Did your parents ever tell you to always eat your vegetables? It turns out monkeys have to, too!
Microbiologist Sally Bornbusch, Ph.D. and clinical nutritionist Erin Kendrick, two authors of a study published earlier this year in the journal FEMS Microbiology Ecology, examined the diets of a range of primates at the Zoo to understand how a reduction in dietary sugar might impact the animals. They say the results were more interesting than they expected.
Kendrick explains the study was born out of a desire to reduce the sugar intake for some of the Zoo’s primates, namely the golden-headed lion tamarins, golden lion tamarins, pale-headed saki monkeys, Geoffroy’s marmosets and Goeldi’s monkeys.
“We can see problems associated with high-sugar diets such as diabetes, heart disease, obesity, dental cavities and potentially some behavior issues in primates in human care," Kendrick said. "To avoid these, we wanted to make the diets more appropriate based on the animals’ own natural diet history.”
All five species included in the study are considered frugivorous to some degree, meaning they eat predominantly fresh fruits. But according to Kendrick, the fruit the animals would have eaten in the wild are significantly different compared to what is commercially available. Wild fruits tend to be higher in nutrients like protein and fiber, while having a lower sugar and water content than fruits we might buy at a grocery store. You can thank humans for that.
At the most basic level, sugar molecules serve as a main source of energy for living beings. As such, humans have evolved to crave sugar and seek it out, even to the point of cultivating our fruits and vegetables to reduce bitterness and increase sweetness. Through nutritional analysis, the research team determined cultivated vegetables are closer nutritionally to wild fruits.
“It’s not an exact match,” Kendrick noted. “Vegetables are still lower in fiber than wild fruits would be, but they’re about as close as we can get commercially. We can’t go out into the wild to collect fruits; that’s not feasible from a fiscal or conservation standpoint.”
The team decided to switch the primates to a primarily vegetable-based diet as a result of these findings. Although the primates’ caloric intake remained stable, their diets were lower in sugar and higher in protein. All of the animals maintained their ideal body condition and energy levels, and several of the animals included in the study successfully bred, so the dietary change didn’t create any fertility issues.
“We know they miss the fruit. It is still a high-reward food item we can use for things they're training for, such as taking medication and participating in their care,” Kendrick said. “But overall, we haven’t seen any issues since we made the change.”