What if nutrition labels told people exactly what calories meant, in practical terms? A bottle of Coke could dole out specific exercise requirements. The calories herein, it might say, are the equivalent of a 50-minute jog. The decision to drink the Coke then becomes, would you rather spend the evening on a treadmill, or just not drink the soda?

Some would say that's a joyless, infantilizing idea. The implication that people can't understand calorie counts is unduly cynical. Have a Coke and a smile, not a Coke and a guilt-wail. Others would protest on grounds that it's impossible to make this kind of exercise requirement universal to people of all ages, body sizes, and levels of fitness. Everyone burns calories at different rates. But Sara Bleich, an associate professor at Johns Hopkins Bloomberg School of Public Health, is not among these people. She describes these labels as her dream.

For the past four years, translating nutrition information into exercise equivalents has been the focus of Bleich's increasingly popular research endeavor. Her latest findings on the effectiveness of the concept are published today in the American Journal of Public Health. In the study, researchers posted signs next to the soda and juice in Baltimore corner stores that read: “Did you know that working off a bottle of soda or fruit juice takes about 50 minutes of running?” or “Did you know that working off a bottle of soda or fruit juice takes about five miles of walking?” (And, long as those distances and times may seem, they may even underestimate the magnitude of the metabolic insult of liquid sugar.)

The signs were a proxy for an actual food label, but they made the point. They effectively led to fewer juice and soda purchases, and to purchases of smaller sizes (12-ounce cans instead of 20-ounce bottles). Bleich also saw learned behavior; even after the signs came down, the local patrons continued to buy less soda and juice.

"The problem with calories is that they're not very meaningful to people," Bleich told me. "The average American doesn't know much about calories, and they're not good at numeracy."

That concern is the impetus for a growing movement to make nutrition information as simple and practical as possible. Some have proposed a three-tiered stoplight system, where healthy foods are labeled with a green light (Go!), and junk bears a damning red. Yellow is ... everything else. Others have proposed an even simpler thumbs-up, thumbs-down dichotomy.

"Let's say you do know that you need to take in about 2,000 calories a day—which most American's don't know," Bleich said. "Let's say that a hamburger at McDonald's has 250 calories. To figure out the percent that 250 represents of 2,000 is tough, mentally. Most people can't do that, and they certainly can't do it quickly when they're trying to place an order."

The notion is only partly cynical, in that most people only glance at labels for a few seconds, so simplicity is apropos. And the people who consume the most junk calories are also those with the least education and health literacy. These are the populations with the highest rates of obesity and related chronic diseases. These labels need to reach and speak to, most importantly, those at-risk groups.

Bleich launched her initial 2011 foray into exercise-labeling investigation after driving around some of Baltimore's low-income neighborhoods. She saw boarded-up houses and drug trade on the corners. "I thought, do the people who live here care about the calories in the food they eat?" She posted the exercise-equivalent signs in one corner store, to good effect. "In fact, they did."

Today's new results explore a larger, more substantial version of that original study, including the subtleties of changes in people's decisions. The research looked exclusively at black middle-school and high-school students in urban Baltimore. On average, black adolescents drink twice as much soda and juice as the American Health Association guidelines recommend at maximum. The exercise equivalents were based on average metabolic rates for 15-year-olds weighing 110 pounds.

So the conversion from calories to exercise is far from universal. But everything in nutrition is based on averages, Bleich notes, including the generic dietary recommendation of 2,000 calories daily, which is a very rough estimate that depends on age, weight, activity levels, basal metabolic rate, and even environmental temperature. Some athletes need closer to 4,000. But, she says, providing a usable benchmark is much better than an absolute number like a calorie count, which has little relevance to many people. "That's the beauty of this system," she said. "Federal regulations already require that this nutrition information is conveyed. Why not give it in the most digestible form, in a way that's shown to have the largest impact on behavior?"

Listing physical activity-equivalents on labels and menus could, in Bleich's vision, either replace or augment calorie counts.

Counting calories is, as I've written before, a terrible approach to eating. As the nutrition mantra goes, "A calorie is not a calorie." Calories from sugars affect the body differently than do calories from fats or protein. Our bodies are great at taking in and storing calories from food, and terrible at burning them. That's because of a stubborn insistence on staying alive.

According to the work of David Ludwig, a professor of nutrition at Harvard Medical School, the vast difference in the effects of different types of calories on the body comes down to the hormone insulin. Eating too many refined carbohydrates releases insulin, which programs fat cells to suck in and store the sugar calories. Blood-sugar levels drop, which triggers a starvation response. We experience that as slowed metabolism and becoming hungry again shortly after eating.

"David is certainly not wrong," Bleich said. "If you have a snack of M&Ms at 3:00 versus an apple snack, you're going to be hungrier again much more quickly. But I think the way to think about the 'calorie is a calorie' argument is, putting aside these sugar spikes, if you're just looking to lose weight, cutting calories, no matter what kind they are, is going to lead to that outcome."

Another problem with that approach is that the food industry has lately embraced calorie counts as a way of marketing junk. In June, Coca-Cola held a marketing stunt on Santa Monica beach where passersby could hop on a giant stationary bike and pedal until they burned enough calories to earn a can of Coke. By the company's calculation, that was an optimistic 23 minutes. The event, part of the company's "taking on obesity" campaign, artfully reinforced the message that junk calories are fine, as long as you are physically active. That's untrue in that even the most active person can develop chronic disease from a high-sugar diet. And it's almost impossible for most people to out-exercise their stomachs, especially when they get into the throes of a sugar-heavy hunger cycle.

Ludwig's recommendation is to focus on limiting foods that over-stimulate fat cells (refined carbohydrates and concentrated sugars) to store energy. Eating this way, he argues, we can basically ignore calories. The body's innate system of hunger and satiety will take care of itself. He and Bleich are on the same page in trying to minimize intake of sugars, at least, as is the consensus of nutrition experts.

By leading kids away from soda, Bleich is convinced that this labeling system is a prudent approach. "It works. It's helping kids, and they're learning from it." Of the kids in today's study who said they saw the signs, 40 percent said they subsequently changed their behavior. Her next step is to expand the intervention to Hispanic populations and to put the signs on solid snacks, presumably to the same promising effect. But as for real-world implementation, while Bleich has seen support from the FDA in the quest to make nutrition labeling as relevant and digestible as possible, she has also seen pushback from industry groups like the National Restaurant Association.

The menu-labeling provisions of the Affordable Care Act require chain restaurants to provide calorie information on their menus and menu boards, along with a statement addressing recommended daily caloric intake, that gross approximation. In the New England Journal of Medicine last year, Bleich and her Johns-Hopkins colleague Lainie Rutkow argued for exercise-equivalents on those menus, but the time has passed for this to be a part of federal law. And new nutrition labels on food packages were proposed earlier this year by the FDA, but they did not include exercise equivalents. Still, for restaurant chains or food companies looking to voluntarily take on a progressive public-health image, Bleich hopes the approach could get traction.