Giant pandas seem to have mastered the art of leisure. They don’t move much, and when they do, it’s usually to eat. A 90-kg panda expends less than half the energy of an equally weighted human; even a person standing motionless still has a higher metabolic rate than an “active” panda. The reason? The panda’s diet requires it. Though its digestive system is built for a carnivore, the giant panda survives almost exclusively on bamboo, making digestion an inefficient process. To fulfill nutrient needs, pandas eat heaping quantities of bamboo, anywhere from 9 kg to 18 kg a day. Because this diet provides so few nutrients, pandas need to slow things down. That means not moving a lot; harboring smaller energy-sucking organs like the liver, brain, and kidneys; and producing fewer thyroid hormones, which slows their metabolism. Sure, we humans move around a lot more—but we don’t have to eat bamboo all day.
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