Monkey diet is richer in vitamins and minerals than human diet, UC Berkeley anthropologist discovers

By Patricia McBroom, Public Affairs

BERKELEY--The fruits and leaves that monkeys eat in the wild are loaded with nutrients, giving these primates a diet far richer in many essential vitamins and minerals than the diet recommended for daily consumption by human beings.

This startling information has emerged from a study of monkey diets carried out at the University of California, Berkeley, by physical anthropologist Katharine Milton, an expert on primate diet.

She found, for instance, that the average 15-pound wild monkey takes in 600 milligrams per day of vitamin C, 10 times more than the 60-milligram recommended daily allowance, or RDA, for humans who weigh on average 150 pounds.

Differences on that order also were found for intakes of other micronutrients such as calcium, potassium and magnesium.

"The monkey diet is amazingly rich in nutrients," said Milton, a professor in the Department of Environmental Science, Policy & Management.

"I wouldn't have believed this before because I don't think of plants as being very nutritious. But then I noticed how much vitamin C was consumed by these monkeys," said Milton, who subsequently compared other nutrients in the wild foods with human RDAs.

"This information suggests that, for their size, many wild primates routinely ingest greater amounts of many minerals, vitamins, essential fatty acids, dietary fiber and other important dietary constituents than most modern human populations," Milton will report in the June issue of the journal "Nutrition: The International Journal of Basic and Applied Nutritional Sciences."

Milton's study took place on Barro Colorado Island, a six-square-mile Panamanian nature preserve covered by a dense tropical forest, much of which is old primary growth that has never been cut.

Four monkey species - howler, spider, cebus and tamarin - live on the island where the Smithsonian Institution maintains a research station. The animals eat wild foods believed to be characteristic of plants across the tropical belt, said Milton. The foods include leaves of many kinds and fruits such as figs, plums, berries, palmfruit and grapes. Free-ranging primates in the tropical forests of Central and South America, Africa and Asia have been observed eating foods from many of the same plant families and even the same species as those on Barro Colorado Island, she added.

The anthropologist followed the monkeys through the forest with plastic bags, picking up the food they dropped or threw down from the trees.

"They would bite off the tips of leaves and throw the rest away," said Milton, who analyzed the leaves by sections and found the tips to be especially nutritious - a fact obviously known to the monkeys.

"Young leaves from tropical trees are far more nutritious than I realized. In fact, the young tips have the same profile of essential amino acids as meat, although in lower concentrations," said Milton. She said that leaf protein is perfectly good and clearly satisfies all the protein needs of the monkeys.

"I was very surprised," she said. "I always thought leafy material was deficient in some amino acids, but it is not."

Another surprise came when Milton analyzed the wild Panamanian fruits eaten by the monkeys and found them to be considerably more nutritious - with more protein, more of certain essential micronutrients and a different sugar content - than the cultivated varieties found in American supermarkets.

The sugars in the pulp of wild fruits occurred mainly as glucose and fructose (like honey), while the sugar in domesticated fruits is mainly sucrose (like plain table sugar), she found.

"Sucrose tastes sweeter than glucose, giving our cultivated fruits strong hedonistic appeal, but we have yet to find out whether there is a physiological cost to this high sucrose content," she said.

Milton also found that the wild fruits had higher levels of calcium, potassium, iron and phosphorus - sometimes as much as a 10-fold difference - compared to domesticated fruits.

"I'm not criticizing our fruits," said Milton. "They are pretty good, but we don't eat enough of them, and you have to remember that they have been bred for sweetness and appearance."

The monkey diets also had a better balance of essential fatty acids than do most American diets, which tend to be deficient in alpha linolenic acid, or ALA, said Milton. Foods high in ALA include soy and canola oil, uncooked cabbage, kale and Brussels sprouts.

Milton doesn't like to draw medical conclusions about humans from her new findings on monkey diets, saying that, "We are not monkeys, and we don't eat wild plants."

But she puzzles over the immense differences between the mineral intake, for instance, of a Panamanian monkey and that recommended for an adult man.

The monkey takes in 4,571 milligrams of calcium per day. The RDA for a human who weighs 10 times more is 800 milligrams. Of potassium, the monkey eats 6,419 milligrams; the human is expected to take in 1,600-2,000 milligrams. Of magnesium, the monkey eats 1,323 milligrams; the human RDA is 350 milligrams.

Unfortunately, many people don't even take in the mineral levels recommended as optimum for health, said Milton.

"Throughout history, humans have suffered from all sorts of diet-related diseases," said Milton. "If we paid more attention to what our wild, primate relatives are eating today, perhaps we could learn new things about our own dietary needs that would help reduce health problems throughout the world."

Milton cautioned, however, that people should not rush into the forest and begin eating leaves and wild fruit because human physiology - particularly the gut - has changed through evolution.

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