This is your brain on sugar — for real. Scientists have used imaging tests to show for the first time that fructose, a sugar that saturates the American diet, can trigger brain changes that may lead to overeating.

After drinking a fructose beverage, the brain doesn't register the feeling of being full as it does when simple glucose is consumed, researchers found.

It's a small study and does not prove that fructose or its relative, high-fructose corn syrup, can cause obesity, but experts say it adds evidence they may play a role. These sugars often are added to processed foods and beverages, and consumption has risen dramatically since the 1970s along with obesity. A third of U.S. children and teens and more than two-thirds of adults are obese or overweight.

All sugars are not equal — even though they contain the same amount of calories — because they are metabolized differently in the body. Table sugar is sucrose, which is half fructose, half glucose. High-fructose corn syrup is 55 per cent fructose and 45 per cent glucose. Some nutrition experts say this sweetener may pose special risks, but others and the industry reject that claim. And doctors say we eat too much sugar in all forms.

For the study, scientists used magnetic resonance imaging, or MRI, scans to track blood flow in the brain in 20 young, normal-weight people before and after they had drinks containing glucose or fructose in two sessions several weeks apart.

Scans showed that drinking glucose "turns off or suppresses the activity of areas of the brain that are critical for reward and desire for food," said one study leader, Yale University endocrinologist Dr. Robert Sherwin. With fructose, "we don't see those changes," he said. "As a result, the desire to eat continues — it isn't turned off."

What's convincing, said Dr. Jonathan Purnell, an endocrinologist at Oregon Health & Science University, is that the imaging results mirrored how hungry the people said they felt, as well as what earlier studies found in animals.

"It implies that fructose, at least with regards to promoting food intake and weight gain, is a bad actor compared to glucose," said Purnell. He wrote a commentary that appears with the federally funded study in Wednesday's Journal of the American Medical Association.

Researchers now are testing obese people to see if they react the same way to fructose and glucose as the normal-weight people in this study did.

What to do? Cook more at home and limit processed foods containing fructose and high-fructose corn syrup, Purnell suggested. "Try to avoid the sugar-sweetened beverages. It doesn't mean you can't ever have them," but control their size and how often they are consumed, he said.

A second study in the journal suggests that only severe obesity carries a high death risk — and that a few extra pounds might even provide a survival advantage. However, independent experts say the methods are too flawed to make those claims.

The study comes from a federal researcher who drew controversy in 2005 with a report that found thin and normal-weight people had a slightly higher risk of death than those who were overweight. Many experts criticized that work, saying the researcher — Katherine Flegal of the Centers for Disease Control and Prevention — painted a misleading picture by including smokers and people with health problems ranging from cancer to heart disease. Those people tend to weigh less and therefore make pudgy people look healthy by comparison.

Flegal's new analysis bolsters her original one, by assessing nearly 100 other studies covering almost 2.9 million people around the world. She again concludes that very obese people had the highest risk of death but that overweight people had a 6 per cent lower mortality rate than thinner people. She also concludes that mildly obese people had a death risk similar to that of normal-weight people.

Critics again have focused on her methods. This time, she included people too thin to fit what some consider to be normal weight, which could have taken in people emaciated by cancer or other diseases, as well as smokers with elevated risks of heart disease and cancer.

"Some portion of those thin people are actually sick, and sick people tend to die sooner," said Donald Berry, a biostatistician at the University of Texas MD Anderson Cancer Center in Houston.

The problems created by the study's inclusion of smokers and people with pre-existing illness "cannot be ignored," said Susan Gapstur, vice-president of epidemiology for the American Cancer Society.

A third critic, Dr. Walter Willett of the Harvard School of Public Health, was blunter: "This is an even greater pile of rubbish" than the 2005 study, he said. Willett and others have done research since the 2005 study that found higher death risks from being overweight or obese.

Flegal defended her work. She noted that she used standard categories for weight classes. She said statistical adjustments were made for smokers, who were included to give a more real-world sample. She also said study participants were not in hospitals or hospices, making it unlikely that large numbers of sick people skewed the results.

"We still have to learn about obesity, including how best to measure it," Flegal's boss, CDC Director Dr. Thomas Frieden, said in a written statement. "However, it's clear that being obese is not healthy - it increases the risk of diabetes, heart disease, cancer, and many other health problems. Small, sustainable increases in physical activity and improvements in nutrition can lead to significant health improvements."

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  • Avocado

    "Instead of using a whopping dollop of mayonnaise on your sandwich, try using thin slices of avocado," suggests Megan Madden, a registered dietitian in New York, NY. A 1996 study done by researchers in Mexico found that people who ate avocado every day for one week experienced an average 17 percent drop in total blood cholesterol. What's more, their levels of LDL ("bad") cholesterol decreased and HDL ("good") cholesterol increased.

  • Whole Grains

    The soluble fiber found in whole grains such as whole-wheat bread, brown rice, and oatmeal binds the cholesterol in your meal and drags it out of your body, Madden says. "And, when your body needs to utilize cholesterol in the future, it draws on your blood cholesterol supply, effectively lowering your total blood cholesterol level and your risk for heart disease." And oatmeal isn’t just for breakfast; you can enjoy it any time of day with these easy recipes.

  • Olive Oil

    A 2011 study found that people ages 65 or older who regularly used olive oil (for both cooking and as a dressing) were 41 percent less likely to have a stroke compared to those who never use olive oil in their diet. Use a little olive oil instead of butter or drizzle some over pasta, salad or veggies to take advantage of its high mono- and polyunsaturated fats, Madden says. "And although it’s a healthier option, remember to use these oils sparingly, as all fats still contain the same number of calories."

