What Do Sloths Eat? Their Diet and Slow Digestion

Sloths eat leaves, and not much else. Both two-toed and three-toed sloths are folivores, meaning their diet revolves around the foliage of tropical trees. But the two groups differ in how picky they are, and a sloth’s body is so thoroughly built around extracting nutrients from tough, low-calorie leaves that its stomach, metabolism, body temperature, and even the algae growing in its fur all play a role in keeping it alive on one of the most nutritionally poor diets in the mammal world.

Three-Toed Sloths and Their Favorite Tree

Three-toed sloths are the pickier eaters. In Central American forests, they are famously associated with Cecropia trees, a fast-growing genus common along forest edges and gaps. Research in Costa Rica found that the density of Cecropia trees in a given area was strongly and positively linked to both adult survival and reproductive success in brown-throated three-toed sloths, underlining just how dependent these animals are on a single genus of tree.¹ That association shapes their gut bacteria too: three-toed sloths carry a low-diversity foregut community dominated by a single bacterial species, a pattern consistent with a narrow, specialized diet.²

Cecropia is not the whole story, though. Studies of the maned sloth in Brazil’s Atlantic Forest found it consuming at least 68 plant species across 20 families, with a strong preference for young leaves. The most frequently eaten plants in one southern Bahia population belonged to the genera Emmotum, Inga, Ficus, and Brosimum, which together made up nearly half the diet.³ So while three-toed sloths in some habitats lean heavily on one tree, the group as a whole can draw from a wider pantry when conditions demand it. The common thread is that they eat leaves, and preferably tender ones.

Two-Toed Sloths Eat More Broadly

Two-toed sloths are relative generalists. In a Costa Rican cacao landscape, two-toed sloths were observed using 34 different tree species for food, compared to 15 species for three-toed sloths in the same area.⁴ Their menu still centers on leaves, but two-toed sloths also eat fruit, flowers, and the occasional small amount of animal matter, such as insects or bird eggs. This broader diet shows up in their gut microbiome, which is more variable and diverse than that of three-toed sloths.²

The practical difference matters for survival in fragmented habitats. Two-toed sloths can show up in a wider range of forest types, including agricultural landscapes with mixed shade trees, because they are not as tied to one genus. Three-toed sloths are more vulnerable when their preferred trees disappear. In the Costa Rican study, both species made use of shade trees in cacao farms and living fence rows, relying on genera like Erythrina, Cecropia, and Cordia, but the three-toed sloths were found in fewer tree species overall.⁴

A Stomach With Seven Compartments

A leaf-based diet is nutritionally stingy. Leaves are packed with cellulose and tough fibers, and extracting anything useful from them requires a digestive system willing to take its time. Sloths solve this problem with a complex, multi-chambered stomach that looks more like something you would find inside a cow than inside a typical mammal their size.

Anatomical studies of the brown-throated three-toed sloth have identified seven distinct regions in the stomach. These include several sacs that make up the cardiac portion, a gastric diverticulum, and a prepyloric stomach that itself has glandular and non-glandular sections.⁵ Histologically, the compartments fall into three broad types: an aglandular, keratinized section that works as a “mechanical stomach” for physical processing, and two glandular sections, one for mucus production and one for acid secretion.⁵ The diverticulum has villi lining its inner surface, a feature more commonly associated with the intestine, suggesting that some nutrient absorption happens before food even leaves the stomach.⁶

The overall architecture resembles what you see in ruminants, with some important differences. Ruminants like cattle chew cud, regurgitating partially digested food to chew it again. Sloths do not appear to do this. Their foregut fermentation relies on resident bacteria to slowly break down plant fibers in the stomach’s large sacs before the material moves onward. It is fermentation without the refining step of re-chewing, and it comes at a cost: the process is agonizingly slow.

Digestion That Takes Days

Food moves through a sloth’s gut at a pace that would seem pathological in almost any other mammal. In three-toed sloths, about 73% of total short-chain fatty acid production (the main energy source from fermentation) happens in the stomach, and a further 17% occurs in the rectum, where feces sit waiting for the sloth’s infrequent trip to the ground.⁷ The rate of fermentation measured in the stomach is dramatically lower than in other small foregut-fermenting herbivores, despite the overall concentration of fatty acids being comparable.⁷

Studies of captive two-toed sloths paint a similar picture. In one experiment, food particles stayed in the gut for more than 140 hours in most individuals, and defecation happened only about once every five days.⁸ Wild sloths of both genera defecate only once every four to eight days, and they do so by making a risky descent to the forest floor rather than simply dropping waste from the canopy.⁹ One oddity worth noting: those long retention times make sloths surprisingly prolific methane producers for their size, because gut microbes have so much time to generate the gas.⁸

Even with all that time, sloths do not extract much from what they eat. Cellulose degradation assays showed that sloths digest only about 3 to 30 percent of the plant material they ingest.¹⁰ Part of the problem is a low abundance of the anaerobic fungi and carbohydrate-active enzymes that other herbivores rely on to break down cellulose effectively.¹⁰ The sloth’s strategy is not to be efficient but to be cheap: keep metabolic costs so low that even a meager yield of energy from leaves is enough to get by.

