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Obesity is measured using body mass index, abbreviated as BMI. BMI is determined by dividing a person's weight in kilograms by a person's height in meters squared. A person whose BMI is 25.0 to 26.9 is considered overweight, while a BMI of 27.0 to 29.9 kg/m2 is considered extreme overweight. A BMI of 30 to 39.9 kg/m2 indicates obesity. A BMI of 40 kg/m2 or more indicates extreme or morbid obesity.

What is going on in the body?

Food is made up of calories, or units of energy. Physical activity and normal body metabolism burn calories. When a person takes in more calories than the body uses, the extra calories are stored as fat. These fat cells enlarge or decrease in size depending on the balance of energy in the body. When fat cells build up or accumulate, it causes obesity.


What are the causes and risks of the condition?

Obesity is a complex condition. It is caused by an interaction among a number of factors. These varied factors fit into these categories:
  • behavioral
  • cultural
  • genetic
  • metabolic
  • physiological
  • social


What can be done to prevent the condition?

Staying at normal body weight by eating healthfully and keeping physically active can usually prevent obesity.


How is the condition diagnosed?

Diagnosis of obesity begins with a medical history and physical exam. The National Institutes of Health (NIH) recommend that healthcare professionals follow these steps:
  • measure height and weight
  • determine the person's body mass index
  • measure waist circumference
  • assess comorbidities, that is, additional risk factors
  • use the treatment algorithm to see if the person should be treated for obesity
  • determine whether the person is ready and motivated to lose weight
Waist circumference
The amount of fat around the abdomen is very important in assessing disease risk. An individual's risk for certain disorders increases when waist circumference is larger than normal. These disorders include:
  • coronary heart disease
  • high blood pressure
  • type 2 diabetes
A waist measurement of more than 40 inches, or 102 cm, in men and more than 35 inches, or 88 cm, in women is above normal. Combined with overweight or obesity, a high waist circumference can raise the person's disease risks from high to extremely high.
Some disorders place a person at high absolute risk for death if they are combined with obesity. An obese person with one or more of these factors should be treated aggressively. These factors include:
  • atherosclerotic diseases, such as peripheral arterial disease and carotid artery disease that causes symptoms
  • coronary artery disease, including a history of heart attack or heart bypass surgery
  • sleep apnea
  • type 2 diabetes
Other comorbidities increase an obese person's risk of death but are not life-threatening. These factors, which should be treated, include:
  • gallstones
  • gynecological problems, such as amenorrhea
  • osteoarthritis
  • stress incontinence
A third set of comorbidities also increases an obese person's risk of death if they are combined. Three or more of these factors increase a person's high absolute risk:
  • an age of 45 or older in men
  • an age of 55 or older in women
  • cigarette smoking
  • family history of early heart disease
  • high blood pressure, or current treatment with medicines to lower blood pressure
  • high LDL, that is, "bad" or "lethal" cholesterol
  • impaired fasting blood glucose levels
  • low HDL, that is, "good" or "healthy" cholesterol
Treatment algorithm
The treatment algorithm developed by NIH helps the provider decide if treatment for obesity is appropriate. It takes into account the person's BMI, waist circumference, and comorbidities.
Readiness and motivation
The healthcare professional needs to ask questions to see if the person is ready and motivated to lose weight. These questions deal with the following issues:
  • attitudes toward physical activity
  • potential barriers to the person's adoption of change
  • previous attempts at weight loss
  • reasons and motivation for weight loss
  • support expected from family and friends
  • time availability
  • understanding of risk and benefits

Long Term Effects

What are the long-term effects of the condition?

Obesity puts a person at risk for other health problems, including:
  • back pain
  • breathing problems
  • certain types of cancer
  • coronary heart disease
  • diabetes
  • gallbladder disease
  • high blood pressure
  • osteoarthritis
  • stroke
Obesity can even lead to an early death. As obesity increases, the risk for these problems also increases.

Other Risks

What are the risks to others?

Obesity is not contagious. It poses no risk to others.


What are the treatments for the condition?

