TIME Obesity

Kindergarteners Watch More Than 3 Hours of TV a Day

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With more screen time, the effects add up fast

For kids as young as kindergarten-age, watching even a small amount of TV daily is linked to obesity and overweight, finds a new study. Kids who watched an hour of television a day were more likely to be overweight or obese than kids who watched less than an hour of TV per day.

Presented at the Pediatric Academic Societies annual meeting, the study looked at data from more than 10,000 kindergarteners and followed them through first grade.

Kindergarten students in the U.S. spent an average of 3.3 hours watching TV every day, the study finds, and that screen time comes at a high price. Kids who watched 1-2 hours of TV per day had an increased odds of obesity 47% above the group that watched less than an hour a day, and an increased odds of overweight 43%.

“Television is a very passive activity,” says study author Mark D. DeBoer, MD, associate professor of pediatrics at the University of Virginia. Combine the ill effects of sitting with TV-related behaviors like more snacking and exposure to commercials selling unhealthy food, and the effects can add up.

It took very little TV time to have a big effect on weight; DeBoer says he didn’t see much difference in the weights of children who watched 1-2 hours a day versus those who watched more than two hours.

That’s likely because kids miss out on physical activity when they’re plopped in front of the tube. “In this age range, when you’re not sitting and doing something, you’re running around,” DeBoer says. “As much as they don’t go out and jog, kindergarteners are still at an age when they are frequently, if not constantly, on the move.”

DeBoer says he hopes his study can help shift guidance from the American Academy of Pediatrics, which currently recommends that children spend no more than two hours a day watching screens. Instead, he says, parents should be encouraged to cut TV time even more and replace it with activities like reading to their children, going to museums and visiting other educational destinations. “This may be a step toward changing that recommendation in the future,” he says.

TIME Parenting

Unhappy Families Can Make Daughters Fat

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A new study suggests that stress at home can have a major impact on our kids' waistlines

Childhood obesity has become such a big problem in the United States that the rate of obese adolescents—21%—exceeds the rate of overweight adolescents (14%). It’s been that way for the last decade.

Dr. Daphne Hernandez, assistant professor at the University of Houston, wants to figure out why despite our efforts, that rate hasn’t budged. “Many times when we’re designing interventions and prevention programs, they’re done in schools because that’s where we have ease of access to all these kiddos,” she says. “But the issue is that in those interventions, we don’t think about the family environment and what could be happening at home.”

In her new study published in the journal Preventive Medicine, she decided to look at three family stressors: family disruption and conflict, the kind a kid would experience after a parent got divorced, remarried, incarcerated or if the child experienced a violent crime or death of a loved one; financial stress, a measure of poverty determined in part by whether a mom was unemployed or had less than a high school education; and maternal poor health, whether the mom was a binge drinker, drug user or had elevated depression.

MORE: Mindfulness Exercises Improve Kids’ Math Scores

Hernandez analyzed data from 4,762 adolescents between 1975-1990 using the National Longitudinal Study of Youth. She measured each adolescent’s exposure to these family factors from birth until age 15, then looked at their weight at age 18. The results showed clear gender differences. In adolescent girls, experiencing family disruption and financial stress repeatedly was linked to overweight or obesity by age 18. That wasn’t true for adolescent boys. Just one stress point—poor maternal health—was linked to being overweight or obese by 18.

When all the findings were lumped together, Hernandez says, the gender differences disappeared. “Not all stress influences females and males the same,” she says. The reason why lies beyond the scope of this study, but Hernandez suspects it has something to do with physiolgocial and behavioral stress responses. Your body secretes cortisol when it’s stressed, she says—which, if chronic, suppresses your body’s ability to feel satiated. “Behaviorally, you then gravitate more towards the more palatable foods, the high calorie, high fat foods, so you’re not reaching for that apple or celery stick,” she says. This pattern seems to be more prevalent in females than in males, she adds.

“We really need to think about how we are teaching our adolescents how to deal with stress, and trying not to use food as a way to deal with stress,” Hernandez says. “Perhaps encouraging physical activity is the way we should be going.”

