Obesity has traditionally been measured with body mass index (BMI), a calculation based on an individual’s weight and height. However, waist-to-hip ratio and waist measurement may provide more useful information.
The connection between excessive weight and the risk for prediabetes and diabetes is well documented. More than 85 percent of people who develop type 2 diabetes are considered overweight or obese, according to the Centers for Disease Control and Prevention (CDC).
Excess weight also increases pregnant women’s risk of developing gestational diabetes. In addition, people with type 1 diabetes who become overweight can develop insulin resistance, a condition known as double diabetes.
Furthermore, obesity increases the risk of many diabetic complications, including heart conditions, stroke, kidney disease and eye disease.
Excessive weight has reached epidemic levels in the United States. About one-third of American adults are obese and an additional one-third are overweight, according to federal health agencies. Rising rates of obesity in America and worldwide are fueling a global increase in diabetes.
Poor diet and lack of exercise are the main causes of obesity, but many other factors may be involved as well, such as genetics, prior health problems, age, culture and medications. Reducing obesity plays a central role in preventing or managing type 2 diabetes. In some cases weight-loss surgery has resolved cases of type 2 diabetes. In addition, some newer diabetes treatments have shown promise in fighting obesity.
About obesity and diabetes
Obesity, a primary risk factor for developing type 2 diabetes, is an abnormally high amount of body fat. U.S. health agencies define obesity as a body mass index (BMI) of 30 or more and overweight as a BMI of 25 to 29.9. BMI is a calculation using a person’s height and weight.
Excessive weight has reached epidemic levels in the United States. Thirty-four percent of American adults are obese, the U.S. Centers for Disease Control and Prevention (CDC) reported in late 2007. In addition, a similar percentage is overweight. The prevalence of morbid obesity (BMI of 40 or more) jumped fourfold between 1986 and 2000, according to the CDC. Obese people have a 50 to 100 percent increased risk of death compared to people of normal weight, the National Institutes of Health reports.
The exact cause of type 2 diabetes is unknown, but obesity is one of the strongest factors in its development. In fact, about 85 percent of people who have type 2 diabetes are overweight or obese, according to the CDC. The International Diabetes Federation estimates that the number of diabetes cases worldwide will grow from about 246 million in 2007 to 380 million in 2025, fueled largely by rising rates of overweight and obesity. Many large studies have concluded that there is a strong link between obesity and diabetes, as strong as the association between smoking and lung cancer.
One reason for the link is that when body fat increases, impaired fasting glucose and impaired glucose tolerance (prediabetes) can develop. Most people with insulin resistance or glucose intolerance are unaware of their condition as there may not be symptoms to warn them of the progression toward diabetes.
Obesity is also a risk factor for gestational diabetes and many diabetic complications. It may cause an earlier onset of type 1 diabetes and can trigger double diabetes, which is the development of insulin resistance in someone with type 1 diabetes.
Measures and standards
Obesity and overweight are often used interchangeably. However, there is a distinct difference between the two terms. The traditional standard used to determine if a person is overweight or obese has been the body mass index (BMI).
BMI is a number that shows body weight adjusted for height. Using standard measurement, divide weight (in pounds) by height (in inches, squared) and multiply by 705. Using the metric system, divide weight (in kilograms) by height (in meters, squared).
For example, a man who weighs 250 pounds and is 6 feet tall would have a BMI of 33.9. This is 250 divided by 5,184 (which is 72 inches squared) and multiplied by 705.
BMI ranges include the following classifications, according to the National Institutes of Health (NIH):
|BMI Range||Classification||% Above Normal|
|18.5 to 24.9||Normal||n/a|
|25.0 to 29.9||Overweight||20 to 25 percent|
|30.0 to 39.9||Obese||25 to 35 percent|
|40+||Extreme/morbid obesity||35 to 40 percent|
The BMI was developed by the NIH in 1998 in an effort to define classes of overweight and obesity. Many physicians believe that BMI offers a better way to calculate body fat and the associated health risks than the previous standard of using height and weight tables.
However, BMI is only an estimate of body fat and does not take a number of factors into account, including the amount of muscle mass. Extremely muscular individuals may have a high BMI but are not obese and do not have increased risks for disease. Conversely, BMI may not provide an accurate measurement of people who have high concentrations of abdominal fat or those with low muscle mass.
