The loss of a fiber optic cable in San Jose, Calif., last year highlighted how crucial lasers have become in our lives. Credit: Henrick5000/iStock

On April 11, 2009, vandals sliced through a handful of fiber-optic cables in San Jose, Calif., a high-tech hub in Silicon Valley.

Instantly, cell phones and land-based phone lines stopped ringing. Internet service crashed. Credit card machines froze. Banks locked their doors. Traffic lights blinked in disarray, snarling traffic. For a short while, no one could call 911.

The reason for the communications breakdown is that most of the information we send and receive, from text messages to Google searches, travels through fiber-optic cables. And the messages racing through these cables are encoded by lasers. So when the cables were cut, so were all forms of communication that are delivered by laser beam.

“Cutting off the lasers was equivalent to having a disaster in that part of the world,” says Thomas Baer, an expert in laser science from Stanford University in California. “That’s how much we depend upon lasers for communicating with one another these days.”

Lasers used in telecommunications blink on and off at blindingly fast speeds of some 10^-12 seconds, or one millionth of one millionth of a second. These pulses create digital codes, sort of like Morse code. The messages are then beamed through fiber-optic cables and carried across classrooms, neighborhoods and oceans. Eventually the messages make their way to our cell phones, televisions and computer screens.

You might be most familiar with laser beams from your teacher’s laser pointer and from Star Wars light sabers. Lasers are remarkable because they are the brightest source of light on Earth, they produce the purest form of color possible, and they can be focused down to the tiniest spot possible. These qualities make them useful for a seemingly endless list of applications.

Now, as scientists this year mark the 50th anniversary of the invention of the laser, it’s clear that lasers have touched and transformed nearly every aspect of our lives.

DVDs contain digital messages that are written by lasers, and those messages are decoded by lasers inside of DVD players. A laser at the grocery store checkout line reads the bar code on your box of cereal. Lasers are used to weld and shape metal. For instance, every major automobile part, from air bags to cloth seats, brakes, clutch and engine is manufactured with the help of lasers. Lasers are used in delicate eye surgeries to improve vision, and they can measure the distance from Earth to the Moon to within a couple of inches. About half the gross domestic product (GDP), the total income of the United States, depends on lasers to manufacture key parts or deliver information, says Baer.

But for all of these practical uses, scientists who are exploring the future applications of lasers — from harnessing the power of the sun for carbon-free energy to altering weather patterns — say that the future of lasers is only getting brighter, and more intense. The next generation of lasers is going to be 10 to 100 times more powerful than present-day lasers.

Light Amplification

Like many scientific discoveries, that of the laser resulted from decades of step-by-step progress. In the early 1950s, during World War II, several teams of scientists were racing to make the first laser. The U.S. military hoped to create a “death ray” that could shoot down missiles. Through trial and error and experimentation with different types of materials, Theodore Maiman at the Hughes Research Laboratories in Malibu, Calif., succeeded in building the first laser in 1960 using a powerful flash bulb wrapped around a short ruby rod about as long as your finger. When the flash bulb fired, it excited atoms in the ruby. Mirrors on the ends of the rod reflected light through the ruby crystal. When some of the light leaked through one of the mirrors, it exited as an intense burst of red light. The first laser was born.

“When these guys invented this, they had a certain application in mind,” says David Fritz, an expert in X-ray physics at the SLAC National Accelerator Laboratory, at Stanford University. “But certainly they didn’t imagine what it would evolve into.”

The word “laser” stands for “Light Amplification by Stimulated Emission of Radiation,” or LASER. In other words, a laser is an intense or “amplified” pulse of light. This pulse results when atoms are stimulated, or excited, by light but then fall down into a lower energy level and give off energy. Atoms can remain in an excited state only for about one-millionth of a second. When atoms return to their usual, non-excited states, they produce photons, which are the basic units of light.

