（美国）茲卡病毒风险分布图

美国国家航空航天局出了一张茲卡病毒风险分布图，给出了（美国各地）茲卡病毒转发成大型流行病的可能性。

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《纽约时报》

Short Answers to Hard Questions About Weight Loss

To Lose Weight, Eating Less Is Far More Important Than Exercising More
To Keep Obesity at Bay, Exercise May Trump Diet

 

 

The Science of Fat
After ‘The Biggest Loser,’ Their Bodies Fought to Regain Weight
GINA KOLATAMAY 2, 2016

Contestants lost hundreds of pounds during Season 8, but gained them back. A study of their struggles helps explain why so many people fail to keep off the weight they lose

Danny Cahill stood, slightly dazed, in a blizzard of confetti as the audience screamed and his family ran on stage. He had won Season 8 of NBC’s reality television show “The Biggest Loser,” shedding more weight than anyone ever had on the program — an astonishing 239 pounds in seven months.
When he got on the scale for all to see that evening, Dec. 8, 2009, he weighed just 191 pounds, down from 430. Dressed in a T-shirt and knee-length shorts, he was lean, athletic and as handsome as a model.
“I’ve got my life back,” he declared. “I mean, I feel like a million bucks.”
Mr. Cahill left the show’s stage in Hollywood and flew directly to New York to start a triumphal tour of the talk shows, chatting with Jay Leno, Regis Philbin and Joy Behar. As he heard from fans all over the world, his elation knew no bounds.
But in the years since, more than 100 pounds have crept back onto his 5-foot-11 frame despite his best efforts. In fact, most of that season’s 16 contestants have regained much if not all the weight they lost so arduously. Some are even heavier now.
Yet their experiences, while a bitter personal disappointment, have been a gift to science. A study of Season 8’s contestants has yielded surprising new discoveries about the physiology of obesity that help explain why so many people struggle unsuccessfully to keep off the weight they lose.
Kevin Hall, a scientist at a federal research center who admits to a weakness for reality TV, had the idea to follow the “Biggest Loser” contestants for six years after that victorious night. The project was the first to measure what happened to people over as long as six years after they had lost large amounts of weight with intensive dieting and exercise.
Photo（图）
Before and at finale
“I won’t be victim to this. It’s the hand I’ve been dealt.”
Danny Cahill
46, speaker, author, land surveyor and musician, Broken Arrow, Okla.
Weight Before show, 430 pounds; at finale, 191 pounds; now, 295 pounds
Metabolic Rate Now burns 800 fewer calories a day than would be expected for a man his size.
The results, the researchers said, were stunning. They showed just how hard the body fights back against weight loss.
“It is frightening and amazing,” said Dr. Hall, an expert on metabolism at the National Institute of Diabetes and Digestive and Kidney Diseases, which is part of the National Institutes of Health. “I am just blown away.”
It has to do with resting metabolism, which determines how many calories a person burns when at rest. When the show began, the contestants, though hugely overweight, had normal metabolisms for their size, meaning they were burning a normal number of calories for people of their weight. When it ended, their metabolisms had slowed radically and their bodies were not burning enough calories to maintain their thinner sizes.
Researchers knew that just about anyone who deliberately loses weight — even if they start at a normal weight or even underweight — will have a slower metabolism when the diet ends. So they were not surprised to see that “The Biggest Loser” contestants had slow metabolisms when the show ended.
What shocked the researchers was what happened next: As the years went by and the numbers on the scale climbed, the contestants’ metabolisms did not recover. They became even slower, and the pounds kept piling on. It was as if their bodies were intensifying their effort to pull the contestants back to their original weight.
Mr. Cahill was one of the worst off. As he regained more than 100 pounds, his metabolism slowed so much that, just to maintain his current weight of 295 pounds, he now has to eat 800 calories a day less than a typical man his size. Anything more turns to fat.
Biggest Losers Fight a Slower Metabolism（图）
A study of contestants from “The Biggest Loser” found their metabolisms slowed during and after the competition, making it difficult to maintain weight loss.
REGAINING LOST WEIGHT
13 of the 14 contestants studied regained weight in the six years after the competition. Four contestants are heavier now than before the competition.
A SLOWING METABOLISM
Nearly all the contestants have slower metabolisms today than they did six years ago, and burn fewer calories than expected when at rest.
Body burns 200 more cal. a day GAINED 50 lbs.
Erinn Egbert is the only contestant who weighs less today than six years ago.
Erinn Egbert
50 200 100 Rudy Pauls regained 80 percent of his lost weight, then had surgery to reduce the size of his stomach.
400 150 600 200
Rudy Pauls
Danny Cahill lost 239 pounds and won the competition, but has regained over 100 pounds.
Danny Cahill now burns 800 fewer calories a day than expected.
Body burns 800 fewer cal. a day LOST 250 lbs. Six years later Six years later
“The Biggest Loser”
Season 8 (2009)
“The Biggest Loser”
Season 8 (2009)
Sources: Obesity; individual contestants
（图）