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TIME Diet/Nutrition

Which Weight Loss Diet Works Best? A New Study Ranks the Evidence

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With so many ways to lose weight, you’d think it would be easy to tell which diet program works best — Weight Watchers or Jenny Craig, Nutri System or Slim Fast. But it might surprise you to learn that there isn’t a lot of good evidence on how effective various diets are, and here’s why

With the American Medical Association now urging doctors to treat obesity as a medical condition, physicians should be screening and treating overweight and obesity just as they would any other chronic disorder. But when it comes to figuring out which methods are proven to work best, physicians may find themselves at a loss. Some studies have found that commercial weight-loss programs work about the same when it comes to the amount of weight they can help consumers lose, while others found that low-carb diets beat out low-fat plans.

To make sense of the noise, Kimberly Gudzune, an assistant professor of medicine at Johns Hopkins University, and her colleagues searched the scientific literature for studies on 11 commercial weight-loss programs. In their results, published Monday in the Annals of Internal Medicine, they assessed which ones have the best data to support them. But they also found there weren’t that many studies actually tracking how much weight people on the programs lose.

Gudzune decided to focus on commercial programs like Weight Watchers and NutriSystem, among others. And of 4,212 studies that involved these diets, only 45 were done under the gold scientific standard of randomly assigning people to a weight-loss program or not, and then tracking their weight changes over time. “The majority [of programs] still have no rigorous trials done,” says Gudzune.

According to her analysis, only two programs, Weight Watchers and Jenny Craig, helped dieters to lose weight and keep it off for at least a year. Those on Weight Watchers shed nearly 3% more of their starting weight after 12 months than those not dieting, and Jenny Craig users lost nearly 5%. Other programs, including Atkins, the Biggest Loser Club and eDiets, also helped people drop pounds, but since the studies only lasted three to six months, it’s impossible to know if that weight loss lasted.

The modest weight loss “may be disappointing to many consumers,” says Gudzune, but she notes that weight-management guidelines suggest that a 3% to 5% sustained weight loss is an important first step toward a healthy weight. “Even that small amount of weight loss can help to lower blood sugar, improve cholesterol profiles, help to lower blood pressure and ultimately prevent things like diabetes,” she says.

“Would 6% or 8% or 10% of body weight lost be better? Yes, but it’s not like the interaction is totally linear,” says Gary Foster, chief scientific officer of Weight Watchers International. Over time, weight-loss rates may change, and other studies show they typically slow after the initial blush of success.

MORE Calorie vs. Calorie: Study Evaluates Three Diets for Staying Slim

Modest weight loss can also seed good eating habits that can keep weight loss going, or maintain weight at a healthy level. “Modest weight loss on average can translate to a big public-health impact” on the obesity epidemic, says Dr. Christina Wee, associate professor of medicine at Harvard Medical School and director of the obesity-and-health-behaviors research program at Beth Israel Deaconess Medical Center. Fewer overweight and obese individuals mean fewer cases of diabetes, heart disease, hypertension, joint disorders and more. So for doctors faced with advising their patients on how to best manage their weight, these are the first bits of evidence that some commercial programs — Weight Watchers and Jenny Craig — might be better than others in helping patients to slim down and stay that way.

Still, a larger robust bank of evidence-based studies is needed. Typically, studies follow dieters for about three months, during which most people are likely to lose the most weight because they are more motivated and simply because they in a study and feel obligated to follow the diet. That’s another problem with the studies on diet programs, says Wee. “When trying to do a scientific study, researchers don’t want too many things going on at the same time, so they end up with a design for the study that doesn’t reflect the real world,” she says. “So the result is the result from an artificial setting.”

MORE: Diet Bake-Off: Jenny Craig Wins, Says Consumer Reports

Another factor that makes studying diets tricky is the fact that participants are assigned a diet. In real life, people tend to try a weight-loss program of their own choosing. When they find that it doesn’t fit with their lifestyle or personality, they try another. They may be more successful with their second or third choice, but in a study, they would fall into the failure category if they didn’t lose the target amount of weight on the first program.