Scientists Yannick Petit and Jérôme Kasparian first tried out their laser in a cloud chamber to see whether water-based clouds could form. Credit: Daniel Giry, Saga Photos

Lasers have unique properties that make them so useful. Ordinary light, such as sunlight, consists of many different colors. In contrast, laser light consists of just one pure color. Light travels in wavelengths with peaks and valleys, just like the waves of the ocean. But while the light waves from sunlight or a flashlight or light bulb scatter in different directions, the wavelengths of a laser flow in perfect formation, sort of like the rows in a marching band. Because the waves of laser light move together so precisely, the light beams can be focused into a tiny area, even much smaller than a pinhead. These qualities create the sharp, powerful beam of light that we recognize as a laser.

Lasers for fusion

As long as lasers have existed, scientists have envisioned harnessing their power to create a fusion reaction that could someday produce an almost limitless stream of carbon-free energy. Scientists plan to soon fire up the most powerful lasers in existence to work toward that goal. The National Ignition Facility, part of Lawrence Livermore National Laboratory in Livermore, Calif., houses a 10-story building that spans the length of three football fields. Inside of that building sit 192 of the world’s largest lasers.

When all of the laser beams are activated, they will generate about 2 million joules of energy, which is about the amount of energy contained in a stick of dynamite. That pulse of energy will be delivered to a small pellet of hydrogen ice. The resulting reaction produces “fusion,” a process that occurs when two heavy hydrogen atoms collide, or fuse, into one helium atom. The explosion is very fast and powerful. Imagine the power of an exploding stick of dynamite. Dynamite can blow up mountains. This fusion reaction happens about a million times faster than a stick of dynamite explodes. And while a stick of dynamite is about the size of a large breadstick, the energy of these lasers will be focused, or concentrated, onto a target that is about as wide as a human hair. “The laser in this case acts as a powerful hammer that drives this reaction,” says Baer.

The speed and concentration of this reaction, Baer estimates, will make it about a trillion times more powerful than the explosion of a stick of dynamite.

This fusion reaction is similar to what powers the sun and other stars. It will release a burst of energy so powerful that it’s comparable to making a miniature star on Earth. And scientists believe the fusion reaction could someday be used to produce carbon-free energy.

“No one knows if fusion energy is going to work,” says Baer. “But it is an important area of research, and it allows us to understand new forms of matter in ways we just haven’t been able to access before.”

Lasers for brain research

Lasers are also helping researchers understand what makes the tiniest brains tick. Fruit flies possess brains the size of a grain of salt, yet they can taste and smell, see and walk. These brains can even learn — not unlike the human brain.

Fruit fly brains are complex enough to provide insights into the workings of the human brain, and they are just the right size for scientists to study using lasers. With laser beams precisely pinpointing areas of the flies’ brains, scientists can map individual brain cells and study these cells in action, tracing the flow of information through a fly’s brain.

For instance, it’s possible to learn what happens when flies process information — like when a fly sees and smells a watermelon on a picnic table and makes the decision to land on the watermelon or to pester the picnic guests. And it’s possible to observe how the fly’s brain tells its limbs whether to walk, fly or jump. In other words, scientists can study the patterns of brain waves, or neural activity, inside the flies’ brains.

“We’re looking at this right at the neural level, so we’re reading the actual thoughts of these fruit flies,” says Baer.

Fruit flies are being used as models to study human brain diseases such as Parkinson’s and Alzheimer’s. Scientists hope that learning about the brain circuitry of the flies can help in understanding what causes these diseases and someday to develop cures.

Lasers for rain

Lasers may even play a role in improving weather forecasting and one day in triggering rainfall.

As far back as the 1930s, during a time known as the Dust Bowl when North America was stricken by drought, people have hoped to control weather patterns and create rain.

Current attempts at rainmaking involve “cloud seeding,” using rockets to scatter substances into the atmosphere. These tiny particles provide surfaces, or nuclei, on which water can condense and around which clouds can form. But the process is not very efficient, and there are concerns over the potential toxic effects of these particles in the air, says Jérôme Kasparian, an optical physicist at the University of Geneva in Switzerland.

