When you hear the word “epidemic,” you probably think of infectious diseases like the seasonal flu. But there is another, potentially more sinister epidemic that has spread throughout America and much of the world: obesity. Predicted to impact 20% of the world’s population by 2030, obesity is simply the presence of too much body fat. It is a major risk factor for more serious conditions, including heart disease, the leading cause of death in the U.S. Obese individuals are also six times more likely to get type 2 diabetes. Fortunately, obesity and its related conditions can be treated — and often reversed — with diet and lifestyle changes or medical interventions. In this article, we’ll discuss everything you need to know about obesity — what causes it, the diseases it puts you at risk for, its relationship with diabetes, and how to prevent or reverse it.

Is obesity a disease?

Historically, obesity has been thought of as simply a consequence of an unhealthy lifestyle characterized by poor diet and lack of exercise. However, the condition isn’t that simple, a realization that led the National Institutes of Health in 1998 to classify obesity as a disease state — a classification that wasn’t backed by the American Medical Association until 15 years later — requiring treatment and prevention efforts.

Although they are commonly referenced together, the conditions medically known as “overweight and obesity” are not the same thing. An individual can be overweight — carrying more weight than what is considered normal for their age and body type — without having an accumulation of excess body fat, as is the case with obesity. Body mass index (BMI) is also used to classify obesity: any individual having a BMI over 30 is considered obese. (However, many physicians are moving away from using BMI due to its limitations in accurately reflecting an individual’s actual amount of body fat.) Compared to overweight, obesity also puts individuals at higher risk for more serious diseases such as heart disease, cancer and diabetes.

What causes obesity?

Historic perceptions of obesity — that it’s not a disease, but simply a physical state caused by poor lifestyle choices — weren’t completely off-track. Poor diet and limited exercise are indeed the most common risk factors associated with obesity; however, the disease is caused by a combination of multiple factors, which can be loosely classified into two groups: medical and environmental.

Medical contributors to obesity

Although the evidence is inconsistent, obesity does appear to have a genetic component:

• Studies on twins, adopted siblings, and other family members have shown that the heritability rate of obesity is between 40-70%.
  
  
• Over 50 genes have been associated with obesity, although most of them have very small effects. Polygenic obesity (the common form of obesity) results from a combination of hundreds of these small-impact genetic changes, together with environmental factors.
  
  
• Monogenic obesity is a very rare form of obesity that is inherited, is very early onset, is severe, and results from a single genetic perturbation with little to no environmental influence.

There are also some medical conditions that can increase a person’s risk for obesity, irrespective of a person’s diet and exercise habits:

• Polycystic ovary syndrome
• Cushing’s disease
• Hypothyroidism
• Hypertension

Several medications have also been associated with weight gain, which don’t necessarily cause obesity but could make the condition more likely in already overweight individuals:

• Antidiabetic medications (including insulin)
• Antidepressants
• Anti-epileptic medications
• Antihistamines
• Antihypertensives
• Antipsychotics
• Anabolic steroids
• Corticosteroids
• Mood stabilizers

If you’re experiencing weight gain and think it might be due to a medication you are taking, it’s important to talk to your doctor first before stopping your medication. The potential effects of stopping your medication could be worse than the impact of weight gain, so medications should always be taken, adjusted and (if recommended) stopped under the supervision of your physician.

Environmental contributors to obesity

Environmental contributors to obesity are those that don’t have a genetic or medical component and include things like diet, lifestyle and socioeconomic factors. Importantly, these factors can interact with and upon genetic and medical factors to cause obesity.

• An unhealthy diet full of processed foods and high in fat and sugar (i.e., the common Western diet) is one of the leading causes of obesity. High-fat diets promote low-grade chronic inflammation, which appears to have a role in promoting obesity.
  
  
• Lifestyle choices such as smoking, consuming excess amounts of alcohol or avoiding exercise also contribute to obesity.
  
  
• Studies have shown that race, poverty, unemployment, and low income are all correlated with higher levels of obesity.

Can obesity cause other diseases?

Obesity is one of the leading causes of non-communicable (i.e., non-contagious) diseases worldwide. It has been associated with several severe and chronic diseases including:

• Cardiovascular disease (CVD)
• Hypertension
• Type 2 diabetes (T2D; see more below)
• Cancer
• Osteoarthritis
• Sleep apnea

Obesity has also been shown to increase an individual’s risk for certain infectious diseases, including COVID-19. Clearly, the impact of obesity goes far beyond surface level. Your long-term health, well-being and quality of life depend on maintaining a healthy weight.

Obesity and diabetes

As mentioned earlier, obesity significantly increases a person’s risk for T2D — and it also makes diabetes get worse, quicker. In fact, chronic post-meal spikes in blood sugar are a major risk factor for both obesity and diabetes. To fully understand the complex relationship between obesity and diabetes, we must first understand fat and insulin:

• Fat is an essential nutrient; in fact, it is critical for the immune response, regulating body temperature, and even insulin resistance. As with most things in the human body, homeostasis is what matters: too much fat, and problems arise. Fat can accumulate in the body in two ways — subcutaneously and viscerally. Subcutaneous fat is fat that is located just under the skin and is usually harmless. Visceral fat is much deeper, surrounding the body’s organs, and is associated with several diseases, including heart disease, metabolic syndrome, and cancer.
  
