Obesity is a chronic, multifactorial metabolic disease defined by a
body mass index (BMI) of 30 or higher. More than 40 percent of adults in the United States have obesity.
“It’s not a willpower problem. The biology behind it involves genetics, hormones, the gut-brain axis, and the way the body regulates appetite and energy storage over time,” says Georgia-based Jessica Duncan, MD, a board-certified obesity medicine physician and the chief medical officer at Ivim Health. The complications of obesity can be wide-ranging and complex.
Cardiovascular Risks: Heart Disease, Stroke, and Hypertension
High blood pressure occurs when blood pushes too hard against the artery walls.
A
healthy blood pressure reading is below 120/80 mmHg, but the risk for future problems builds when the top number (systolic blood pressure) remains between 120 and 129 mmHg. Once blood pressure reaches and remains at 130/80 mm Hg, doctors officially diagnose the condition as stage 1 hypertension. A reading above 180/120 mmHg is considered a medical emergency.
It matters where the body stores fat as well. Visceral fat, the kind stored deep within the abdominal cavity that wraps around internal organs, is more harmful to blood vessels than fat stored elsewhere. For this reason, many healthcare providers now also consider a person’s waist circumference in addition to their BMI when diagnosing obesity.
Abdominal obesity is considered a cardiovascular disease risk marker that’s independent of BMI. A waist circumference of 35 inches or more in women or 40 inches or more in men indicates an elevated risk for cardiometabolic and cardiovascular disease.
People of Asian descent are at an increased risk for cardiometabolic disease at a lower waist circumference than people of European descent.
Considering this measurement alongside BMI gives healthcare providers a better picture of a person’s overall health.
“BMI alone is an imperfect measure of health,” says Savita Srivastava, MD, a board-certified gastroenterologist in Virginia. “It misses an important group of individuals who look lean on the outside but carry dangerous visceral fat on the inside. Waist circumference measures visceral fat. It’s a better predictor of heart disease risk than BMI alone.”
Metabolic Health: Diabetes, Liver, and Gallbladder
Obesity, along with other contributing factors such as genetics, poor diet, a sedentary lifestyle, and age, exacerbates
insulin resistance. When the body’s cells stop responding effectively to insulin, blood sugar levels rise, and the pancreas works continuously to try to stabilize them.
Over time, insulin resistance can lead to
type 2 diabetes, a chronic condition in which a person has too much glucose (sugar) in their bloodstream.
Obesity and type 2 diabetes overlap so frequently that some medical experts use the term “diabesity” to describe the dual diagnosis.
About 100 million people in the United States have MASLD, with up to 70 percent of people with type 2 diabetes having the condition. MASLD develops when more than 5 percent of the liver’s weight is made of fat.
If left untreated, about 20 to 30 percent of people with MASLD will develop MASH, a more severe stage that involves swelling, inflammation, and liver damage. This ongoing damage can eventually lead to permanent liver scarring (cirrhosis) and liver failure.
Obesity and insulin resistance also increase a person’s risk of developing gallstones.
“Insulin resistance tells the liver to dump more cholesterol into the bile,” says Dr. Srivastava. “When bile becomes supersaturated with cholesterol, it crystallizes to form gallstones.”
These metabolic conditions actively influence one another in synergistic, bidirectional relationships, meaning that having one condition can worsen the course of another. For example, MASLD can make type 2 diabetes more difficult to manage.
Physical Impacts: Joints and Respiratory Function
Carrying extra weight affects how a person moves, breathes, and sleeps by putting both physical and chemical stress on the body.
Excess weight puts direct pressure on weight-bearing joints like the knees and hips, with obesity responsible for about 20 percent of the global disability linked to
osteoarthritis.
The damage to joints isn’t just physical. Adipose tissue (body fat) is an active organ that communicates with the rest of the body through chemical signals. When fat cells become enlarged due to obesity, they trigger a state of chronic inflammation. This internal inflammatory response helps explain why people with obesity may develop joint pain in non-weight-bearing joints, like the hands.
