Losing battle: the science of shedding weight – and putting it all back on again
Tara Parker-Pope, The Australian, February 04, 2012
For 15 years, Joseph Proietto has been helping people lose weight. When these obese patients arrive at his weight-loss clinic in Melbourne they are determined to slim down. And most of the time, he says, they do just that.
But then, almost without exception, the weight begins to creep back. In a matter of months or years, the entire effort has come undone and the patient is fat again. “It has always seemed strange to me,” says Proietto, a professor of medicine at the University of Melbourne. “These are people who are very motivated to lose weight, who achieve weight loss most of the time without too much trouble and yet, inevitably, gradually, they regain the weight.”
Anyone who has ever dieted knows that lost kilos often return, and most of us assume the reason is a failure of willpower. But Proietto suspected there was more to it, and he decided to take a closer look at the biological state of the body after weight loss.
Beginning in 2009, he and his team recruited 50 obese men and women. The men weighed an average of 105kg; the women about 90kg. Although some dropped out of the study, most stuck with the extreme low-calorie diet, which consisted of a special brand of shakes called Optifast and two cups of low-starch vegetables, totalling just 2100-2310 kilojoules a day for eight weeks. Ten weeks in, they’d lost an average of 13.6kg.
At that point, the 34 patients who remained stopped dieting and began working to maintain the new, lower weight. Nutritionists counselled them in person and by phone, promoting regular exercise and urging them to eat more vegetables and less fat. But despite the effort, they slowly began to put on weight. After a year, the patients already had regained, on average, 5kg. They also reported feeling far more hungry and preoccupied with food than they’d been before they lost the weight.
While researchers have known for decades that the body undergoes various metabolic and hormonal changes while it’s losing weight, the Melbourne team detected something new. A full year after significant weight loss, these men and women remained in what could be described as a biologically altered state. Their still-plump bodies were acting as if they were starving and were working overtime to regain the kilos they’d lost. For instance, a gastric hormone called ghrelin, often dubbed the “hunger hormone,” was about 20 per cent higher than at the start of the study. Another hormone associated with suppressing hunger, peptide YY, was also abnormally low. Levels of leptin, a hormone that suppresses hunger and increases metabolism, also remained lower than expected. A cocktail of other hormones associated with hunger and metabolism all remained significantly changed compared to pre-dieting levels. It was almost as if weight loss had put their bodies into a unique metabolic state, a sort of post-dieting syndrome that set them apart from people who hadn’t tried to lose weight in the first place.
“What we see here is a coordinated defence mechanism with multiple components all directed toward making us put on weight,” Proietto says. “This, I think, explains the high failure rate in obesity treatment.”
While the findings, published in The New England Journal of Medicine, are not conclusive – the study was small and the findings need to be replicated – the research has nonetheless caused a stir in the weight-loss community, adding to a growing body of evidence that challenges conventional thinking about obesity, weight loss and willpower. For years, the advice has been to simply eat less and exercise more. While there is truth to this guidance, it fails to take into account that the human body continues to fight against weight loss long after dieting has stopped. This translates into a sobering reality: once we become fat, most of us, despite our best efforts, will probably stay fat.
I have always felt perplexed about my inability to keep weight off. I know the medical benefits of weight loss, and I don’t drink sugary drinks or eat fast food. I exercise regularly – a few years ago, I even completed a marathon. Yet during the past 23 years I’ve lost 5kg or 10kg at a time, maintained it for a little while and then gained it all back and more, to the point where I am now more than 25kg overweight.
I wasn’t overweight as a child, but I can’t remember a time when my mother, whose weight probably fluctuated between 70kg and 110kg, wasn’t either on a diet or, in her words, cheating on her diet. Sometimes we ate healthy, balanced meals; on other days dinner consisted of a bucket of Kentucky Fried Chicken. As a high-school cross-country runner I never worried about weight but in college, when my regular training runs were squeezed out by studying and socialising, the numbers on the scale slowly began to move up. My three sisters also now struggle with weight, as do many members of my extended family. My mother died of esophageal cancer six years ago; it was her great regret that in the days before she died, the closest medical school turned down her offer to donate her body because she was obese.
