These tomatoes were genetically engineered to make a compound that is in the "miracle berry." Credit: Kato et al/Amer. Chem. Society

Be careful if you ever decide to eat a tomato grown in the laboratory of Kazuhisa Kato and his colleagues. You might get more than you bargained for, and afterward, things might not taste the same.

In the garden, tomatoes grow like fruit. In the kitchen, chefs treat tomatoes like vegetables. And now, Kato and his colleagues have found a way to make ‘maters even more confusing. Kato’s tomatoes have been engineered to change an eater’s sense of taste. For about an hour after a person eats one of these morsels, sour foods will taste sweet.

Say you eat one of Kato’s tomatoes before lunch. Then you take a bite of a lemon — only to discover that it tastes like supersweet lemonade. You won’t even notice the sour sting of grapefruit or cranberry juice. Just think what these tomatoes could do for Halloween: Sour Patch Kids would taste more like gummy bears, and healthy eaters could give trick-or-treaters sour fruits like pomegranates and limes.

The key ingredient to Kato’s taste-shifting tomatoes is called “miraculin.” That word sounds like “miracle,” which might refer to its unusual power. Miraculin is a kind of biological molecule called a glycoprotein — a protein like those in our bodies, and with a carbohydrate molecule attached. Miraculin is found in berries growing on shrubs that mainly flourish in a part of West Africa. These fruits are sometimes called (and sold as) “Miracle Fruit” berries.

People have long known about the ability of miracle berries to alter taste buds. In some countries, the berries are used as a way to help people lose weight. For example, a dieter could eat a berry and then snack on low-calorie sour foods that would taste wonderfully sweet.

Scientists identified the miracle berry’s glycoprotein for the first time in 1968. Since then, people have wondered how to make a lot of it. One way could be to harvest berries from the plants; but if demand gets too large, the plants could be driven to extinction.

That’s where Kato and other researchers come in. They have been looking at DNA. Inside almost every cell of every living organism are chromosomes, and chromosomes are made of DNA, a coiled molecule that contains the set of directions for how to make the proteins that make life possible.

A gene is a unique segment of DNA that can direct the cell to build a specific protein. The miracle berry has a gene that contains the instructions for how to make miraculin.

Kato and his colleagues inserted the gene for miraculin into the genetic code of a tomato. As a result, cells in the tomatoes made miraculin. Those tomatoes had just as much miraculin as miracle berries do. These “miracle” tomatoes could be grown in large numbers, protected indoors. If scientists can grow other foods with miraculin inside, then there won’t be any need to harvest all the miracle berries.

The researchers don’t know yet how the tomato-based miraculin can be used. Perhaps it could be sold as a dieting aid, to be taken before meals.

In any case, be vigilant on Halloween, especially if someone gives you a lemon and it tastes like lemonade. It might be more trick than treat.

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

gene A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and can determine a particular characteristic in an organism.

DNA A molecule, shaped like a spiral staircase, that carries the genetic information stored in genes and chromosomes.

miraculin A glycoprotein found in the miracle berry, Synsepalum dulcificum.

protein Fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of an organism.

Diet fads come and go, but in the end, there’s really only one rule for losing weight: Burn more energy than you consume. In April, scientists from California reported on a chemical that might help people burn fat. It’s called dihydrocapsiate, it comes from a pepper, and in a recent study it was shown to boost the body’s energy burn.

Its name, dihydrocapsiate (di-HI-droh-CAP-see-ate), isn’t easy to say. And Peter Piper never picked it. But it might be easy to find: It is a chemical cousin of capsaicin (kap-SAY-sin), the chemical that makes chili peppers so hot. But unlike its fiery family members, dihydrocapsiate won’t send you running for a glass of water if you eat it. In fact, you won’t even know it’s in your body.

Painful foods — like the ones that contain capsaicin — stimulate pain receptors in the mouth. Once stimulated by a fiery food, these pain receptors signal nerves, which send a message to the brain. Dihydrocapsiate, however, is too big to fit into the receptors and tickle those nerve endings, which means it enters and passes through the body without causing pain.

The main compound that gives peppers (pictured are red savina habaneros of New Mexico) their sting has a close cousin that may burn body fat without irritating the mouth or stomach.