So Kasparian and his colleagues came up with an alternative. They discovered that lasers can produce charges, or ions, in the atmosphere that act as cloud nuclei. The team recently fired a powerful laser through a cloud chamber the size of a small box. To the researchers’ delight, clouds formed before their very eyes. The clouds were small: just 20 to 30 centimeters in diameter, about the length of two pencils end to end, across the cloud chamber.

“The key point is it works — we shot the laser and saw the clouds forming,” says Kasparian.

To test the experiment outside, Kasparian and his team launched a high-powered laser into the sky. Then they fired a second laser. The laser allowed them to see how much light gets scattered back to the ground by water droplets. When it was really humid out, the scientists were able to trigger formation of clouds in the atmosphere.

The experiment is not yet ready for practical applications, says Kasparian. But soon, the work could be used to improve local weather forecasting, he says. By shooting lasers into the atmosphere and analyzing the size of rain droplets and how quickly droplets are growing, meteorologists could gain a better understanding of the way certain air masses behave. Through “customized” forecasts it could soon be possible to know whether it’s going to rain over a sports stadium during a major event, for instance.

“Having very detailed characterization of the atmosphere can feed this kind of forecast,” says Kasparian.

Lasers for biochemistry

This fall, scientists at the SLAC National Accelerator Lab are doing some of the first experiments on the world’s first X-ray laser, which was unveiled in September 2009. Since the wavelength of X-rays is similar to the distance between atoms, this laser can take snapshots of very small stuff, such as, for example, the bonds between atoms in proteins. Proteins are strings of molecules that fold into complex structures and perform lots of services, such as breaking down the food we eat and using it to build muscles. In an upcoming experiment, researchers plan to use the X-ray lasers to study how proteins change shape as one chemical bond is broken and another is formed.

The story of lasers and its many applications illustrates the value of basic research, says Fritz. When the laser was invented, “no one could have envisioned how much of an impact it would have on society.”

POWER WORDS (from the Yahoo! Kids Dictionary)

laser Any of several devices that emit highly amplified and coherent radiation of one or more discrete frequencies.

physics The science of matter and energy and of interactions between the two, grouped in traditional fields such as acoustics, optics, mechanics, thermodynamics, and electromagnetism, as well as in modern extensions including atomic and nuclear physics, cryogenics, solid-state physics, particle physics and plasma physics.

cloud chamber A gas-filled device. In it, particles smaller than atoms form chains of droplets on ions formed in the gas. These chains help show that the particles were present. It is also used to infer the presence of neutral particles and to study certain nuclear reactions.

wavelength The distance between one peak or crest of a wave of light, heat, or other energy and the next corresponding peak or crest.

fiber optics The science or technology of light transmission through very fine, flexible glass or plastic fibers. A bundle of optical fibers.

But sugar is high in calories, and eating too much of it can cause weight gain and other health problems. That’s why millions of people drink diet sodas and eat foods that contain artificial sweeteners in place of sugar. These synthetic chemicals taste sweet, but they have no calories.

It can be hard to resist the temptation of chocolate and other sweet treats.

André Karwath/Wikipedia

But are sugar substitutes safe to use? The answer is complicated.

Sweet controversy

For as long as artificial sweeteners have been around, they’ve been surrounded by controversy. Some studies have suggested that they cause cancer, allergies, and other health problems, while other studies question those findings.

It’s also unclear whether eating sugarfree foods can actually help people control their weight. Some researchers even think artificial sweeteners are helping fuel a widespread addiction to sugar.

Regular or diet, drinking lots of soda can fuel a constant desire for sweets.

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“The more [sweets] you get, the more you need to feel satisfied,” says David L. Katz, director of the Yale-Griffin Prevention Research Center in New Haven, Conn.

