We’ve noted a number of the conditions highly associated with obesity, including insulin resistance and type 2 diabetes, atherosclerosis, hypertension, and abnormal blood lipid levels. All these disorders are serious, and all are related to metabolic syndrome. There are, however, many more serious health conditions associated with obesity that you should know about.
Gastroesophageal Reflux Disease (GERD)
In acid reflux, stomach acid flows up from the stomach into the esophagus, the tube that connects your mouth with your stomach. Acid reflux creates the discomfort known as heartburn. Gastroesophageal reflux disease (GERD) is severe and chronic acid reflux. Untreated GERD can lead to esophageal cancer due to changes in cells damaged by stomach acid.
Obesity tends to worsen GERD. Studies have shown that the frequency of acid reflux is directly related to BMI: Frequency increases as BMI goes up. It's unclear as to why this is the case.
One theory is that increased pressure inside the abdomen (due to excess fat) squeezes and forces the contents of the stomach into the esophagus. Another theory suggests that if more fat is present at the gastroesophageal junction (the place where your stomach and esophagus meet), it can interfere with the natural mechanisms that exist to prevent acid reflux.
One thing is clear: The prevalence of GERD in the general population is increasing, probably because of the surge in rates of obesity.
Cancer
Certain cancers are linked to obesity. These include cancers of the colon and rectum, breast (in postmenopausal women), endometrium (lining of the uterus), kidney, and esophagus. There’s evidence that obesity is also linked to cancers of the gallbladder, ovaries, and pancreas.
High blood sugar levels and type 2 diabetes increase the risk of cancer and make it harder to treat. That’s because cancer cells consume glucose in far greater amounts than any other available nutrient. In rapidly growing cancer cells, rates of glycolysis (using glucose to produce energy) are up to 200 times faster than in normal cells.
Another result of too much blood sugar, as you know, is high levels of insulin. Insulin stimulates cancer cell growth. A structurally similar protein, called insulin-like growth factor (IGF-1), also plays key roles in tumors’ growth and proliferation.
Together, abnormally high blood glucose and the resulting elevated levels of insulin provide a feast for cancer cells.
Infertility
Obesity increases the risk of infertility in both men and women. In men, excess fat can cause overheating of the sperm. Hormonal imbalances due to obesity can lead to low sperm count and poor motility (sperm movement) as well as sperm abnormalities.
Obese women may have difficulty conceiving due to the high levels of estrogen secreted by fat tissue. Estrogen is the main reproductive hormone in women. When levels are either too high or too low, estrogen makes the uterus less receptive to a fertilized egg. Elevated insulin levels also disrupt the proper functioning of the pituitary gland, which releases hormones critical for ovulation.
Sexual Dysfunction
Obesity takes a toll on male sexuality. The reasons for this seem to be physical, not emotional or psychological. One problem is a lack of testosterone, which is necessary for erections. Fat cells transform testosterone (a male sex hormone) in the body into estrogen (a female sex hormone).
Diabetes, a frequent companion to obesity, is strongly associated with erectile dysfunction (inability to have an erection). In fact, 35-50% of men with diabetes in the US have erectile dysfunction. Diabetes causes erectile dysfunction by injuring nerves and blood vessels.
This damage is caused by elevated levels of glucose in the blood. Glucose acts as a toxin on nerve cells when it’s present in large amounts. Damaged nerves can no longer properly transmit signals, including signals from the brain that trigger an erection.
Erections also require healthy arteries and capillaries in the penis. High glucose causes arteries to become stiffer, weaker, and clogged with plaque. It also makes tiny capillaries more fragile, so that they develop leaks. Without healthy blood vessels, it’s difficult or impossible to sustain an erection.
Back Pain
Carrying too much weight, and especially having a big belly, increases the risk of straining your back.
Being out of shape and overweight adds to the burden on your spine and your muscles. Your back muscles may weaken and tighten, making it more likely that you’ll get strains and sprains. If you’re carrying a lot of weight in your abdomen, you probably have weak abdominal muscles. This lack of muscle support can also lead to back pain.
Obesity is often accompanied by clogged arteries, and the resulting obstruction of healthy blood circulation robs your back muscles and discs of vital nutrients. Inflammation caused by the dangerous substances secreted by excess fat can also harm these tissues. Both of these factors not only increase your risk of being injured but also slow down the healing process when you are injured.
Osteoarthritis
When you’re obese, you greatly raise your risk of developing osteoarthritis (OA), especially of the knee. Women who are overweight have four times the risk and overweight men have five times the risk of developing knee OA as people of normal body weight.
IMAGE: Smooth as glass cartilage caps the ends of bones and reduces friction as your joint moves (left image). In osteoarthritis, the cartilage between your joint breaks down and the bone found underneath changes (right image).