Running on Almost Nothing

Sloths have some of the lowest metabolic rates of any mammal. Measurements of resting metabolic rate in two-fingered sloths found values about 39% lower than the standard prediction for a mammal of their size.¹¹ Their heart rates are similarly depressed, running at roughly 38% of what allometric equations predict.¹² Their skeletal muscle mass is reduced compared to other mammals of similar build, which limits power output but also limits the energy needed to maintain tissue.¹³

This extreme economy extends to temperature regulation. Most mammals burn significant calories keeping their bodies at a constant temperature, but sloths let their core temperature fluctuate with the environment. In the Amazon, wild three-toed sloths maintained skin temperatures higher than air temperature over 99% of the time, yet increases in skin temperature and heart rate did not coincide, meaning the warmth was not coming from internal heat generation. Instead, sloths appear to warm themselves passively by choosing sunlit branches and exposed perches.¹² It is essentially free heating, and it matters for digestion: researchers have found that food intake in brown-throated sloths increases with ambient temperature, likely because warmer conditions speed up the fermentation by gut microbes.¹⁴ Since these sloths keep their stomachs constantly full, faster fermentation means faster throughput, which means the animal can eat more and absorb more energy.

This link between warmth and digestion raises real concerns about climate change. Metabolic rate measurements showed that at temperatures above 32°C, high-altitude sloths experienced a sharp rise in metabolic rate, suggesting heat stress rather than comfortable warmth.¹¹ For animals whose entire survival strategy depends on keeping energy costs near zero, an environment that forces them to spend energy on cooling could be devastating.

Eating the Algae in Their Own Fur

One of the strangest supplements to the sloth diet comes from their own bodies. Sloth fur hosts a miniature ecosystem: moths, beetles, algae, and fungi all live in the coarse, grooved hairs. A 2014 study revealed that this is not just accidental hitchhiking but a mutualistic cycle that feeds back into the sloth’s nutrition.

The cycle works like this. Sloths descend to the ground to defecate. Moths that live in the sloth’s fur lay their eggs in the fresh dung. New moths eventually emerge and fly up to colonize the fur of a sloth in the canopy. When moths die in the fur, their bodies decompose and release nitrogen, which fertilizes algal growth on the sloth’s hair. Researchers found that three-toed sloths, which carried more moths, also had higher concentrations of inorganic nitrogen and greater algal biomass in their fur. The algae turned out to be highly digestible and rich in lipids, and sloths were observed consuming it directly from their own coats.⁹

For an animal that squeezes so little energy out of leaves, a supplemental source of digestible, fatty algae grown on your own body is a meaningful bonus. The risky ground visit for defecation, which exposes sloths to predators they can barely outrun, starts to make more ecological sense in light of this cycle: the trip keeps the moth population going, the moths keep the algae growing, and the algae keep the sloth a little better fed. It is one of the more elegant examples of mutualism in mammalian biology.

How Baby Sloths Learn What to Eat

Sloth infants face a unique dietary challenge. They need to figure out which leaves to eat in a forest with hundreds of tree species, many of which contain toxic compounds. The solution is straightforward: they eat what their mother eats, because she feeds them directly. Observations of captive brown-throated three-toed sloths found that mothers supplied food to their young, and babies were seen feeding only on the same plants their mothers ingested and provided to them.¹⁵

This behavior probably serves a dual purpose. It teaches the infant which species are safe and nutritious, and it likely inoculates the baby’s gut with the specific microbial communities needed to ferment those particular leaves. Since sloth digestion depends so heavily on the right bacteria doing the right work in those stomach compartments, inheriting both the food preferences and the gut flora from your mother is a practical necessity. Young sloths typically stay with their mother for several months before striking out on their own, occupying overlapping home ranges and often inheriting the mother’s territory and, with it, her preferred feeding trees.

What Extinct Sloths Ate

Modern sloths are small, arboreal, and restricted to tropical forests, but their extinct relatives were a different story. Ground sloths ranged from dog-sized to elephant-sized and roamed across North and South America until roughly 10,000 years ago. Their diets were broader and adapted to very different ecosystems. DNA analysis of a roughly 20,000-year-old dung sample from Shasta ground sloths in the American Southwest identified plant sequences from seven different plant groups, and the species assemblage that formed part of that sloth’s diet now grows at elevations about 800 meters higher than the cave where the dung was found.¹⁶ That shift suggests the climate at the cave site was considerably cooler when the sloth lived there, and that ground sloths were browsing on a mix of desert and montane plants quite unlike the tropical canopy leaves their living relatives depend on.

The contrast highlights how specialized modern sloths have become. Their ancestors could walk between feeding sites and exploit a range of vegetation types. Today’s sloths are locked into the canopy, reliant on a handful of tree genera, with a metabolic rate so low they can barely afford to move. That trade-off has been remarkably successful in stable tropical forests, where leaves are always available and temperatures stay warm enough to keep gut fermentation going. But it leaves modern sloths with almost no margin for environmental disruption, whether from deforestation that removes their preferred trees or from temperature shifts that upset the delicate balance between their metabolism and their digestion.

The Trees That Matter Most for Sloth Conservation

Because sloths depend so completely on specific trees for both food and shelter, their conservation is inseparable from the conservation of particular tree species. In agricultural landscapes, the picture is not as bleak as it might seem. Sloths can persist in cacao farms, pastures with scattered shade trees, and areas with living fence rows, as long as the right species are present. In the Costa Rican study of cacao agroforest, key food and refuge trees included Erythrina, Cecropia, Cordia, and Coussapoa, and both sloth species used them in different habitat patches.⁴ Riparian forests along streams and rivers also served as corridors, with species like Pterocarpus and Spondias providing both canopy connectivity and forage.

For three-toed sloths, the message is simple: protect Cecropia. These trees colonize gaps and edges quickly, so maintaining forest fragments and allowing natural regrowth along clearings tends to produce exactly the habitat three-toed sloths need. Two-toed sloths, being more flexible, benefit more from overall tree diversity. In either case, the lesson for land managers in tropical regions is that a relatively small number of tree species can disproportionately support sloth populations, and that keeping those species in the landscape, even outside intact forest, can mean the difference between sloths persisting or disappearing from an area entirely.