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A poll of parents last fall found 40% of teens consumed some type of protein supplement in the past year. Boys took it to bulk up; girls took it to replace meals. / Getty Images

Emiliano Slesaransky, 17, joined Santa Monica High School's football team as a freshman and — at the urging of coaches and teammates— started hitting the gym whenever possible: in the morning, after school, and on the weekends. The people he met there would share their strategies for bulking up.

"They would take protein powders, other supplements like some people I know take ashwagandha, and maybe creatine," he says, citing popular energy and exercise-enhancing supplements. Emiliano started taking some of them, too.

But his dad, Eduardo Slesaransky, wanted to make sure his son's diet — and attitude — remained balanced: "My concern was the influence that social media has on these supplements and these kinds of things and the culture of body building and the gyms."

Protein supplements are big on social media, where influencers are helping drive sales of protein bars, shakes and powders. A poll of parents by the Mott Children's Hospital at the University of Michigan last fall found 40% of teens consumed some type of protein supplement in the past year.

"Teen boys were more likely — twice as likely — to consume protein every day," says Sarah Clark, a research scientist and co-director of the poll.

Girls, she says, more often relied on supplements as meal replacements, and the inspiration to consume protein shakes, bars or powders often came from coaches, peers, or influencers on social media. But Clark says parents were also among those promoting protein to their children.

"I wonder if, as parents, we are recognizing how much messaging we have taken in about protein being good," she says. "We have absorbed this messaging: That's the key to being healthy," she says, when in fact it is only one factor in a balanced, healthy diet.

The vast majority of teens already get enough protein in their diet without supplements, pediatric dietician Abriana Cain says.

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The vast majority of teens already get enough protein in their diet without supplements, pediatric dietician Abriana Cain says. / iStockphoto/Getty Images

How much is enough?

There is also such a thing as too much protein, says Abriana Cain, a pediatric dietician with Children's National Hospital in Washington, D.C. As a general rule, Cain tells teens and parents to gauge protein intake based on size — benchmarked at roughly 1 gram of protein a day per kilogram of body weight. (For a 150-pound teen, that amounts to about 68 grams of protein per day — or the rough equivalent of a cup of cooked chicken, a cup of yogurt, and a cup of black beans.)

"It might even increase from there, based on their physical activity needs," she says.

Cain says more than 100 grams a day can damage the kidney and liver in the longer term. It can also cause stomach pain, as it did for one of her patients. "They were eating protein supplements with all of their meals and also with all of their snacks, and they were having a lot of abdominal pain."

The vast majority of teens, Cain says, already get enough protein in their diet without supplements.

There are also concerns about the marketing of supplements.

There is no quality control for these products, notes pediatrician and eating disorder expert Dr. Jason Nagata, at the University of California San Francisco. Supplements, including protein bars and powders, are not regulated by the Food and Drug Administration — so they're not tested, and their ingredients aren't verified.

"I think it's important for teens and parents to know that there isn't that kind of rigorous quality control, especially when you're getting mixtures of muscle building supplements and products," he says. "I would just be very cautious."

Nagata advises researching, reading ingredient labels and buying directly from known companies. Some products have been found to have contaminants such as heavy metals, bacteria, or chemicals or adulterants not listed on the label.

Eating disorders are up

Separately, Nagata is concerned that the protein craze is contributing to the alarming increase in eating disorders among boys over the past two decades, worldwide. He observes that over that time period, action figures like Batman and Superman are sold with bigger muscles, and pressures on ordinary teenagers to post attractive photos of themselves to be popular online have increased.

"The masculine body ideal has become increasingly large and muscular, and so more and more boys are trying to become muscular now than they have ever before," he says.

Emiliano Slesaransky stopped using protein powders about a year ago, he says, largely because he started forgetting to take it.

His father, Eduardo, says his son still looks very strong and fit, but is no longer fixated with bulking up for sports. "He's focusing on getting into college."