The trouble with obesity is that it leads to a myriad of health issues including coronary heart disease, high blood pressure and stroke, type 2 diabetes, respiratory problems (such as sleep apnea), colon cancer, breast and endometrial cancer, gallbladder cancer, joint problems and pregnancy complications. 
Someone with a BMI of 40% or more is TWICE as likely to die prematurely as a normal-weight person.
People who are obese and have a family history of chronic diseases—such as heart disease or diabetes are more likely to develop these problems.
Finally, people who have an apple shape—where their extra weight is concentrated around the waist (rather than the hips and legs) are at greater risk for developing heart disease, diabetes or cancer.
Chronic illnesses caused by obesity
Coronary heart disease occurs when plaque builds up in the walls of your arteries. The accumulation of plaque increases the risk of blood clots and narrows the flow of blood to the heart, which can result in a heart attack or stroke. People with a BMI above 30 are three times more likely to have coronary heart disease than those with a BMI less than 21, according to the National Heart Lung and Blood Institute.
A heart disease indicator with cardio-c reactive protein (CRP-hs) test can estimate your change of developing cardiovascular disease and your risk of sudden heart attack.
People with a BMI over 30 also tend to have unhealthy cholesterol and triglyceride levels, which contribute to the build-up of plaque that can lead to coronary heart disease.
A Super Chemistry Heart test provides an important summary of cardiovascular health—including a full lipid profile.
The Vertical Auto Profile (VAP) reports on 15 components of blood cholesterol
The NMR Lipoprofile Heart and Cholesterol test uses nuclear magnetic resonance spectroscopy to detect the levels of plaque build-up on artery walls. People with diabetes, high blood pressure or with a family history of heart disease or heart attacks, people who are overweight or have high triglycerides should consider the NMR Lipoprofile blood test once per year.
Obesity is now recognized as a major, independent risk factor for heart disease. If you’re overweight or obese, you can reduce your risk for heart disease by successfully losing weight and keeping it off.
If you are on medications to treat obesity-related diseases, read Side Effects of Medications that Treat Obesity-related Conditions.