14.6 Diet and Obesity

Obesity and energy balance have already been covered in depth in chapter 9.  Here we will summarize and focus on causes and health effects or complications of obesity.

Obesity

Overweight and obesity have become one of America’s national epidemics. According to the National Institutes of Health, over two-thirds of American adults are overweight, and one in three is obese. Obesity puts people at risk for a host of health problems, including Type 2 diabetes, heart disease, high cholesterol, hypertension, osteoarthritis, and some forms of cancer. The more overweight a person is, the greater his or her risk of developing life- threatening complications. There is no single cause of obesity and no single way to treat it.

Obesity results from a combination of causes and contributing factors, including individual factors such as behavior and genetics. Behaviors can include dietary patterns, physical activity, inactivity, medication use, and other exposures. Additional contributing factors in our society include the food and physical activity environment, education and skills, and food marketing and promotion.

Obesity is a serious concern because it is associated with poorer mental health outcomes, reduced quality of life, and the leading causes of death in the U.S. and worldwide, including diabetes, heart disease, stroke, and some types of cancer. However, a healthy, nutritious diet is generally the first step, including consuming more fruits and vegetables, whole grains, and lean meats and dairy products.

Healthy behaviors include a healthy diet pattern and regular physical activity. Energy balance of the number of calories consumed from foods and beverages with the number of calories the body uses for activity plays a role in preventing excess weight gain. A healthy diet pattern follows the Dietary Guidelines for Americans which emphasizes eating whole grains, fruits, vegetables, lean protein, low-fat and fat-free dairy products and drinking water. The Physical Activity Guidelines for Americans recommends adults do at least 150 minutes of moderate intensity activity or 75 minutes of vigorous intensity activity, or a combination of both, along with 2 days of strength training per week.

Having a healthy diet pattern and regular physical activity is also important for long term health benefits and prevention of chronic diseases such as Type 2 diabetes and heart disease.

Obesity is having excess body weight and is influenced by a combination of factors, which usually results in consuming more calories than the body needs. These factors may include:

• physical inactivity
• diet
• genes
• lifestyle
• ethnic and socioeconomic background
• exposure to certain chemicals, certain conditions, and use of certain drugs.

Some strategies to treating obesity include:

• Increasing activity and reducing caloric intake are essential to treating obesity, but some people benefit from also taking drugs.
• Losing as little as 5 to 10% of body weight can help lessen weight-related problems, such as diabetes, high blood pressure, and high cholesterol levels.
• People who are obese or overweight and have weight-related problems (such as diabetes) may be treated with weight-loss drugs.
• People who are very obese and who have serious weight-related problems may benefit from weight-loss surgery.

Obesity has become increasingly common throughout the world. In the United States, obesity is very common. More than one third (36.5%) of adults are obese, and more than 25% of children and adolescents are overweight or obese. Also, severe obesity has become more common.

Obesity is much easier to prevent than treat. Once people gain excess weight, the body resists losing weight. For example, when people diet or reduce the number of calories they consume, the body compensates by increasing appetite and reducing the number of calories burned during rest.

Causes

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 by helping it digest food (among other things). Changes in the number and types of bacteria in the digestive system may change how the body processes food.

Physical inactivity

In developed 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.

Diet

The diet in developed countries is energy dense. That is, it consists of foods that have a large number of calories in a relatively small amount (volume). 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.

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. 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.

Genes

Obesity tends to run in families. 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.

Pregnancy and menopause

Gaining weight during pregnancy is normal and necessary. However, pregnancy can be the beginning of weight problems if women do not return to their pre-pregnancy 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 pre-pregnancy weight.

If a pregnant woman is obese or smokes, weight regulation in the child 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 problem.

Aging

Obesity becomes more common as people age. 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).

Other Lifestyle Factors

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 often results in weight gain. Nicotine decreases appetite and increases the metabolic rate. When nicotine is 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%.

Hormones

Hormonal disorders rarely cause obesity. The following are among the most common:

• Cushing syndrome is caused by excessive levels of cortisol in the body. The syndrome can result from a benign tumor in the pituitary gland (pituitary adenoma) or from a tumor in the adrenal gland or elsewhere, such as in the lungs. Cushing syndrome typically causes fat to accumulate in the face, making it look full (called moon face), and behind the neck (called a buffalo hump).
• Polycystic ovary syndrome affects about 5 to 10% of women. Affected women tend to be overweight or obese. Levels of testosterone and other male hormones are increased, causing fat to accumulate in the waist and abdomen, which is more harmful than the fat that is distributed throughout the body.

Drugs

Many drugs used to treat common disorders promote weight gain. These drugs include some drugs used to treat psychiatric disorders including depression, some drugs used to treat seizures, some drugs used to treat high blood pressure (antihypertensives, such as beta- blockers), corticosteroids, and some drugs used to treat diabetes mellitus.

Complications

Being obese increases the risk of many health problems. Virtually every organ system can be affected. These weight-related health problems can cause symptoms, such as shortness of breath, difficulty breathing during activity, snoring, skin abnormalities including stretch marks, and joint and back pain.

Obesity increases the risk of the following:

• Abnormal levels of cholesterol and other fats (lipids), called dyslipidemia
• High blood pressure (hypertension)
• Metabolic syndrome, which includes resistance to the effects of insulin (called insulin resistance), abnormal levels of cholesterol and other fats in the blood, and high blood pressure
• Coronary artery disease
• Heart failure
• Diabetes or a high blood sugar level that is not high enough to be considered diabetes (prediabetes)
• Cancer of the breast, uterus, ovaries, colon, prostate, kidneys, or pancreas
• Gallstones and other gallbladder disorders
• Gastroesophageal reflux (GERD)
• A low testosterone level, erectile dysfunction, and reduced fertility in men
• Menstrual disorders, infertility, and increased risk of miscarriage in women
• Skin infections
• Varicose veins
• Fatty liver and cirrhosis
• Blood clots (deep vein thrombosis and pulmonary embolism)
• Obstructive sleep apnea
• Arthritis, gout, low back pain, and other joint disorders
• Depression and anxiety

Obstructive sleep apnea can develop if excess fat in the neck compresses the airway during sleep. Breathing stops for a few moments, as often as hundreds of times a night. This disorder is often undiagnosed. It can cause loud snoring and excessive daytime sleepiness and increases the risk of high blood pressure, abnormal heart rhythms, metabolic syndrome, heart attacks, heart failure, and strokes.

Obesity can increase the risk of early death. The more severe the obesity, the higher the risk. In the United States, 300,000 deaths a year are attributed to obesity. It is the second most common cause of preventable death (cigarette smoking is the most common).

Obesity can lead to social, economic, and psychologic problems. For example, obese people may be underemployed or unemployed, or they may have a poor body image and low self- esteem.