Waist measurement may be used in combination with BMI to calculate a person’s risk for diabetes. People with central obesity (abdominal fat, sometimes referred to as an “apple shape”) are at an increased risk of diabetes. The following chart provides healthy versus obese ranges for men and women:
|Waist Measurements by Sex|
in inches and centimeters (cm)
|Men||< 37 inches (94 cm)||> 40 inches (102 cm)|
|Women||< 32 inches (81 cm)||>35 inches (89 cm)|
Another tool is the waist-to-hip ratio. This ratio is determined by measuring the circumference of the waist and dividing it by the circumference of the hips. If the stomach measurement is larger than the hip measurement, indicating abdominal or visceral fat, the risk is increased for development of diabetes, as well as many cardiovascular diseases. Some recent research suggests the waist-to-hip ratio may be a more valuable tool than the BMI in identifying cardiovascular and diabetic risks, especially in elderly people.
These are general tools most health practitioners can use to gauge risk. Other tools provide more precise information but may be expensive or impractical for many patients:
- Bioelectrical impedance analysis (BIA). A noninvasive electrical current is sent through the body and conductivity is measured. The higher the conduction, the more muscle and lean tissue.
- Body composition tracking system. A test that uses a computerized, pod-like chamber to measure a person’s volume and mass. The person’s whole-body density can then be calculated, including fat and muscle percentages.
- Bone density scan. Often used to measure bone density and screen for osteoporosis, dual energy x-ray absorptiometry (DEXA) also shows the percentage of body fat, as well as where and how much fat a person has.
- Skinfold thickness. Skin calipers measure the thickness of skin and subcutaneous fat just beneath the skin on the back of the arm, waist or thigh.
- Underwater (hydrostatic) weighing. The patient is weighed underwater, showing how much lean body mass and body fat there is.
Related conditions and complications
Obesity is strongly linked to the development of type 2 diabetes. It is also associated with other diabetic conditions and complications, including:
- Prediabetes. A condition in which glucose (blood sugar) levels are higher than normal, but not high enough for a diagnosis of diabetes. According to the American Diabetes Association, 54 million Americans have prediabetes. Insulin resistance is a closely related state. Recent research shows that some people with prediabetes have complications that were once associated with diabetes, including cardiovascular damage and nerve disease (diabetic neuropathy).
For more than half of the people with prediabetes, healthier eating, increasing exercise and moderate weight loss could mean delaying the development of diabetes or preventing it altogether. For example, a 200-pound man who loses just 5 percent of his body weight (10 pounds) may drop his glucose level down below prediabetic levels.
- Hyperinsulinemia. An excess of insulin in the blood. Hyperinsulinemia can lead to complications including hypoglycemia (low blood sugar), excessive blood clotting, cardiovascular disease, kidney stones and gout.
- Gestational diabetes. A temporary form of diabetes that can develop only among pregnant women. Women who have gestational diabetes also have a greater risk of developing type 2 diabetes later in life. Obesity also increases the risk of pregnancy complications such as preeclampsia.
- Type 1 diabetes. An autoimmune condition in which the pancreas stops producing insulin. Many people with type 1 diabetes are of normal weight or even underweight. However, excess weight in those predisposed to type 1 diabetes may cause the disease to develop earlier in life. In addition, people with type 1 diabetes who become overweight or obese can develop insulin resistance, a condition known as double diabetes.
- Cardiovascular disorders. These are the primary cause of death in people with diabetes. Obesity is linked to dyslipidemia (unhealthy levels of cholesterol and other blood fats), blood vessel diseases (e.g., diabetic angiopathy, atherosclerosis), elevated blood pressure, heart conditions, stroke and metabolic syndrome.
- Kidney conditions. Overweight and obesity increase the risk of proteinuria, diabetic nephropathy and end-stage renal disease.
- Eye diseases. Obesity and two conditions that often accompany it, high blood pressure and unhealthy cholesterol levels, may accelerate diabetic retinopathy. High blood pressure is also linked to increased risk of cataracts and glaucoma.
- Cancer risk. Obesity is believed to account for part of the reason diabetes increases the risk of several cancers.
- Acanthosis nigricans. This skin condition may appear in overweight people who are insulin resistant.
- Polycystic ovarian syndrome (PCOS). This hormonal imbalance in women is linked to insulin resistance and type 2 diabetes.
Obesity also increases the risk of many other conditions, including arthritis, back pain, respiratory problems, sleep apnea, nonalcoholic fatty liver disease, gallbladder disease and prostate enlargement (benign prostatic hyperplasia).
Obesity often reflects poor dietary habits and a sedentary lifestyle, both of which can lead to unhealthy fluctuations in glucose (blood sugar). Conversely, people with diabetes who are able to lose even modest amounts of weight can see dramatic decreases in their risk for developing complications and increase their ability to control glucose.
Risk factors and potential causes of obesity
A combination of poor diet and lack of exercise is the main cause of obesity. This typically involves a high-calorie, highly processed diet combined with a sedentary lifestyle.