It’s possible that the biological cards were stacked against me from the start. Researchers know that obesity tends to run in families, and recent science suggests that even the desire to eat higher-kilojoule foods may be influenced by heredity. But untangling how much is genetic and how much is learned through family eating habits is difficult. What is clear is that some people appear to be prone to accumulating extra fat while others seem to be protected against it.
While there is widespread agreement that at least some risk for obesity is inherited, identifying a specific genetic cause has been a challenge. In 2010 the journal Nature Genetics reported that researchers have so far confirmed 32 distinct genetic variations associated with obesity or body-mass index. One of the most common of these variations was identified in 2007 by a British team studying the genetics of Type 2 diabetes. According to Timothy Frayling at the Institute of Biomedical and Clinical Science at the University of Exeter, people who carried a variant known as FTO faced a much higher risk of obesity – 30 per cent higher if they had one copy of the variant; 60 per cent if they had two.
This FTO variant is surprisingly common; about 65 per cent of people of European or African descent and an estimated 27 to 44 per cent of people of Asian descent are believed to carry at least one copy of it. Scientists don’t understand how the FTO variation influences weight gain, but studies in children suggest the trait plays a role in eating habits. In one 2008 study, Scottish schoolchildren were given snacks of orange drinks and muffins and then allowed to graze on a buffet of grapes, celery, chips and chocolate buttons. All the food was carefully monitored so the researchers knew exactly what was consumed. Although all the children ate about the same amount of food, as weighed in grams, children with the FTO variant were more likely to eat foods with higher fat and calorie content. They weren’t gorging themselves, but they consumed, on average, about 420kJ more than children who didn’t carry the gene. Those who had the gene variant had about 1.8kg more body fat than non-carriers.
I have been tempted to undergo a DNA test to find out if my family carries a genetic predisposition for obesity. But even if the test came back negative, it would only mean that my family doesn’t carry a known, testable genetic risk for obesity. And a positive result might be self-fulfilling – if being fat is one’s genetic destiny, what’s the point fighting it? While knowing my genetic risk might satisfy my curiosity, I also know that heredity, at best, would explain only part of why I became overweight. I’m much more interested in figuring out what I can do about it now.
The National Weight Control Registry in the US tracks 10,000 people who have lost weight and kept it off. “We set it up in response to comments that nobody ever succeeds at weight loss,” says Rena Wing, a professor of psychiatry and human behaviour at Brown University’s Alpert Medical School, who helped create the registry with James O. Hill, director of the Centre for Human Nutrition at the University of Colorado. “We had two goals: to prove there were people who did, and to try to learn from them about what they do to achieve this long-term weight loss.”
Wing says she agrees that physiological changes probably do occur that make permanent weight loss difficult, but she says the larger problem is environmental, and that people struggle to keep weight off because they are surrounded by food, inundated with food messages and constantly presented with opportunities to eat. “We live in an environment with food cues all the time,” she says. “We’ve taught ourselves over the years that one of the ways to reward yourself is with food. It’s hard to change the environment and the behaviour.”
There is no consistent pattern to how people in the registry lost weight – some did it on WeightWatchers, others with Jenny Craig, some by the Atkins diet and a very small number through surgery. But their eating and exercise habits appear to reflect what researchers find in the lab: to lose weight and keep it off, a person must eat fewer kilojoules and exercise far more than a person who maintains the same weight naturally. Registry members exercise about an hour or more each day. They get on a scale daily in order to keep their weight within a narrow range. Most watch less than half as much TV as the overall population. They eat the same foods and in the same patterns consistently each day and don’t “cheat” on weekends or holidays. They also appear to eat less than most people, with estimates ranging from 200 to 1200 fewer daily kilojoules.
Janice Bridge, a registry member who has maintained a 60kg weight loss for about five years, is a perfect example. “It’s one of the hardest things there is,” she says. “It’s something that has to be focused on every minute.” Bridge, 66, was overweight as a child and went on her first diet at 14. At the time, her slow pace of weight loss prompted her doctor to accuse her of cheating. Friends told her she must not be paying attention to what she was eating. “No one would believe that I was doing everything I was told,” she says. “You can imagine how tremendously depressing it was and what a feeling of rebellion and anger was building up.”