“Now that obesity is coming under the medical umbrella, it’s really going to put more pressure on whether commercial programs or medical clinics have really good evidence to show their programs are effective,” says Gudzune. “For so long obesity was just in a no-man’s land, which I think did it a disservice because it didn’t push the industry to have better scientific evidence on what works and what doesn’t work.”

And it’s not just physicians seeking this proof. With the Affordable Care Act now covering obesity screening and counseling, and providing incentives to states to reimburse for comprehensive obesity treatments, it’s critical for insurers and policymakers who decide which weight-loss programs are worth paying for and which ones to deny.

Read next: Popular Diets Are Pretty Much the Same for Weight Loss, Study Finds

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TIME medicine

This Is What Binge Watching TV Does to Your Health

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Every hour spent sitting in front of the TV can increase your risk of diabetes

It’s easy—and tempting—to settle in for a marathon session with your favorite TV show, but that indulgence may come back to haunt you.

In a study of people at higher risk of developing diabetes, researchers say that every hour spent sitting can increase the risk of developing the metabolic disorder by 3.4%. For a day-long binge, that could be as much as a 30% higher risk. “With streaming TV, you can watch a program continuously; instead of watching just half an hour once day a week, you can watch a whole season in a day, so we expect to see increases in sitting to continue,” says Andrea Kriska, an epidemiologist at the University of Pittsburgh and senior author of the paper on the effects of TV on diabetes risk in the journal Diabetologia.

Kriska is part of the Diabetes Prevention Program Research Group, which found that people who spent more time sitting, whether in front of the TV or at work, were more likely to develop diabetes than those who sat less, regardless of how much they exercised.

MORE: Sitting Is Killing You

The group started with the population of people at higher risk of developing diabetes who were enrolled in the Diabetes Prevention Program. Some were assigned to exercise at least 150 minutes at a moderate level each week and change their diet with the goal of losing 7% of their body weight. Others were given the diabetes drug metformin, and another group was given a placebo. In 2002, after more than three years, those who adopted the lifestyle changes lowered their risk of developing diabetes by 58%, compared to 31% for those taking the drug.

More and more data suggest that to reduce disease, it’s not just enough to exercise more; you have to sit, less too. The scientists wanted to see what role, if any, sitting played in this reduction. Did being more physically active lead to helping people be less sedentary? And did time spent sitting have any connection with the rate of diabetes?

MORE: Sitting Can Increase Your Risk of Cancer By Up to 66%

“What we found was yes, and yes,” says Bonny Rockette-Wagner, from the department of epidemiology at Pittsburgh. “There is an independent effect of sitting behavior on diabetes incidence that does not have to do with physical activity. It’s an independent, additional effect.”

The researchers asked the 3,232 people in group how much time they spent sitting at work and how much time they spent watching TV, as a proxy for their total sedentary time. They also asked them about their leisure time physical activity and measured their blood glucose levels. After three years, the lifestyle group spent fewer hours sitting than the metformin and placebo groups, despite the fact that sitting less was not a specific goal of the program. And the more time they spent off their chairs, the lower their risk of going on to develop diabetes.

MORE: An Hour of Exercise Can Make Up for a Day of Sitting Down

The results suggest that efforts to help high-risk people avoid diabetes should include a goal of sitting less. That’s what Kriska and Rockette-Wagner are starting to do in their community sessions in which they teach people about the Diabetes Prevention Program. Instead of focusing exclusively on the target of 150 minutes of exercise each week, they’re asking people to think about sitting less, starting by spending a few minutes fewer on the couch each day and building up to becoming more active.

MORE: Sitting All Day Isn’t As Bad If You Do This

The researchers admit that simply sitting less won’t replace being physically active, but after so much focus on getting sedentary people to move, getting them to think about sitting less may be just as productive.

TIME Cancer

How We’re Failing at Preventing Cancer

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JUAN GARTNER—Getty Images/Science Photo Library RF Illustration of cancer cells in middle of dividing

We’ve made lots of progress in preventing cancer, but still have a long way to go in convincing people to drop the most prevalent cancer-causing habits

You have to know your enemy in order to defeat it, and in cancer’s case, we know quite a bit about how to keep tumors from growing. But how well are we exploiting this knowledge?

