For decades, scientists believed that excess body fat was mere storage for unused calories. However, research conducted over the past 20 years suggests added fat is more than a little extra cushion—fat cells are actually “toxic factories,” each one producing inflammatory cytokines (chemical messengers of inflammation) throughout the body and causing potentially serious damage to your health. It is this understanding that has led experts to more closely examine the effects of being overweight, even when an individual is considered physically fit.
In 1998, the National Institutes of Health (NIH) published Clinical Guidelines on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults. These guidelines noted being overweight but in good physical health would reduce the risk of premature death— in other words, being physically fit mattered more than body fat percentage.
But in 2015, the International Journal of Epidemiology released the results of a study that suggested the “fat but fit” theory wasn’t true, based on the health data of more than 1.3 million Swedish men whom researchers followed for 30 years. Those study authors found that the beneficial effects of exercise declined as obesity rates increased. Compared to physically fit obese men, normal-weight men who were not physically fit had a lower risk of dying.
These results are backed by a prior study published in January 2015 that identified a link between increased levels of fat in the body— regardless of physical fitness— and high levels of inflammation. Inflammation is the root cause of all disease, especially chronic conditions, such as heart disease, diabetes, cancer and Alzheimer’s disease. Another study published in the journal Clinical Cancer Research in 2015 observed a correlation between increased levels of white fat tissue and poorer prognosis in early-stage breast cancer. White fat, known as white adipose tissue, is fat stored for energy, but it also plays a role in raising inflammation levels when found in excess throughout the body.
Abdominal obesity, which is fat centralized in the belly, is a sign of high levels of visceral fat in the body. Visceral fat is the type of fat that accumulates in arteries and around organs, and has been credited with increased inflammation and disease risk. Emerging research has found that while this still holds true, fat may be further differentiated. A December 2014 study found that fat deposits may exist on the surface of the myocardium (muscular wall of the heart) and be contained completely beneath the membrane that encloses the heart— in contact with major coronary arteries and their branches. This fat, known as epicardial adipose tissue (EAT), is highly correlated with obesity, and thought to play a role in the development and vulnerability of plaque in the coronary arteries.
