I found this from John Durant's Hunter-Gatherer.com:
Captive Gorillas Succumbing to Human Disease
Life for humans is much easier than for animals in the wild. On a day-to-day basis, we generally do not have to worry about being eaten or starving to death. Depending on the individual's job, some can get by just fine by sitting around all day. However, this lifestyle brings forth its own set of health issues such as diabetes and heart disease, illnesses rarely found in the wild. These "human" diseases have spread to gorillas that are raised in captivity.
The only species of gorilla kept at North American zoos is the Western Lowland Gorilla. The number one killer of males in captivity is heart disease, much like humans. After a 21 year old gorilla named Brooks died of heart failure at Cleveland Metroparks Zoo in 2005, a group of researchers decided to examine how the gorilla’s lifestyle affect their health. The team was led by Elena Hoellein Less, a PhD candidate in biology at Case Western Reserve University.
The researchers believe that heart disease can be stopped by switching captive gorillas back to their natural diets in the wild. For decades, zoos have fed gorillas bucket loads of high vitamin, high sugar, and high starch foods to make sure their got all their nutrients. At the Cleveland zoo, they have started feeding food such as romaine lettuce, dandelion greens, endives, alfalfa, green beans, flax seeds, and even tree branches which they strip of bark and leaves. To top it off, they give the gorillas three Centrum Silver multivitamins inside half a banana.
Going back to this natural diet has changed gorilla behavior. Before, gorillas only ate during a quarter of their day because the food was so packed with nutrients. Now at Cleveland, they spend 50-60 percent of their day eating which is the same amount as in the wild. With all this extra eating, the gorillas have doubled their caloric intake, yet at the same time have dropped 65 pounds each. This brings their weight more in line with their wild relatives.
"We're beginning to understand we may have a lot of overweight gorillas," said Kristen Lukas, an adjunct assistant professor of biology at Case Western Reserve and chair of the Gorilla Species Survival Plan®. "And, we're just recognizing that surviving on a diet and being healthy on a diet are different. We've raised our standards and are asking, are they in the best condition to not only survive but to thrive?"
Less and her crew are continuing their studies of captive gorillas by measuring the fat on their backs to create a gorilla body mass index. This can be used to gauge healthy weight for gorillas much as it is used for humans. The next step, says Less, is to exercise gorillas at the zoo to get their muscles to a similar level as their wild relatives.
Watch video from Case Western Reserve University: http://www.youtube.com/watch?v=P9A74LvPxU8