The latest report, published Wednesday morning, from the American Cancer Society lays out the major risk factors for cancer, along with the screening strategies we have in place and documents whether people have been avoiding risky behaviors and complying with screening guidelines.

The results, says Stacey Fedewa, director of risk factors and screening surveillance and one of the co-authors, are mixed.

MORE: The Cancer Gap

When it comes to tobacco use, the largest preventable cause of cancer, rates of smoking have declined, from 23.5% in 1999 to 17.8% in 2013. But there are still pockets of the country, both geographically and demographically, where rates remain close to what they were 10 years ago. In West Virginia, for example, 27.3% of adults smoked cigarettes, and 22.7% of American Indians lit up. About 22% of high school graduates smoked, compared to 5.6% of those with a graduate degree. Smoking tobacco increases the risk of lung, mouth, larynx, esophagus, stomach and other cancers

The survey also found that smokeless tobacco and e-cigarettes are also becoming popular, particularly among younger people. These forms of tobacco have been linked to higher rates of oral, pancreatic and esophageal cancer. People aged 18 to 24 years were twice as likely to use smokeless products like chewing tobacco and snuff than older adults.

The creep of tobacco use into younger cohorts is concerning, since studies show that the younger smokers start, the harder it is for them to quit. In fact, the ACS study found that even one in 10 cancer patients smoked nearly a decade after their diagnosis.

MORE: 66% of People Diagnosed with Cancer Survive At Least 5 Years

Fedewa says that obesity is also connected to a number of cancers, including breast, colon, kidney, pancreas and certain lymphomas and myelomas. And while obesity rates have stabilized, they remain high, with more than two thirds of adults considered overweight or obese. That rate may not change for a while, given the fact that in 2013, 30% of adults said they had no recreational physical activity at all. “I was surprised to see how low the percent of adults who reach the recommended physical activity levels was,” says Fedewa. Government guidelines suggest at least 150 minutes of moderate activity each week, and only about half of adults accomplish this.

Screening is another area with both good news and bad news. Public health messages about the importance of getting mammograms to detect breast cancer, and colonoscopy to pick up colorectal cancer, have raised awareness about these diseases. But rates of colon cancer screening have remained around 58%. Part of the reason may have to do with cost; studies showed that uninsured people tend to have the lowest rates of cancer screening, something that the Affordable Care Act should change. It’s also possible that conflicting news about the benefits and risks of screening, and changing advice about who should be screened and when — in 2009 groups said that women between ages 40 and 40 years no longer needed annual mammograms — may also hamper compliance.

More studies are also throwing out clues about the best anti-cancer diet, with fruits and vegetables at the top of the list. But, says Fedewa, “only 15% of adults ate the recommended three or more servings of vegetables a day. That’s surprising, and pretty low given all the messages about eating healthier.”

Also discouraging is the continued use of tanning beds despite the fact that the International Agency for Research on Cancer lists the devices as cancer-causing to people. In 2014, 4.4% of adults, and 20% of high school girls, reported using the beds in the previous year. That may explain why rates of melanoma, unlike some other cancers, have been increasing in the past 30 years.

“I don’t think there is one message” about how we’re doing in preventing cancer, says Fedewa. “It’s not all doom and gloom. There is a lot to be appreciated for what we’ve done in tobacco control; that’s a great public health accomplishment. But there is room to grow.”

TIME Obesity

This Place Just Became the First Part of the U.S. to Impose a Tax on Junk Food

TIME.com stock photos Food Snacks Candy
Elizabeth Renstrom for TIME

It also eliminated a 5% sales tax on healthy produce

The Navajo Nation, which suffers from a 10% obesity rate, is imposing a 2% junk-food tax on its reservation beginning April 1.

Navajo president Ben Shelly approved the Healthy Dine Nation Act last November, which from this week will also eliminate a 5% sales tax on healthy fare including fresh fruits and vegetables.

Revenues from the sin tax will reportedly be channeled toward community wellness projects like farmer’s markets, vegetable gardens and greenhouses in the 27,000 sq. mi. of Navajo reservation spanning from Arizona and New Mexico to Utah.