“So, when it comes time for dinner,” he says, “pasta sauce without added sugar tastes bland. When it’s time for dessert, intense sweetness is required” for people to be happy.

Despite the debate, plenty of people continue to down artificial sweeteners. In the United States alone, nearly 200 million people consume sugarfree or low-calorie products, according to the Calorie Control Council, a group that represents the diet-food industry. About half of the people who eat and drink sugarfree products make a habit of it—consuming an average of four such items every day.

People develop lifelong preferences for certain tastes and flavors during childhood, Katz says. So the choices you make now may affect eating habits for the rest of your life.

Acquired tastes

Some flavors, such as spicy and sour, require practice to enjoy, and our tongues are highly sensitive to these tastes. Just a dash of cayenne pepper, for example, can make a dish too fiery for some people to eat. A preference for sweet, on the other hand, comes naturally. Even babies like sugar—and lots of it.

That’s because sugar is a rich source of calories, and calories provide energy. For our ancestors, craving sweet foods was an important way to ensure that they would get enough energy to survive, says Eric Walters, a biochemist at Rosalind Franklin University of Medicine and Science in North Chicago, Ill.

Sugar comes in a variety of forms or flavors—all sweet.

Romain Behar/ Wikipedia

Since more calories mean more energy, our taste buds developed a fairly high tolerance for sugar, Walters says. That means most people can handle—and enjoy—huge doses of sweet stuff.

Artificial sweeteners stimulate the same cells in our tongues as sugar does. Thanks to the substitutes’ chemistry, however, they are hundreds to tens of thousands of times as sweet as sugar. That means that far less of them is required to make something taste sweet.

So, where a 12-ounce can of regular cola contains about 10 teaspoons of sugar, a can of diet cola contains less than a tenth of a teaspoon of the artificial-sweetener aspartame.

Because sugar substitutes work in such small quantities, they add almost no calories to a product. That’s good news to many people on weight-reduction diets.

People with a disease called diabetes also often turn to artificial sweeteners because these products don’t raise levels of sugar in the blood, as sugar does. Diabetics have to be extra careful about controlling blood-sugar levels.

But artificial sweeteners are chemicals, and they’re made in labs. Sugar, by contrast, comes from living plants. Many people are concerned that artificial sweeteners, like some other synthetic chemicals, may cause health problems. Over the decades, the fears have waxed and waned, but questions about their safety are still debated.

Scary sweeteners

Five artificial sweeteners are currently available in the United States (and several more in other countries). Saccharin, the oldest artificial sweetener, was first produced in 1879. It’s sold as Sweet’N Low in the United States. It’s used in diet soda, candy, and other sugarfree products.

Some studies have linked saccharin to cancer in rodents. But other studies have shown that animals must consume the equivalent of hundreds of cans of saccharin-containing soda every day to experience any ill effects.

In the minuscule amounts that people actually consume it, Walters says, “I think saccharin is very, very safe.”

Aspartame (which is marketed as NutraSweet or Equal and appears in products such as Diet Coke and Diet Pepsi) has aroused similar health concerns since it was first produced more than 40 years ago. In the most recent scare, a group of Italian researchers found evidence that rats fed lots of aspartame developed cancer.

People criticize full-sugar sodas and diet versions for different reasons.

David Shay/Wikipedia

A panel of 10 American scientists examined the Italian research and found major flaws. The rats used in the experiments, for example, were sick to begin with. And the researchers didn’t keep good track of exactly how much aspartame each rat consumed.

The U.S. panel also reviewed more than 500 aspartame studies and concluded the substance is safe. The majority of the studies, the scientists found, show that an average adult can eat as many as 19,400 packets of Equal a day without any permanent ill effects.

“I have no question in my mind that it is safe to consume aspartame, and I’d rather consume that than the calories of a full-sugar soda,” says University of Maryland toxicologist Bernadene Magnuson, a member of the review panel. She encourages her kids to adopt the same attitude.

