People have long referred to breast milk as liquid gold, so perhaps the idea was bound to come up: Why reserve it for babies? Some body-builders and athletes are paying upwards of $2.50 an ounce, proclaiming human milk the best, all-natural sports drink.

“It gives me incredible energy I don’t get from other food and drinks,” one man told New York Magazine. “I want natural stuff that’s God-given, and if it’s okay with moms looking to get rid of it, I’ll take it.”

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Not surprisingly, perhaps, there’s no evidence to back up such claims.

“There’s no peer-reviewed research investigating human milk as a muscle-building supplement or as any kind of post-workout recovery drink,” said E.A. Quinn, who researches human milk as an assistant professor in anthropology at Washington University in St. Louis. “Human milk has tons of beneficial stuff, but I don’t think it’s targeting what (athletes) hope it would target. Professionally, I can’t think of any reason why it would work.”

Recovery drinks generally contain about 10-20 grams of protein per 8 ounces. Human milk contains fewer than 4. The protein in breast milk is particularly easy to digest -- a benefit for babies, but not necessarily for adults.

Some athletes say it gives them an energy boost;. Breast milk does contain a large amount of sugar in the form of lactose. But it also contains cannabinoids, which are associated with hunger and sleepiness in babies.

Others say they sip it for its immune properties. But while the probiotics and immunoglobulins in breast milk can help protect infants who haven’t fully developed their immune systems, it’s unclear how they would interact with the microflora colonies in adults.

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“It’s possible they would be overwhelmed, because an adult has larger established colony of billions and billions of bacteria,” Quinn said.

Still, most experts agree it can’t hurt adults to drink it.

“There are many things in breast milk which are potentially useful even for adults,” said Dr. Jack Newman, co-creator of Breastfeeding Inc. In addition to vitamins and immune properties, "the milk has other very useful properties like the delivery of long chained polyunsaturated fatty acids, which many people are buying in pharmacies and health food stores.

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"Basically, if the milk is properly screened or comes from a reliable source, it can’t hurt to drink it.  Why would it be considered ‘normal’ to drink cow’s milk but not human milk?”

While studies haven’t focused on athletic performance, some research shows that a component of breast milk called HAMLET can kill cancer cells.

Even if breast milk were discovered to be the next Muscle Milk, there’s the issue of cost and demand.

“For jocks, my instinct would be to say it seems unlikely to have much benefit unless you could drink very large quantities of it, as the normal 3-ounce dose wouldn’t mean much to an adult,” said Florence Williams, author of "Breasts: A Natural and Unnatural History." “Any more of that would be very expensive and probably overkill, since the major benefits of breast milk are nutrition and immune-boosting, neither of which a very fit, post-workout guy likely needs.”

Some, however, argue that since supply is so limited -- there’s never enough for babies who need it, Quinn said -- it should be reserved for infants only.

“I would be concerned if it became a widespread fad,” Quinn said. “The benefits are enormous for babies, particularly those at high risk, so we should be prioritizing it for infants.”