NSF; Chile Pepper Institute

David Heber, a scientist at the University of California, Los Angeles reported on the dihydrocapsiate research in April during a meeting of scientists who study nutrition. He and his colleagues tested the chemical on 33 obese men and women. For four weeks, these volunteers consumed only 800 calories per day, and all of those calories came from a nutritious liquid, instead of from solid foods. These liquids did not contain any fat.

At every meal, the participants were also given pills. People in one group received pills that didn’t do anything. Drugs that don’t do anything are called placebos, and they help experimenters figure out whether the drug being tested really works. Other participants were given a small dose of dihydrocapsiate. Finally, other participants were given a high dose of dihydrocapsiate.

All of the pills looked the same, so neither the participants nor the doctors knew who had consumed placebos and who had consumed the pepper chemical.

After the end of the dihydrocapsiate-enhanced (or placebo-“enhanced”) diet, the scientists determined how much fat the participants were burning.

The scientists observed that not everyone burned the same amount of fat. People who were given high doses of dihydrocapsiate were burning more body fat than people who had been given placebos, UCLA’s Heber says. So much more, he says, that the people taking high doses of dihydrocapsiate may have been losing one more pound per month than the people taking placebos. But that’s a guess: The scientists didn’t measure that number, so they don’t know for sure.

Heber and his team think that the pepper chemical works by attaching itself to another type of receptor, this one in a person’s gut. This receptor helps send a message to the brain, which then starts a process that causes a body to burn, burn, burn calories. This process is the same that, when triggered by capsaicin, causes some people to sweat while they eat hot foods. The scientists say that capsaicin could have the same effect as the dihydrocapsiate, but capsaicin causes intense pain to a person’s mouth and gut.

Dihydrocapsiate could help people lose weight, delivering the positive effects of hot peppers without the fiery side effects. In theory, the chemical could be consumed safely and help a 100-pound person burn an extra 160 calories per day.

Of course, it would be very easy to undo these sizzling effects with one slice of cake or a sugary soft drink. A chemical like dihydrocapsiate may help a person burn more than he consumes — but it can’t change a person’s eating habits.

“As I always say,” Heber told Science News, “a supplement doesn’t make up for diet.”

This story and other Science News for Kids features describing research in medicine and biology are supported with funding from The Lasker Foundation. The foundation and its programs are dedicated to the support of biomedical research toward conquering disease, improving human health and extending life.

Going Deeper:

Raloff, Jane. 2010. “Chili pepper holds hot prospects for painfree dieting,” Science News, April 27. Available at http://www.sciencenews.org/view/generic/id/58689/title/Science_%2B_the_Public__Chili_pepper_holds_hot_prospects_for_painfree_dieting

Picked a pepper? Find out how hot it is using the Scoville scale: http://www.chilliworld.com/FactFile/Scoville_Scale.asp

Sohn, Emily. 2006. “Hot pepper, hot spider,” Science News for Kids, November 15. http://sciencenewsforkids.org/articles/20061115/Note2.asp

Sohn, Emily. 2009. “Greener diet,” Science News for Kids, February 25. http://sciencenewsforkids.org/articles/20090225/Note2.asp

It can be tough to figure out which types of fish — and how much — a person can eat. But with a little reading and good information, a person can still eat fish and be healthy. In recent weeks, researchers have come up with some advice for how to get the fishy benefits and avoid the toxic mercury.

Take tuna as an example. There are many different species of tuna, but grocery stores and restaurants often sell it without specifying which kind. But the amount of mercury tends to vary with the type of tuna. In one of the new studies, researchers studied 100 samples of sushi tuna purchased from grocery stores and restaurants. Jacob Lowenstein, a scientist at Columbia University in New York City, worked on the study. Sushi is a Japanese style of food presentation, usually involving fish that is served raw.

Some types of canned tuna contain the amount of mercury that EPA says is concerning, a recent study found.

TheGiantVermin/Flickr

Lowenstein and his colleagues studied the genetic material in the cells of the tuna. They discovered that the tuna came from three types: bigeye, bluefin and yellowfin species. As the scientists expected, bigger fish had more mercury. So tuna that came from yellowfin, the smallest type on average, had less mercury than tuna from bluefin, which are larger.

But the scientists were surprised to discover that restaurant tuna contained more mercury than fish from the grocery store. Worse, yet, restaurant tuna had, on average, more mercury than the maximum amount recommended by the U.S. Environmental Protection Agency, or EPA.