‘A Basic Biological Reality’
The struggles the contestants went through help explain why it has been so hard to make headway against the nation’s obesity problem, which afflicts more than a third of American adults. Despite spending billions of dollars on weight-loss drugs and dieting programs, even the most motivated are working against their own biology.
Their experience shows that the body will fight back for years. And that, said Dr. Michael Schwartz, an obesity and diabetes researcher who is a professor of medicine at the University of Washington, is “new and important.”
“The key point is that you can be on TV, you can lose enormous amounts of weight, you can go on for six years, but you can’t get away from a basic biological reality,” said Dr. Schwartz, who was not involved in the study. “As long as you are below your initial weight, your body is going to try to get you back.”
The show’s doctor, Robert Huizenga, says he expected the contestants’ metabolic rates to fall just after the show, but was hoping for a smaller drop. He questioned, though, whether the measurements six years later were accurate. But maintaining weight loss is difficult, he said, which is why he tells contestants that they should exercise at least nine hours a week and monitor their diets to keep the weight off.
“Unfortunately, many contestants are unable to find or afford adequate ongoing support with exercise doctors, psychologists, sleep specialists, and trainers — and that’s something we all need to work hard to change,” he said in an email.
The study’s findings, to be published on Monday in the journal Obesity, are part of a scientific push to answer some of the most fundamental questions about obesity. Researchers are figuring out why being fat makes so many people develop diabetes and other medical conditions, and they are searching for new ways to block the poison in fat. They are starting to unravel the reasons bariatric surgery allows most people to lose significant amounts of weight when dieting so often fails. And they are looking afresh at medical care for obese people.
Photo （图）
Dina Mercado at home with one of her sons, Jericho, in Commerce, Calif. Credit Emily Berl for The New York Times
Photo
Before and at finale
Credit Left: Chris Haston/NBC Universal via Getty; Right: Trae Patton/NBC Universal via Getty

“It’s hard. The cravings are there.”
Dina Mercado
35, maintenance worker for Commerce, Calif.
Weight Before show, 248 pounds; at finale, 173.5 pounds; now, 205.9 pounds
Metabolic Rate Now burns 437.9 fewer calories per day than would be expected for a woman her size.
The hope is that this work will eventually lead to new therapies that treat obesity as a chronic disease and can help keep weight under control for life.
Continue reading the main story
Most people who have tried to lose weight know how hard it is to keep the weight off, but many blame themselves when the pounds come back. But what obesity research has consistently shown is that dieters are at the mercy of their own bodies, which muster hormones and an altered metabolic rate to pull them back to their old weights, whether that is hundreds of pounds more or that extra 10 or 15 that many people are trying to keep off.
There is always a weight a person’s body maintains without any effort. And while it is not known why that weight can change over the years — it may be an effect of aging — at any point, there is a weight that is easy to maintain, and that is the weight the body fights to defend. Finding a way to thwart these mechanisms is the goal scientists are striving for. First, though, they are trying to understand them in greater detail.
Dr. David Ludwig, the director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital, who was not involved in the research, said the findings showed the need for new approaches to weight control. He cautioned that the study was limited by its small size and the lack of a control group of obese people who did not lose weight. But, he added, the findings made sense.
“This is a subset of the most successful” dieters, he said. “If they don’t show a return to normal in metabolism, what hope is there for the rest of us?”
Still, he added, “that shouldn’t be interpreted to mean we are doomed to battle our biology or remain fat. It means we need to explore other approaches.”
Health By DEBORAH ACOSTA, ANDREW GLAZER and KAYLE HOPE 3:01
Why It’s Hard to Keep the Pounds Off
Video
Why It’s Hard to Keep the Pounds Off
Rebecca Wright and her husband, Daniel Wright, have gained back a lot of the weight they lost six years ago on Season 8 of "The Biggest Loser." A study of the contestants helps explain why. By DEBORAH ACOSTA, ANDREW GLAZER and KAYLE HOPE on Publish Date May 2, 2016. Watch in Times Video »

