Obesity

Source: Centers for Disease Control and Prevention FastStats - Overweight Prevalence

Measurement of overweight and obesity

As carrying excess weight can affect many aspects of your health, your doctor may ask to weigh and measure you and regularly discuss your weight.

There are a number or measures that can be applied to determine whether a person's weight may cause health problems. Two of the most commonly used are:

• Body mass index (BMI), and;
• Waist circumference.

Body mass index

BMI is a tool that is used to classify the weight of adults into healthy, overweight and obese. BMI is also used to classify the weight of boys and girls aged 2-18, but it is interpreted differently to adults.

It is recommended by the World Health Organization and used as the main measurement in many guidelines for obesity around the world.

Your BMI is calculated by dividing your weight (in pounds or kilograms) by your height (in inches or meters) squared described in more detail below.

Pounds and inches: Formula: weight (lb) / [height (in)]2 x 703
Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.
Example: Weight = 150 lbs, Height = 5'5″ (65″)
Calculation: [150 ÷ (65)]2 x 703 = 24.96
Formula: weight (kg) / [height (m)]2

Kilograms and meters (or centimeters): With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Because height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.
Example: Weight = 68 kg, Height = 165 cm (1.65 m)
Calculation: 68 ÷ (1.65)2 = 24.98

It is important to remember that the BMI is an approximate guide and is not accurate for everyone. One reason for this is that people with the same weight can carry different amounts of fat compared to their lean body mass (bone and muscle).

Also, BMI does not take into account where body fat is accumulated on the body. Not all body fat contributes equally to health problems. Fat underneath the skin, particularly on the hips and thighs, does not tend to cause as many problems as fat around your abdomen. In particular, fat that builds up around the organs inside the abdominal cavity can cause inflammation within the body and contributes to many of the health problems associated with carrying extra weight.

At any given weight, different people will carry varying amounts of fat around their abdomen. The greater the abdominal fat, the greater the risk of health problems. People from some ethnic groups can tend to carry more fat around their abdomen.

For this reason, waist circumference, which can be a good indicator of how much abdominal fat a person is carrying, is also often used to assess how much of a risk a person's extra weight may pose to their health.

Waist circumference

To measure waist circumference with a tape measure:

• Stand straight with feet fairly close together, about 15cm apart, and breathe normally;
• Place a tape directly on the skin by removing any bulky clothes before measuring;
• Place the tape horizontally around the waist at around the level of the bellybutton, and;
• Breathe out and take the measurement.

Measuring waist circumference. 

Waist measurements and health risk

Just as with BMI, waist circumference does not apply equally to everyone:

• For people of South Asian, Japanese and Chinese heritage, increased risk occurs for men at 35.43 inches (90 centimeters) and women at 31.5 inches (80 centimeters), and;
• Health risk may be slightly overestimated for people of some ethnic groups, such as Pacific Islanders and people of African-American descent.

Also, for people who have greater-than-average waist circumferences for medical reasons, such as women during pregnancy and people with health conditions that cause the belly to swell or distend, these measurements are not a good health indicator.

Causes

In some respects, the cause of obesity is quite simple; it occurs because you take in more energy through food and drink than your body uses, so the extra energy gets converted into fat.

Energy in

Energy in food is measured in kilojoules or calories (4.2 kilojoules = 1 calorie). Foods vary in the amount of energy they provide. For example, vegetables tend to be low in energy and high in dietary fiber and nutrients that the body requires. Foods that contain a lot of carbohydrates and fats tend to be high in energy.

Beverages also contribute to energy intake. While water contains no energy, soft drinks, fruit juices and alcoholic beverages are all high in energy.

The portion size of the foods you eat is also important. Even foods with moderate amounts of energy can contribute to weight gain if they are eaten to excess.

Energy out

Metabolism describes the chemical processes that occur inside the cells in your body in order for the body to function. These processes require energy and this is called your basal metabolism.

Physical activity also uses up energy. The more vigorous the exercise (such as running), the more energy the body will use, although all activities, such as housework, walking to the shops and even standing still, contribute to the amount of energy the body uses every day.

With high-energy foods, you can take in large amounts of energy very quickly, while it takes much more time and effort to work off that energy.

