Obesity is harmful to your health and is a risk factor for many conditions. Patients with a BMI of over 40 have a reduced life expectancy. Obesity increases the risk of developing chronic conditions such as type 2 diabetes, hypertension, high cholesterol, stroke, heart attack, and insulin resistance, among others.
Insulin is necessary for transporting blood sugar into the cells to be used for energy. This helps keep the level of blood sugar in check. When there is diminished effectiveness of blood sugar transportation, the condition is known as insulin resistance. Obesity is a major cause of insulin resistance, because fat cells are more resistant to insulin than muscle cells. This can go on as long as the pancreas can release more insulin but if it can no longer keep up, blood sugar levels rise, resulting in type 2 diabetes.
Type 2 diabetes is associated with central obesity, that is, having excess fat around the waist. Additionally, fat tissues are important in the production of the hormone estrogen. Having excess fat means producing large amounts of estrogen. Prolonged exposure to high levels of estrogen is a risk factor for breast cancer.
A person's weight is determined by one factor; the balance between your calorie intake and energy expenditure. If you consume more calories than you can metabolize or burn, the excess calories are stored as fat, increasing your weight. Eating fewer calories than you metabolize means you lose weight.
Thus, the most common causes of obesity are physical inactivity and overeating. People with sedentary lifestyles burn fewer calories while eating foods high in sugar or fat, such as fast food, sweets, and fried food. Eating these types of foods increases the energy density, contributing to obesity.
However, there are other factors that cause obesity, including genetics, behavior, and metabolism, among others. If one or both parents are obese, then it's likely that you will also develop obesity. Genetics also affect hormones involved in fat regulation, for example, hormone leptin deficiency. Leptin controls weight by signaling the brain that one is full. Medications associated with obesity include antidepressants, anticonvulsants, and some diabetes medications. Certain contraceptives and corticosteroids also increase weight.