What is obesity and overweight?
Obesity and overweight don’t mean exactly the same thing – obesity is a more severe form of being overweight. Because your ideal weight is related to how tall you are, doctors use a scale called the body mass index (BMI) to determine what a healthy weight for you might be. Your BMI is calculated by taking your weight in kilograms and dividing it by your height in meters squared. You can calculate your own BMI (it will do the conversion to kilograms and meters for you).
A BMI between 25 and 29.9 is considered overweight, while obesity is defined as having a BMI of 30 or more. A woman with a BMI of 30 is about 30 pounds overweight. Obesity is then further broken down into 3 categories: Class I, Class II, and Class III. The table below shows the BMI cutoff points for underweight, normal weight, overweight, and the 3 classes of obesity.
|BMI Categories of Overweight & Obesity|
|Less than 18.5||Underweight|
|18.5 to 24.9||Normal weight|
|25 to 29.9||Overweight|
|30 to 34.9||Class I Obesity|
|35 to 39.9||Class II Obesity|
|More than 40||Extreme Obesity|
The main causes of being overweight or obese are eating too much and not being active enough. If you eat more calories than your body burns up, the extra calories are stored as fat. Other factors that may affect your weight include your genes (obesity tends to run in families), your metabolism (how your body processes food), and your age (your metabolism slows down as you get older). Sometimes an illness or medication can contribute to weight gain.
How common is overweight and obesity?
The National Center for Health Statistics estimates that 64% of all Americans over 20 years old are overweight or obese. Since 1993, obesity in the US increased 61%. More than 62% of all American women are overweight or obese. Obesity tends to vary between racial and ethnic groups, and is particularly common in black and hispanic women. It is also a growing problem among children.
How accurate is BMI?
For some people, BMI might not accurately gauge their health risk. For example, because muscle weighs more than fat, a very muscular person may have a BMI over 25, even though they are not really overweight or at increased risk for heart disease. For South Asians, Arabs, and mixed-race Africans, BMI can also be inaccurate because people with this ancestry tend to have a higher percentage of body fat than white people. For Asian Americans, BMI may underestimate their health risk. BMI may overestimate the risk of heart disease in older people.
Increasingly, studies show that waist measurement (for Chinese people and black Africans) and/or waist-to-hip ratio are better than BMI for assessing the risk your weight poses to your heart health.
What about weight gain during pregnancy?
When a woman is pregnant, it is normal for her to gain weight. The recommended weight gain during pregnancy depends upon your weight before you became pregnant. Women who are of normal weight should gain 25 to 35 pounds during pregnancy. Overweight women should only gain 15 to 25 pounds, and obese women should gain no more than 15 pounds. You should not try to lose weight if you are pregnant.
Excess Weight & Heart Risk
Does overweight and obesity affect my risk of heart disease?
Yes. In the Nurses’ Health Study of more than 115,000 women, as a woman’s BMI increased, so did her risk of dying from heart disease. In this study, obese women had about 4 times the risk of dying from heart disease as normal-weight women. Overweight and obesity can also affect your risk of heart disease indirectly by increasing your likelihood of developing risk factors for heart disease. These risk factors include:
- High blood pressure: Obese women are nearly 3 times as likely to have high blood pressure as those who are at a healthy weight. Overweight women are nearly twice as likely. Weight loss can lower your blood pressure if you are overweight or obese.
- Diabetes: Diabetes is a condition where a person’s body either doesn’t make enough, or doesn’t respond to insulin the chemical in the body that regulates how sugar is used and stored. Overweight women are more than twice as likely to develop type 2 diabetes as people who are not overweight. Weight loss can lower your risk of developing diabetes if you are overweight or obese.
- High cholesterol: Excess fat sends chemical signals that affect how we digest our food. It raises our LDL (bad) cholesterol and lowers our HDL (good) cholesterol, causing fatty plaques to build-up along the walls of blood vessels and lead to heart disease. Weight loss can improve your cholesterol levels if you are overweight or obese.
Being overweight is one step towards developing the metabolic syndrome. Metabolic syndrome is a group of risk factors for heart disease that tend to occur together. These include a large waistline, and higher than normal blood sugar, blood pressure, and triglyceride levels. Obesity can also activate parts of the inflammatory response – the body’s response to injury – which increases the level of a chemical called C-reactive protein (CRP) in your blood. Having high levels of CRP may increase your risk of heart disease.
Overweight and obesity also increase the risk of many other health problems such as breast, colon, and uterine cancer, osteoarthritis, and breathing problems.
Why does the excess weight have such unhealthy effects on my heart?
Overweight and obesity can lead to risk factors for heart disease, but the extra pounds also take their toll on the heart directly. When a body becomes larger, the heart has to work much harder to move the blood around the body. Like an overworked pump, the hearts of overweight and obese people can simply wear out more quickly.
Didn’t a recent study show that being overweight isn’t that bad?
You may have heard about a 2005 study that suggested there were actually a lot fewer deaths due to obesity than previously thought and that being overweight was really not so bad for your health. Several flaws in this study have since been pointed out: for example, the researchers did not properly account for smokers who tend to be slim but have greater health risks and they included people in the study who were possibly thin because of a serious illness. In reality, many more studies have shown that being overweight increases your chances of developing serious health problems and dying young, particularly from heart disease.
Obesity – Pear vs Apple, Fit vs Fat
Is pear-shaped really better than an apple-shaped figure?
The location of your body fat makes a difference to your risk of heart disease. People with excess fat in their belly area (so-called “apple” shape) have a greater risk of developing and dying from heart disease than people who carry their weight in their hips and thighs (pear-shaped).
To see if your weight puts you at risk for heart disease, you should measure the distance around your waist, at the level of your belly button. BMI tells you roughly how much fat you have on your body, but not where that fat is located. In the Nurses’ Health Study of more than 44,000 women aged 40 to 65 years, those who had a waist measurement of more than 38 inches were 3 times more likely to die of a heart attack or heart disease than women who had a waistline less than 28 inches.
A waistline greater than 35 inches for women and 40 inches for men increases the risk for having obesity related risk factors and heart problems. However, these cutoffs may be too high for very short people (less than 5 feet tall) and people from Asia and East India.
Another way to measure abdominal obesity is the waist-to-hip ratio, which is the distance around your waist divided by the distance around your hips. But just measuring your waist is a slightly more accurate way to measure abdominal fat. Waist-to-hip ratio is a better measure of risk than BMI for people of all ethnicities.
|High Risk||More than 35 inches (88 cm)||More than 40 inches (102 cm)|
|Waist-to-Hip Ratio = Waist ÷ Hip|
|Desirable||0.80 or less for women|
|At-risk||1.0 or more|
I’m overweight, but I’m fit. Do I still need to lose weight?
You may have heard of the “fit versus fat” debate, which argues that it doesn’t matter if you are overweight or obese as long as you are fit. Several studies have shown that exercising may reduce the heart disease risks of being overweight or obese even if you don’t lose weight.
However, while being fit may lower your risk, you will still have a higher chance of developing heart disease than someone who isn’t overweight. Being fit doesn’t cancel out the dangers of being overweight. In one study of more than 116,000 women, those who were obese and inactive were nearly 5 times more likely to die of a heart attack or heart disease than women who were active and trim. Obese women who were active for at least 3½ hours a week had a lower risk of heart attack and heart disease than obese women who were inactive, but still had a 3-fold higher risk than active women of a healthy weight.