Can doctors tell me what does obesity cause to the human bodies?

Yes. heart disease, high cholesterol and triglycerides, diabetes, insulin resistance, gallbladder disease, stress and strain on joints and their mobility, back pain, increased risk of certain cancers, liver disease- fatty liver, sleep apnea, increased risk of stroke, high blood pressure, kidney disease, asthma.
So many problems. It puts excessive strain on joints, muscles, the cardiovascular system, heart, lungs, glandular health, disrupts normal hormonal functioning, can disrupt normal menstrual function, etc, etc. Being obese is a serious medical condition, and is responsible for many disease states.