  • Nuts

    Grabbing a handful of nuts is a heart-healthy way to beat the afternoon itch for a cookie, Madden says. "Almonds are very high in heart-healthy monounsaturated fats, vitamin E and fiber, while walnuts are a great plant-based source of an omega-3 fatty acid called alpha-linolenic acid." According to the American Heart Association, monounsaturated fats can help reduce levels of bad cholesterol in your blood and lower your risk of heart disease and stroke.

  • Foods Fortified By Plant Sterols

    Sterols are compounds that compete with the cholesterol in your food for absorption within your digestive tract, Madden says. "Sterols have been shown to lower both total and LDL cholesterol and can be found in certain brands of fortified orange juice, margarine spreads, and milk." Just be sure to check the label -- make sure the margarine is trans fat-free and that "partially hydrogenated oil" does <em>not</em> appear on the ingredient list.

  • Salmon (Or Other Fatty Fish)

    Fatty fish such as mackerel, herring, tuna and salmon are chock full of omega-3 fatty acids, Madden says. "Eating fish twice a week can reduce your risk of developing heart disease by decreasing inflammation and lowering triglyceride levels, and it may even help boost your HDL levels."

  • Asparagus

    Asparagus is one of the best, natural artery-clearing foods around, says Shane Ellison, an organic chemist and author of "Over-The-Counter Natural Cures". "Asparagus works within the 100,000 miles of veins and arteries to release pressure, thereby allowing the body to accommodate for inflammation that has accumulated over the years." It also helps ward off deadly clots, Ellison says.

  • Pomegranate

    Pomegranate contains phytochemicals that act as antioxidants to protect the lining of the arteries from damage, explains Dr. Gregg Schneider, a nutritionally-oriented dentist and expert on alternative medicine. A 2005 study published in the <em>Proceedings of the National Academy of Sciences</em> found that antioxidant-rich pomegranate juice stimulated the body’s production of nitric oxide, which helps keep blood flowing and arteries open.

  • Broccoli

    Broccoli is rich in vitamin K, which is needed for bone formation and helps to keep calcium from damaging the arteries, Schneider says. Not to mention, broccoli is full of fiber, and studies show a high-fiber diet can also help to lower blood pressure and cholesterol levels.

  • Turmeric

    "The spice turmeric is a powerful anti-inflammatory," Schneider says. "It contains curcumin which lowers inflammation -- a major cause of arteriosclerosis (hardening of the arteries." A 2009 study found that curcumin helps reduce the fatty deposits in arteries by as much as 26 percent.

  • Persimmons

    Forget the old 'an apple a day' adage -- it seems eating a daily persimmon is a better way to keep the doctor away. Research shows the polyphenols found in this fruit (which has twice as much fiber and more antioxidants than an apple) can help decrease levels of LDL cholesterol and triglycerides.

  • Orange Juice

    A 2011 study published online in the <em>American Journal of Clinical Nutrition</em> found that drinking two daily cups of 100-percent orange juice can help reduce diastolic (resting) blood pressure. OJ contains an antioxidant that has been found to help improve blood vessel function.

  • Spirulina

    A daily 4,500-milligram dose of this blue-green algae (usually found in supplement or powder form) can help relax artery walls and normalize blood pressure. It may also help your liver balance your blood fat levels -- decreasing your LDL cholesterol by 10 percent and raising HDL cholesterol by 15 percent, according a recent study.

  • Cinnamon

    Just one teaspoon a day of antioxidant-rich cinnamon can help reduce fats in the bloodstream, helping to prevent plaque build up in the arteries and lower bad cholesterol levels by as much as 26 percent, according to recent research. Sprinkle some on your morning coffee or on these delicious crepes.

  • Cranberries

    Research shows that potassium-rich cranberries can help reduce LDL cholesterol levels and help raise the good HDL levels in your body, and regular consumption of the holiday favorite may help reduce your overall risk of heart disease by as much as 40 percent.

  • Coffee

    According to researchers in the Netherlands, people who drank more than two, but no more than four, cups of coffee a day for 13 years had about a 20 percent lower risk of heart disease than people who drank more or less coffee or no coffee at all. Moderation is the key to coffee's heart-health benefits -- the caffeine is a stimulant which can cause a temporary increase in blood pressure, and in excess, can lead to irregular heart beat.

  • Cheese

    Believe it or not, cheese could help lower your blood pressure! A recent study from Brigham and Women's Hospital and Harvard Medical School found that people who eat three servings a day of low-fat dairy have lower (three points less) systolic blood pressure than those who eat less.

  • Green Tea

    Green tea is rich in catechins, compounds that have been shown to decrease cholesterol absorption in your body. Another bonus? It may help prevent cancer and weight gain, too!

  • Watermelon

    Talk about a perfect snack -- watermelon is not only a diet-friendly food, but it can help protect your heart, too! A Florida State University study found that people given a 4,000-milligram supplement of L-citrulline (an amino acid found in watermelon) lowered their blood pressure in just six weeks. Researchers say the amino acid helps your body produce nitric oxide, which widens blood vessels.

  • Spinach

    The potassium and folate found in spinach can help lower blood pressure, and according to recent research, one serving of nutrient-packed leafy greens (like spinach) a day can help reduce your risk of heart disease by 11 percent.

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