Portion sizes have ballooned in restaurants, homes and schools. Many people favor sugars, starches and saturated fats over vegetables, fruits, high-fiber whole grains, lean protein and monounsaturated fats. In addition, fewer than one-third of Americans meet basic levels of physical activity, often defined as at least 30 minutes a day most days of the week.
However, the development of obesity is complex, and there are many reasons, including environmental and inherited factors, that can lead to a person becoming obese. Some of the most common are:
- Alcohol. Consuming too much alcohol can lead to obesity because alcohol is high in calories without offering nutritional benefit.
- Medications. Drugs that can cause weight gain include insulin, some antidiabetic agents (sulfonylureas, thiazolidinediones, meglitinides) corticosteroids and some medications used for psychiatric conditions.
- Eating disorders or other psychological issues. An estimated 10 percent of mildly obese people who attempt to lose weight through weight loss programs or on their own have a binge eating disorder, according to the National Institute of Diabetes and Digestive and Kidney Diseases. Among those who are severely obese, this disorder is even more common. Also, some people eat, even when they are not hungry, as a way of dealing with stress, anger, sadness or other emotions.
- Genetic predisposition. If one or both parents are obese, the child’s chances of becoming obese are increased. Though there is no escaping some familial traits, it is possible to maintain control when it comes to weight.
- Race and ethnicity. Rates of obesity and diabetes are higher among minority populations, especially Native Americans, black Americans and Hispanics. For example, black Americans and Puerto Ricans have diabetes rates that are 1.8 times higher than non-Hispanic whites, according to the National Diabetes Education Program (NDEP). Rates among Mexican Americans are 1.7 times higher than in white Americans and 2.2 times higher in American Indians and Alaska Natives than in whites. Factors that may contribute to these discrepancies include genetics as well as culture, diet and economic status.
- Medical conditions. An overproduction of hormones by the adrenal glands (Cushing’s syndrome), low thyroid function (hypothyroidism), polycystic ovarian syndrome, low metabolic rate or other medical problems can all lead to obesity. However, these conditions account for less than 2 percent of all cases of obesity.
- Physiological influences. Metabolic rates vary by the individual. This means that two people with the same height, weight and body type can require a different number of calories to maintain a normal body weight.
Diagnosis and treatment of obesity
A diagnosis of obesity can come from calculating body mass index (BMI). A BMI of 30 or more is considered obese.
Waist-to-hip ratio divides the circumference of the waist by the circumference of the hips. A high ratio reveals central obesity.
A physician determines whether or not someone is clinically obese – and therefore at an increased risk for the development of type 2 diabetes and other diseases. It is likely that in addition to measuring a patient’s BMI and waist circumference, a patient’s medical history will be reviewed to take into consideration other risk factors, including smoking, drinking alcohol and high levels of stress.
Patients with diabetes, including type 1 diabetes and gestational diabetes, can often achieve better control of their glucose (blood sugar) levels by losing excess weight, becoming more active and following a healthy eating plan.
Even losing as little as 5 to 7 percent of body weight can result in a dramatic decrease in risk for diabetes, heart disease and stroke. Most physicians agree that management and treatment of obesity requires permanent changes to the diet. To lose weight, numerous options are available, including:
- Good nutrition. For most people, a balanced diet containing no more than 2,000 calories a day for women and 2,500 for men is recommended. Crash diets are not recommended as they can lead to additional health problems.
- Regular exercise. Exercise without an associated change in diet will likely reduce weight by only a few pounds. Physical exercise of at least 150 minutes a week along with a balanced diet is crucial for long-term weight loss. For those already diagnosed with diabetes, exercise has also been proven to reduce the risk of developing complications, including coronary artery disease.
- Nutrition counseling. Several studies have confirmed that obese patients who receive nutritional counseling from a dietitian achieved better weight-loss outcomes, including better metabolic control and reduced waist circumferences.
- Diet pills. Some diet pills are available over the counter, and others require a physician’s prescription. The U.S. Food and Drug Administration has approved only one over-the-counter weight-loss drug, a form of orlistat known as Alli. The usefuless of many of the other nonprescription substances marketed as weight-loss aids has not been proven, and there may be concerns about side effects and safety. Anyone considering use of these drugs should discuss the potential risks with a physician. It is also important to eat right and exercise regularly.
Prescription diet pills may be recommended for some patients. However, most people who use them regain the weight when they stop taking the medication. Also, the long-term effects of taking these drugs are not known. Research is continuing on improved weight-loss medications.