Slimmer and Hungrier
Some scientists say weight maintenance has to be treated as an issue separate from weight loss. Only when that challenge is solved, they say, can progress truly be made against obesity.
“There is a lot of basic research we still need to do,” said Dr. Margaret Jackson, who is directing a project at Pfizer. Her group is testing a drug that, in animals at least, acts like leptin, a hormone that controls hunger. With weight loss, leptin levels fall and people become hungry. The idea is to trick the brains of people who have lost weight so they do not become ravenous for lack of leptin.
While many of the contestants kept enough weight off to improve their health and became more physically active, the low weights they strived to keep eluded all but one of them: Erinn Egbert, a full-time caregiver for her mother in Versailles, Ky. And she struggles mightily to keep the pounds off because her metabolism burns 552 fewer calories a day than would be expected for someone her size.
“What people don’t understand is that a treat is like a drug,” said Ms. Egbert, who went from 263 pounds to just under 176 on the show, and now weighs between 152 and 157. “Two treats can turn into a binge over a three-day period. That is what I struggle with.”
Six years after Season 8 ended, 14 of the 16 contestants went to the N.I.H. last fall for three days of testing. The researchers were concerned that the contestants might try to frantically lose weight before coming in, so they shipped equipment to them that would measure their physical activity and weight before their visit, and had the information sent remotely to the N.I.H.
The contestants received their metabolic results last week. They were shocked, but on further reflection, decided the numbers explained a lot.
Photo（图）
Sean Algaier taking communion at Providence Road Church of Christ in Charlotte, N.C., where he is a pastor. Credit George Etheredge for The New York Times
Photo
Before and at finale
Credit Left: Chris Haston/NBC Universal via Getty; Right: Trae Patton/NBC Universal via Getty
“It’s not as dramatic as being told you have a disease, but it’s along those lines.”
Sean Algaier
36, worship pastor, Charlotte, N.C.
Weight Before show, 444 pounds; at finale, 289 pounds; now, 450 pounds
Metabolic Rate Now burns 458 fewer calories a day than would be expected for a man his size.
“All my friends were drinking beer and not gaining massive amounts of weight,” Mr. Cahill said. “The moment I started drinking beer, there goes another 20 pounds. I said, ‘This is not right. Something is wrong with my body.’”
Sean Algaier, 36, a pastor from Charlotte, N.C., feels cheated. He went from 444 pounds to 289 as a contestant on the show. Now his weight is up to 450 again, and he is burning 458 fewer calories a day than would be expected for a man his size.
“It’s kind of like hearing you have a life sentence,” he said.

Losing a Key Hormone
Slower metabolisms were not the only reason the contestants regained weight, though. They constantly battled hunger, cravings and binges. The investigators found at least one reason: plummeting levels of leptin. The contestants started out with normal levels of leptin. By the season’s finale, they had almost no leptin at all, which would have made them ravenous all the time. As their weight returned, their leptin levels drifted up again, but only to about half of what they had been when the season began, the researchers found, thus helping to explain their urges to eat.
Leptin is just one of a cluster of hormones that control hunger, and although Dr. Hall and his colleagues did not measure the rest of them, another group of researchers, in a different project, did. In a one-year study funded by Australia’s National Health and Medical Research Council, Dr. Joseph Proietto of the University of Melbourne and his colleagues recruited 50 overweight people who agreed to consume just 550 calories a day for eight or nine weeks. They lost an average of nearly 30 pounds, but over the next year, the pounds started coming back.
Dr. Proietto and his colleagues looked at leptin and four other hormones that satiate people. Levels of most of them fell in their study subjects. They also looked at a hormone that makes people want to eat. Its level rose.
“What was surprising was what a coordinated effect it is,” Dr. Proietto said. “The body puts multiple mechanisms in place to get you back to your weight. The only way to maintain weight loss is to be hungry all the time. We desperately need agents that will suppress hunger and that are safe with long-term use.”