The EPA recommends that fish not contain more than 0.5 parts per million of mercury. The tuna from restaurants had 0.75 parts per million, on average, and some restaurant samples had levels as high as 1 to 2 parts per million. These numbers may seem small, but long term ingestion of even tiny amounts of mercury can lead to heart or nervous-system disease.

As a result of their study, Lowenstein and his colleagues recommend that government “health agencies should consider adding bigeye and bluefin tuna to mercury advisories.” These advisories caution that people, especially pregnant women and young children, should avoid certain types of fish. Mercury is neurotoxic, which means it can injure developing brains.

In another study, scientists from the University of Nevada Las Vegas looked at three kinds of canned tuna: solid-white, chunk-white and chunk-light. On average, light tuna had 0.28 parts per million, which is safely below the EPA’s recommendation.

But solid and chunk-white types averaged 0.5 parts per million, right at the level of concern. The researchers calculated that a 55-pound child can safely eat only one serving every two weeks.

The Nevada scientists recommend that government agencies be stricter about allowable mercury levels in fish. The EPA, the researchers recommend, should produce a clear policy that will tell people how much mercury they can consume — and where it comes from. The scientists would like to see a similar policy from the Food and Drug Administration (FDA). Right now, the FDA safety limit is 1 part per million, or twice that of the EPA.

In a third study, Edward Groth III studied FDA’s database that documents mercury contamination in 51 different types of fish and found that some types have 100 times the amount of mercury typically found in other types. This means there is no easy rule about mercury and fish — it depends on the species of fish and how contaminated the waters were in which it had lived. Groth produced a chart to make it easy for consumers to check the mercury content of the fish they’re about to eat or buy. The chart is small enough for a person’s pocket.

In June, experts from around the world will get together in Stockholm, Sweden, to develop a world policy on mercury. Mercury can come from natural sources, like volcanoes, but it is also pollution produced by industrial sources like coal-fired power plants.

Once mercury gets in the water and into the fish, it can get into you. But in this case, a little information can go a long way in keeping the mercury at bay.

Going Deeper:

Raloff, Janet. 2010. “Studies aim to resolve confusion over mercury risks from fish,” Science News, April 21. http://www.sciencenews.org/view/generic/id/58464/title/Studies_aim_to_resolve__confusion_over_mercury_risks_from_fish

Ramsayer, Kate. 2005. “Cleaning up fish farms,” Science News for Kids, May 11. http://www.sciencenewsforkids.org/articles/20050511/Feature1.asp

Learn all about mercury: http://www.epa.gov/mercury/

Thousands of years ago, though, only babies drank milk — and that milk came from their mothers. Now, scientists are investigating the beginnings of mankind’s long-lasting love for daily products. They are looking back thousands of years, to the days when people first squeezed milk out of cows and other animals for use as food and drink.

Tracking down the first milk drinkers could give insight into some bigger questions. For example, why do so many people today still get sick from drinking milk? In some countries, almost nobody can digest dairy products.

The work could also help explain major events in human history. Before refrigerators and grocery stores kept a steady supply of fresh food around, dairying probably transformed societies.

“If you can have an animal supply nutrition without killing it, that’s a real step in agriculture,” says Richard Evershed, a chemist at the University of Bristol in the United Kingdom. “That’s spectacular in terms of human nutrition.”

As easy as milk is to find these days, though, its history is challenging to piece together. Like detectives, researchers are tackling the milk mystery in more ways than one.

They are analyzing ancient milk scum on extremely old pots. They’re tracking down the genes that allowed people to digest milk, which is surprisingly hard for many people to stomach. They’re even looking for clues in the buried bones of cows, sheep, horses and other milk-making animals.

“Milk was probably the world’s first superfood,” says Mark Thomas, a scientist at University College London who studies how genes have changed throughout history. The advantages of being able to drink it, he adds, “are just out of this world.”

Thanks, moms

To most people, milk comes in a carton. But milk originally comes from the bodies of mammals. Human as well as other mammal mothers, including dogs, cats, pigs and mice, produce milk to feed their babies.

Mammal babies, including goats, get milk from their mothers. Human mothers also provide milk to their very young children, but most people get milk from the store.

isaact/iStockphoto

Most of the milk in U.S. grocery stores comes from cows. In other countries, it is common to drink the milk of sheep, goats, camels, even horses. Each type of milk has a different flavor. Some types are easier to stomach than others.

Evershed recently sampled milk from horses in Kazakhstan. “It was the most disgusting drink I’ve ever tasted,” he says. “I just didn’t like it.”