Why does obesity so greatly increase the risk of OA? The answer may lie in the increased mechanical stress that obesity creates. Your knee and hip joints are the major load-bearing joints of your body. If you’re overweight or obese, you hugely increase the load that your knees and hips must carry. When you’re walking, a force of 3 to 6 times your body weight is exerted across your knee. Being just 10 pounds (4.5 kilograms) overweight increases the force on your knee by 30-60 pounds (13-27 kg) with each step. If you’re 50 pounds (~27 kilograms) overweight, you increase that force by 150-300 pounds (68-136 kilograms)!
The force exerted across your hip is estimated to be a maximum of 3 times your body weight. That means if you weigh 200 pounds (~91 kilograms), up to 600 pounds (272 kilograms) of force are being exerted on your hip joints with each step.
In addition to mechanical stress, there may well be other factors linking obesity and OA. Studies have shown there’s an association between being overweight and developing OA of the hand, even though the joints of the hand are not load bearing. The systemic inflammation that accompanies obesity may be one such factor.
Your quality of life and your life expectancy are worsened by obesity as well as by OA. Researchers found that obesity reduces life expectancy and quality of life by 12%, and osteoarthritis of the knee reduces both by an additional 12%.
Obstructive Sleep Apnea
If you snore loudly, sleep restlessly, or wake up often, or if you gasp or stop breathing when sleeping, you may have obstructive sleep apnea (OSA). Snoring is very often associated with sleep apnea—but not everyone who has sleep apnea snores, and not everyone who snores has OSA.
Obstructive sleep apnea happens when a person’s pharynx, or upper airway, collapses while he or she sleeps. Air flow into the lungs is blocked for anywhere from 10 seconds to over a minute. (If air is blocked for less than 10 seconds, it’s not considered sleep apnea.) As the person struggles for breath, blood oxygen level falls, and the brain responds by waking the person up just enough to cause the upper airway muscles to constrict. This opens the airway, allowing for a breath. The person may snort or gasp and then fall back asleep. Snoring resumes (if the person snores). This cycle may be repeated literally hundreds of times a night. Sleep is fragmented and the amount of time spent in the deeper levels of sleep is decreased.
Because people who have sleep apnea usually don’t fully regain consciousness when they wake after a sleep apnea episode, they often have no idea that they are waking up so many times a night. Until someone else notices their sleep patterns, they may have no idea why they wake up with a headache or feel so tired during the day.
Sleep apnea is much more than just annoying. People with sleep apnea have higher rates of type 2 diabetes, cardiovascular disease, and stroke as well as an increased risk of death from any cause. As many as 50% of people with sleep apnea have high blood pressure. Having disrupted sleep can cause personality changes and make you feel sleepy and fatigued during the day. You may also become irritable and depressed. Finally, lack of sleep can disrupt the hormones that control your appetite.
Rates of sleep apnea are on the rise, and there’s no question that’s because sleep apnea is so closely associated with obesity, now a global epidemic. It’s estimated that as many as 40% of obese people have sleep apnea, and about 70% of people with OSA are obese. With every 22-pound (10 kilogram) increase in body weight, the risk of developing OSA doubles. Sleep apnea can affect anyone, male or female, of any age—even children. It’s hard to say exactly how many people have sleep apnea because it’s so often missed, but it’s estimated that over 85% of Americans with sleep apnea have never been diagnosed.
Decreased Lung Function
As visceral fat accumulates inside of your abdomen, it starts to crowd your internal organs and muscles, particularly your diaphragm. The diaphragm is a dome-shaped sheet of muscle that separates your chest from your abdominal cavity—the area deep inside your lower torso. When you inhale, your diaphragm contracts (tightens) and moves downward, creating a vacuum in your lungs and causing air to rush into them. The downward contraction of your diaphragm increases the space in your chest cavity, allowing your lungs to expand. The muscles between your ribs also help to enlarge the space in your chest. These muscles contract as you inhale, pulling your rib cage both upward and outward.
When you’re obese, and especially if you’re carrying a lot of visceral fat, the downward movement of your diaphragm is limited by the excess fat tissue filling your abdomen. Your diaphragm can’t move fully down into your abdomen, so your lungs can’t fill deeply with air.
What’s more, if you have a lot of subcutaneous fat, it can add a lot of weight on your chest wall. Your chest wall may become so heavy that the muscles between your ribs are unable to pull the rib cage upward and outward.
This combination of subcutaneous fat weighing down your chest, and visceral fat stuffing your insides, decreases the ability of your lungs to function properly and makes it harder for you to breathe.
