People who consume tofu and other plant-based foods might enjoy a better sex life than meat-eaters, suggests a new study that found certain plant products can influence hormone levels and heighten sexual activity.

The research, published in the journal Hormones and Behavior, is the first to observe the connection between

plant-based estrogenic compounds, or phytoestrogens, and behavior in

wild primates. In this case, it was a group of red colobus monkeys in Uganda.

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As primates, we humans would likely experience similar effects from the compounds.

"It's one of the first studies done in a natural setting providing

evidence that plant chemicals can directly affect a wild primate's

physiology and behavior by acting on the endocrine system," study

lead author Michael Wasserman said in a press release. He conducted the research as a graduate

student at UC Berkeley's Department of Environmental Science, Policy and


"By altering hormone levels and social behaviors important

to reproduction and health, plants may have played a large role in the

evolution of primate — including human — biology in ways that have been

underappreciated," he added.

For 11 months, Wasserman and his team followed a group of red colobus

monkeys in Uganda's Kibale National Park and recorded what the primates

ate. For behavioral observations, the researchers focused on aggression,

as marked by the number of chases and fights, the frequency of mating

and time spent grooming. The scientists also collected fecal samples to assess changes in hormone levels.

The researchers found that the more male red colobus monkeys dined on the leaves of Millettia dura,

a tropical tree containing estrogen-like compounds, the higher their

levels of estradiol and cortisol. They also found that with the altered

hormone levels came more acts of aggression and sex, and less time spent

grooming — an important behavior for social bonding in primates.

The tropical tree is a close relative of soy, which is also considered to be high in phytoestrogens. Women going through menopause often take soy-based products to relieve some symptoms, so I was interested to read how such foods impact males. Males seem to become more macho instead of what would be expected.

"With all of the concern today about phytoestrogen intake by humans

through soy products, it is very useful to find out more about the

exposure to such compounds in living primates and, by analogy, human

ancestors," said study co-author Katharine Milton, professor in UC

Berkeley's Department of Environmental Science, Policy and Management

and an expert on the dietary ecology of primates. "This is particularly

true when determining the influence of phytoestrogens on reproductive

behavior, which is the whole keystone of natural selection."

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The authors are quick to point out that multiple factors influence primate hormone levels and behavior. Goodness knows, we don't want another Twinkie defense-like situation, with a rapist saying he ate too much tofu or something ridiculous like that. In the study, the primates' own

endogenous hormone levels were the stronger predictor of certain

behaviors, while phytoestrogens played a secondary role.

Wasserman, who is now a post-doc at McGill University's Department of Anthropology, and his colleagues are now

examining the relationship between phytoestrogens and other primate

species, including our closest-living relative, the chimpanzee, to

determine how common estrogenic plants are in the diets of wild


He said, "Human ancestors took most of their diet from wild tropical plants,

and our biology has changed little since this time, so similar

relationships as those found here are expected to have occurred over our

evolutionary history."

For this latest study, the researchers note that the red colobus diet contains a

high percentage of leaves, while the diet of chimpanzees, other apes and

human ancestors consists primarily of fruits. One of Wasserman’s

current goals then is to compare the presence of phytoestrogens in wild

leaves and fruits.

"If phytoestrogens make up a significant proportion of a fruit-eating

primate's diet, and that consumption has similar physiological and

behavioral effects as those observed in the red colobus, then estrogenic

plants likely played an important role in human evolution," he said. "After studying the effects of phytoestrogens in apes and

fruit-eating primates, we can then get a better sense of how these

estrogenic compounds may influence human health and behavior."