Fat is one of the most talked about, troublesome and baffling components of the human body. Test your knowledge to see if you're up to date.
* Are fat cells simply a storage compartment for our gluttonous behavior? No. Fat cells are the most important cells in the body. "In fact, if we didn't have fat cells, we would probably be extinct," says Roger H. Unger, a diabetes researcher at the University of Texas.
"Fat is a major endocrine tissue, producing hormones that regulate varied body processes like insulin sensitivity, thyroid and immune function, clotting, blood pressure, appetite and satiety and many others," says Evan Rosen, professor of endocrinology at Harvard Medical School.
Are there different types of fat?
While all fat is essentially the same, location makes all the difference. Subcutaneous fat is below the skin and gives bodies a "pear" shape. Intra-abdominal fat is behind the stomach muscles and around the organs, giving bodies an "apple" shape. Most women store their fat subcutaneously in the breasts, hips, buttocks and thighs. Most men store fat in the abdomen, lower back, chest and nape of the neck.
Intra-abdominal fat is considered more dangerous. "All the potential health risks -- including diabetes, hypertension and heart disease -- are related to intra-abdominal fat," says David Heber, director of the UCLA Center for Human Nutrition. Oh, and don't think you can simply suck out the "bad" fat with liposuction -- research shows it doesn't improve health.
* True or false: We are born with a fixed number of fat cells, and that's all we'll ever have. False. According to Samuel Klein, professor of medicine and nutrition at Washington University School of Medicine in St. Louis, the most widely accepted theory is that fat cells grow in size (up to about 1 microgram) and then, at some point, begin to recruit other cells to be converted to fat. Fat also starts to accumulate in organs and other tissues. According to Klein, healthy individuals have about 40 billion fat cells, while the very obese have 100 billion or more.
Can you ever get rid of a fat cell once you have it?
Yes. You can shrink fat cells by losing weight, and fat cells do die off once they're not needed as storage depots, although scientists are unsure how long that takes, says Christopher B. Newgard, professor of pharmacology and cancer biology at Duke University Medical Center. However, it's much easier to add fat cells than to get rid of them, says Klein.
* Are you at a disadvantage if you have more fat cells than someone else?
Maybe. Although it hasn't been proved scientifically, diabetes researcher Unger says it is plausible that once you lose weight and have "empty" fat cells sitting around, they're just waiting to be filled up. So those additional fat cells you created could be what's increasing your appetite when you're trying to lose weight.
* True or false: Our bodies are programmed to preserve body fat.
True. Long before we had supermarkets and easy access to highly palatable food, we were hunters and gatherers. Because food availability was unpredictable, the body had to be prepared for feast and famine. The more we ate, the more fat we stored, and the better prepared we were for famine. Each excess pound of fat provided additional days of life. In fact, our body typically stores about 150,000 calories at any given time, says Klein. This is what enables us to survive for months with just water.
When we go on a diet, the body's ancient survival mechanisms kick in, refusing to use up valuable stored fat, making it difficult to burn calories by slowing the metabolism and decreasing energy levels. The body doesn't know if it's being starved voluntarily (to lose weight) or involuntarily (because there's no food).
* Will you instantaneously gain a pound if you eat an extra 3,500 calories of food in one day? Yes, technically, but...
"The storage of excess calories depends on the composition of those calories and the time frame," says William T. Donahoo, professor of endocrinology at the University of Vermont College of Medicine. Since we eat meals that combine carbs, fats and proteins and are constantly burning calories, it's hard to say exactly when and how much of the food we eat will end up on our bodies.
If your extra 3,500 calories is all fat, about 75-85 percent will end up on your body as fat, says Klein. Some will also end up as lean muscle tissue and an increase in fluid accumulation. About 10 percent is used to process the excess calories. How soon will it show on your body? An all-fat meal (versus all carbs or protein or a combination) is the slowest to be absorbed, taking about four to six hours.
Where does the fat go? In a perfect world, fat cells comprise the bulk of lipid storage -- exactly where it's supposed to go. However, if you consistently overeat, fat will be stored in places it doesn't belong, such as the liver and muscles, which can cause disease, says Philipp E. Scherer, professor of cell biology at Albert Einstein College of Medicine in New York City.
Charles Stuart Platkin is a syndicated health, fitness and nutrition columnist. Write to firstname.lastname@example.org.