Q. WHICH ANIMALS ARE MOST AND LEAST EFFICIENT AT DIGESTING FOOD?

A. Digestive efficiency varies, depending on the food and the animal, said Michael Schlegel, chief nutritionist at San Diego Zoo Global, which operates the San Diego Zoo.

When carnivores eat meat, they are very efficient in extracting its nutrients, Dr. Schlegel said. And some animals that consume foods high in plant fiber — like cows, colobus monkeys and kangaroos — have digestive systems with “foregut” areas in which fermentation effectively breaks down cellulose into absorbable nutrients.

In animals with “hindgut” fermentation — like horses, elephants, wombats, gorillas and to some extent humans — microorganisms in the lower digestive tract also help extract nutrients from plant fiber.

But the process doesn’t work as well as in cattle, sheep and other animals that chew cuds, Dr. Schlegel said. Many of the nutrients are lost in feces.