370, 400, 460, 485
Mr. Cahill, 46, said his weight problem began when he was in the third grade. He got fat, then fatter. He would starve himself, and then eat a whole can of cake frosting with a spoon. Afterward, he would cower in the pantry off the kitchen, feeling overwhelmed with shame.
Over the years, his insatiable urge to eat kept overcoming him, and his weight climbed: 370 pounds, 400, 460, 485.
“I used to look at myself and think, ‘I am horrible, I am a monster, subhuman,’” he said. He began sleeping in a recliner because he was too heavy to sleep lying down. Walking hurt; stairs were agony. Buying clothes with a 68 waist was humiliating.
“I remember sitting in a dressing room one day, and nothing would fit. I looked at the traffic outside on the street and thought, ‘I should just run out in front of a car.’”
He eventually seized on “The Biggest Loser” as his best chance to lose enough weight to live a normal life. He tried three times and was finally selected.
Before the show began, the contestants underwent medical tests to be sure they could endure the rigorous schedule that lay ahead. And rigorous it was. Sequestered on the “Biggest Loser” ranch with the other contestants, Mr. Cahill exercised seven hours a day, burning 8,000 to 9,000 calories according to a calorie tracker the show gave him. He took electrolyte tablets to help replace the salts he lost through sweating, consuming many fewer calories than before.
Eventually, he and the others were sent home for four months to try to keep losing weight on their own.
Mr. Cahill set a goal of a 3,500-caloric deficit per day. The idea was to lose a pound a day. He quit his job as a land surveyor to do it.
His routine went like this: Wake up at 5 a.m. and run on a treadmill for 45 minutes. Have breakfast — typically one egg and two egg whites, half a grapefruit and a piece of sprouted grain toast. Run on the treadmill for another 45 minutes. Rest for 40 minutes; bike ride nine miles to a gym. Work out for two and a half hours. Shower, ride home, eat lunch — typically a grilled skinless chicken breast, a cup of broccoli and 10 spears of asparagus. Rest for an hour. Drive to the gym for another round of exercise.
If he had not burned enough calories to hit his goal, he went back to the gym after dinner to work out some more. At times, he found himself running around his neighborhood in the dark until his calorie-burn indicator reset to zero at midnight.
On the day of the weigh-in on the show’s finale, Mr. Cahill and the others dressed carefully to hide the rolls of loose skin that remained, to their surprise and horror, after they had lost weight. They wore compression undergarments to hold it in.
Mr. Cahill knew he could not maintain his finale weight of 191 pounds. He was so mentally and physically exhausted he barely moved for two weeks after his publicity tour ended. But he had started a new career giving motivational speeches as the biggest loser ever, and for the next four years, he managed to keep his weight below 255 pounds by exercising two to three hours a day. But two years ago, he went back to his job as a surveyor, and the pounds started coming back.
Photo
Armanda Arlauskas walking her dog, Jax, in her neighborhood in Raleigh, N.C. Credit George Etheredge for The New York Times
Photo
Before and at finale
Credit Left: Chris Haston/NBC Universal via Getty; Right: Trae Patton/NBC Universal via Getty
“I could tell something wasn’t right with my body. I just knew it was an issue with my metabolism.”
Amanda Arlauskas
26, wellness coach and social media consultant, Raleigh, N.C.
Weight Before show, 250 pounds; at finale, 163 pounds; now, 176 pounds
Metabolic Rate Now burns 591.1 fewer calories per day than would be expected for a woman her size.
Soon the scale hit 265. Mr. Cahill started weighing and measuring his food again and stepped up his exercise. He got back down to 235 to 240 pounds. But his weight edged up again, to 275, then 295.
His slow metabolism is part of the problem, and so are his food cravings. He opens a bag of chips, thinking he will have just a few. “I’d eat five bites. Then I’d black out and eat the whole bag of chips and say, ‘What did I do?’”

