WEDNESDAY, May 7 (HealthDay News) -- A new brain imaging study reveals that a gut hormone known for its appetite-promoting powers actually stimulates key reward centers in the brain to make food look more tasty and irresistible.

The feeding culprit is ghrelin, and the finding suggests that this hormone's so-called "hedonic effect" on the senses unfolds in the same brain regions that researchers have long-associated with drug addiction -- motivating people to eat even when there is no nutritional reason to do so.

"For hundreds of years, people used to think that you eat only because you're hungry," observed study author Dr. Alain Dagher, an associate professor with the Montreal Neurological Institute of McGill University, in Canada. "But we found that the actual system involves a drive for food that is not at all related to hunger."

"The reason for this," he added, "is that almost every animal -- including us, until very recently -- was living in a world where there wasn't enough food, so that the big risk is starving to death. This creates a real pressure to eat. And obtaining food is risky. It requires effort and putting yourself at the mercy of predators. So you need something to get you out of your cave, and the only way that's going to happen is if the food is attractive enough to get you to overcome those costs and risks. And we've found a hormone that does this by acting on the pleasure and reward centers of the brain and making food you see seem more appealing and more desirable."

Dagher and his colleagues reported their findings in the May issue of Cell Metabolism.

The authors analyzed functional MRIs of brain activity among 20 healthy men while they viewed food and non-food imagery.

Within three hours of eating a standard breakfast -- so that the men were neither full nor hungry -- all viewed an initial series of 45 images during which they answered questions about their mood and appetite.

Following the first viewing, 12 of the men received two intravenous infusions of ghrelin, while the other eight did not.

Following blood sampling to gauge hormonal levels, the men viewed a second set of 45 different images.

Dagher and his associates found that during the second viewing, reports of hunger were significantly higher among men who received an infusion of ghrelin.

This increased hunger response correlated with an increase in brain activity in a broad range of brain regions associated with reward -- but only when viewing food imagery. Activated regions included the amygdala, the right hippocampus, the anterior and mid-dorsal insula, and the left pulvinar regions.

By contrast, men who never received ghrelin expressed no change in hunger over the course of the two viewing sessions and were less likely to remember the food imagery they saw following the viewings.

The researchers suggested that the findings could ultimately lead to treatments for obesity based on a disruption of the ghrelin effect.

"The problem today is that we have this evolutionary imperative to eat, but we now live in an environment where you don't have to spend any energy to get food," he noted. "Which means that it makes sense to think of appetite as a kind of addiction. So, if we want to address the fact that obesity is now the number one killer in the world, we're going to have to tackle the problem in the same way that we tackle cigarette smoking."

But Dr. Barbara B. Kahn, chief of the division of endocrinology, diabetes, and metabolism at Beth Israel Deaconess Medical Center in Boston, cautioned that equating ghrelin-fueled overeating with drug addiction may do a public disservice.

"This study provides us with new information about additional ways in which this particular hormone may work," she said. "And overeating and drug addiction may converge on some of the same neurons. But other pathways are also involved. And from a biochemical point of view, the two are not the same thing. Drug addictions are much stronger. So to suggest that they are the same makes people feel that they can't do anything about overeating. That it's out of their control.

"So, I don't really buy that the parallel," added Kahn. "There may be aspects of overeating that may be related to aspects of addiction. But overeating is not just another addiction."

In the same journal, a separate animal study out of Duke University Medical Center highlights a potentially new way to help people curb their appetites and achieve weight control.

Study researchers report that by blocking activation of a key brain enzyme (CaMKK2), they were able to short-circuit the normal flow of the ghrelin pathway in mice, preventing the activation of a second enzyme (AMPK) that directly triggers the desire to eat. The finding, they said, appears to open up a fresh target for drugs geared at reducing appetite.

More information

For additional information on weight management, visit the National Institute of Diabetes and Digestive and Kidney Diseases.

FRIDAY, April 25 (HealthDay News) -- You can grow a healthier tomato by watering it with diluted seawater, a new study shows.

In an experiment in which researchers grew cherry tomatoes in either freshwater or a diluted solution of 12 percent seawater, the salt-water tomatoes developed higher levels of vitamin C, vitamin E, dihydrolipoic acid and chlorogenic acid. Each substance is an antioxidant that may help fight heart disease, cancer, aging and other conditions.

The findings, expected to be published in the May 14 issue of the American Chemical Society's Journal of Agricultural and Food Chemistry, hold promise not only for health reasons, but also because using salt water to irrigate tomato crops could ease potable-water shortages in some parts of the world, the researchers noted.

In recent years, tomatoes have been linked to several possible health benefits, including protection against prostate cancer and heart disease.

More information

The U.S. National Cancer Institute has more about antioxidants and cancer protection.

TUESDAY, April 8 (HealthDay News) -- Just four weeks of moderate exercise is enough to boost the cardiac performance and breathing capacity of patients with heart failure, a new study finds.

This slightly more strenuous exercise program -- in standard use in Europe for people with heart failure -- works at least as well as the less intense American regimen, the researchers noted. They presented the findings Tuesday at the Experimental Biology conference in San Diego.

