CHARLESTON, W.Va. -- "Start with this fact," Dr. Sally Swisher said. "If you eat more sugar than you burn with exercise, your body generates fat."
Swisher is a neurologist and bariatric doctor at Charleston's Medical Weight Loss and Skin Care Clinic.
The body turns food into glucose, she explained. It's straightforward, almost mathematical. Your muscle cells use most of the glucose for fuel. If you exercise a lot, your muscles burn up a lot of glucose. If you're a couch potato, your glucose doesn't burn up -- and the body converts it into fat.
Globs of sunny yellow fat -- unused glucose -- float through your arteries in your blood to the organ or tissues where they are deposited.
"Picture your arteries coming out of your heart like big rivers," Swisher said. "The farther they are from the heart, the smaller they get, and the easier it is for fat to clog them up. By the time arteries get to your feet and hands, they're tiny."
Fat cells float through these arteries. Along the way, they are deposited on tissue and organs. When fat finds a home in an organ, it can cause problems. If enough fat is deposited, it causes big problems.
That's an "extremely simplified version of the way it happens," Swisher said.
Inside the arteries, fat aggravates the walls as it floats along, then inflames them, Swisher said. "Fat cells slip underneath the inflamed lining. That constricts the artery. It used to be called hardening of the arteries."
If the inner artery wall becomes harder and rougher, the blood has a harder time getting through, and blood clots are more likely to form.
"There is bad fat and good fat," Swisher said. Exercise generates good fat, known as HDL cholesterol. It lowers all kinds of health risks. Bad fat -- called triglycerides and LDL cholesterol -- inflames artery walls. "It's not just innocent baby fat," Swisher said.
"When we are children, our bodies create the number of fat cells we will have for the rest of our lives, research shows," she said. "If people have too many fat cells when they reach adulthood, they are more likely to have trouble with weight for the rest of their lives."
Extra weight can raise a person's risk of many different kinds of problems:
Heart failure:"A hundred extra pounds makes your heart muscle thicken, just like any muscle working overtime," Swisher said. "A bigger heart eventually leads to heart failure."
A heart has to work extra hard to pump blood through a large body. The strain can cause a heart attack or stroke.
Fat can be especially dangerous inside arteries that supply the heart. It interferes with heart function and can set off heart attacks.
Sleep apnea, which is almost always caused by obesity, Swisher said. "Obese people often have fat in the back of their throats. When they lie down, the weight of their chest is on top of them. They don't have enough oxygen, so they wake up tired, or their spouse hears them struggling to breathe."
Diabetes: Belly fat has a lot to do with Type 2 diabetes, which used to be called "adult onset" diabetes. Thirty years ago, people under 20 almost never got it. Now it is showing up in obese teenagers and children.
Type 2 diabetes -- 90 to 95 percent of all diabetes -- can be prevented with exercise and healthy diet.