 

Brain Sets the Calories
Dr. Lee Kaplan, an obesity researcher at Harvard, says the brain sets the number of calories we consume, and it can be easy for people to miss that how much they eat matters less than the fact that their bodies want to hold on to more of those calories.
Dr. Michael Rosenbaum, an obesity researcher at Columbia University who has collaborated with Dr. Hall in previous studies, said the body’s systems for regulating how many calories are consumed and how many are burned are tightly coupled when people are not strenuously trying to lose weight or to maintain a significant weight loss. Still, pounds can insidiously creep on.
“We eat about 900,000 to a million calories a year, and burn them all except those annoying 3,000 to 5,000 calories that result in an average annual weight gain of about one to two pounds,” he said. “These very small differences between intake and output average out to only about 10 to 20 calories per day — less than one Starburst candy — but the cumulative consequences over time can be devastating.”
“It is not clear whether this small imbalance and the resultant weight gain that most of us experience as we age are the consequences of changes in lifestyle, the environment or just the biology of aging,” Dr. Rosenbaum added.
Continue reading the main story
Continue reading the main story
Photo
Rudy Pauls and his wife, Beth, disinfecting a newborn lamb on their farm in Belchertown, Mass. Credit Nathaniel Brooks for The New York Times
Photo
Before and
at finale
Credit Left: Chris Haston/NBC Universal via Getty; Right: Trae Patton/NBC Universal via Getty
“‘The Biggest Loser’ did change my life, but not in a way that most would think. It opened my eyes to the fact that obesity is not simply a food addiction. It is a disability of a malfunctioning metabolic system.”
Rudy Pauls
37, electrical engineer, Belchertown, Mass.
Weight Before show, 442 pounds; at finale, 234 pounds; in 2014, 390 pounds; now, after bariatric surgery, 265 pounds
Metabolic Rate Now burns 516 fewer calories a day than would be expected for a man his size.
The effects of small imbalances between calories eaten and calories burned are more pronounced when people deliberately lose weight, Dr. Hall said. Yes, there are signals to regain weight, but he wondered how many extra calories people were driven to eat. He found a way to figure that out.
He analyzed data from a clinical trial in which people took a diabetes drug, canagliflozin, that makes them spill 360 calories a day into their urine, or took a placebo. The drug has no known effect on the brain, and the person does not realize those calories are being spilled. Those taking the drug gradually lost weight. But for every five pounds they lost, they were, without realizing it, eating an additional 200 calories a day.
Those extra calories, Dr. Hall said, were a bigger driver of weight regained than the slowing of the metabolism. And, he added, if people fought the urge to eat those calories, they would be hungry. “Unless they continue to fight it constantly, they will regain the weight,” he said.
All this does not mean that modest weight loss is hopeless, experts say. Individuals respond differently to diet manipulations — low-carbohydrate or low-calorie diets, for example — and to exercise and weight-loss drugs, among other interventions.
But Dr. Ludwig said that simply cutting calories was not the answer. “There are no doubt exceptional individuals who can ignore primal biological signals and maintain weight loss for the long term by restricting calories,” he said, but he added that “for most people, the combination of incessant hunger and slowing metabolism is a recipe for weight regain — explaining why so few individuals can maintain weight loss for more than a few months.”
Dr. Rosenbaum agreed. “The difficulty in keeping weight off reflects biology, not a pathological lack of willpower affecting two-thirds of the U.S.A.,” he said.
Mr. Cahill knows that now. And with his report from Dr. Hall’s group showing just how much his metabolism had slowed, he stopped blaming himself for his weight gain.
“That shame that was on my shoulders went off,” he said.
Continue reading the main story
Continue reading the main story
Photo
Tracey Yukich walks regularly at Lake Johnson Park in Raleigh, N.C. Credit George Etheredge for The New York Times
Photo
Before and at finale
Credit Left: Chris Haston/NBC Universal via Getty; Right: Trae Patton/NBC Universal via Getty
“I eat very clean and stay away from sugar, and I take supplements. I want to know what do we do now, because I am a doer.”
Tracey Yukich
44, exercise physiologist, Raleigh, N.C.
Weight Before show, 250 pounds; at finale, 132 pounds; now, 178 pounds
Metabolic Rate Now burns 211.7 fewer calories per day than would be expected for a woman her size.

