Carrying excess weight—especially in the form of body fat—affects nearly every organ system in the body. Obesity isn't just a number on the scale; it's a complex condition that alters your body's structure, function, and metabolism in ways that increase your risk for serious health problems.

How Fat Impacts the Body

Fat Tissue as an Active Organ

Many people think of body fat as passive storage, but it’s actually an active endocrine organ. Adipose (fat) tissue releases hormones, enzymes, and inflammatory substances called cytokines that disrupt normal bodily processes.

• These substances can interfere with insulin signaling, making it harder for cells to absorb glucose from the blood. Over time, this disruption may lead to insulin resistance, a key contributor to type 2 diabetes.  
• Fat tissue also produces leptin, a hormone that regulates appetite. In individuals with obesity, leptin levels are elevated but often ineffective, leading to increased hunger and difficulty feeling full.
• Chronic inflammation from fat tissue contributes to a range of issues, including atherosclerosis (hardening of the arteries), which increases the risk for heart disease and stroke.  

Visceral Fat and Organ Function

Where fat is stored on the body matters. Visceral fat, which surrounds internal organs in the abdomen, poses a greater health risk than subcutaneous fat (the fat under your skin).

• Visceral fat is metabolically active and more likely to release inflammatory substances into the bloodstream.
• This type of fat is strongly associated with metabolic syndrome—a cluster of conditions including high blood pressure, elevated blood sugar, high cholesterol, and abdominal obesity—that dramatically raises your risk for cardiovascular disease and type 2 diabetes.
• Excess abdominal fat also puts pressure on internal organs like the liver, impairing its ability to filter blood and increasing the risk of nonalcoholic fatty liver disease (NAFLD).

Musculoskeletal Strain and Joint Damage

Carrying extra weight puts significant mechanical stress on your bones, joints, and muscles.

• The knees, hips, and lower back are particularly vulnerable to damage. With every step, your knees bear forces several times your body weight—so additional pounds amplify the wear-and-tear on cartilage and ligaments.
• This often leads to osteoarthritis, a degenerative joint disease that causes pain, stiffness, and reduced mobility.
• Obesity may also alter posture and gait, increasing the risk for chronic musculoskeletal pain, especially in the lower back.

Hormonal and Reproductive Disruption

Obesity influences several key hormones, affecting reproductive and sexual health.

• In women, excess fat can interfere with estrogen and progesterone levels, leading to irregular menstrual cycles, polycystic ovary syndrome (PCOS), and reduced fertility.
• Pregnancy complications are more common in individuals with obesity, including gestational diabetes, high blood pressure, and increased risk of cesarean delivery.
• In men, obesity is associated with lower testosterone levels, erectile dysfunction, and reduced sperm quality.

Respiratory and Sleep Health

Extra fat—particularly around the chest and abdomen—can compress the lungs and diaphragm.

• This results in reduced lung capacity, making it harder to breathe during physical activity.
• Many individuals with obesity suffer from obstructive sleep apnea, a serious sleep disorder where breathing repeatedly stops and starts during sleep due to blocked airways.
• Poor sleep contributes to fatigue, mood disturbances, and even increased appetite the next day, creating a cycle that makes weight loss more difficult.

Immune System Impairment

Chronic inflammation driven by excess fat can compromise your immune system.

• People with obesity may have weakened immune responses, making them more susceptible to infections like the flu, pneumonia, and even COVID-19.
• Obesity may also reduce the effectiveness of vaccines, including flu shots, due to impaired immune cell function.

Mental and Emotional Health

The impact of weight isn’t only physical. People with overweight or obesity are at greater risk for:

• Depression, anxiety, and low self-esteem, often exacerbated by social stigma or weight-based discrimination.
• Emotional or binge eating patterns, which can further fuel weight gain and increase psychological distress.
• A reduced quality of life, due to limited mobility, chronic illness, or poor sleep.

Cancer Risk and Disease Progression

Excess weight is now recognized as a significant risk factor for several types of cancer, including:

• Breast (postmenopausal)  
• Colorectal  
• Endometrial  
• Esophageal
• Kidney
• Pancreatic

Adipose tissue can produce estrogen and growth factors that promote tumor development and progression. Obesity may also hinder cancer treatment outcomes and recovery.