Although there are genetic and hormonal influences on body weight, obesity occurs when you take in more calories than you burn through exercise and normal daily activities. Your body stores these excess calories as fat. Obesity usually results from a combination of causes and contributing factors, including:
Inactivity. If you're not very active, you don't burn as many calories. With a sedentary lifestyle, you can easily take in more calories every day than you use through exercise and normal daily activities.
Unhealthy diet and eating habits. Having a diet that's high in calories, lacking in fruits and vegetables, full of fast food, missing breakfast, and laden with high-calorie beverages and oversized portions all contribute to weight gain.
If you're obese, you're more likely to develop a number of potentially serious health problems, including:
High triglycerides and low high-density lipoprotein (HDL) cholesterol
Type 2 diabetes
High blood pressure
Metabolic syndrome — a combination of high blood sugar, high blood pressure, high triglycerides and low HDL cholesterol
Heart disease
Stroke
Cancer, including cancer of the uterus, cervix, endometrium, ovaries, breast, colon, rectum, esophagus, liver, gallbladder, pancreas, kidney and prostate
Breathing disorders, including sleep apnea, a potentially serious sleep disorder in which breathing repeatedly stops and starts
Gallbladder disease
Gynecologic problems, such as infertility and irregular periods
Erectile dysfunction and sexual health issues
Nonalcoholic fatty liver disease, a condition in which fat builds up in the liver and can cause inflammation or scarring
Osteoarthritis
Skin conditions, including poor wound healing