 

 

Short Answers to Hard Questions About Weight Loss

GINA KOLATA MAY 4, 2016

Almost everyone who has ever dieted knows how hard it is to keep the weight off. And almost everyone, including many scientists, has wondered what works. An article on Monday about what happened to contestants from “The Biggest Loser” television show is a vivid illustration of the problem. Although there is no magic formula for weight maintenance, here are answers to some questions that arise over and over.

Are you more likely to maintain weight loss if you lose weight slowly?
That is the advice dieters often get, but studies have not found that to be the case. For example, a recent Australian study, funded by the Australian National Health and Medical Research Council and the Sir Edward Dunlop Medical Research Foundation, randomly assigned 204 obese people to subsist on just 450 to 800 calories a day for 12 weeks, or to cut a more modest 400 to 500 calories a day from their diets over 36 weeks. The goal for both groups was a 15 percent weight loss. Three years after the study began, almost everyone had regained the weight they lost, despite counseling on diet and exercise. There was also no difference in the levels of two hormones, leptin and ghrelin, that drive hunger. The main difference between the groups was that more people in the rapid weight loss group lost at least 12.5 percent of their weight (80 percent, compared with 50 percent in the slow loss group) and fewer dropped out (3 percent, compared with 18 percent).

The Science of Fat
Articles in this series are exploring new research to understand obesity, its damaging health effects and how best to treat it.

To maintain weight loss, should you avoid snacks?
Although it seems to make sense that snacks can pack on the pounds, studies that randomly assigned people to snack or not have failed to confirm this, and even observational studies have not found evidence that snacks undermine weight loss.

If you build muscle with exercise, including weight lifting, will you be able to maintain a higher metabolism?
Muscle burns more calories than fat, so it might stand to reason that the more muscle you have the faster you will burn calories. But it turns out that building muscles has almost no effect on resting metabolism, which determines how many calories a person burns when at rest. The reason is that any muscle you add is small compared with the total amount of skeletal muscle on your body. And most of the time that muscle is at rest. (You can’t go around flexing your biceps nonstop.) Muscles have a very low metabolic rate at rest. One researcher calculated that if a man weighing about 175 pounds lifts weights and puts on about 4½ pounds of muscle — a typical amount for men who lift weights for 12 weeks — he will burn an extra 24 calories a day, the amount in a couple of Life Saver candies.

Can you defeat your body’s slowed metabolism after weight loss by doing vigorous cardiovascular exercises?
You can as long as you do not eat more calories to make up for the ones you burned. It sounds simple enough, but “this is not as easy a proposition as it sounds,” says Dr. Michael Rosenbaum, a doctor and obesity researcher at Columbia University. The brain controls your hunger and your cravings for food, and it is all too easy to accidentally consume more calories than you burned exercising. That is a major reason studies that use exercise alone to help people lose weight have generally failed to find an effect.

Exercise also has an unexpected effect, documented by Dr. Rosenbaum and Dr. Rudolph Leibel at Columbia University. They found that after you lose 10 percent or more of your weight by diet alone, your muscles start using genes that make them more efficient. They burn 20 to 30 percent fewer calories for the same exercise.

Is there a type of diet that helps keep weight off?
Many people swear by diets that are low in carbohydrates or gluten free, or revolve around fasting two days out of seven. Dr. Lee Kaplan, an obesity researcher at Harvard, says there is no diet or weight-loss regimen that is guaranteed to work but that people can often maintain a loss of 5 percent of their weight, which is enough for health benefits to kick in. He tells his patients to try one weight-loss program after another in hopes of finding something that works for them.

So what hope is there for weight maintenance?
Anecdotal reports by people who have succeeded in keeping weight off tend to have a common theme: constant vigilance, keeping close track of weight, controlling what food is eaten and how much (often by weighing and measuring food), exercising often, putting up with hunger and resisting cravings to the best of their ability. Those who maintain a modest weight loss often report less of a struggle than those trying to keep off large amounts of weight.

 

 

To Lose Weight, Eating Less Is Far More Important Than Exercising More
Aaron E. Carroll, JUNE 15, 2015

 

One of my family’s favorite shows is “The Biggest Loser.” Although some viewers don’t appreciate how it pushes people so hard to lose weight, the show probably inspires some overweight people to regain control of their lives.
But one of the most frustrating parts of the show, at least for me, is its overwhelming emphasis on exercise. Because when it comes to reaching a healthy weight, what you don’t eat is much, much more important.