NIH recommends weight loss treatment for people who have one or more of the following conditions:
  • a BMI between 25 and 29.9 and two or more risk factors
  • a BMI of 30 or higher
  • a high-risk waist circumference and two or more risk factors
The first weight loss goal should be a 10% weight loss over a 6-month period. The rate of weight loss should be 1 to 2 pounds a week. Faster weight loss does not improve the long-term results. After the first 6 months, additional weight management goals can be discussed with the healthcare professional. Sometimes more weight loss is needed. Others may be ready to maintain their weight loss.
No one treatment works for everyone. The healthcare professional should follow these guidelines in planning treatment:
  • know how the treatment fits into other healthcare and self-care needs of the person
  • make changes based on the person's preferences and responses
  • set weight loss goals with the individual
  • schedule regular office visits to track and support weight loss
A successful weight management plan will include the following components:
  • behavior therapy
  • dietary therapy
  • regular physical activity
The plan may also include medicines or surgery.
Dietary therapy
Dietary therapy is works best when it meets the needs of the individual. NIH recommends the following general dietary guidelines.
  • A diet with 1,000 to 1,200 calories a day is appropriate for most women.
  • A diet with 1,600 calories a day is appropriate for most men.
  • A diet with 1,600 calories a day may be appropriate for women who exercise regularly or weigh over 165 pounds.
  • A 1,200-calorie diet may be recommended for a person who is not losing weight on a 1,600-calorie diet.
  • If a person is hungry, the healthcare provider may recommend adding 100 to 200 calories a day.
  • Specific dietary recommendations should be given to be sure the person gets enough essential nutrients.
Physical activity
To begin treatment of obesity, NIH recommends moderate levels of physical activity 30 to 45 minutes a day, 3 to 5 days a week. The activity should be started slowly and gradually increased in intensity. Some moderate physical activities are as follows:
  • bicycling 5 miles in 30 minutes
  • gardening for 30 to 45 minutes
  • raking leaves for 30 minutes
  • walking 2 miles in 30 minutes
  • water aerobics for 30 minutes
Behavior therapy
Behavior therapy provides ways to overcome barriers to dietary therapy or physical activity. A good behavior therapy plan has the following characteristics:
  • incorporates the person's attitudes, beliefs, and history
  • includes a partnership with the healthcare provider
  • sets reasonable goals
  • includes self-monitoring, with appropriate rewards
  • focuses on what matters
  • includes frequent contact with the healthcare provider


The Food and Drug Administration (FDA) has approved only two medications for long-term use for weight loss. They are orlistat (i.e., Xenical), and sibutramine (i.e., Meridia). These medicines are recommended for people with a BMI of 27 to 29.9 with comorbidities. NIH also includes them as a consideration for people with a BMI of 30 or higher. As of 2007, the FDA is recommending the orlistat be made available over-the-counter, without a prescription.
Three other medications - diethylpropion (i.e., Tenuate), phendimetrazine (i.e., Bontril, Plegine, Prelu-2, X-Trozine, Adipost), and phentermine (i.e., Adipex-P, Fastin, Ionamin, Oby-trim, Pro-Fast, Zantryl) are FDA approved for short term (a few weeks) use only. They function as appetite suppressants.
Bariatric SurgeryThe principle of this surgery is to alter the digestive tract in such a way that either restricts the amount of food a person can eat at a time, through smaller stomach size, or routes much of the calorie content out of the body rather than letting it be absorbed. This surgery has become more popular and more successful in recent years.
NIH includes bariatric surgery as an option for people with a BMI or 40 or higher, or 35 or higher with comorbidities. An individual must be willing to make major lifestyle changes, including the timing and content of meals, exercise, vitamin and mineral supplementation, and rigorous medical follow-up.
Tools NIH provides sample tools to aid in weight management. These include the following:
  • dietary information
  • guide to behavior change
  • guide to physical activity
  • weekly food and activity diary
  • weight and goal records
Contraindications NIH states that these groups of people should be excluded from weight loss treatment:
  • women who are pregnant or breastfeeding
  • people with a serious uncontrolled psychiatric illness, such as major depression
  • individuals with serious illnesses that might be worsened by calorie restriction
NIH also recommends that certain individuals be referred to specialists for weight loss as needed. These include people with a history of eating disorders, such as anorexia nervosa or bulimia. People who are currently abusing drugs should also be referred to a specialist.

Side Effects

What are the side effects of the treatments?

Losing weight is not risk-free. Diets that are not carefully planned increase the risk of vitamin deficiencies. Rapid weight loss can cause nausea, tiredness, weakness, hair loss, and low blood pressure. Dieting can also lead to emotional changes and binge eating. Medicines may cause increased blood pressure and heart rate, decreased absorption of fat soluble vitamins, and loose stools. Surgery for weight loss has all the risk of any major surgery. Nutrient deficiencies can also occur if parts of the digestive system are bypassed.

After Treatment

What happens after treatment for the condition?

After the person has reached the weight loss goal, weight maintenance needs to be lifelong. The person should have regular treatment to continue with these measures:
  • behavior therapy
  • dietary therapy
  • regular physical activity
The ongoing therapy can be given in a number of ways. Some options recommended by NIH include:
  • e-mail reminders
  • group meetings
  • regular visits with the healthcare professional
  • telephone communications
Weight loss in an obese person can have the following effects:
  • lower blood pressure in those with high blood pressure
  • lower elevated blood glucose levels in people with diabetes
  • lower elevated cholesterol, LDL cholesterol, and triglyceride levels
  • increase low levels of HDL cholesterol
While these effects are beneficial, they may also signal a need for a change in medicines. For example, the person may need lower doses of a medicine to lower blood pressure. Other people may need different medicines or be able to stop medicine completely for elevated blood glucose levels.


How is the condition monitored?

After successful treatment for obesity, the person can check his or her weight regularly. The individual also needs to make regular visits to the healthcare professional. NIH recommends an appointment at 6 months and again one year after the start of the weight management plan. The healthcare professional will look at the person's weight, BMI, and waist circumference during these visits. Any new or worsening symptoms should be reported.

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