Weight Control and Diet
DescriptionAn in-depth report on losing and managing weight safely for health benefits.
Alternative NamesDietary Recommendations; Obesity
General Adverse Effects of Obesity. Obesity, defined as a body mass index (BMI) of 30 or over, accounts for nearly 300,000 deaths in the US each year. It is associated with more chronic health problems than smoking, heavy drinking, or being poor. Furthermore, given the current increase in obesity, it will surpass smoking as the most important preventable cause of death in America.
Some studies indicate that the following health risks by body mass:
Anyone with chronic health problems (e.g., heart or lung disease, stroke, or arthritis) or risk factors for them must be concerned about extra weight. In general, obesity may contribute to disease in several ways:
General Adverse Effects of Being Overweight (but not obese). It is still not clear if being overweight (a BMI of 25 to 29.9) hurts healthy people with no risk factors for serious illnesses.
According to one 2001 study, just being overweight increases the risk for developing diabetes, gallstones, hypertension, heart disease, stroke, and colon cancer. The risk rose proportionally with the degree to which the individuals were overweight. In any case, adults who are overweight in middle age face a poor quality of life as they age, with the quality declining the greater the weight. (One study suggested, however, that being over 65 and overweight but not obese is not associated with any higher mortality rates).
Some experts argue, in fact, that in anyone who is not severely obese, it is the unhealthy diet and sedentary lifestyle that causes harm--not weight per se. In support of this argument, a British study found that overweight fit individuals had half the death rate of unfit trim individuals.
Being somewhat overweight may also have some benefits under specific circumstances:
It should be stressed, however, that obesity itself is never healthful in anyone.
Heart Disease and Stroke
Individuals with a BMI of at least 30 have a 50% to 100% increased risk for death compared with individuals at a BMI of 20 to 25. Mortality rates from many causes are higher in obese people, but heart disease is the primary cause of death. People who are obese have almost three times the risk for heart disease as people with normal weights. Being physically unfit adds to the risk.
Weight concentrated around the abdomen and in the upper part of the body (apple-shaped) is particularly associated with insulin resistance and diabetes, heart disease, high blood pressure, stroke, and unhealthy cholesterol levels. Fat that settles in a "pear-shape" around the hips and flank appears to have a lower association with these conditions.
Obesity poses many dangers to the heart and circulatory system.
Damage in the Blood Vessels. Changes in body fat as people age, particularly increasing abdominal fat, have specifically been associated with stiffness in the aorta, the major artery leading from the heart. Studies are finding higher levels of a factor called C-reactive protein (CRP) in people with obesity and abdominal fat. CRP is now considered to be a marker for inflammation and damage in the arteries. (Losing weight reduces CRP levels.)
High Blood Pressure. Hypertension is the health problem most commonly associated with obesity, and the greater the weight, the greater the risk. Hypertension carries serious risks for stroke, heart attack, and heart failure. The link between obesity and high blood pressure is complex and may reflect interactions of genetic, demographic, and biologic factors. Many studies have reported that modest weight loss is beneficial for reducing existing blood pressure. [For more information, seeWell-Connected Report #14, High Blood Pressure.]
Heart Failure. An important 2002 study reported that obesity might account for 11% of heart failure cases in men and 14% in women. This link existed independently of other risk factors, such as high blood pressure, sleep apnea, and diabetes, which are also associated with obesity. The biologic mechanisms involved in obesity that lead specifically to heart failure are not clear. [For more information, seeWell-Connected Report #13, Heart Failure.]
Unhealthy Cholesterol Levels and Lipid Levels. The effect of obesity on cholesterol levels is complex. Although obesity does not appear to be strongly associated with overall cholesterol levels, among obese individuals triglyceride levels are usually high while HDL (the so-called "good" cholesterol) levels tend to be low, both risk factors for heart disease. [For more information, seeWell-Connected Report #23, Cholesterol, Other Lipids, and Lipoproteins.]