Think about it this way: If an overweight man is consuming 1,000 more calories than he is burning and wants to be in energy balance, he can do it by exercising. But exercise consumes far fewer calories than many people think. Thirty minutes of jogging or swimming laps might burn off 350 calories. Many people, fat or fit, can’t keep up a strenuous 30-minute exercise regimen, day in and day out. They might exercise a few times a week, if that.

Or they could achieve the same calorie reduction by eliminating two 16-ounce sodas each day.

Proclamations that people need to be more active are ubiquitous in the media. The importance of exercise for proper weight management is reinforced when people bemoan the loss of gym class in schools as a cause of the obesity epidemic. Michelle Obama’s Let’s Move program places the focus on exercise as a critical component in combating excess weight and obesity.

Exercise has many benefits, but there are problems with relying on it to control weight. First, it’s just not true that Americans, in general, aren’t listening to calls for more activity. From 2001 to 2009, the percentage of people who were sufficiently physically active increased. But so did the percentage of Americans who were obese. The former did not prevent the latter.

Studies confirm this finding. A 2011 meta-analysis, a study of studies, looked at the relationship between physical activity and fat mass in children, and found that being active is probably not the key determinant in whether a child is at an unhealthy weight. In the adult population, interventional studies have difficulty showing that a physically active person is less likely to gain excess weight than a sedentary person. Further, studies of energy balance, and there are many of them, show that total energy expenditure and physical activity levels in developing and industrialized countries are similar, making activity and exercise unlikely to be the cause of differing obesity rates.

Moreover, exercise increases one’s appetite. After all, when you burn off calories being active, your body will often signal you to replace them. Research confirms this. A 2012 systematic review of studies that looked at how people complied with exercise programs showed that over time, people wound up burning less energy with exercise than predicted and also increasing their caloric intake.
Other metabolic changes can negate the expected weight loss benefits of exercise over the long term. When you lose weight, metabolism often slows. Many people believe that exercise can counter or even reverse that trend. Research, however, shows that the resting metabolic rate in all dieters slows significantly, regardless of whether they exercise. This is why weight loss, which might seem easy when you start, becomes harder over time.

This isn’t to say that exercise plays no role. There are many studies that show that adding exercise to diets can be beneficial. A 1999 review identified three key meta-analyses and other randomized controlled trials that found statistically significant, but overall small, increases in weight loss with exercise.

A meta-analysis published last year found that, in the long term, behavioral weight management programs that combine exercise with diet can lead to more sustained weight loss (three to four pounds) over a year than diet alone. Over a six-month period, though, adding exercise made no difference. Another systematic review from last fall found similar results, with diet plus exercise performing better than diet alone, but without much of an absolute difference.
All of these interventions included dietary changes, and the added weight-loss benefit from activity was small. Far too many people, though, can manage to find an hour or more in their day to drive to the gym, exercise and then clean up afterward — but complain that there’s just no time to cook or prepare a healthful, home-cooked meal. If they would spend just half the time they do exercising trying to make a difference in the kitchen, they’d most likely see much better results.

Many people think of dieting as a drastic and rigid change, with a high risk of putting the pounds back on. What is more likely to succeed is gradual change, made in a much more sustainable way. I also don’t mean to make it seem that weight loss with diet is easy and exercise is hard. They’re both hard. The challenge of a slowing metabolism, and the desire to eat more, occurs in both cases, although dietary change still works better than exercise.

But I can’t say this enough: Exercise has a big upside for health beyond potential weight loss. Many studies and reviews detail how physical activity can improve outcomes in musculoskeletal disorders, cardiovascular disease, diabetes, pulmonary diseases, neurological diseases and depression. The Academy of Medical Royal Colleges declared it a “miracle cure” recently, and while I’m usually loath to use that term for anything in medicine, a fairly large evidence base corroborates that exercise improves outcomes in many domains.

But that huge upside doesn’t seem to necessarily apply to weight loss. The data just don’t support it. Unfortunately, exercise seems to excite us much more than eating less does. After all, as a friend said to me recently, “The Biggest Loser” would be really boring if it were shot after shot of contestants just not overeating.

