42 percent higher chance of developing colorectal cancer. Almost 80 percent of patients with Type 2 diabetes mellitus, also known as noninsulin-dependent diabetes mellitus, are obese.
Obese people also experience social and psychological problems. Stereotypes about “fat” people often translate into discriminatory practices in education, employment, and social relationships. The consequences of being obese in a world preoccupied with being thin are especially severe for women, whose appearances are often judged against an ideal of exaggerated slenderness.
IV.
CAUSES OF OBESITY
A calorie is the unit used to measure the energy value of food and the energy used by the body to maintain normal functions. When the calories from food intake equal the calories of energy the body uses, weight remains constant. But when a person consumes more calories than the body needs, the body stores those additional calories as fat, causing subsequent weight gain. Consuming about 3,500 calories more than what the body needs results in a weight gain of 0.45 kg (1 lb) of fat.
A.
Biological Factors
Research has revealed the important role of biological factors in the regulation of body weight. For instance, basal metabolic rate, the minimum energy required to maintain normal body function, affects body weight and weight loss because some individuals naturally use more calories to sustain basic body processes. The size and number of an individual’s fat cells also help determine the amount of weight loss that is possible.
B.
Genetics
Obesity is partially determined by a person’s genetic makeup. One groundbreaking study published in 1986 followed children who were adopted shortly after birth. The adoptees grew up to achieve adult weights that were more similar to their biological parents than their adoptive parents, indicating the influence of a person’s genetic makeup in determining body weight.
Scientists are unclear about which genes affect human obesity. More than 250 genes that may play a role in obesity have been identified in mice and humans. Researchers believe that the cause of obesity in humans is complicated and most likely involves the interactions of multiple genes with lifestyle factors such as diet and physical activity.
C.
Lifestyle
Changing lifestyles over the last century, including increased calorie consumption and reduced physical activity, have played a key role in the prevalence of obesity seen today. In the United States and other developed nations, the availability of wider food options has contributed to a change in eating habits. Grocery stores stock their shelves with a greater selection of products. Prepackaged foods, soft drinks, and fast-food restaurants have become more accessible. While such food choices offer convenience, they also tend to be high in fat, sugar, and calories.
Portion size has also increased. People eat more during a meal or snack because of larger portion sizes. Surveys indicate that people eat at restaurants more frequently than in the 1970s, and restaurants typically serve larger portions of food than those served at home. In the United States, experts believe that high-calorie food choices and larger portions have become the basis of the typical diet, resulting in excessive calorie intake and increasing the prevalence of obesity.
Both adults and children spend less time devoted to exercise as a result of longer work hours at sedentary jobs, a decline in physical education programs in schools, and increased participation in sedentary recreational activities such as browsing the Internet, playing video games, and watching television. In addition, many of the laborsaving devices of the modern lifestyle, such as cars, elevators, personal computers, and remote controls, promote a sedentary lifestyle. According to some studies, more than 26 percent of adults reported no leisure-time physical activity. This lack of physical activity has reduced the overall amount of energy expended in the course of a day, contributing to the development of obesity.
V.
TREATMENTS FOR OBESITY
Obesity can become a chronic lifelong condition caused by overeating, physical inactivity, and even genetic makeup. No matter what the cause, however, obesity can be prevented or managed with a combination of diet, exercise, behavior modification, and in severe cases, weight-loss medications and surgery.
A.
Diets
The most common and conservative treatment for obesity utilizes a nutritionally balanced, low calorie diet. Most health-care professionals and commercial weight-loss programs recommend diets consisting of 1,200 to 1,500 calories per day, usually in the following proportions: 60 percent carbohydrate, 30 percent fat, and 10 percent protein. Research from university obesity treatment centers indicates that patients who follow a low calorie diet lose 10 percent of their initial weight in 20 weeks. Without further treatment, however, patients usually regain one-third of the weight in the following year.
A more aggressive approach for persons who are more than 20 kg (40 lb) overweight includes very low calorie diets ranging from 400 to 800 calories per day. These diets are usually based on four to five servings of a liquid formula each day. Candidates must be carefully screened and medically supervised while on the diet. People on very low calorie diets lose approximately 15 to 20 percent of their initial body weight in 16 weeks. Once they go off a very low calorie diet, they typically regain approximately one-half of that weight within a year.
Meal replacements are liquid shakes or portion-controlled meals that are substituted for one or two meals a day. They are typically used as part of a 1,200 to 1,500 calorie diet. Studies have shown that meal replacements are often more effective than very low calories diets, resulting in an increase in the amount of initial weight loss and enabling dieters to maintain their weight loss. Unlike very low calorie diets, meal replacements do not require that candidates receive extensive medical monitoring.
B.
Exercise
Caloric restriction alone will not produce long-term weight loss. While the data from studies on the effect of exercise for short-term weight loss are contradictory, research clearly indicates that regular exercise is the single best predictor for achieving long-term weight control. Regular exercise will also improve some of the medical conditions associated with obesity, including elevated blood cholesterol, hypertension, and diabetes mellitus.
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参考文献：encarta 2006
附件：INTRODUCTIO3.doc