What is obesity?
Obesity is a more severe form of being overweight. Doctors use a scale called the body mass index (BMI) to evaluate your body weight in relation to your height and determine your ideal weight. Your BMI is calculated by taking your weight in kilograms and dividing it by your height in meters squared. Calculate your own BMI here. An adult with a BMI between 25 and 29 is considered overweight, and an adult with a BMI of 30 or more is considered obese. A woman with a BMI of 30 is about 30 pounds overweight.
Obesity is 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.
|Cutoffs for Overweight and Obesity by BMI|
|Underweight||Less than 18.5|
|Normal weight||18.5 to 24.9|
|Overweight||25 to 29.9|
|Class I obesity||30 to 34.9|
|Class II obesity||35 to 39.9|
|Class III (extreme) obesity||More than 40|
The main causes of being overweight or obese are eating too many calories and not being physically 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. However, total caloric intake and physical activity remain the keys to weight control.
How does obesity affect my risk of heart failure?
Women who are overweight or obese are more likely to develop heart failure than women who are not overweight. A study that followed 5881 participants (54% were women) in the Framingham Heart Study found that excess weight increased a person’s risk of developing heart failure:
- Overweight (BMI 25 to 29.9) = 34% increased risk
- Obesity (BMI 30 or higher) = 104% increased risk
The study found that for each one-point increase in BMI, there was a 7% increase in the risk of heart failure in women (5% increase in men). Another study, of more than 2400 adults in their 70s (56% were women) found that a waist of more than 35 inches nearly doubled the risk of heart failure in women.
Obesity has a direct effect on your risk of developing heart failure because the extra weight makes your heart work harder to supply blood to the added fatty tissue. The more fatty tissue you carry, the more blood your heart has to pump. As the heart works harder to pump blood, the main pumping chamber becomes thicker and can eventually expand. Over time, this limits your heart’s ability to fill with and pump out blood, setting the stage for heart failure. The longer you are overweight or obese, the longer your heart is exposed to the extra strain and subsequent damage.
Obesity also increases your risk of heart failure by making you more likely to develop other risk factors that can damage your heart and lead to heart failure:
- High blood pressure: Obese women are nearly 3 times as likely to have high blood pressure as women who are at a healthy weight. Overweight women are nearly twice as likely. Women who are obese and have high blood pressure develop thicker heart muscle walls than women who are only obese or only have high blood pressure. Weight loss – even modest weight loss – can lower your blood pressure if you are overweight or obese.
- Diabetes: Overweight women are more than twice as likely to develop type 2 diabetes as women 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 plaque to build up along the walls of blood vessels. When this happens in the blood vessels of the heart, it can damage your heart muscle. Weight loss can improve your cholesterol levels if you are overweight or obese.
- Obstructive Sleep Apnea: Obesity is the main cause of obstructive sleep apnea, a condition in which you repeatedly stop breathing for at least 10 seconds during sleep. Tissue in the throat or mouth (in the soft palate or the tongue) causes it to narrow and block the airway when the muscles relax during sleep. This can stress the heart because of the fluctuating blood pressure levels and the reduced amount of oxygen supplied to the heart muscle. Being obese (BMI of 30 or higher) increases your risk of developing obstructive sleep apnea by up to 40%.
Obesity can also trigger the body’s defensive response to injury—called the inflammatory response—by increasing blood levels of key immune system proteins such as C-reactive protein (CRP), interleukin 6, and fibrinogen. The prolonged inflammation of heart tissue can damage cells and cause the buildup of scar tissue, increasing the risk of heart failure. A study of nearly 7000 racially diverse adults (53% were women) found that obese participants with elevated levels of these proteins had an increased risk of heart failure that ranged from 36% to 84%. A recently published results of a major trial of nearly 18,000 (38% were women) adults with low cholesterol but high C-reactive protein levels showed that statin treatment significantly reduced their risk of heart attack and stroke.