Asthma
Asthma is a condition in which the airways of your lungs are chronically inflamed. Allergens or other triggers can cause the smooth muscle tissue that surrounds your airways to constrict (narrow). These triggers can also prompt an inflammatory response from the immune cells that line your airways, causing them to release an excessive amount of mucus. The constriction and the mucus narrow your airways, creating symptoms that can include shortness of breath, wheezing, coughing, and chest tightness.
IMAGE: Healthy lung airway (left image). In asthma the walls of the airways may produce mucus and thicken, restricting airflow (right image).
There is a strong link between obesity and asthma. All over the world, studies have found that obese individuals are more likely to develop asthma. In fact, being even moderately overweight increases your risk of having asthma. Overweight and obese individuals have a 38% and 92% higher risk, respectively, for developing asthma than people of normal weight.
Obese people aren’t just more likely to have asthma, they’re also more likely to have severe and persistent asthma. The more obese the individual, the more severe and persistent the asthma is likely to be. Obese people with asthma are also more likely to be hospitalized than non-obese people with asthma.
Asthma is harder to control in someone who is obese as well. Obese individuals with asthma are more likely to need asthma medications than nonobese people with asthma. However, these obese individuals are less responsive to standard asthma medications, such as inhaled corticosteroids. The more obese someone is, the less responsive that person is likely to be to asthma medication.
It is clear that obesity can cause asthma, but the relationship between obesity and asthma is complex. How, exactly, the two disorders are related remains a mystery. The cause-and-effect relationship is not totally clear cut, because not everyone who is obese has asthma. It may be that a combination of factors, including lung mechanical function, associated conditions such as GERD and sleep apnea, genetics, some form of inflammation, and other factors all work together to cause asthma in someone who is obese.
Depression
The burden of obesity extends to your psychological well-being, too. Depression frequently goes hand in hand with obesity: If you are obese, you’re approximately 20% more likely to have depressive disorders than someone who isn’t obese. People who are obese are more likely to become depressed, and people who are depressed are more likely to become obese.
Does obesity cause depression, or vice versa? There are probably a number of reasons why obesity and depression are associated. Some of these reasons are psychological. If you’re obese, you may experience yourself as being in poor health, criticize your own behavior and your appearance, and have low self-esteem. This can be especially true if you belong to a social group that prizes thinness. These negative self-perceptions may lead to depression. Then, too, if you are obese you may actually be in poor health, because obesity brings with it so many related disorders. Poor health can be a causative factor in depression as well.
On the other side of cause and effect, it seems the physiological changes to the hormonal and immune systems that occur in the body due to depression can to lead to obesity, too. And if you’re depressed, you’re more likely to neglect your health. You may have trouble staying physically active and find it difficult to avoid overeating and unhealthy food—leading to overweight and obesity.
The hormone leptin keeps popping up as a possible agent in many of the disorders associated with obesity. It’s theorized that low levels of leptin are a causative factor in depression. However, leptin is found at high levels in people who are obese, so at first glance such a link would seem unlikely. But people who are obese seem to develop a resistance to leptin, in much the same way that someone with type 2 diabetes develops a resistance to insulin. This resistance is demonstrated by the fact that giving leptin to nonobese people decreases their appetite but has no effect on obese people. It’s this resistance that’s thought to lead to high levels of leptin in people who are obese.
Depression may cause you to put on more visceral fat. One study found that, over 5 years, the waist circumference of people with high levels of depression grew faster than the waist circumference of people with low levels of depression. This may be because cortisol, a stress hormone, is associated with depression. Cortisol affects fat distribution by causing you to store more fat centrally, as visceral fat.
Alzheimer’s Disease
Who are you as a person? Many would say that you are the sum collection of all your experiences, your entire life, stored as memories.
Alzheimer’s disease is a progressive condition that targets some of the most critical brain functions: memory, thinking, and behavior. Alzheimer’s is not a normal part of aging. In Alzheimer’s, abnormalities occur in the brain cell structures and interfere with the normal activity of nerve cells.
People who are obese have an almost four times greater risk of developing dementias, such as Alzheimer’s, in later life. Obesity also accelerates cognitive decline and the progression of Alzheimer’s.
IMAGE: Healthy brain cross section (left image). Brain cross section with Alzheimer’s disease (right image).
The reasons for the association between obesity and Alzheimer’s aren’t entirely clear, but it appears very likely that blood vessel damage caused by obesity (and its related disorders, including hypertension and type 2 diabetes) has a great deal to do with it. Up to a quarter of the blood pumped out from each heart beat is dedicated to the brain, and any decrease in that flow can boost the risk of nerve damage and promote Alzheimer’s.
High glucose and insulin levels due to type 2 diabetes and metabolic syndrome are probably also to blame. Both glucose and insulin can damage blood vessels by causing inflammation. Excess glucose may also damage the brain cells directly.