Control of body weight

Taking in small amounts of unneeded extra energy on a daily basis can eventually add up to carrying quite a lot of extra weight if you do it over a long period of time. However, the way the body regulates weight is more complex. It involves a complex system of hormones, including insulin, leptin and ghrelin, that:

• Increase hunger;
• Decrease appetite and food intake, and;
• Increase metabolism and the amount of energy the body uses.

Generally speaking, this system works to try to maintain body weight at the same level over time. This level is sometimes called a set-point and when your weight increases or decreases from your set-point, the hormones will try to work together to get your weight back to that level.

When a person gains a lot of weight, the body can change the set-point to a higher level and this is one reason why it can be difficult to lose excess weight once it has been gained.

Medical conditions that can contribute to weight gain

There are some medical conditions that can contribute to weight gain and make it harder to lose weight.

These include:

• Hypothyroidism;
• Cushing's syndrome;
• Polycystic ovary syndrome (PCOS);
• Inherited conditions, such as Prader-Willi syndrome, and;
• Depression.

Medications that can contribute to weight gain

Some medications have been shown to cause weight gain. They include:

• Medications for bipolar disorder (including lithium, clozapine and olanzapine);
• Medications for type 2 diabetes (sulphonylureas such as chlorpropamide and thiazolidenes such as pioglitazone);
• Beta-blocker medications for high blood pressure (hypertension) such as propranolol;
• Tricyclic antidepressants such as amitriptyline;
• Steroids, and;
• Insulin.

Quitting smoking

People who quit smoking tend to gain weight. How much weight is gained varies from person to person and the health benefits of quitting smoking will most likely outweigh any health risks caused by any weight gain.

Health consequences of being overweight or obese

Carrying extra weight has a range of consequences on the body. Not only can it increase levels of inflammation in the body and affect the body's metabolic processes, it also places additional stress on the joints, airways and bladder.

Generally speaking, the more weight a person carries, the greater the risk they will also develop a range of other serious health conditions, including:

• Cardiovascular disease including heart attack and stroke;
• High blood pressure (hypertension);
• Type 2 diabetes;
• A range of cancers including bowel, breast, ovarian, endometrial, esophageal, gall bladder, pancreatic and kidney cancer;
• Asthma;
• Obstructive sleep apnea;
• Osteoarthritis, spinal problems and lower back pain;
• Gout;
• Kidney disease;
• Heartburn;
• Stress urinary incontinence and fertility problems in women;
• Gall bladder, liver and pancreatic disease, and;
• Mental health problems such as depression and anxiety.

Carrying very large amounts of extra weight can also make it more difficult for doctors to treat a wide range of other health problems. For example, surgery can be more complicated and it can take longer to recover.

Types of treatment

Losing weight can be challenging and its important to have realistic expectations about how fast you can lose weight and how much weight you plan to lose. Your doctor and other health professionals can provide guidance and support towards achieving a healthy weight.

The good news is that even relatively small reductions in weight (as little as a few kilograms) can be effective in reducing your risk of many of the health conditions associated with overweight and obesity.

Recommended approaches to weight loss include:

• Reducing energy intake via a healthy eating plan, and;
• Increasing your physical activity levels to increase your energy output.

Healthy eating is important for maintenance of a healthy weight and prevention of obesity. 

Options such as medication to assist weight loss and bariatric surgery, also known as obesity surgery, may be considered for people who:

• Have not been able to lose weight or prevent weight gain despite trying lifestyle changes;
• Are obese and have a lot of weight to lose, and;
• Have related health problems such as type 2 diabetes.

Your doctor can discuss whether these options are suitable for you.

Prognosis

Being overweight or obese increases your risk of a range of serious health conditions and can be linked with reduced life expectancy; however, even losing relatively small amounts of weight can help to reduce these risks.

For example, for people who are overweight or obese, losing 5% of their initial body weight can help to:

• Reduce the risk of cardiovascular disease;
• Reduce blood pressure;
• Help to prevent, delay or improve control of type 2 diabetes;
• Improve kidney disease;
• Improve sleep apnea;
• Reduce heartburn;
• Reduce symptoms of musculoskeletal problems such as osteoarthritis, and;
• Reduce symptoms of urinary incontinence.

With greater weight loss, the health benefits can be largely increased.

Prevention

It is easier to prevent weight gain than to try and lose it. The same lifestyle changes that can help to lose weight can also help to prevent weight gain.

Exercise will enable weight loss and prevention of obesity.