Some scientists and antisweetener activists remain concerned that previous safety studies have been biased in favor of artificial sweeteners. (The U.S. experts-panel study cited above, for example, was funded by a company that produces aspartame.)

“The only ones with the incentive to study [artificial sweeteners] are the companies marketing them,” says Michael Jacobson, executive director of the Center for Science in the Public Interest in Washington, D.C. “If they say it causes cancer, they’re out of business.”

Diet food?

Millions of people have been consuming artificial sweeteners for many decades, and no diseases have broken out as a result. That’s pretty good evidence that these substances are probably harmless to our health at the concentrations we eat them, Katz says.

Still, Katz himself avoids them, partly because he says there’s no convincing evidence that “diet” products are a good diet strategy. In fact, eating artificially sweetened foods may actually sabotage weight-reduction efforts.

Packets of artificial sweeteners sit next to packets of sugar in many restaurants.

iStockphoto.com

In a 2004 study, for example, rats that drank a lot of a saccharin-sweetened drink ended up eating much more other food than did rats that had drunk equal amounts of a beverage sweetened with sugar.

What’s behind the surprising result? Perhaps, Katz says, artificial sweeteners confuse the brain’s ability to connect sweet tastes with the calories in sweet foods. So, rats that eat a lot of sugarfree foods may end up eating more high-calorie foods to compensate. The same might be true of people.

Katz also suspects that bathing the tongue all day in any kind of sweetener—plant based or artificial—only increases desire for supersweet foods. Today, he says, most store-bought salad dressings and pasta sauces contain more sugar per gram than chocolate syrup does. We’ve become so used to the taste of these products that many people prefer them to unsweetened versions. (Artificially sweetened versions of these products are now available too).

Sugar, sugar everywhere . . .

Despite the questions and controversies, artificial sweeteners, like sugar, are more popular than ever. They’re appearing in more and more foods, from ice cream to jellies to cough drops. And the U.S. Food and Drug Administration is reviewing even more sugar substitutes for approval.

The more sugar you eat, the more you probably want.

iStockphoto.com

In an attempt to eat a healthy diet, Katz and his family try to avoid sugar as well as artificial sweeteners. The effort has influenced the taste preferences of his five children.

Because his kids eat so little sugar at home, Katz says, they experience sweetness overload when they eat cake or other sweet treats at a birthday party.

“They take one bite and then look for the wastebasket to spit it out,” he says, “because [to them] it’s sickeningly sweet.”

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Cosmic rays are particles that travel from space into Earth’s atmosphere. Ultra-high-energy cosmic rays are tiny, very rare particles that contain extremely large amounts of energy. These rays have more energy than any other known particles in the universe.

This illustration shows the shower of particles produced when Earth’s atmosphere is struck by ultra-high-energy cosmic rays (the most energetic particles known in the universe).

Simon Swordy/University of Chicago, NASA

For decades, scientists have speculated about where ultra-high-energy cosmic rays come from. Now, an international team of researchers has found the first solid evidence that these energetic particles come from supermassive black holes in galaxies near ours.

“This is a landmark finding,” says Paul Mantsch of the Fermi National Accelerator Laboratory in Batavia, Ill. Along with scientists from 17 countries, he helped make the discovery at the Pierre Auger Observatory in Argentina.

For the new study, the observatory recorded 27 ultra-high-energy cosmic rays. Results showed that 20 of those particles came from points in the sky where galaxies that contain massive black holes are already known to be. The link is too strong to be a coincidence, the researchers say.

The researchers suggest that the cosmic rays are coming from extrabright areas at the centers of galaxies. Each such area is known as an active galactic nucleus (called AGN). All the AGNs identified in the new study lie fairly close to the Milky Way. None is more than 326 million light-years away.

How do AGNs produce such high-energy particles? For one thing, black holes inside AGNs feed on swirling disks of gas and dust. As the material spirals in, it heats up and spits out radiation with lots of energy.

