One hundred years ago, medical researchers noted that upper-body obesity was associated with high blood sugar (diabetes), high blood pressure (hypertension), and hardening of the arteries (atherosclerosis.)  Fifty years later the term "metabolic syndrome" was coined. In 1988,  a prominent researcher introduced Syndrome X, in which he claimed that the underlying problem with obese, diabetic, hypertensive patients with heart disease was related to the body becoming unresponsive or resistant to the effects of their own insulin. The X was used to highlight insulin resistance was then a medical mystery.  Today, we've come to understand insulin resistance as the underlying mechanism causing type 2 diabetes, obesity being its primary cause.