 

 

To Keep Obesity at Bay, Exercise May Trump Diet
Gretchen Reynolds May 4, 2016

Young rats prone to obesity are much less likely to fulfill that unhappy destiny if they run during adolescence than if they do not, according to a provocative new animal study of exercise and weight. They also were metabolically healthier, and had different gut microbes, than rats that keep the weight off by cutting back on food, the study found. The experiment was done in rodents, not people, but it does raise interesting questions about just what role exercise may play in keeping obesity at bay.

For some time, many scientists, dieting gurus and I have been pointing out that exercise by itself tends to be ineffective for weight loss. Study after study has found that if overweight people start working out but do not also reduce their caloric intake, they shed little if any poundage and may gain weight.
The problem, most scientists agree, is that exercise increases appetite, especially in people who are overweight, and also can cause compensatory inactivity, meaning that people move less over all on days when they exercise. Consequently, they wind up burning fewer daily calories, while also eating more. You do the math.

But those discouraging studies involved weight loss. There has been much less examination of whether exercise might help to prevent weight gain in the first place and, if it does, how it compares to calorie restriction for that purpose.
So for the new study, which was published last week in Medicine & Science in Sports & Exercise, researchers at the University of Missouri in Columbia and other schools first gathered rats from a strain that has an inborn tendency to become obese, starting in adolescence. (Adolescence is also when many young people begin to add weight.)

These rats were young enough, though, that they were not yet overweight.

After weighing them, the researchers divided the animals into three groups.
One group was allowed to eat as much kibble as they wished and to remain sedentary in their cages. These were the controls.

Another group, the exercise group, also was able to eat at will, but these animals were provided with running wheels in their cages. Rats like to run, and the animals willingly hopped on the wheels, exercising every day.

The final group, the dieting group, was put on a calorie-restricted meal plan. Their daily kibble helpings were about 20 percent smaller than the amount that the runners ate, a portion size designed to keep them at about the same weight as the runners, so that extreme differences in body size would not affect the final results.

After 11 weeks, all of the animals were moved to specialized cages that could measure their metabolisms and how much they moved around. They then returned to their assigned cages for several more weeks, by which time they were effectively middle-aged.

At that point, the control animals were obese, their physiques larded with fat.
The runners and the lower-calorie groups, however, although they also had gained ounces, had put on far less weight than the controls. None were obese.
Both exercise and portion control, in other words, had effectively protected the animals against their fated fatness.

But beneath the skin, the runners and the dieters looked very unalike. By almost all measures, the runners were metabolically healthier, with better insulin sensitivity and lower levels of bad cholesterol than the dieters. They also burned more fat each day for fuel, according to their metabolic readings, and had more cellular markers related to metabolic activity within their brown fat than the dieting group. Brown fat, unlike the white variety, can be quite metabolically active, helping the body to burn additional calories.

Interestingly, the runners also had developed different gut microbes than the dieters, even though they ate the same food. The runners had greater percentages of some bacteria and smaller populations of others than the dieters or the control group; these particular proportions of gut bugs have been associated in a few previous studies with long-term leanness in both animals and people.

Perhaps most striking, “the runners showed no signs of compensatory eating or compensatory inactivity,” said Victoria Vieira-Potter, an assistant professor of nutrition and exercise physiology at the University of Missouri who oversaw the study. They didn’t scarf down more food than the control group, despite running several miles every day and, according to the specialized cages, actually moved around more when not exercising than either of the other groups of rats.
In essence, the runners, while weighing the same as the dieters at the end of the study, seemed better set up to avoid weight gain in the future.

Of course, these were rats, which do not share our human biology or our tangled psychological relationships with food and body fat.

This study also involved young, normal-weight rodents and cannot tell us whether exercise or dieting alone or in combination would aid or hinder weight loss in people (or animals) who already are overweight, Dr. Vieira-Potter said. Metabolisms change once a body contains large amounts of fat, and it becomes increasingly difficult to permanently drop those extra pounds.

So better to avoid weight gain in the first place, if possible. And in that context, she said, “restricting calories can be effective,” but exercise is likely to be more potent in the long term and, of course, as common sense would tell us, doing both—watching what you eat and exercising—is best of all.