Also, AGNs typically spit out huge jets of high-speed gas. These jets might blast some cosmic rays to extraordinarily high energies, the researchers say.

The Auger observatory, which opened in 2004, is enormous—and it has to be. It works by detecting the particles created when cosmic rays smack into Earth’s upper atmosphere. These secondary particles fall to Earth in a wide shower that can spread out over 40 square kilometers (15 square miles) by the time they reach Earth.

And the particles are hard to catch. One square kilometer (less than half a square mile) of Earth’s upper atmosphere gets hit by ultra-high-energy cosmic rays just once every 100 years or so. To detect as many of the particles as possible, the observatory sprawls out over 3,000 km² (1,160 miles²).

The exciting new discovery has some scientists convinced that it’s time to build a second facility just like the Auger, which is in the Southern Hemisphere. To catch as many particles as possible, they say, the new observatory should be built in the Northern Hemisphere.—Emily Sohn

Going Deeper:

Cowen, Ron. 2007. Ray tracing: Energetic cosmic rays linked to giant black holes. Science News 172(Nov. 10):291-292. Available at http://www.sciencenews.org/articles/20071110/fob2.asp .

For more information about ultra-high-energy cosmic rays and the Pierre Auger Observatory, go to www.auger.org/ (Pierre Auger Cosmic Ray Observatory).

Cells in the green leaves of plants work like tiny factories to convert sunlight, carbon dioxide, and water into sugars and starches—stored energy that the plants can use. This conversion process is called photosynthesis. Unfortunately, unless you’re a plant, it’s difficult and expensive to convert sunlight into storable energy. That’s why scientists are taking a closer look at exactly how plants do it.

Plants such as this sunflower efficiently convert the sun’s light into energy that they can use.

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In a world with increasing energy needs, researchers are always looking for new ways to power everything from cars to computers without putting more stress on the environment. That’s another reason why scientists are so interested in solar power—it doesn’t pollute the air, water, or land. And since the sun lights and warms the entire planet, the ability to harness its energy could provide a clean energy source for everyone.

Focusing on fuel

The main sources of energy that people use today are called fossil fuels, such as natural gas, oil, and coal. Unfortunately, the supply of fossil fuel is limited. Once we use all the coal and oil in the Earth, they’re gone for good. The sun, on the other hand, is a renewable energy source. No matter how we tap it for energy, the sun will be around—at least for the next few billion years.

There’s another problem with burning fossil fuels—pollution. The ideal energy sources of the future will be “clean”: they won’t produce carbon dioxide and other gases that pollute the environment as fossil fuels do.

The air pollutants spewed by this oil refinery illustrate one drawback to relying on energy from fossil fuels.

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Hydrogen is one alternative to fossil fuels that interests many researchers today. Hydrogen burns clean—it produces only water, not carbon dioxide. Researchers are trying to come up with ways to make large quantities of hydrogen cheaply and cleanly, and one way involves using plants or plant-like organisms, such as algae.

Putting plants to work

Some scientists are trying to get plants, or biological cells that act like plants, to work as miniature photosynthetic power stations. For example, Maria Ghirardi of the National Renewable Energy Laboratory in Golden, Colo., is working with green algae. She’s trying to trick them into producing hydrogen instead of sugars when they perform photosynthesis. Once the researchers can get the algae working efficiently, the hydrogen that they produce could be used to power fuel cells in cars or to generate electricity.

The algae (green) are grown in flasks to produce hydrogen in the lab.

Courtesy of DOE/NREL, Warren Gretz

During photosynthesis, plants normally make sugars or starches. “But under certain conditions, a lot of algae are able to use the sunlight energy not to store starch, but to make hydrogen.” Ghirardi says. For example, algae will produce hydrogen in an airfree environment. It’s the oxygen in the air that prevents algae from making hydrogen most of the time.

