Determining which animal eats the least is complex, as “least” can refer to consumption frequency, daily volume, or energy expenditure relative to size. The true measure of minimal eating is energy efficiency, achieved through unique biological strategies. Animals have evolved physiological mechanisms to survive long periods without food or subsist on an extremely low daily energy budget.
The Biological Basis of Minimal Eating
The amount of food an animal requires is directly linked to its baseline energy expenditure, known as the metabolic rate. For warm-blooded animals (endotherms), this is the Basal Metabolic Rate (BMR), reflecting the energy needed to maintain a constant, high body temperature. Because endotherms constantly burn calories to generate internal heat, their energy demands are perpetually high.
In contrast, cold-blooded animals (ectotherms) have a Standard Metabolic Rate (SMR) that is far lower and varies with ambient temperature. Ectotherms often require 90% less energy than comparable endotherms because they do not use metabolic heat to regulate their core temperature. This makes reptiles and amphibians inherently more energy-frugal than mammals and birds. Body size is also a factor, as smaller endotherms have a higher BMR per unit of body mass due to greater surface area for heat loss, forcing them to eat more frequently.
Animals That Fast: Surviving Extended Periods Without Food
One way to “eat the least” is to eat very rarely, a strategy mastered by animals that rely on long-term fasting. This adaptation is common among sit-and-wait predators and species that enter long periods of dormancy. Large, infrequently feeding reptiles, such as the Burmese python, are masters of this feast-or-famine lifestyle.
During fasting, the python’s digestive system is dramatically downregulated to conserve energy. The small intestine atrophies and enzyme activity is depressed, allowing them to fast for up to a year while waiting for prey. When a large meal, sometimes exceeding 100% of their body weight, is consumed, the snake undergoes a massive, rapid and reversible physiological change. Their metabolic rate can increase 20- to 44-fold to process the food, and the small intestine can double in size through physiological hypertrophy.
Mammals that undergo true hibernation also achieve minimal consumption by severely suppressing their metabolism. Obligate hibernators, such as the thirteen-lined ground squirrel, enter a state of deep torpor. Their body temperature drops to near ambient levels, often 4–6°C, accompanied by a profound metabolic slowdown.
The ground squirrel’s oxygen consumption drops to 2–3% of its active state, and its heart rate plummets from 200–400 beats per minute down to 3–10 beats per minute. This physiological suppression conserves the fat reserves needed to last through the winter. This ability to actively reset the body’s metabolic “thermostat” allows these endotherms to temporarily adopt an energy expenditure rate closer to that of an ectotherm.
Case Studies in Ultra-Low Daily Energy Consumption
Other animals eat daily but subsist on an incredibly small absolute amount of energy, making them models of ultra-low daily consumption. This strategy is defined by an extremely low BMR coupled with a specialized, energy-poor diet. The three-toed sloth exemplifies this approach, maintaining the lowest BMR of any non-hibernating mammal relative to its mass.
Sloths survive on a diet of low-nutrient leaves, and their slow movement is a direct consequence of their limited energy budget. Their sluggish metabolism means a single meal can take weeks to digest. A three-toed sloth may survive on as little as 80 calories per day, the energetic equivalent of a small handful of potato chips.
Koalas follow a similar, specialized path, surviving exclusively on eucalyptus leaves, which are low in nutrition and mildly toxic. They possess one of the lowest metabolic rates among mammals, roughly half that of comparable placental mammals. Koalas minimize energy expenditure by sleeping for 18 to 22 hours per day, dedicating the few active hours they have to eating and digesting the difficult foliage.
Ultimately, the animal that eats the least depends on the metric used. The python eats the least frequently, sometimes fasting for a year, while the three-toed sloth and koala subsist on the lowest absolute daily caloric intake among mammals. In terms of sheer metabolic efficiency, ectotherms like the python and the hibernating ground squirrel possess the lowest overall energy requirements.