爱思英语编者按：如何判定肥胖？目前常用的体重指数（body mass index）简称BMI，又译为体质指数。它是一种计算身高比体重（weight for height）的指数。具体计算方法是以体重（千克，kg）除以身高（米，m）的平方，即BMI=体重/身高/身高（kg/m2）。以体重指数对肥胖程度的分析，国际上通常用世界卫生组织（WHO）制定的体重指数界限值，即体重指数在25.0~29.9为超重，大于等于30为肥胖。
20 Things You Didn't Know About... Fat
1 They’re doing something right out West. Sixty-six percent of Americans are overweight or obese, with the national obesity rate doubling between 1976 and 1999. But as of 2007, California was the only state not getting any fatter.
2 The root of the problem? Depending on gender and how active they are, adults should eat 2,000 to 3,000 calories per day. U.S. agriculture now produces 3,900 calories of food per inhabitant per day.
3 People who regularly eat dinner or breakfast in restaurants double their risk of becoming obese.
4 Being overweight reduces a woman’s chances of getting pregnant.
5 The National Institutes of Health believes obesity is one of the reasons why the fastest-growing group of women experiencing infertility are those under 25.
6 We’re trying. Each year nearly $50 billion is spent on diet programs.
7 People who lose just 10 percent of their weight report significant improvement in their sex lives.
8 Biology is trying to help too. Leptin is a hunger-slaking hormone pumped into the bloodstream by fat cells. The more fat you have, the more leptin you make and the less hungry you feel.
9 Want to get your hands on some leptin? The hormone never panned out as a diet aid because most overweight people have become insensitive to it.
10 Over the course of a year, about 10 percent of an adult’s fat cells die. Alas, the body promptly replaces them.
11 The total number of fat cells in your body remains constant once you reach adulthood. Even after radical weight-loss procedures such as stomach stapling, fat cells return to their presurgery numbers within two years.
12 Try the vacuum instead. Liposuction is the only way to actually reduce the number of fat cells in your spare tire. Diet and exercise just shrink them.
13 New Zealander Pete Bethune gave a whole new meaning to biofuel when he used his liposuctioned fat to power the world’s fastest eco-boat. A way to solve the obesity epidemic and the fuel crisis?
14 It may make you prettier, but not healthier. Liposuction doesn’t remove fat from around the internal organs, so your fat-related health risks are unchanged.
15 Blame Mom and Dad. Obesity is more heritable than schizophrenia, high blood pressure, and alcoholism.
16 Cutting saturated fat intake to the recommended 10 percent of your calories will prolong your life, but only by a few months at most, researchers found.
17 The brain is about 70 percent fat.
18 Bottlenose dolphins use fatty tissue in the head, concentrated in an organ called the melon, to focus sound waves, giving them their sonar ability.
19 Think you have a spare tire? Whales are wrapped in fat—a thick layer of blubber—as vital insulation against the cold. Some whales have a blubber layer up to 20 inches thick.
20 Camels have the opposite problem: Living in hot climates, they want as little heat-trapping insulation as possible, so they concentrate their fat in their humps.