Working in an airfree environment, however, is difficult. It’s not a practical way to produce cheap energy. But Ghirardi and her colleagues have discovered that by removing a chemical called sulfate from the environment that the algae grow in, they will make hydrogen instead of sugars, even when air is present.

Unfortunately, removing the sulfate also makes the algae’s cells work very slowly, and not much hydrogen is produced. Still, the researchers see this as a first step in their goal to produce hydrogen efficiently from algae. With more work, they may be able to speed the cells’ activity and produce larger quantities of hydrogen.

Maria Ghirardi observes one of her algae reactors.

Courtesy of DOE/NREL, Warren Gretz

The researchers hope that algae will one day be an easy-to-use fuel source. The organisms are cheap to get and to feed, Ghirardi says, and they can grow almost anywhere: “You can grow them in a reactor, in a pond. You can grow them in the ocean. There’s a lot of flexibility in how you can use these organisms.”

Making sun catchers from scratch

Other scientists interested in alternate fuel sources are also focusing on plants. But these researchers want to re-create what plants do without actually using them.

Plants have molecules that catch and store solar energy. Scientists want to create molecules that mimic what plant molecules do.

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Plants have specific molecules that catch the energy of sunlight during photosynthesis. Some biochemists have used special techniques to take a snapshot of these molecules inside a cell. “We finally know what the little factory looks like,” says Daniel Nocera, a professor of chemistry at the Massachusetts Institute of Technology (MIT).

Chemists in Nocera’s lab have an ambitious plan to capture the sun’s energy. Instead of tweaking the sun-catching molecules found naturally in plants and algae, these researchers want to build artificial sun-catching molecules from scratch. “We’re all busily working away to try to figure out how to make [photosynthesis] happen outside of the leaf,” Nocera says.

Their goal—even though it is still many years away—is to have the artificial molecules produce hydrogen for everyday use.

Sunlight is already Earth’s chief energy source. If humans can learn to harness solar energy more efficiently, sunlight will provide even more energy than it does now.

iStockphoto.com

Finding solutions to our energy problems is one of the great scientific challenges of our time, Nocera says. But it’s the challenge of the unanswered questions that keeps him excited about his work. “It’s like we need to paint a picture,” he says. “At some points, we don’t even have the paints yet.”

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New food guidelines and the food pyramid that goes with them emphasize that we should eat more fruits, more vegetables, and more whole grains than we typically do now. We should also avoid lots of sugar, salt, and certain types of fats. And we should get plenty of exercise.

The best way to stay healthy is to eat foods packed with nutrients.

USDA

As a young person, you might not think that these recommendations apply to you. After all, you might consume greasy pizza and sugared soda pop every day and feel just fine. Or perhaps you stay skinny no matter how many French fries and candy bars you eat.

There are plenty of reasons to swallow your pride instead of a milkshake and pay attention to the guidelines, says Joan Lyon. She’s a nutritionist at the United States Department of Agriculture (USDA) in Alexandria, Va.

Evidence continues to build that eating certain kinds of foods protects people from cancer, heart disease, obesity, diabetes, weak bones, and other health problems. Eating the wrong kinds of foods, on the other hand, causes your body harm.

As a dietician in the U.S. Army for 21 years, Lyon worked with a lot of young soldiers. They didn’t think it mattered what they ate, she says. They felt like they were going to live forever.

But, if you don’t pay attention to what you eat when you’re young, Lyon says, it’s really, really hard when you’re old and you find yourself sick and unable to do much about it.

New information

Every 5 years, the U.S. government enlists scientists to update a document called “Dietary Guidelines for Americans” and a food pyramid illustration that goes with it. (See “Building a Food Pyramid.”) As scientists learn more about the human body, nutrition, and disease, they adjust the guidelines to reflect the new information.

The cover of the latest edition of “Dietary Guidelines for Americans.”

USDA

Lyon was a member of a large staff that helped a team of 13 scientists put together the latest set of guidelines. The USDA and the Department of Health and Human Services released the guidelines in January.

