By: Jessica Wang
If you were to google the question “can you survive without nutrients?”, the first answer that pops up would be “no”. All living organisms need nutrients to survive, and in animals, these nutrients are water, carbohydrates, lipids, proteins, vitamins, and minerals. The three main nutrients–carbohydrates, lipids, and proteins–provide the body with energy to function. Typically, humans strive to follow a well-balanced diet, consisting of meats, grains, dairy, fruits, and vegetables, to obtain these nutrients from a variety of sources. However, the diet of koalas is based heavily on one type of plant, eucalyptus, that has very low nutritional value. If all animals require these essential nutrients to function, how are koalas able to survive on a diet of solely eucalyptus, given that it provides such little nutrition?
What Are Nutrients?
A nutrient is defined as “a substance that provides nourishment essential for growth and the maintenance of life.” (Oxford Languages Dictionary) Unlike plants, who can make their own food, animals are heterotrophs that need to consume plants or other animals to derive their nutrition. Food contains stored chemical energy and is digested by stomach acids after being chewed and swallowed in the mouth. The small intestine absorbs nutrients in food, and the circulatory system carries nutrients to other body parts to use as fuel. Apart from its function as the main source of energy for the body, nutrients help repair body tissues, give structure to blood vessels, bones, and ligaments, and assist in maintaining homeostasis of the body. Nutritional needs vary between animal species, and animals are classified into three categories based on their diet. Herbivores, such as cows, sheep, and koalas, rely on only plants for their nutrition. Carnivores, such as lions, tigers, and wolves, only eat other animals. Omnivores, such as humans, dogs, and foxes, depend on both plants and animals for food. Koalas are considered herbivores because they feed on the leaves of eucalyptus, a native Australian plant traditionally used by humans for medical purposes.
Koalas and Eucalyptus
Koalas are tree-climbing marsupials native to southeast and eastern Australia. The majority of their diet consists of eucalyptus leaves, a plant that is poisonous to most other animals, including humans. Koalas, however, have a unique, specially adapted digestive tract that makes them one of the only known mammals able to survive on a diet of eucalyptus. Interestingly, eucalyptus leaves provide very low nutritional value. Research has revealed eucalyptus to be high in fiber (34.50%) and carbohydrates (41.07%), while rather low in protein (13.8%) and other nutrients. Despite their low-protein diet, koalas are able to survive because of their special adaptations, such as an extended sleep schedule. Koalas sleep for 18-20 hours daily to conserve energy and digest food slowly. These animals have a very slow metabolic rate that allows them to keep the eucalyptus within their digestive system for an extended period, maximizing the amount of energy extracted from food. The slow metabolic rate also conserves energy and minimizes the need for more nutrition. Every day, koalas eat around 200 to 500 grams of eucalyptus. Their special tooth adaptations and shapes help them eat the leaves. Sharp front incisors allow koalas to bite off leaves from the tree, and their molars allow them to cut the leaves without crushing them. A gap between their front and back teeth allows koalas to move eucalyptus leaves around their mouth effectively. The special bodily adaptations of koalas help them survive, even when their diet contains little nutrients.
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