Why You Can’t Lose Weight on a Diet
The problem isn’t willpower. It’s neuroscience.
You can’t — and shouldn’t — fight back.
SIX years after dropping an average of 129 pounds on the TV program “The Biggest Loser,” a new study reports, the participants were burning about 500 fewer calories a day than other people their age and size. This helps explain why they had regained 70 percent of their lost weight since the show’s finale. The diet industry reacted defensively, arguing that the participants had lost weight too fast or ate the wrong kinds of food — that diets do work, if you pick the right one.
But this study is just the latest example of research showing that in the long run dieting is rarely effective, doesn’t reliably improve health and does more harm than good. There is a better way to eat.
The root of the problem is not willpower but neuroscience. Metabolic suppression is one of several powerful tools that the brain uses to keep the body within a certain weight range, called the set point. The range, which varies from person to person, is determined by genes and life experience. When dieters’ weight drops below it, they not only burn fewer calories but also produce more hunger-inducing hormones and find eating more rewarding.
The brain’s weight-regulation system considers your set point to be the correct weight for you, whether or not your doctor agrees. If someone starts at 120 pounds and drops to 80, her brain rightfully declares a starvation state of emergency, using every method available to get that weight back up to normal. The same thing happens to someone who starts at 300 pounds and diets down to 200, as the “Biggest Loser” participants discovered.
This coordinated brain response is a major reason that dieters find weight loss so hard to achieve and maintain. For example, men with severe obesity have only one chance in 1,290 of reaching the normal weight range within a year; severely obese women have one chance in 677. A vast majority of those who beat the odds are likely to end up gaining the weight back over the next five years. In private, even the diet industry agrees that weight loss is rarely sustained. A report for members of the industry stated: “In 2002, 231 million Europeans attempted some form of diet. Of these only 1 percent will achieve permanent weight loss.”
The specific “Biggest Loser” diet plan is probably not to blame. A previous study found similar metabolic suppression in people who had lost weight and kept it off for up to six years. Whether weight is lost slowly or quickly has no effect on later regain. Likewise — despite endless debate about the relative value of different approaches — in head-to-head comparisons, diet plans that provide the same calories through different types of food lead to similar weight loss and regain.
As a neuroscientist, I’ve read hundreds of studies on the brain’s ability to fight weight loss. I also know about it from experience. For three decades, starting at age 13, I lost and regained the same 10 or 15 pounds almost every year. On my most serious diet, in my late 20s, I got down to 125 pounds, 30 pounds below my normal weight. I wanted (unwisely) to lose more, but I got stuck. After several months of eating fewer than 800 calories a day and spending an hour at the gym every morning, I hadn’t lost another ounce. When I gave up on losing and switched my goal to maintaining that weight, I started gaining instead.
I was lucky to end up back at my starting weight instead of above it. After about five years, 41 percent of dieters gain back more weight than they lost. Long-term studies show dieters are more likely than non-dieters to become obese over the next one to 15 years. That’s true in men and women, across ethnic groups, from childhood through middle age. The effect is strongest in those who started in the normal weight range, a group that includes almost half of the female dieters in the United States.
Some experts argue that instead of dieting leading to long-term weight gain, the relationship goes in the other direction: People who are genetically prone to gain weight are more likely to diet. To test this idea, in a 2012 study, researchers followed over 4,000 twins aged 16 to 25. Dieters were more likely to gain weight than their non-dieting identical twins, suggesting that dieting does indeed increase weight gain even after accounting for genetic background. The difference in weight gain was even larger between fraternal twins, so dieters may also have a higher genetic tendency to gain. The study found that a single diet increased the odds of becoming overweight by a factor of two in men and three in women. Women who had gone on two or more diets during the study were five times as likely to become overweight.
The causal relationship between diets and weight gain can also be tested by studying people with an external motivation to lose weight. Boxers and wrestlers who diet to qualify for their weight classes presumably have no particular genetic predisposition toward obesity. Yet a 2006 study found that elite athletes who competed for Finland in such weight-conscious sports were three times more likely to be obese by age 60 than their peers who competed in other sports.
To test this idea rigorously, researchers could randomly assign people to worry about their weight, but that is hard to do. One program took the opposite approach, though, helping teenage girls who were unhappy with their bodies to become less concerned about their weight. In a randomized trial, the eBody Project, an online program to fight eating disorders by reducing girls’ desire to be thin, led to less dieting and also prevented future weight gain. Girls who participated in the program saw their weight remain stable over the next two years, while their peers without the intervention gained a few pounds.