After peaking at 150kg in 2004, she tried again to lose weight. She managed to drop 14kg, but then her weight loss stalled. In 2006, aged 60, she joined a medically supervised weight-loss program with her husband, Adam, who weighed 140kg. After nine months she slimmed down to 75kg and is now maintaining a higher weight of 88kg. Adam lost about 50kg and now weighs about 90kg.
“It doesn’t take a lot of variance from my current maintenance for me to pop on another kilogram or more,” says Bridge. “It’s been a real struggle to stay at this weight, but it’s worth it, it’s good for me, it makes me feel better. But my body would put on weight almost instantaneously if I ever let up.”
So she never lets up. Since October 2006 she has weighed herself every morning and recorded the result in a weight diary. She also knows about everything in the kitchen. She knows that lettuce is about 20kJ a cup, while flour is about 1680kJ. If she goes out to dinner she conducts a web search first to look at the menu and calculate kilojoules to help her decide what to order. She avoids anything with sugar or white flour, which she calls her “gateway drugs” for cravings and overeating. She has also found that drinking copious amounts of water seems to help. She writes down everything she eats and at night transfers all the information to an electronic record. Adam also keeps track but prefers to keep his record with pencil and paper.
Bridge supports her careful diet with an equally rigorous regimen of physical activity. She exercises from 100 to 120 minutes a day, six or seven days a week. Adam is also a committed exerciser, riding his bike at least two hours a day, five days a week.
Janice Bridge has used years of her exercise and diet data to calculate her own fuel efficiency. She knows her body burns about 13kJ a minute during gardening, about 17kJ a minute during water aerobics, and about 21kJ a minute riding her pushbike. “Practically anyone will tell you someone biking is going to burn 46 kilojoules a minute,” she says. “That’s not my body. I know it because of the statistics I’ve kept.”
Based on metabolism data she collected from the weight-loss clinic and her own calculations, she has discovered that to keep her current weight of 88kg she can eat 8400kJ a day as long as she burns 2100kJ in exercise. She avoids junk food, bread and pasta and many dairy products and tries to make sure nearly a third of her calories come from protein. The Bridges will occasionally share a dessert, or eat an individual portion of ice cream, so they know exactly how many kilojoules they are ingesting. Because she knows errors can creep in, either because a rainy day cuts exercise short or a mismeasured snack portion adds hidden kilojoules, she allows herself only 7560 daily kilojoules of food. (The average estimate for a similarly active woman of her age and size is about 9660kJ.)
Just talking to Bridge about the effort required to maintain her weight is exhausting. I find her story inspiring, but it also makes me wonder whether I have what it takes to be thin. I have tried on several occasions to keep a daily diary of my eating and exercise habits, but it’s easy to let it slide. I can’t quite imagine how I would ever make time to weigh and measure food when some days it’s all I can do to get dinner on the table between finishing my work and carting my daughter to dance class or volleyball practice. And while I enjoy exercising for 30- or 40-minute stretches, I also learnt from six months of marathon training that devoting one to two hours a day to exercise takes an impossible toll on my family life.
Bridge concedes that having grown children and being retired make it easier to focus on her weight. “I don’t know if I could have done this when I had three kids living at home,” she says. “We know how unusual we are. It’s pretty easy to get angry with the amount of work and dedication it takes to keep this weight off. But the alternative is to not keep the weight off. “
“I think many people who are anxious to lose weight don’t fully understand what the consequences are going to be, nor does the medical community fully explain this to people,” says Rudolph Leibel, an obesity researcher at Columbia University in New York. “We don’t want to make them feel hopeless, but we do want to make them understand that they are trying to buck a biological system that is going to try to make it hard for them.”
Leibel and his colleague Michael Rosenbaum have pioneered much of what we know about the body’s response to weight loss. For 25 years they have meticulously tracked about 130 individuals for six months or longer at a stretch. The subjects reside at their research clinic where every aspect of their bodies is measured. A special hood monitors their oxygen consumption and carbon dioxide output to precisely measure metabolism. Kilojoules burned during digestion are tracked. Exercise tests measure heart rate, while blood tests measure hormones and brain chemicals. Muscle biopsies are taken to analyse their metabolic efficiency. (Early in the research, even stool samples were tested to make sure no kilojoules went unaccounted for.)