Being overweight is also one step towards developing the metabolic syndrome, which is also characterized by increased inflammatory markers. Metabolic syndrome is a group of risk factors for heart disease—including heart failure—that tend to occur together. These include a large waistline, low HDL (good) cholesterol, and higher than normal blood sugar, blood pressure, and triglyceride levels. Having 3 of these 5 risk factors means you have metabolic syndrome. Metabolic syndrome may increase your risk of heart failure if you have the following 3 from its group of 5 risk factors: high blood pressure, high blood sugar, and a large waistline.
How common is obesity?
The National Center for Health Statistics estimates that nearly 62% of American women over 20 years old are overweight or obese. The prevalence of obesity tends to vary between racial and ethnic groups, being the most common in African Americans, followed by Hispanics and whites. It is also a growing problem among children.
|2005 Rates of Obesity Among – US Women Age 20 and Older|
|% of Women Who are Overweight (BMI 25 to 29.9)||% of Women Who are Obese (BMI 30 or higher)|
|*Total for both men and women 18 years of age and older|
Defining a Healthy Weight
Is BMI a good measure of a healthy weight for me?
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. BMI can also be inaccurate for South Asians, Arabs, and mixed-race Africans, because people with this ancestry tend to have a higher percentage of body fat than white people do. For Asian Americans, BMI may underestimate their health risk. Increasingly, studies show that waist measurement and/or waist-to-hip ratio may be better than BMI for assessing the risk your weight poses to your overall health.
Is pear-shaped really better than an apple-shaped figure?
The location of your body fat, not just how much you have, makes a difference in the impact on your risk of developing heart failure. People with excess fat in their belly area, or abdominal adiposity(so-called “apple” shape), are more at risk of developing heart failure risk factors such as diabetes and high blood pressure than people who carry their weight in their hips and thighs (pear-shaped). The fat around the organs in the gut (called visceral fat) has been shown to produce high levels of interleukin 6, an inflammatory protein. The accumulation of visceral fat may increase a woman’s risk of dying from heart disease 8 times compared with 2 times in men, although this increase may be higher in women than in men because women tend to live longer than men.
Increasingly, studies show that waist measurement and/or waist-to-hip ratio may be better than BMI for assessing the risk your excess weight poses to your overall health. One recent study of more than 2400 adults (56% were women) found that otherwise healthy people who carried excess weight around the waist—measuring 35 inches or more—had double the risk of developing heart failure compared with those who were slimmer around the middle.
|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|
Your waist circumference is the distance around your waist, measured at the level of your belly button. 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. An ideal waist-to-hip ratio for women is 0.80 or less; a waist-to-hip ratio of 1.0 or more increases your risk for heart disease.
Regardless of where you carry your weight, being overweight or obese increases your risk of developing heart failure.
Obesity & Heart Failure Prevention
Will losing weight reduce my risk of heart failure?
So far, no clinical trial has tested the effect of losing weight on your risk of heart failure. Obesity contributes to many heart failure risk factors such as high blood pressure and diabetes. Losing weight lowers your blood pressure and blood sugar levels and improves your physical endurance, making it easier to stay physically active. Obesity also directly affects your heart by making it work harder to pump blood. Losing the excess weight reduces the extra strain placed on your heart.
Maintaining a healthy weight is an important aspect of reducing your risk of developing heart failure.
To minimize your risk, aim for:
- A BMI of 18.5 to 24.9
- A waist circumference of 35 inches or less
- A waist-to-hip ratio of 0.8 or less
- A minimum of 30 minutes of moderate-intensity physical activity (such as brisk walking) on most—preferably all—days of the week
How can I lose weight?
To learn about your options for losing weight and reducing the associated heart failure risks, see our Weight Loss Guide.
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 reduces the health 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 failure 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, obese women who were active for at least 3½ hours a week had a lower risk of heart disease than obese women who were inactive, but still had 3 times the risk of active women who were a healthy weight. Regular exercise lowers your risk of heart failure even if you don’t lose weight, but to minimize your risk you will also need to shed the extra pounds.
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 on 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.