Unlike meat, milk does not require that an animal be slaughtered. But the first dairy farmers had to figure out for themselves how to turn wild animals into ones that could be raised in captivity. Then, they needed to herd the animals, care for them and continue to milk them even after the animals’ babies grew up.

Another complication: Milk drinking doesn’t come naturally to older kids and adults. Milk contains a type of sugar called lactose. In order to turn lactose into energy, our bodies need an enzyme called lactase. Enzymes are proteins that help the body do its work.

Like other newborn mammals, baby humans have plenty of lactase, which allows them to gulp down their mothers’ milk. After age 2 or so, though, lactase levels drop.

Without lactase, people can get very sick from dairy products. Symptoms include gas, stomach cramps and severe diarrhea. The condition is called lactose intolerance.

None of our early ancestors could digest milk as adults because their bodies never had to — milk drinking simply wasn’t an option. As people began to extract milk from animals, though, some people developed the ability to keep drinking it throughout their lives.

That biological switch proved to be a huge boost toward survival. Milk is full of calories, fat, protein, calcium and other nutrients. For ancient man, it would have been a valuable and steady source of food.

Scientists now know of a milk-related mutation in our genes — the chemical instructions for life that we carry in almost every cell in our bodies. People who have a mutated form of one particular gene can drink milk just fine. People without the mutation tend to get sick from milk.

“The ability to digest milk, Thomas says, “has been incredibly important for people’s survival for the last 8,000 to 10,000 years. We still just don’t know why.”

The first milk drinkers

To figure out where, and possibly why, milk drinking started, some scientists have been looking at who has the milk-digesting mutation today. Patterns are striking.

Most adults in Northern and Central Europe are able to digest milk — and they do. Cheese, butter and other dairy products are popular in countries such as Sweden, Denmark, Germany and England. Because European settlers dominated North America, most people here can handle milk just fine, as well. That may explain why ice cream is such a popular dessert in the United States.

In much of Africa, Asia and South America, on the other hand, people tend to avoid dairy products because they lead to diarrhea and other stomach problems. (That’s why you won’t typically find cheese on the menu at a Chinese, Japanese or Ethiopian restaurant.) Native Americans are also unable to digest lactose.

Based on these genetic patterns, scientists have long thought that milk drinking started in Northern Europe, where dairy is an institution and the milk-digesting mutation is everywhere.

The different circles of color on this map of Europe show where lactose tolerance—the ability for older children and adults to drink milk without it causing illness or discomfort—developed in a particular area. The red area in the center shows w

Yuval Itan, Adam Powell, Mark G. Thomas

A recent study painted a different picture. With a computer model, Thomas and colleagues looked at the spread of the milk-drinking mutation, farming and other related factors. Working backward, the scientists concluded that the first milk-drinkers lived in Central Europe around what’s now Hungary about 7,500 years ago. The practice didn’t start farther north, as scientists had thought before.

Around that time, a farming culture called the Linearbandkeramik also sprouted in the area that’s now Hungary. The culture spread quickly over the next few hundred years into most of northwestern Europe.

Milk drinking, Thomas says, was probably responsible for the success of the Linearbandkeramik. And milk-drinking Linearbandkeramik may have transformed Europe.

“They probably shaped the language and cultural map of Northern Europe over the last several thousand years,” Thomas says. “We now think the ability to digest milk was crucial to [their] spread.”

Dairy before milk

The story doesn’t start or end there. It’s now clear that people ate dairy foods before they actually drank milk.

Over the last decade, Evershed has analyzed pottery remains from many hundreds of ancient vessels at dozens of sites in Europe.

His group has also identified dried-up milk fat on the oldest pottery shards ever found, dating back 9,000 years from an area outside Europe, in the Middle East, called the Fertile Crescent. The region now includes Iraq, Syria and Israel. It’s probably where people first domesticated animals.

In fact, milking may have started even earlier than that. Although archaeologists haven’t found older pottery remains, scientists do have evidence that early sheep herds were mostly female. That might mean that the herd was used for milk, rather than meat. It’s the females, after all, that produce milk.

Despite those clues, Thomas — who has pulled genetic material out of the bones of early European farmers — has found no sign that people had the gene mutation for digesting lactose before 7,500 years ago.

So, why were people milking animals if they couldn’t digest the milk?