  
• Insulin is a hormone normally produced by the body that moves glucose (i.e., sugar) out of the bloodstream and into your liver and muscles. Insulin resistance is the condition in which liver and muscle cells no longer respond to insulin well, causing blood sugar levels to increase in the blood.

So, how are the two related? Think of it this way: in obesity, body fat content increases — particularly in your liver. So, when insulin is released in response to blood sugar levels increasing (say, after a meal), that glucose then tries to enter the liver but it can’t, as all the space is taken up by fat cells. The glucose stays in the bloodstream, so your pancreas produces more insulin to try to force the glucose out of the blood. Eventually, the pancreas wears out, producing less and less insulin over time. Viola — diabetes.

Having obesity doesn’t always mean you have a diabetic future, however. Studies have shown that there are some individuals who maintain normal insulin levels and function despite being obese. Nevertheless, it’s important to remember that obesity is one of the five risk factors (abdominal obesity, hypertension, high blood sugar, high triglycerides and low levels of “good” HDL cholesterol) that comprise metabolic syndrome, which increases an individual’s risk for several serious conditions, not just diabetes:

• Heart disease
• Aortic stenosis (i.e., when the aortic valve narrows)
• Atrial fibrillation (i.e., arrhythmia)
• Stroke
• kidney, gallbladder, colon, and prostate cancers 
• Eclampsia (i.e., seizures occurring during pregnancy that result from high blood pressure)
• Decreased cognitive performance

So, whether you’re diabetic or not, if you are obese, getting yourself back to a healthy weight can help you avoid one of the many other serious health conditions connected to obesity.

How to lose weight

The fastest way to lose weight is to restrict calories; however, losing weight too quickly can be dangerous. Any weight loss plan should be developed in collaboration with your doctor. There are several dietary and even non-dietary options that your doctor may discuss with you, and which option is best for you can depend on a number of different factors, including how overweight you are and your risk for or existence of severe adverse health effects or even death.

• The Mediterranean Diet is the most well-supported diet scientifically to not only reduce the risk of obesity, but also of heart disease, stroke, diabetes, and the list goes on. Researchers have cited its importance as not only a food model, but as “the most appropriate regime for disease prevention, a sort of complete lifestyle plan for the pursuit of healthcare sustainability.” Typically, a Mediterranean diet includes a plentiful amount of fiber-rich whole fruits and vegetables, nuts and seeds and healthy fats; together with modest amounts of lean proteins (fish, meats, eggs) and dairy foods.
  
  
• Certain dietary supplements have shown promise for reducing obesity risk or helping to lose weight. Omega-3s, for instance, have been shown to reduce the risk for obesity by reducing the size of fat-storing cells in your body and by increasing a hormone called adiponectin, which increases the capacity of your muscles to use glucose and fatty acids. Animal studies have also shown that supplementing with butyrate, a short-chain fatty acid, can reduce body weight and reduce liver inflammation; however, these studies are early and haven’t  been replicated in humans.
  
  
• Bariatric surgery has been used as an effective way to quickly yet safely reduce body weight and body fat in patients with severe obesity. Surgery, obviously, is very invasive and patients must be carefully followed post-surgery to avoid surgical, nutritional and even psychiatric complications. It’s not for everyone, but is recommended for individuals with severe obesity (BMI > 40) and other serious health issues.
  
  
• Certain prescription medications for weight management are available to people with obesity as well. They work in a variety of ways, such as making you feel full sooner or by interfering with fat absorption. Several of these medications are quite new, and aren’t for everyone, but they may be recommended for people with obesity and other related health problems.
  
  
• Exercise, when combined with a healthy diet (such as the Mediterranean Diet) also plays an important role in weight loss and control. Even a little bit goes a long way: gains in metabolic health can be seen with weight reductions of as little as 5%. The Diabetes Prevention Program showed that 150 minutes of physical activity no more intense than brisk walking enabled participants to lose 7% of their body weight (for a 200 pound individual, that’s only 14 pounds) and reduce their incidence of diabetes by over 50%. 

Key takeaways

Obesity is a serious medical condition affecting nearly one-fifth of the global population. Rates are rising in individuals of all ages, including children. Obesity increases the risk for several severe chronic diseases, including cardiovascular disease, type 2 diabetes, stroke and cancer. Fortunately, a healthy diet and exercise can help you lose weight and prevent or reverse obesity and related diseases, but severe cases might require surgical or pharmaceutical interventions. If you’re overweight or obese and at risk for diabetes, heart disease or other conditions, talk with your doctor to determine the best weight loss approach for you. Maintaining a healthy weight is one of the best ways to ensure you enjoy good health now and in the future.