This physical impact also affects how a person sleeps.
Obstructive sleep apnea is a disorder in which a person repeatedly stops and starts breathing throughout the night. Obesity is considered the only truly reversible risk factor for this condition; weight gain of 10 percent can increase a person’s risk sixfold.
People with obesity have a higher risk of
asthma, too. Extra weight puts physical pressure on the lungs and limits their capacity, making it harder to take deep breaths. At the same time, the low-grade inflammation that damages the joints also targets the airways, leaving them sensitive to asthma triggers.
“I will often tell my patients that belly fat is an organ itself designed to increase chronic inflammation,” says Srivastava. “These very same inflammatory cytokines are known triggers for conditions like asthma and osteoarthritis.”
The Link Between Obesity and Mental Health
People with obesity have an 18 to 55 percent higher risk of developing depression. Similarly, people diagnosed with depression have a 37 to 58 percent increased risk of developing obesity.
Societal stigma and weight-based discrimination play a significant role in this connection, with these experiences often leading to feelings of shame and isolation.
This emotional distress can act as a barrier to seeking healthcare, as well as trigger emotional eating.
Chronic stress also causes physical changes in the body. It raises cortisol levels, which increase the desire for rewarding, high-calorie foods, and this hormonal shift creates a cycle of stress-induced eating that makes weight management even more challenging.
To help break this cycle, healthcare providers may recommend these therapies:
- Cognitive behavior therapy
- Dialectical behavior therapy
- Interpersonal psychotherapy
- Motivational interviewing
- diethylpropion (Tenuate)
- liraglutide (Saxenda)
- naltrexone/bupropion (Contrave)
- orforglipron (Foundayo)
- orlistat (Xenical)
- phendimetrazine (Bontril)
- phentermine (Adipex-P)
- phentermine/topiramate (Qsymia)
- semaglutide (Wegovy)
- setmelanotide (Imcivree)
- tirzepatide (Zepbound)
Cancer Risk and Obesity
Obesity-associated cancers make up 40 percent of all cancer diagnoses in the United States each year.
While more research is needed to explain exactly how excess weight influences a person’s cancer risk, 13 types of cancer may occur more frequently in people with obesity:
- Adenocarcinoma of the esophagus
- Breast (postmenopausal)
- Colon and rectum
- Gallbladder
- Kidney
- Liver
- Meningioma (a type of brain cancer)
- Multiple myeloma
- Ovary
- Pancreas
- Thyroid
- Upper stomach
- Uterus
Insights From Obesity Specialists
“The gut produces hormones like ghrelin, GLP-1, and PYY that tell the brain when to eat and when to stop,” says Dr. Duncan. In people with obesity, these signals are often dysregulated. The hunger hormone, ghrelin, stays elevated while fullness signals become blunted.
“It’s one contributor to what my patients describe as 'food noise,' a constant background hum of thinking about food, planning the next meal, or fighting cravings that are not about hunger at all,” she says. “It would be pretty tough to out-discipline a hormone.”
The medical community is also shifting how it approaches treatment.
“The biggest shift is the move away from treating obesity primarily as a weight problem and toward treating it as a chronic, relapsing disease with the end goal of preventing organ damage, not just hitting a number on a scale,” says Toronto-based Fady Hannah-Shmouni, MD, an endocrinologist and geneticist, and the medical director at Eli Health.
People with obesity don’t need to lose drastic amounts of weight to see real health benefits. “Overall, a 5 to 10 percent decrease is clinically meaningful and, importantly, achievable and sustainable for most of the population,” says Dr. Hannah-Shmouni. He explains that losing 5 percent of one’s total body weight can reduce strain on the heart, lower blood pressure, and improve cholesterol levels. Some people can even reverse conditions like prediabetes and mild diabetes with this moderate weight loss.