Approximately 24,600 Navajo tribe members face obesity, according to the Navajo Area Indian Health Service. Type 2 diabetes has emerged as a growing public health concern afflicting up to 60% of reservation residents in some areas.

With nearly half of the Navajo youth population facing unemployment and 38% of the Navajo reservation at the poverty level, supporters say the act may serve as a prototype for sin taxes to curb obesity in low-income communities across the U.S.

By comparison, around one-third of Americans nationwide are classified as obese, the highest rate in the world.

TIME Exercise/Fitness

10 Reasons Your Belly Fat Isn’t Going Away

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The choices you make every day can supercharge your ability to burn belly fat

A little bit of belly fat is actually good for you: it protects your stomach, intestines, and other delicate organs. But too much fat is anything but healthy. Extra fat cells deep in your abdomen (aka visceral fat) generate adipose hormones and adipokines—chemical troublemakers that travel to your blood vessels and organs, where they cause inflammation that can contribute to problems like heart disease and diabetes. The good news? Every pound you shed can help reduce your girth. “Once women start losing weight, they typically lose 30% more abdominal fat compared with total fat,” says Rasa Kazlauskaite, MD, an endocrinologist at the Rush University Prevention Center in Chicago. Even better, the choices you make every day can supercharge your ability to burn belly fat. Here are 10 common pitfalls—and ways to undo each one.

Read more: 20 Best Superfoods for Weight Loss

You’re on a low-fat diet

To shed belly fat, it’s good to eat fat—specifically monounsaturated fatty acids (MUFAs). When researchers in one study asked women to switch to a 1,600-calorie, high-MUFA diet, they lost a third of their belly fat in a month. “MUFAs are satiating, so they help you eat fewer poor-quality foods,” says David Katz, MD, director of the Yale Prevention Research Center.

Belly blaster: Have a serving of MUFAs—like a handful of nuts, a tablespoon of olive oil, or a quarter of an avocado—with every meal and snack.

Read more: 9 Low-Fat foods You Should Never Eat

You’ve been feeling blue for a while

Women with depressive symptoms were far more likely to have extra belly fat, found a recent Rush University Medical Center study. That may be because depression is linked to reduced physical activity and poor eating habits.

Belly blaster: Exercise! “It improves levels of brain chemicals that regulate metabolism of fat, as well as your mood,” Dr. Kazlauskaite says. This enhances your motivation to do other things that help ward off depression, like seeing friends. But if you’re so bummed out that you don’t want to do things you used to enjoy, it’s time to seek the help of a therapist.

Your food comes from a box

Simple carbs (like chips) and added sugar (in items like sweetened drinks) cause your blood sugar to spike, which triggers a flood of insulin—a hormone that encourages your liver to store fat in your middle.

Belly blaster: Instead of focusing on cutting out junk, center your efforts on adding in healthy fare (think extra servings of vegetables at each meal). As Dr. Katz says, “Filling your tank with high-quality fuel thwarts hunger.”

You’re skimping on the miracle mineral

Magnesium regulates more than 300 functions in the body. No surprise, then, that a 2013 study found that people who consumed more of it had lower blood sugar and insulin levels.

Belly blaster: At least twice a day, reach for magnesium-rich foods such as dark leafy greens, bananas, and soybeans.

You’re hooked on diet soda

A study in Obesity found that diet soda drinkers were more likely to have a high percentage of fat in their bellies. The researchers think that diet drinkers may overestimate the calories they’re “saving,” and then overeat.

Belly blaster: If you’re not ready to kick your habit, the researchers suggest reducing the number of food calories in your diet.

Read more: 10 Reasons to Give Up Diet Soda

You love burgers

When Swedish researchers gave one group of adults 750 extra daily calories, mainly from saturated fat, and another group the same amount of calories but mostly from polyunsaturated fatty acids (PUFAs) for seven weeks, the saturated fat group accumulated two times as much visceral fat.

Belly blaster: Dine on fatty fish like salmon or trout once a week to get a good dose of PUFAs. The rest of the time, reduce your intake of red meat and opt instead for protein low in saturated fat, such as legumes and chicken.

