An experimental drug that dramatically reduced the appetite of rodents caused obese baboons to double or triple their food intake and is now being considered as a treatment for cancer patients and those who need to gain weight. Monkeys are better research models because they are more like humans than rats or mice, not only physiologically, but also in eating behavior; they will eat when they are bored, even if they are not hungry. Fat monkeys are providing some interesting findings about what causes obesity and diabetes.
"Nonhuman primates don't lie to you," said neuroscientist, Dr. Kevin L. Grove, who directs the "obese resource" at the Oregon National Primate Research Center. "We are trying to induce the couch-potato style. We believe that mimics the health issues we face in the United States today."
The monkeys are fattened on a diet of dried chow pellets with one-third of the calories from fat plus adequate protein and nutrients. They can eat all the pellets they want plus a chunk of peanut butter and sometimes popcorn and peanuts. They also get a fruit-flavored punch containing the amount of fructose equivalent to one can of soda per day. It adds up to twice the calories consumed by a normal-weight monkey and 60% of them get fat on it.
One of the monkeys, named Shiva, gained 15 pounds in six months and weighs twice as much as normal for his age. Most of his excess weight is belly fat, an indication that he suffers from the same metabolic disorder that affects two-thirds of Americans.
According to Dr. Grove and researchers in other centers working with fat primates, it is the high-fructose corn syrup that appears to accelerate the development of obesity and diabetes. "It wasn't until we added those carbs that we got all those other changes, including those changes in body fat," said Anthony B. Comuzzie, of the Southwest National Primate Research Center in San Antonio.
Dr. Barbara C. Hansen of the University of South Florida has been doing research on obese monkeys for four decades. She prefers animals that naturally become fat with age, just as many humans do. One of her test subjects, Fat Albert, who was at one time the world's heaviest rhesus at 70 pounds, ate "nothing but an American Heart Association-recommended diet," she said. "To suggest that humans and monkeys get fat because of a high-fat diet is not a good suggestion," she said.
The scientists are seeking clues that may lead to the development of new drugs, since much of the research is funded by pharmaceutical companies. Most of them have little incentive to discover the best diet for primates, but the evidence indicates that the problem may not be the couch potato life-style after all. It may a matter of what we eat and drink while vegetating on the couch.