Stroke. Obesity is also associated with a higher risk for stroke. [For more information, seeWell-Connected Report #45, Stroke.]
Insulin Resistance, Type 2 Diabetes, and Syndrome X (Metabolic Syndrome)
Type 2 Diabetes and Insulin Resistance. Most people with type 2 diabetes are obese and, in fact, studies strongly suggest that weight loss may be the key in controlling the current epidemic in diabetes type 2. The connection between obesity and diabetes is not entirely clear, since most obese people are not diabetic.
The common factor appears to be insulin resistance. Insulin is a critical hormone in the metabolism of sugar. In type 2 diabetes, different factors cause the body to become insulin resistant--that is, it can no longer use it. This has the effect of increasing blood glucose (sugar in the blood), the hallmark of diabetes. Both obesity and insulin resistance at different phases are marked by elevated levels of certain chemicals (e.g., free fatty acids and the hormones resistin and leptin). It is not known yet if the higher levels are simply a product of obesity or play some causal role in diabetes.
Insulin resistance is also associated with high blood pressure and abnormalities in blood clotting. Some research indicates that obesity, in fact, is the one common element linking insulin resistance, diabetes type 2, and high blood pressure. [For more information, see the Well-Connected Report #60, Diabetes Type 2.]
Metabolic Syndrome. Metabolic syndrome (also called syndrome X) is a pre-diabetic condition that is significantly associated with heart disease and higher mortality rates from all causes. The syndrome consists of obesity marked by abdominal fat, unhealthy cholesterol levels, high blood pressure, and insulin resistance. A 2002 study estimated that nearly a quarter of the U.S. population now has this condition. Even worse, according to a 2003 study, nearly a million American teenagers have this syndrome. A combination of weight loss and exercise is an effective treatment for this syndrome.
Obesity has been associated with a higher risk for cancer in general and specific cancers in particular. Studies have also suggested that restricting calories reduces the risk for cancer. Some experts believe that effective weight control for children and adults could reduce cancer rates by 30% to 40%. One way obesity may increase the risk for cancer is its association with high levels of hormones called growth factors, which can trigger rapid cell proliferation leading to cancer.
Uterine Cancers. Women who are obese appear to have two to three times the risk for uterine cancer as thinner women.
Prostate Cancer. A 2001 study reported that obesity was associated with a modest increase in prostate cancer mortality, although not with the risk for prostate cancer itself. Some evidence suggests that it is a high-calorie intake rather than obesity or fat intake increases the risk for prostate cancer.
Breast Cancer. Studies have reported mixed effects on the association between obesity and breast cancer. A number of studies have linked obesity to breast cancer in postmenopausal women, particularly in women who begin to gain weight after age 18. One study, in fact, suggested that being heavier as a child conferred a lower risk for breast cancer after menopause.
Gallbladder Cancer. Obese women are at higher risk for gallbladder cancer.
Gastrointestinal Cancers. A number of cancers in the gastrointestinal tract have been associated with obesity:
(Obesity does not appear to be related to a higher risk for stomach cancer.)
Muscles and Bones
Obesity places stress on bones and muscles, and overweight people are at higher risk for hernias, low back pain, and aggravation of gout and other arthritic conditions. Studies report that the incidence of osteoarthritis is significantly increased in people who are overweight. People who are obese are also at higher risk for carpal tunnel syndrome and other problems involving nerves in their wrists and hands. It should be noted that some weight may be protective against osteoporosis (loss of bone density).
Eyes and Mouth Disorders
Obesity increases the risk for the following mouth and eye disorders:
Reproductive and Hormonal Problems
Infertility. Abnormal amounts of body fat, either 10% to 15% too high or too low, can contribute to infertility in women. Obesity is specially related to certain problems related to infertility, such as uterine fibroids or menstrual irregularities. In men, obesity can contribute to reduced testosterone levels.