You think girls don’t get beer guts

According to a 2013 Danish study, beer may indeed be linked with abdominal obesity. And though beer appears to have the greatest impact, wine won’t save you from a spare tire: One study found that the amount of alcohol of any type that women drank contributed to weight gain.

Belly blaster: Stick with seven or fewer alcoholic beverages a week. Light to moderate drinkers are the least likely to carry excess weight anywhere, shows a recent Archives of Internal Medicine study.

You can’t recall when you last said “om”

Menopause-related hormonal changes (which typically begin in your 40s) make it harder to shed stomach pudge—but vigorous yoga can help offset the effects. A 2012 study found that postmenopausal women who did an hour-long yoga session three times a week for 16 weeks lost more than 1/2 inch around their waists.

Belly blaster: Not a fan of Sun Salutations? “Take an hour to do something nice for yourself,” which could help control your stress hormones, advises Sheila Dugan, MD, a physical medicine and rehabilitation specialist in Chicago.

Read more: Try This Flat-Belly Yoga Pose

Your meals are beige

Brightly colored fruits and veggies are loaded with vitamin C, which reduces cortisol. What’s more, a recent study in The Journal of Nutrition showed that people who ate more of the nutrients in red, orange, and yellow produce had smaller waists as a result.

Belly blaster: Add color to your plate by topping fish with a mango salsa, or throw diced red pepper into your turkey meatballs.

Your sweat sessions don’t involve sweat

Research has shown that high-intensity interval training, or HIIT—bursts of vigorous activity followed by short periods of gentle activity or rest—boasts belly-shrinking benefits. “High-intensity exercise seems to be more effective at reducing insulin, triglycerides, and cortisol, and it burns more calories in less time, too,” notes Shawn Talbot, PhD, a fellow of the American College of Sports Medicine.

Belly blaster: If you enjoy biking or running, for example, accelerate to a pace that makes it hard to talk for two minutes; then slow down for a minute, and repeat until you’re done. Like resistance training? Try a series of moves like squats or push-ups for two minutes each with a 60-second break between them.

This article originally appeared on Health.com.

Read next: What Diet Soda Does to Belly Fat

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TIME Diet/Nutrition

How Los Angeles Tried—and Failed—to Curb Obesity

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A study finds that an L.A. law to cut back on fast food may not have worked

A Los Angeles law meant to improve obesity rates didn’t work out as planned, a new study shows.

In 2008, South Los Angeles passed an ordinance that restricted the opening or expansion of new stand-alone fast food restaurants, in hopes of making residents healthier. However, new research published in the journal Social Science & Medicine reveals that little happened to the diets and obesity rates of people living in the region.

The researchers looked at both the number of food outlets opening in the city, as well as data on neighborhood eating habits and weight. The number of residents who were overweight or obese increased from 2007 to 2012—including in South Los Angeles. Only sugary drink consumption dropped.

“Environmental change is slow, so we should not expect dramatic immediate effects,” the study authors write. But they acknowledge another explanation, too: that the ordinance didn’t target the outlets it should have. The researchers report that South Los Angeles is characterized by smaller food outlets or convenience stores rather than typical fast-food chains. Food outlets that were added since the ordinance looked similar to the outlets that were already there, the authors say.

“It would seem unlikely that changes in the food environment due to the regulation could have had a meaningful impact on dietary choices in South LA,” says study author Roland Sturm, a senior economist at the non-profit research organization RAND.

But the study authors note that in the long run, the fast-food ban could help effect change in a more symbolic way: by helping to shift the mindset of how residents of the area approach food.

TIME Research

This New Drug Turns ‘Bad’ White Fat Into ‘Good’ Brown Fat

GC-1 could have the potential to treat obesity and metabolic disease

Scientists claim they have found an experimental drug that turns “bad” white fat cells into “good” brown ones.

Known as GC-1, the drug speeds up metabolism, or the burning off of fat cells, reports Science Daily. Researchers found it caused weight loss in fat mice.

“GC-1 dramatically increases the metabolic rate, essentially converting white fat, which stores excess calories and is associated with obesity and metabolic disease, into a fat like calorie-burning brown fat,” said study author Kevin Phillips of the Houston Methodist Research Institute.