Coming up with new guidelines every 5 years is a complicated process. More than a year before the new report is due, experts gather the latest scientific evidence on vitamins, minerals, and various foods. They discuss the findings. Sometimes, different studies seem to give opposite results. Sometimes, the evidence is incomplete.

“It’s a very long process,” Lyon says. “People can interpret science in different ways even when they’re looking at the same data.” It’s sometimes tough to come up with firm conclusions that everyone agrees with.

And new discoveries keep coming along. A team of researchers in England and Denmark, for example, recently discovered a compound in carrots that appears to reduce a rat’s chances of developing cancer.

This kind of study wouldn’t have carried much weight with the USDA committee, though, because the scientists prefer to look at studies involving people. If researchers were to repeat the rat experiment with people and got similar results, the 2010 guidelines might end up suggesting that we eat more carrots.

Weight control

More than the old guidelines, the 2005 recommendations focus on weight control, Lyon says. (See “Packing Fat.”)

“There’s an energy equation,” she says. “The calories you take in need to balance the amount of energy you expend in terms of physical activity and exercise, or you’ll end up gaining weight. You need to make your calories work for you.”

Getting plenty of exercise is an important part of controlling your weight.

USDA

The best way to stay healthy, Lyon says, is to eat foods that are packed full of nutrients.

Instead of the five servings of fruits and vegetables that used to be recommended, the new guidelines suggest that adults eat even more than that: 2 cups of fruit and 2 1/2 cups of vegetables each day.

Kids should adjust the amounts of fruits and vegetables based on energy needs and size. It might be worth talking to your doctor or school nurse for advice on the amounts that are best for you.

The widths of the colored triangles in the new food pyramid show roughly how much of different food groups a person should eat: Grains (orange), vegetables (green), fruits (red), oils (yellow), milk (blue), and meat and beans (violet). The new pyramid als

USDA

The guidelines also recommend that people 9 years old and up should drink three cups of low-fat or fat-free dairy products each day and eat lots of whole grains. Brown rice and whole-wheat bread, for example, are better choices than white rice and plain bagels.

Whole grains are important because they don’t go through all of the processing that strips fiber, magnesium, calcium, and other nutrients from many starchy foods. Look on labels for ingredients such as whole oats and whole wheat.

The new recommendations distinguish between different kinds of fats, as well. Young people between the ages of 4 and 18 should get between 25 and 35 percent of their calories from fat, the experts say.

But most of this fat should come from nuts, vegetable oils, and fish. You should avoid a type called “trans fats,” which appear on labels for cookies, crackers, and other foods as “hydrogenated” or “partially hydrogenated” oils.

As far as exercise goes, the document recommends 30 to 60 minutes of activity for adults on most days of the week and at least 60 minutes of exercise for kids every day.

Changing habits

As much sense as the new guidelines make, many people still have a hard time changing their habits, even when they know what’s best for their health.

Eating lots of fruits and whole grains is an important part of a balanced diet.

USDA

If you already eat lots of fruits, veggies, and whole grains, then keep up the good work. If you don’t, Lyon says, try to start with just a few small changes, one at a time.

“Reach for fruit instead of candy,” she says. “Try unsweetened beverages instead of soda. Get out and exercise and do physically active things with your friends.” Eventually, these will become your new habits.

Long blamed for encouraging people to eat unhealthily, some companies are now joining in to help improve diets. Kraft Foods, for example, recently announced that it will stop advertising Oreos and other snack foods to kids younger than 12. And General Mills recently began making all of its cereals with whole grains.

More than ever, kids are making their own choices about how to spend their time and what to put in their mouths. Even if you feel fine, it might be worth learning how to read labels on the food you eat—and keeping the food guidelines in mind next time you order a meal.

“If you follow the guidelines,” Lyon says, “they can help you feel better and look better. They can help you have clearer skin, healthier hair, and give you more energy.”

Who could complain about that?

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Word Find: Food Pyramid