Effect on Pregnancy. The dangerous effects of obesity on pregnancy are multifold. They include high blood pressure, gestational diabetes (diabetes, usually temporary, that occurs during pregnancy), urinary tract infections, blood clots, prolonged labor, a higher fetal mortality rate in late stages of pregnancy, and cesarean delivery. Infants of women who are obese are also at higher risk for neural tube birth defects, which affect the brain or spine. Folic acid supplements, ordinarily effective in preventing these conditions, may not be as protective in overweight women.
Effects on the Lungs
Obesity is thought to be a risk factor for adult-onset asthma, although there is some evidence that although obesity causes wheezing and shortness of breath, it does not appear to be strongly associated with the disease mechanisms in the lungs that cause true asthma.
Obesity also puts people at risk for hypoxia, in which oxygen is insufficient to meet the body's needs. Obese people need to work harder to breathe and tend to have inefficient respiratory muscles and diminished lung capacity. The Pickwickian syndrome, named for an overweight character in a Dickens novel, occurs in severe obesity when lack of oxygen produces profound and chronic sleepiness and, eventually, heart failure.
Effect on the Liver
Nonalcoholic Fatty Liver Disease. People with obesity, particularly if they also have diabetes type 2, are at higher risk for a condition called nonalcoholic fatty liver disease, also called nonalcoholic steatohepatitis (NASH). It may occur in about half of people with diabetes and 20% to 50% of obese people, depending on how severe the obesity is. It can also occur in overweight children. This condition causes liver damage that is similar to liver injury seen in alcoholism. In some cases, it can be very serious and require liver transplantation.
Gallstones. The incidence of gallstones is significantly higher in obese women and men. The risk for stone formation is also high if a person loses weight too quickly. In people on ultra-low calorie diets, gallstones may be prevented by taking ursodeoxycholic acid (Actigall).
People who are obese and nap tend to fall asleep faster and sleep longer during the day. At night, however, it takes them longer to fall asleep and they sleep less than people with normal weights. In an apparent vicious circle, studies have suggested that obesity not only interferes with sleep but that sleep problems may actually contribute to obesity.
Sleep Apnea. Obesity, particularly the apple-shape, is strongly associated with sleep apnea, which occurs when the upper throat relaxes and collapses at intervals during sleep, thereby temporarily blocking the passage of air. Sleep apnea is increasingly being viewed as a potentially serious health problem, including heart disease and stroke. Some studies suggest that among overweight people, those who have sleep apneas have a greater heart risk than those without them. Obesity may contribute to sleep apnea simply by fatty cells infiltrating the throat tissue, which could narrow the airways. In one study, the more obese a person with sleep apnea was, the higher the pressure on the airway and therefore the greater the obstruction of the airway. (Obstructive sleep apnea may also cause obesity itself, however, as sleepy people tend to be sedentary.) Some studies are even indicating that treating sleep apnea may help people lose abdominal fat.
Narcolepsy. A small European study found a link between narcolepsy (a sleep disorder characterized by excessive daytime sleepiness with frequent daily sleep attacks) and high BMI.
Emotional and Social Problems
Depression. A number of studies have reported an association between depression and obesity, particularly in obese women. There may be a number of factors to explain the link. In some cases of atypical depression, people overeat and may gain weight. Overweight people may also become depressed because of social problems and a poor self-image. In these cases, depression is usually resolved when people lose weight. There is also some evidence, however, that obesity itself may impair levels of tryptophan--a precursor of serotonin, which is a brain chemical associated with mental well-being. In one study, even after people lost weight, tryptophan levels were lower than normal. In any case, there does not appear to be any association between depression and obesity in men.
Social Problems. One long-term study reported that overweight young women completed fewer years of school, were 20% less likely to be married, and had 10% higher rates of household poverty than their thinner peer. Obese young men were also less likely to be married their incomes were lower than their thinner peers. Nevertheless studies consistently show that overweight males (both boys and men) are not as severely emotionally affected as females of any age. Women and girls tend to blame themselves for being heavy while males tend to attribute being overweight to outside factors.