Until recently, scientists thought only animals and human infants had these energy-burning “good” brown-fat cells.

“It is now clear that human adults do have brown fat, but appear to lose its calorie-burning activity over time,” Phillips added.

He calls white fat a “metabolic villain” when you have too much of it, whereas people with more brown fat have a reduced risk of obesity and diabetes.

GC-1 works by activating receptors for the thyroid hormone, which help regulate how your body turns food into energy.

Phillips’ team tested the drug on hundreds of mice who were genetically obese or who had diet-induced obesity. They found genetically obese mice lost weight and nearly 50% of their fat mass in two weeks. Diet-induced obese mice also showed improvements.

The drug was also tested on white fat cells grown in a lab, and researchers say they found evidence that the drug turned white fat into the brown variety.

Phillips hopes the drug, which has not yet been tested on humans, has the potential to treat obesity and metabolic disease.

The results of the study will be presented at the Endocrine Society’s 97th annual meeting in San Diego on Friday.

[Science Daily]

TIME medicine

One Hour of Sleep Makes a Difference In What You’ll Eat

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Lynn Koenig—Getty Images/Flickr RF

When it comes to teens and sleep, it’s not how much sleep, but how consistently they sleep the same amount that’s important for their health

Plenty of studies have documented that teens don’t get enough sleep. They’re supposed to be in bed for eight to nine hours a night, but most get seven or less. Now the latest sleep research, presented at the American Heart Association EPI/Lifestyle 2015 meeting, shows when it comes to weight gain—which has been tied to sleep deprivation and disturbances—it’s not necessarily the amount of sleep that tips the scales but rather the consistency of that nightly rest.

Fan He, an epidemiologist at Penn State University College of Medicine, and his colleagues found a strong correlation between the variation in sleep patterns among a group of teens and the amount of calories they consumed. And for every hour difference in sleep on a night-to-night basis over a week, for example, they ate 210 more calories—most of it in fat and carbohydrates. Those with uneven sleep patterns were also more likely to snack.

Previous studies have linked poor or disrupted sleep to obesity; people not getting enough shut-eye, for example, may experience changes in the hormones that regulate appetite and how well they break down glucose in their diet. Levels of the hormone leptin, for instance, drop in those who are sleep deprived, and less leptin prompts the body to feel hungry.

MORE: The Power of Sleep

In the current study, however, all the teens got an average of seven hours a night, so it wasn’t as if some of the teens were sleeping for extremely long or short periods of time. Any metabolic changes they would have experienced due to their sleeping less than the recommended eight to nine hours would have been similar among the consistent and inconsistent sleepers.

Dr. Nathaniel Watson, president-elect of the American Academy of Sleep Medicine and co-director of the University of Washington Medicine Sleep Center, stresses that good quality sleep involves three things — getting enough sleep, making sure the timing of the sleep if appropriate, and avoiding sleep disorders. While the amount of sleep has gotten the lion’s share of attention in recent years, a new phenomenon called social jet lag, which the current study investigates, may deserve equal consideration. “We live in a society of yo-yo sleep in which people sleep less because of social or work demands, then try to catch up,” says Watson. “There haven’t been a lot of studies that looked at what kind of impact this has on our health, but teenagers may be particularly susceptible to social jet lag than older adults, and this study assessed that.”

MORE: This Is What’s Keeping Teens From Getting Enough Sleep

These results show that it was the variability in their sleep that was most strongly linked to their eating habits.

Why? The researchers guess that teens who aren’t sleeping consistently are more likely to get too little sleep on one night, for example, and therefore be more tired or sedentary the following day, which leads them to sit around and eat more. It may also be possible that teens with irregular sleep habits are more likely to stay up later on weekends; He found that these adolescents had a 100% higher chance of snacking on weekends compared to those who slept more regularly.

MORE: School Should Start Later So Teens Can Sleep, Urge Doctors

That suggests that health experts should focus not just on the amount of sleep teens are getting, but on their sleep patterns. “Instead of focusing on how much we sleep, we also need to pay attention to maintaining a regular sleep pattern,” says He. Such consistency, however, may not be so easy for teens to master.

 

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