- Gastric surgery. In cases of morbid obesity (BMI greater than 40), doctors may recommend gastroplasty (stomach stapling) or gastric bypass. These bariatric operations allow limited amounts of food to be eaten at one time. There have been reports of bariatric surgery resolving some cases of type 2 diabetes, but it is important to note that these procedures carry risks and can have considerable side effects.
For people who take medication for type 2 diabetes, some newer antidiabetic agents may be an option. A recently introduced class of injected medications called incretin mimetics has helped many patients lose weight.
Prevention methods for obesity & diabetes
For the millions at risk for developing diabetes, action can be taken to delay and possibly even prevent the disease. Typically this involves weight loss.
Prevention of obesity requires a healthy lifestyle, including a well-balanced diet that is high in fiber and low in fat and refined sugars. It is estimated that 64 to 74 percent of all cases of type 2 diabetes could be prevented by reducing body mass index (BMI) to below 25, according to the Nurses’ Health Study. The Nurses’ Health Study followed more than 120,000 registered nurses to investigate the risk factors for major illnesses that affect women.
Time after time, studies have shown that weight loss and exercise can significantly reduce the risk of developing serious diseases, such as diabetes. The landmark Diabetes Prevention Program (DPP) showed that even a moderate increase in activity levels combined with a weight loss of just 5 to 7 percent of body weight can delay and possibly prevent the onset of diabetes in people considered to be at high risk of developing the disease. In fact, those who made modifications to their lifestyle were able to reduce their risk of developing type 2 diabetes by 58 percent.
Weight loss is best achieved gradually, under a physician’s supervision, through regular exercise and sensible meal planning. Nutrition counseling and support groups may benefit some people. Patients considering weight-loss drugs or surgery are urged to consult their physician about the risks and benefits.
Ongoing research regarding obesity & diabetes
Researchers continue to investigate the link between obesity and diabetes. Though scientists realize it is a major factor in the development of type 2 diabetes, exactly how the excess fat causes the disease is not clearly understood. The search for the link at the molecular level involves clinical research to not only find the connection, but also develop measures to combat these conditions.
One line of research involves examining the pathway that is responsible for a series of reactions within the body that lead to insulin resistance. Researchers have discovered that obesity leads to stress within a system of cellular membranes known as endoplasmic reticulum (ER). The stress in this system in turn causes the ER to suppress the insulin receptor signals, which leads to insulin resistance.
Other researchers have located a primary trigger for type 2 diabetes – a genetic “master switch” in the liver that is flipped on when people become obese. Once on, this switch creates low-level inflammation, which in turn disrupts the body’s ability to process insulin, resulting in the development of type 2 diabetes.
A hormone called resistin is also being studied as a potential link between obesity and diabetes. The hormone, discovered in mice, causes cells to be resistant to insulin. Too much of this hormone is believed to result in insulin resistance. In mice, limiting their resistin activity showed an improvement in their glucose (blood sugar) level and response to insulin.
Resistin, along with leptin and adiponectin, are signaling proteins released by fat cells. Leptin is released by fat cells after a meal, signaling the body to stop eating. Researchers have found that mice lacking the leptin gene were not receiving the signal and therefore becoming obese. However, in trials, leptin failed to combat obesity. This led researchers to conclude that additional factors must be at work in the development of obesity.
Too little of the hormone adiponectin may lead to insulin resistance. In mice models, scientists have found that drugs that lower resistin levels also increase adiponectin levels. At least in mice, adiponectin appears to help the muscles burn more energy and also reduce body weight. It is hoped that adiponectin will become a good target for new diabetes treatments in humans.
Scientists are continuing to identify genes implicated in obesity and diabetes, including the recently discovered ENPP1. Such discoveries may one day lead to treatments.
In recent years there has been growing interest into weight-loss surgery as a way to prevent or treat type 2 diabetes. Experts such as the American Diabetes Association describe type 2 diabetes as a chronic condition with no known cure, but some researchers have reported resolution of the disease in severely obese patients who underwent bariatric surgery. However, these procedures have risks and side effects, and the long-term health of such patients continues to be assessed.
Questions for your doctor on obesity and diabetes
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about obesity and diabetes:
- Am I overweight or obese?
- What should my ideal weight be?
- How should I control my weight?
- What risks does being too heavy have for me?
- Are there risks if I lose weight too fast or with certain diets?
- How much exercise should I get?
- Which activities should I do, and are there any I should avoid?
- Do you recommend any medications to help me lose weight? What are the risks and benefits? Are any weight-loss supplements OK, or should I avoid them?
- Will it do any good if I can lose just a few pounds?
- If nothing else works for me, should I consider weight-loss surgery? Which type? What are the risks and benefits? Could bariatric surgery cure my diabetes?
- How can I help my diabetic spouse or child lose weight?