Fat is a national obsession. Virtually everyone is concerned about how “fat” they are. It’s the hottest topic in the medical literature and at scientific conferences. And government health agencies are spending tens of millions of dollars to find ways to reverse what has been called an epidemic of obesity.
All of this concern is for good reason. Over the past two decades, the number of cases of obesity, defined as more than 30 pounds overweight, in the United States has increased by more than 50%—from 14.5% of the adult population to 22.5%—and another 40% of American adults are overweight, defined as up to 30 pounds overweight. The cost of diseases associated with obesity—including Type 2 diabetes, heart disease, high blood pressure, gallbladder disease, stroke, some types of cancer, and many other conditions—has been estimated at almost $100 billion per year. What’s more, there doesn’t seem to be any indication that this trend toward obesity will slow down or turn around any time soon.
As much time as we spend talking and worrying about how much fat we eat, how much it clogs our arteries, and how the prevalence of obesity in America is skyrocketing, most people know surprisingly little about what fat is, how the human body stores it, or how the body can get rid of it.
What is fat?
First, a bit of chemistry, but nothing you can’t handle. Fat is an oily compound composed of the elements carbon, hydrogen, and oxygen. In the body, the carbon, hydrogen, and oxygen molecules bind together like links to form chains of fatty acids. When chains of fatty acids connect together with a molecule called glycerol, it’s called a glyceride. Triglycerides—three fatty acid chains connected to a glycerol molecule—are the main type of fat in the foods we eat and in our bodies.
Even though body fat would appear to just sit there on our hips, thighs, and abdomens, it actually serves many roles. It insulates us from the cold, pads and supports our vital organs, muscles, and bones, and is part of the structure of every cell membrane. It’s an active organ, too. Scientists have discovered that fat cells behave very much like endocrine glands, secreting many different substances. At last count, more than 27 different enzymes, hormones, and neurotransmitters have been identified that are secreted by fat cells. They are responsible for, among other functions, controlling and regulating appetite, blood pressure, some nervous system and hormonal signals, gene expression, and the formation of testosterone and some forms of estrogen. In short, fat cells are important organs with vital regulatory functions that help our bodies run smoothly.
Humans have anywhere from 25 billion to 275 billion fat cells stored in their bodies. The average person has around 35 billion. For the average man, fat accounts for about 22% of his body weight; for the average woman, 28%. (In comparison, a trained, male athlete has about 10% body fat, and an obese person has between 40% and 50% body fat.) Fat cells are microscopic, 10–20 times smaller than the diameter of a human hair (which is about 100 microns), but they are packed with energy. The average person has more than 100,000 calories stored as fat on his body, theoretically enough fuel to jog from New York City to Chicago.
Fat is stored in special compartments called adipocytes, which are located all over the body and are often referred to as fat cells. Your genes determine where fat accumulates on your body; you don’t have any control over it. Women tend to accumulate it in the adipocytes on the hips, buttocks, and thighs, and men tend to accumulate it in the abdomen. The reason for the different accumulation patterns between sexes has not been identified, but one thing is certain: The fat that accumulates in the abdomen is associated with a high risk for Type 2 diabetes, high blood pressure, cardiovascular disease, and other medical conditions. The fat that accumulates in the lower extremities, although it may not be cosmetically appealing for some, does not present any cardiovascular or metabolic health risk.