Losing weight has never been an easy endeavor, as anyone who has ever tried knows. Among the challenges: changing ingrained habits that led to the weight gain. Everyone attributes his or her success to different strategies and programs, be it Weight Watchers, gastric bypass surgery or sheer willpower, but all tend to agree that eating less and moving more are at the heart of any successful effort.

But what makes one person able to put that simple formula into action, whereas another fails in the attempt? Only about one fifth of people who lose at least 10 percent of their weight keep it off for at least a year, according to a 2005 study in the American Journal of Clinical Nutrition. Of course, numerous biological factors play a role in weight loss, including the size of your body, its muscle and fat content, and your metabolic rate. In recent years psychologists have begun looking at personality traits as critical variables in the dieting equation.

Personality is important because it shapes our behavior. In fact, your personality may well be the strongest predictor of how likely you are to shed pounds, says psychiatrist C. Robert Cloninger of the Washington University School of Medicine in St. Louis. Personality traits affect your motivation to reduce portion sizes, to avoid fatty foods, to exercise, and the like. In particular, research suggests that your tendency toward optimism, neuroticism and novelty seeking has a big influence on your ability to slim down. “[Personality] does not act alone, but it is a moderator of people’s motivations and attitudes toward what and how much they eat and how much they exercise,” Cloninger says. And although you cannot completely alter your character, you can temper certain aspects of it and sidestep traits that get in the way of weight loss.

The Pollyanna Pitfall
Research into personality and weight loss is relatively new. In 1995 Cloninger became one of the first to study the effect of personality on lifestyle choices. Although some studies have not shown a strong connection between specific personality traits and weight loss—pointing instead to a person’s resolve to lose weight and expectation of success—more recent studies are suggesting that some personal qualities do play an outsize role.

Character traits often considered detrimental for mental well-being may actually improve a person’s chances of losing weight—and some otherwise positive traits can make dieting an uphill battle. In work published in 2007 clinical psychologist Hitomi Saito of Doshisha University in Japan and her colleagues gave personality assessments to participants starting a weight-loss program at the university, measuring their weight before and after six months. They found two personality traits, in particular, to be strongly associated with weight loss (albeit in opposite ways): neuroticism and agreeableness. The participants who were the most neurotic and the least agreeable lost more weight than those who scored lower on neuroticism and higher on agreeableness. The more neurotic you are, the researchers reasoned, the more you may worry about your health and the more willing you are to make sacrifices to meet that goal. And the less agreeable you are, the less likely you may be to give in to social pressures to eat, even if you have to hurt Mom’s feelings by saying no to her apple pie.

More recently, Saito and her colleagues have learned that another positive personality trait—optimism—can similarly impede efforts to lose. In a study published in 2009 the team examined the psychological characteristics of 101 obese patients in a six-month weight-loss program at the center’s obesity clinic to identify the traits that encourage people to adopt healthier eating habits and exercise more. They also wanted to see how psychological counseling, offered as part of the program, altered some of these characteristics.

The researchers found that people who scored high on optimism were less likely to slim down. Being overly optimistic, it appears, may cause you to underestimate your risk for developing a serious disease such as diabetes and make you more likely to assume that you will be okay regardless of your actions. “Being too optimistic could harm weight-loss efforts because patients become careless about their disease,” Saito says. That attitude, she adds, “may prevent them from controlling their behavior.” In other words, if someone is too optimistic, he or she may be more apt to grab that extra doughnut or skip the morning walk, thinking everything will work out just fine anyway.

Those who lost the most weight also scored high on a psychological “ego” state characterized by skill at self-monitoring. People who are adept at self-monitoring have a penchant for gathering facts, considering alternatives and being objective. Such individuals are more likely to collect information about portion sizes and calories and to use those data to select healthy meals. They may also be more apt to create a realistic exercise schedule and stick to it. Performing these activities—and watching the pounds come off—will in turn boost that individual’s confidence in his or her ability to achieve a healthy way of life.

Novel Solutions
Like optimism, a need for novelty and adventure may also be incompatible with successfully slipping into those skinny jeans. In a study published in 2006 Cloninger and his colleagues gave a standard personality questionnaire to 264 lean and 56 obese individuals living in St. Louis, along with 183 obese patients in the university’s weight-loss program, which included weekly group behavioral therapy and diet education sessions. The questionnaire measured seven basic traits: novelty seeking, harm avoidance, reward dependence (bias toward and sensitivity to social rewards for behavior), persistence, self-directedness, cooperativeness and self-transcendence (the ability to reach beyond yourself to find meaning in life experiences).

The researchers found that obese people in the community were more likely to score high on novelty seeking—a trait associated with being quick-tempered and impulsive—than the lean folks were, a result that jibes with other work suggesting that novelty seekers are more likely to be overweight. In fact, Cloninger says, novelty seeking is correlated with body mass index (BMI) in the general population: the higher a person’s BMI, the higher that person tends to score on the trait.

Cloninger’s team also tied novelty seeking to pounds lost. Obese patients in the weight-loss program who dropped more than 10 percent of their weight in 22 weeks were less likely to score high on novelty seeking than those in the program whose weight fell less than 5 percent. Apparently the novelty seekers among us value exploration more than the comfort of familiar habits and the rules that often accompany a weight-loss regimen. Exploring often requires letting go of inhibitions and fears, the kind of temperament that can trip up dieters. “Novelty seeking involves the pursuit of sensual gratification,” Cloninger says. “People who are high in novelty seeking give in to their cravings and appetites, so novelty seeking is increased in people who are impulsive, substance abusers, bingers or obese.”

Does this mean that novelty seekers inclined to joyful optimism are doomed to remaining overweight? Not at all, Saito says. In fact, some optimism may even be helpful if it is offset by the right traits. If you tend to look on the bright side but can still remain realistic and self-aware, then you can make behavioral changes that lead to weight loss. Being so optimistic that you ignore reality, however, may make you less inclined to adopt the necessary habits.

Although altering your personality might be a difficult weight-loss strategy, you can tailor your diet to your personality type, minimizing the effects of detrimental traits. If you hunt for what is new, for instance, look for different ways to exercise. “People who are high on novelty seeking like to be active, so exercise can be a good way to increase awareness of one’s body and burn calories at the same time,” Cloninger advises. Novelty seekers should also train themselves to eat slowly. Learning to savor the taste, texture and smell of food is more likely to appeal to the person who enjoys sensual gratification.

In some cases, personality changes might be worth trying to make. To rein in impulsiveness, for example, try becoming more self-aware as you go about your day. Meditate, write in a journal, or simply reflect on what is most important and satisfying to you. Adopting a calm and thoughtful mind-set enables you to make more considered decisions and helps buffer you from external temptations such as commercials for food. Making this kind of psychological change might, in fact, be one of the most successful strategies not just for achieving short-term weight loss but also for staying slim and fit over the long haul.