The Diet Detective: How Do Animals Eat, Part II

This is the second part of my interview with Bruce Rengers, Ph.D., R.D., a professor at Metropolitan State College of Denver and a former zoo employee, and Jennifer Watts, a nutritionist at the Brookfield Zoo in Chicago.
Do animals get fat in the wild? Is that common or rare?

Bruce Rengers: I have seen massively obese animals in the wild, but it is always because they are eating human food that is brought to them. For example, monkeys in temples in Thailand are considered sacred and receive food from people every day even though they live "in the wild." These monkeys are so obese they can barely move. But I guess this really wouldn't be considered "in the wild" since they are protected and fed.

I would suspect that truly living in the wild animals do not get enough food to allow them to become obese. But if they did, they would become food for another animal very quickly because they would not be able to move fast enough to escape a predatory situation. There are, however, animals such as polar bears and seals that are naturally fat in the wild because they need the fat for warmth. Also, some animals naturally become fat before winter sets in so they can survive the winter. It may be hard to define what is abnormal obesity in some animals.

Have you ever used high-fiber foods to increase satiety among the animals?

Bruce Rengers: With obese animals in the zoo we often used fiber to dilute the caloric density of foods while maintaining the food's bulk. My impression is that it was never very successful. Trying to get animals in captivity to lose weight is not an easy task. When I went to the zoo I thought it would be easy to deal with overweight animals since the animals only get what we give them for food. I was definitely wrong about this. Some animals become agitated when they feel hungry and start engaging in aggressive or odd behavior. For example, orangutans start eating feces or throwing it at people. Definitely not desirable in a zoo exhibit!
Jennifer Watts: Absolutely! Only in omnivorous or herbivorous mammals though, since there's not a whole lot I can do with carnivores. Our grizzly bears are perpetually hungry during the summer, as they are programmed to put on weight, but they are not as active as they would be in the wild. So, they get a lot of greens in order to feel full and not get aggressive with each other or with keepers. For them, I am OK with giving them iceberg lettuce since it's strictly for bulk, but for other animals I try to stay away from iceberg.

Orangutans naturally have a very high-fiber diet, so their diet is about 70 percent greens, but it does help with satiety as well. For many hoofed animals, the feeling of satiety is important for the health of the GI tract. There are species that are basically grazers, and they've adapted to eat a lot of low-quality forage, so I will offer them low-quality hay to allow them to eat and "graze" normally.

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