In heart failure, the heart progressively loses the ability to pump blood. In the United States, doctors typically recommend three-times-a-week exercise sessions for eight to 12 weeks to help ease the condition, noted study author Stephen F. Crouse, a professor of kinesiology and internal medicine at Texas A&M University, in College Station.

His team looked at data from an Austrian rehabilitation center where 366 heart failure patients (average age 63) exercised 14 to 22 minutes on stationery bicycles six times a week. Participants also did a brisk 45-minute walk each day.

Four weeks of that regimen were enough to produce a significant increase in the participants' breathing capacity, Crouse said.

"This is something that we can recommend continuing for the rest of their lives," he added.

The benefits of exercise for people with heart failure are well-established, Crouse acknowledged. "There are some data from U.S. studies showing that the European regimen has at least equal benefits," he said.

The study used such standard measures of heart function as VO2max, which measures oxygen consumed; resting heart rate; and blood pressure. But of greater interest was the measurement of blood levels of the protein NT-proBNP, which is secreted when heart muscle cells are stressed, Crouse said.

"We have this biomarker in the blood that can be followed very well and that correlates with [cardiac] performance," he said.

Levels of NT-proBNP went down as standard measures of heart performance went up, Crouse said. Blood levels of the protein dropped by 33 percent in the study group after four weeks of the exercise regimen.

Measuring NT-proBNP "is something we would suggest could become a routine clinical test, of treatment and performance," Crouse said. A blood test for the protein is not expensive and is a better alternative for more costly tests such as echocardiography, he said.

The longer-term effects of a continued exercise program for heart failure will be assessed by the Texas A&M team, Crouse said. "We need data to follow them out," he said.

The results were not surprising and will not affect advice on exercise now given to people with heart failure, said Dr. William E. Kraus, research director at the Duke University Center for Living. His center is currently leading a major trial of long-term exercise training for people with heart failure, with results expected later this year.

Use of NT-proBNP as a measure of performance is "a new wrinkle, but not so much of one that it makes me want to change practice," Kraus added.

More information

Guidelines for exercise in heart failure are provided by the Cleveland Clinic  .

SUNDAY, March 16 (HealthDay News) -- Could the key to weight loss for some people be as simple as getting some extra shuteye?

Possibly. New research suggests that people who don't get enough sleep tend to weigh more -- and that sleep can affect levels of the appetite-regulating hormones leptin and ghrelin.

"There is a dynamic balance between proper sleep and proper health. Sleep deprivation affects weight and a lot of other things. If you cheat sleep, there are a number of consequences, including affecting your hormones, appetite and mood," said Dr. Patrick Strollo, medical director of the University of Pittsburgh Medical Center's Sleep Medicine Center.

Two out of three Americans are overweight, and almost one in five are obese, according to the U.S. Centers for Disease Control and Prevention. And, while most people are aware of the relationship of diet and exercise to excess weight, few realize that the amount of sleep they get each night can also affect their weight.

Researchers at the Sleep Disorders Center at Sentara Norfolk General Hospital in Virginia conducted two studies, each included 1,000 men and women, and they found that those who reported sleeping less tended to weigh more.

Of course, it could be that being overweight might make it harder to get a restful night sleep.

"People who are overweight may have less restful sleep due to heartburn, snoring or more serious sleep disorders like sleep apnea or night eating syndrome," said Dr. Michelle May, author of "Am I Hungry? What To Do When Diets Don't Work."

But, she said, "It works both ways," and that a lack of sleep can affect your weight. Sleep deprivation affects your body chemistry, appetite and the choices that you make throughout the day, May said.

Another recent study included 12 healthy men in their 20s. Each of the men slept only four hours for two nights. The study found that levels of leptin, a hormone that tells the brain it's time to stop eating because the stomach is full, decreased by 18 percent during the two-day study period. Levels of another hormone, ghrelin, which turns the hunger mechanism on, increased by 28 percent.

On average, the men reported that their hunger pangs increased by 24 percent.

"Hormones change with sleep loss and deprivation," said Strollo. "Sleep deprivation can affect appetite and also the type of food that one desires. When you're sleep-deprived, you generally don't crave carrot sticks."

May agreed, adding, "When you're tired, you're less resilient to stress and other common emotional triggers for eating. When you eat to help you cope with emotions, you're more likely to choose comfort foods like chocolate, ice cream or chips. And, since eating only helps temporarily, you may find yourself reaching for food again and again to try to make yourself feel better.

"Getting enough sleep is the best way to prevent sleep deprivation from contributing to weight gain," May advised. "When you aren't able to get your Zzzs, pay more attention to how much you eat and how you handle fatigue and stress. A short walk will be a better energy boost than a trip to the candy machine."

Strollo said that while most people need between seven and eight hours of sleep a night, there are some people who need as many as 10 and others who may do well on just five hours.

The best way to figure out how much sleep you need, he said, is to take a long vacation and after a couple of days of catching up on your sleep debt, see how many hours of sleep you need to wake without an alarm clock. Since many Americans don't take long vacations, if you feel that you're not fully functional all day, or that you're doing things to stay awake, like a double-espresso shot, you're probably not getting enough sleep, he said.

May added that it's important to remember that "healthy eating, physical activity and sleep are not luxuries, they are necessities."

More information

To learn more about the connection between sleep and your weight, visit the National Sleep Foundation  .