Sloths take an entire month to digest a single meal

In the animal kingdom, sloths operate at a pace that makes even the most patient observer seem hyperactive. These arboreal mammals have evolved one of the slowest digestive systems on Earth, taking up to a month to process a single leaf. The extreme digestion time results from their highly specialized metabolism, which operates at just 40-45% of the rate typical for mammals their size. Sloths are folivores—leaf-eaters—and leaves present significant challenges: they are difficult to break down, provide minimal calories, and contain toxins. To handle this low-energy diet, sloths developed large, multi-chambered stomachs that function like fermentation vats. Symbiotic bacteria slowly break down the cellulose in leaves, but the process is extraordinarily sluggish. A sloth's stomach can hold up to 30% of its total body weight in slowly digesting material. This means a well-fed sloth is literally carrying around one-third of its body weight in undigested food. The slow digestion has cascading effects on sloth behavior. Because they extract so little energy from each meal, sloths must move slowly and limit their activity to conserve calories. They also cannot regulate their body temperature like other mammals, instead relying on their environment—a further energy-saving adaptation. Interestingly, sloths must maintain warm body temperatures to digest; if they get too cold, the digestive bacteria die, potentially causing starvation even on a full stomach. This remarkable metabolic strategy allows sloths to thrive on one of nature's least nutritious food sources.