Obesity

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 genetics. 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.

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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. 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. Sleep may also play a role. One study reported that people who sleep more than nine hours a night, or less than six, are more likely to be obese.

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.

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