disorders of nutrition
Obesity
Causes of Obesity
Obesity results from a combination of factors, including the reduced opportunity for physical activity, the increased availability of high-calorie foods, and the presence of genes that make obesity more likely. But ultimately, obesity results from consuming more Calories than the body needs over a long period of time. Excess calories are stored in the body as fat (adipose tissue). The number of calories needed varies from person to person, depending on age, sex, activity level, and metabolic rate. A person’s resting (basal) metabolic rate—the amount of calories the body burns while at rest—is determined by the amount of muscle (lean) tissue a person has and the person's total body weight. The more muscle people have, the higher their metabolic rate. Changes in the bacteria that are normally present in the digestive system (called gut flora) may increase the risk of obesity. Normally, these bacteria help the body digest food among other things. Changes in the number and types of bacteria in the digestive system may change how the body processes food. Where a person lives can affect lifestyle choices and behavior. Some communities do not have access to fresh fruits and vegetables. These communities tend to have a higher rate of obesity. Access to safe recreational spaces (parks and biking lanes) help encourage physical activity. Taking public transportation, instead of driving, can also help because it involves more walking and less sitting. Obesogens are chemical compounds that disrupt normal development and metabolism (for example, cigarette smoke, bisphenol A, air pollution, flame retardants, phthalates, polychlorinated biphenyls). Being exposed to obesogens early in life can increase the risk of developing obesity. In technologically advanced countries, lack of physical activity is common and contributes to the increase in obesity. Opportunities for physical activity have been engineered away by technological advances, such as elevators, cars, and remote controls. More time is spent doing sedentary activities, such as using the computer, watching television, and playing video games. Also, people’s jobs have become more sedentary as office or desk jobs have replaced manual labor. Sedentary people use fewer calories than more active people and thus require fewer calories in the diet. If caloric intake is not reduced accordingly, people gain weight. Energy-dense foods, which are foods that have a large number of calories in a relatively small amount (volume), promote weight gain. Most of these foods contain more processed carbohydrates, more fat, and less fiber. Fats, by nature, are energy dense. Fat has 9 calories per gram, but carbohydrates and proteins have 4 calories per gram. Energy-dense foods are common in technologically advanced countries. Convenience foods, such as energy-dense snacks offered at vending machines and fast food restaurants, contribute to the increase in obesity. High-calorie beverages, including soda, juices, many coffee drinks, and alcohol, also contribute significantly. For example, a 12-ounce soda or bottle of beer has 150 calories, and a 12-ounce coffee beverage (containing dairy and sugar) or fruit smoothie can have 500 or more calories. High-fructose corn syrup (used to sweeten many bottled beverages) is often singled out as being particularly likely to cause obesity. However, recent studies show that it is no more likely to cause obesity than other foods with a similar number of calories in sugar. Larger portion sizes at restaurants and in packaged foods and beverages encourage people to overeat. Also, restaurant and packaged foods are often prepared in ways that add calories. As a result, people may consume more calories than they realize. Obesity tends to run in families. Genes help determine body mass index (BMI) in over 60% of people. However, families share not only Genes but also environment, and separating the two influences is difficult. Genes can affect how quickly the body burns calories at rest and during exercise. They can also affect appetite and thus how much food is consumed. Genes may have a greater effect on where body fat accumulates, particularly fat around the waist and in the abdomen, than on how much body fat accumulates. Many genes influence weight, but each gene has only a very small effect. Obesity rarely results when only one gene is abnormal. Rarely, mutations in the following genes result in obesity: The gene for the melanocortin 4 receptor: Receptors are structures on the surface of cells that inhibit or produce an action in the cell when certain substances (such as chemical messengers) bind with them. Melanocortin 4 receptors are located mainly in the brain. They help the body regulate its use of energy. A mutation in this gene may account for obesity in 1 to 4% of children. Theobgene: This gene controls the production of leptin, a hormone made by fat cells. Leptin travels to the brain and interacts with receptors in the hypothalamus (the part of the brain that helps regulate appetite). The message carried by leptin is to decrease food intake and increase the amount of calories (energy) burned. A mutation in theobgene prevents leptin production and results in severe obesity in a very small number of children. In these cases, administration of leptin reduces weight to a normal amount. Certain characteristics can increase the risk of becoming overweight or obese. They include the following: Certain racial and ethnic backgrounds, such as Black, Hispanic, and Pacific Islander A lower education level Obesity in Adolescents , which tends to persist into adulthood Adverse childhood events or a childhood history of verbal, physical, or sexual abuse are associated with a higher risk of obesity. According to the Centers for Disease Control and Prevention's adverse childhood events study, a history of verbal, physical, or sexual abuse during childhood increases the risk of obesity by 8% and the risk of severe obesity by 17.3%. Gaining weight during pregnancy is normal and necessary. However, pregnancy can be the beginning of weight problems if women do not return to their prepregnancy weight. About 15% of women permanently gain 20 pounds or more with each pregnancy. Having several children close together may compound the problem. Breastfeeding can help women return to their prepregnancy weight. If a pregnant woman is obese or smokes, weight regulation may be disturbed, contributing to weight gain during childhood and later. After Menopause , many women gain weight. This weight gain may result from reduced activity. Hormonal changes may cause fat to be redistributed and accumulate around the waist. Fat in this location increases the risk of health problems (such as Obesity becomes more common as people age (see Obesity in Older Adults ). As people age, body composition may change as muscle tissue decreases. The result is a higher percentage of body fat and a lower basal metabolic rate (because muscle burns more calories). Sleep deprivation or lack of sleep (usually considered less than 6 to 8 hours per night) can result in weight gain. Sleeplessness results in hormonal changes that increase appetite and cravings for energy-dense foods. Stopping smoking usually results in weight gain and may deter people from stopping smoking.Nicotinedecreases appetite and increases the metabolic rate. Whennicotineis stopped, people may eat more food, and their metabolic rate decreases, so that fewer calories are burned. As a result, body weight may increase by 5 to 10%. Hormonal disorders rarely cause obesity. The following are among the most common: Cushing Syndrome None Polycystic Ovary Syndrome (PCOS) None Hormonal disorders rarely cause obesity. Two eating disorders are associated with obesity: Binge Eating Disorder None Night-eating syndromeinvolves not eating much during the day, consuming a lot of food or calories in the evening, and awakening to eat in the middle of the night. Rarely, taking the sleeping pillzolpidemcan cause similar problems. Many medications used to treat common disorders promote weight gain. These medications include those used to treat the following: Some mental health disorders including depression ( Medications for Treatment of Depression ) Seizures ( Antiseizure medications ) High blood pressure ( Medications for Treatment of High Blood Pressure , such as beta-blockers) Corticosteroids None Medication Treatment of Diabetes Mellitus None 