WHY would dieting lead to weight gain? First, dieting is stressful. Calorie restriction produces stress hormones, which act on fat cells to increase the amount of abdominal fat. Such fat is associated with medical problems like diabetes and heart disease, regardless of overall weight.
Second, weight anxiety and dieting predict later binge eating, as well as weight gain. Girls who labeled themselves as dieters in early adolescence were three times more likely to become overweight over the next four years. Another study found that adolescent girls who dieted frequently were 12 times more likely than non-dieters to binge two years later.
My repeated dieting eventually caught up with me, as this research would predict. When I was in graduate school and under a lot of stress, I started binge eating. I would finish a carton of ice cream or a box of saltines with butter, usually at 3 a.m. The urge to keep eating was intense, even after I had made myself sick. Fortunately, when the stress eased, I was able to stop. At the time, I felt terrible about being out of control, but now I know that binge eating is a common mammalian response to starvation.
Much of what we understand about weight regulation comes from studies of rodents, whose eating habits resemble ours. Mice and rats enjoy the same wide range of foods that we do. When tasty food is plentiful, individual rodents gain different amounts of weight, and the genes that influence weight in people have similar effects in mice. Under stress, rodents eat more sweet and fatty foods. Like us, both laboratory and wild rodents have become fatter over the past few decades.
In the laboratory, rodents learn to binge when deprivation alternates with tasty food — a situation familiar to many dieters. Rats develop binge eating after several weeks consisting of five days of food restriction followed by two days of free access to Oreos. Four days later, a brief stressor leads them to eat almost twice as many Oreos as animals that received the stressor but did not have their diets restricted. A small taste of Oreos can induce deprived animals to binge on regular chow, if nothing else is available. Repeated food deprivation changes dopamine and other neurotransmitters in the brain that govern how animals respond to rewards, which increases their motivation to seek out and eat food. This may explain why the animals binge, especially as these brain changes can last long after the diet is over.
In people, dieting also reduces the influence of the brain’s weight-regulation system by teaching us to rely on rules rather than hunger to control eating. People who eat this way become more vulnerable to external cues telling them what to eat. In the modern environment, many of those cues were invented by marketers to make us eat more, like advertising, supersizing and the all-you-can-eat buffet. Studies show that long-term dieters are more likely to eat for emotional reasons or simply because food is available. When dieters who have long ignored their hunger finally exhaust their willpower, they tend to overeat for all these reasons, leading to weight gain.
Even people who understand the difficulty of long-term weight loss often turn to dieting because they are worried about health problems associated with obesity like heart disease and diabetes. But our culture’s view of obesity as uniquely deadly is mistaken. Low fitness, smoking, high blood pressure, low income and loneliness are all better predictors of early death than obesity. Exercise is especially important: Data from a 2009 study showed that low fitness is responsible for 16 percent to 17 percent of deaths in the United States, while obesity accounts for only 2 percent to 3 percent, once fitness is factored out. Exercise reduces abdominal fat and improves health, even without weight loss. This suggests that overweight people should focus more on exercising than on calorie restriction.
In addition, the evidence that dieting improves people’s health is surprisingly poor. Part of the problem is that no one knows how to get more than a small fraction of people to sustain weight loss for years. The few studies that overcame that hurdle are not encouraging. In a 2013 study of obese and overweight people with diabetes, on average the dieters maintained a 6 percent weight loss for over nine years, but the dieters had a similar number of heart attacks, strokes and deaths from heart disease during that time as the control group. Earlier this year, researchers found that intentional weight loss had no effect on mortality in overweight diabetics followed for 19 years.
Diets often do improve cholesterol, blood sugar and other health markers in the short term, but these gains may result from changes in behavior like exercising and eating more vegetables. Obese people who exercise, eat enough vegetables and don’t smoke are no more likely to die young than normal-weight people with the same habits. A 2013 meta-analysis (which combines the results of multiple studies) found that health improvements in dieters have no relationship to the amount of weight they lose.
If dieting doesn’t work, what should we do instead? I recommend mindful eating — paying attention to signals of hunger and fullness, without judgment, to relearn how to eat only as much as the brain’s weight-regulation system commands.
Relative to chronic dieters, people who eat when they’re hungry and stop when they’re full are less likely to become overweight, maintain more stable weights over time and spend less time thinking about food. Mindful eating also helps people with eating disorders like binge eating learn to eat normally. Depending on the individual’s set point, mindful eating may reduce weight or it may not. Either way, it’s a powerful tool to maintain weight stability, without deprivation.
I finally gave up dieting six years ago, and I’m much happier. I redirected the energy I used to spend on dieting to establishing daily habits of exercise and meditation. I also enjoy food more while worrying about it less, now that it no longer comes with a side order of shame.
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