Eventually, the Columbia subjects are placed on liquid diets of 3360kJ a day until they lose 10 per cent of their body weight. Once they reach that goal, they are subjected to another round of intensive testing as they try to maintain it. The findings suggest that once a person loses about 10 per cent of body weight, he or she is metabolically different to a similar-sized person who is naturally the same weight.
The research shows that the changes that occur after weight loss translate to a huge disadvantage of about 1000 to 1700 kilojoules. For instance, one woman who entered the Columbia studies at 104kg was eating about 12,600kJ a day. Once she dropped to 86kg, losing 17 per cent of her body weight, metabolic studies determined that she needed about 9660kJ a day to maintain the new lower weight. That may sound like plenty, but the typical 30-year-old 86kg woman can consume about 10,920kJ and maintain the same weight – 1260 more kilojoules than the woman who dieted to get there.
Scientists are still learning why a weight-reduced body behaves so differently to a similar-sized body that has not dieted. Muscle biopsies taken before, during and after weight loss show that once a person drops weight their muscle fibres undergo a transformation, making them more like highly efficient “slow twitch” muscle fibres. A result is that after losing weight, your muscles burn 20 to 25 per cent fewer kilojoules during moderate aerobic exercise than those of a person who is naturally the same weight. That means a dieter who thinks she is burning 840kJ during a brisk half-hour walk is probably burning closer to 650kJ.
Another way that the body seems to fight weight loss is by altering the way the brain responds to food. Rosenbaum and his colleague Joy Hirsch, a neuroscientist also at Columbia, used MRI scans to track the brain patterns of people before and after weight loss while they looked at objects and food. After weight loss, when the dieter looked at food the scans showed a bigger response in the parts of the brain associated with reward and a lower response in the areas associated with control.
“After you’ve lost weight, your brain has a greater emotional response to food,” Rosenbaum says. “You want it more, but the areas of the brain involved in restraint are less active.” Combine that with a body that is now burning fewer kilojoules than expected, he says, “and you’ve created the perfect storm for weight regain”.
What’s not clear is whether there is a window during which we can gain weight and then lose it without creating biological backlash. Leibel says that whether such “temporary” kilos become permanent probably depends on a person’s genetic risk for obesity and, perhaps, the length of time a person carries the extra weight before trying to lose it. But researchers don’t know how long it takes for the body to reset itself permanently to a higher weight. The good news is that it doesn’t seem to happen overnight.
“For a mouse, I know the time period is somewhere around eight months,” Leibel says. “Before that time, a fat mouse can come back to being a skinny mouse again without too much adjustment. For a human we don’t know, but I’m pretty sure it’s not measured in months, but in years.”
Nobody wants to be fat. In most modern cultures, even if you are healthy – in my case, my cholesterol and blood pressure are low and I have an extraordinarily healthy heart – to be fat is to be perceived as weak-willed and lazy. It’s also just embarrassing. If anything, the emerging scientific knowledge about weight loss teaches us that perhaps we should rethink our biases about people who are overweight. It is true that people who are overweight, including myself, get that way because they eat too many kilojoules relative to what their bodies need. But a number of biological and genetic factors can play a role in determining exactly how much food is too much for any given individual. Clearly, weight loss is an intense struggle, one in which we are not fighting simply hunger or cravings, but our own bodies.
While the public discussion about weight loss tends to come down to which diet works best (Atkins? Jenny Craig? Plant-based? Mediterranean?), those who have tried and failed at all of these diets know there is no simple answer. Fat, sugar and carbohydrates in processed foods may very well be culprits in the world’s obesity problem. But there is tremendous variation in an individual’s response.
For me, understanding the science of weight loss has helped make sense of my own struggles to lose weight, as well as my mother’s endless cycle of dieting, weight gain and despair. I wish she were still here so I could persuade her to finally forgive herself for her dieting failures. While I do, ultimately, blame myself for allowing my weight to get out of control, it has been liberating to learn that there are factors other than my character at work when it comes to gaining and losing weight. And even though all the evidence suggests that it’s going to be very, very difficult for me to reduce my weight permanently, I’m surprisingly optimistic. I may not be ready to fight the battle this month or even this year. But at least I know what I’m up against.
Linked from 5/3/2013 Journal