It turns out that fermenting and processing milk into yogurt, cheese and other products removes much of the lactose. Even people who are lactose-intolerant can often eat these foods without getting sick.

Dairy foods last longer than milk without spoiling. And fermenting, for instance, is not hard to do: In a hot country, people would have just needed to leave milk in a pot outside for most of the day to turn the milk into a nutritious, digestible yogurt.

“We are now pretty convinced,” Thomas says, “that the ability to digest milk came after the skills necessary to produce it.”

From when and where, to why?

Now that scientists know more about when and where milking started, they are struggling to explain why people started drinking milk in the first place.

Among a variety of theories about milk, Thomas likes the idea that animals provide a steady supply of it. Crops boom and then bust. Meat comes with finality: the end of an animal’s life. But on the other hand, as long as you keep feeding and milking a cow, her milk keeps coming.

There would have been other advantages, too. Milk is cheap. It’s nutritious. And it harbors fewer dangerous bacteria compared with liquids like river water, which could have made people terribly sick.

Investigating milk, scientists say, is a great way to help people connect with their food and where it comes from. In a recent presentation for schoolkids, Evershed included a poster of someone squeezing milk from the udders of a cow into a pot.

“It was a lovely picture,” Evershed says, and the image was symbolic, too. “It brought home man’s intimate relationship with animals and the way we live with them and rely on them. The supermarket makes you forget that.”

Going Deeper:

Eating lots of junk food may make it get harder to choose healthy food over time.

It sounds like a science experiment designed by Willy Wonka: Take a lot of junk food, feed it to some rats, and see what happens.

Scientist Paul Johnson of the Scripps Research Institute and his team did just that. But their science experiment was no fiction. They had a serious goal: to try to understand how parts of the brain play a role in obesity. (Obesity is the condition of being very overweight, which has been linked to a variety of health problems.)

The scientists observed that the more junk food the rats ate, the more they wanted to eat—a behavior very similar to that of rats addicted to heroin, a dangerous drug. Johnson told Science News the experiment shows that the brain chemistry of obesity and drug addiction may be quite similar.

In their experiment, Johnson and his team studied the “pleasure center” of rats’ brains. The pleasure center is a complicated network of nerve cells. Together, these cells work as the body’s reward system. If the animal exercises or eats, the cells reward the animal by releasing chemicals into the body that make it feel good. And when the body feels good, the animal—or person—will want to do the behavior again.

Pleasure centers can release these chemicals in less healthy ways, too. Drugs like heroin can cause the pleasurable chemicals to be released.

For the experiment, Johnson fed foods like cheesecake, bacon and Ho Hos to one group of rats. These foods are all high in calories and high in fat. Another group of rats received a regular, nutritious diet. The rats that ate junk food started to eat more and more.

“They’re taking in twice the amount of calories as the control rats,” says Paul Kenny, also at Scripps Research Institute. Kenny worked with Johnson on the study.

Kenny and Johnson wanted to know what was going on in the brains of rats that were overeating. To find out, they came up with a simple reward system. They first devised a way to deliver a small electrical charge to the rats’ brains. This electrical charge would stimulate the pleasure centers to release pleasure-causing chemicals. The rats could control how much stimulation—and how much pleasure—they received by running on a wheel. The more the rat ran, the more pleasure it received.

The rats that had been eating junk food started running more and more. This behavior suggested that the junk-food–eating rats needed more brain stimulation to feel good compared with rats on a normal diet. In other words, their pleasure centers were becoming less sensitive and the junk food didn’t make them feel good unless they ate more and more. The same process happens in the brains of drug addicts. As the pleasure center becomes numb, the addict has to consume more of the drug to feel good.

“They lose control,” Kenny says. “This is the hallmark of addiction.”

Kenny and Johnson also found out that the effects are hard to reverse. After they took away the junk food and offered the rats a nutritious diet, the fat rats refused to eat. “They starve themselves for two weeks afterward,” Kenny says.

Experiments like this one could help scientists understand how chemicals in the brain contribute to obesity. With that information, they may be able to help people avoid obesity—and all of its health problems—in the first place. Not bad for a bunch of rats with Ho Ho’s in their paws.

POWER WORDS

stimulate To increase temporarily the activity of a body organ or part.

obese   Extremely overweight.

nerve cell   The body of a neuron without its axon and dendrites.

chemical A substance with a distinct molecular composition that is produced by or used in a chemical process.

Going Deeper: