General Mills' Nature Valley Protein bars sold so well that the packaged food giant launched protein bars under its Fiber One brand, too.

More success followed — and so did another protein bar, this one under General Mills' organic brand, Cascadian Farm.

Across the entire packaged food industry, consumer concerns about health are driving a protein proliferation. Protein, after all, is a fundamental building block of nutrition, responsible for the body's basic upkeep.

"Protein has been getting momentum and driving a lot of our decisions from an innovation standpoint," said Joe Ens, vice president and marketing director for snacks at General Mills. Protein is so popular that it has become a big buzzword in product launches. Last year, 6.6 percent of all new food items made a claim of "high protein," a six-year high and an increase from 4.7 percent in 2012, according to market researcher Datamonitor.

Ironically, protein is a nutrient that's plentiful in the American diet — unlike, say, fiber or calcium.

"Most Americans already — without even trying — are getting two to three times the amount of protein they need," said Deb Sheats, a nutrition professor at St. Catherine University in St. Paul.

High-protein diets have come and gone for years, from the Atkins diet to the currently trendy "Paleolithic" regime, a mix of meat, nuts and vegetables that a caveman would love.

Protein, whole grains and fiber make up a dietary trinity that Americans want more of in their food. Fifty-four percent of U.S. adults say they are trying to get more protein in their diets, according to market researcher NPD Group. Only whole grains rank higher.

"They have an idea that if they can get more [protein], they can do better for their health," said Darren Seifer, an NPD food and beverage analyst.

Foodmakers are getting into protein in all sorts of ways. Austin, Minn.,-based Hormel Foods last year launched Rev, a ready-to-eat wrap filled with meat and cheese, its packaging trumpeting high protein content.

Golden Valley-based General Mills and Kellogg, the nation's biggest cerealmakers, both have come out with high-protein cereal offerings. And what else but a protein craze would account for the Oscar Mayer "Portable Protein Pack" — lunchmeat, cheese and peanuts — that Kraft Foods brought to market last month?

"Protein is really one of the hottest trends right now," said Lynn Dornblaser, an analyst at market researcher Mintel.

The rise of Greek-style yogurt, she said, has been a key driver of protein's surge. Five years ago, Greek, which has two to three times as much protein as conventional yogurt, was a niche product. But Greek yogurt's high-protein level combined with its thicker, tangier taste profile proved a winner with consumers.

Portable protein

Today, Greek makes up more than 40 percent of the overall U.S. yogurt market, a fact General Mills knows only too well. A yogurt titan with its Yoplait brand, General Mills was late to adapt to the Greek trend, a big blow to its yogurt sales.

Still, General Mills has improved its Greek yogurt offerings over the past year. And it's made several protein plays in its booming snacks business, home to Nature Valley and Fiber One bars.

The Nature Valley Protein bar — with 10 grams of protein compared to 4 grams in a regular crunchy Nature Valley bar — was introduced in 2012 and did $100 million in sales in its first year.

"It's been a home run for us," Ens said. Indeed, only 2 percent of new packaged food items do even $50 million in their first year. Fiber One Protein bars did north of $60 million.

The portability of snack bars, like Greek yogurt, has been important to their success. "There has certainly been an interest in protein that is more convenient," said Jenny Peterson, General Mills' consumer insights director. "We hear that continually from consumers."

Part of the allure of protein for snacking is its satiety effect. "Protein is a great tool to help you feel full and keep you satisfied longer from meal to meal," said Katherine Zeratsky, a dietitian at the Mayo Clinic in Rochester. That's partly because protein takes longer to digest.

Protein's fullness factor is transforming breakfast for many Americans, said Melissa Abbott, director of culinary insights at the Hartman Group, a food market researcher. Consumers increasingly believe protein at breakfast helps tide them over better until lunch, she said.

"When I'm interviewing consumers, I hear, 'I used to have cereal or a bagel for breakfast, but now If I don't have protein, my day starts off entirely on the wrong foot.' " That may help explain why the breakfast cereal business has been rather stagnant the past few years.

Dinner is normally prime time for protein. So with more protein at breakfast and snack time, consumers are piling it on.

Too much protein?

The recommended daily amount of protein for adult women and men is respectively 46 grams and 56 grams. For a man, a cup of milk, a cup of dried beans, an 8-ounce serving of yogurt and a 3-ounce piece of meat will meet that 56-gram daily threshold.

But many people get 100 grams of protein a day, said St. Catherine's Sheats. "We eat a lot of meat, and our meat proportions are a half a plate when they should be a deck of cards."

All that extra protein doesn't really help much. In fact, in really heavy doses, protein can be hard on the kidneys, Sheats said. "We don't store protein. We use it and what we don't need, we convert to fat."