The primary food source of koalas is eucalyptus leaves. These leaves are highly fibrous and relatively low in nutritional value, making them a unique and specialized diet. Koalas possess a complex digestive system, including a large cecum and colon, which helps them process the tough eucalyptus leaves. Despite being high in toxins and low in calories, koalas have adapted to thrive on this diet, relying on their keen sense of smell to choose the best leaves. Eucalyptus leaves also contain moisture, which is vital for koalas, as they rarely drink water directly.