We’re getting fatter. An intelligent understanding of personality can help us to understand why we eat what we eat, and what we can do about it.

Openness

For a start, openness to experience has been negatively linked to BMI — that is, being open can help keep you slim. There are probably two reasons for this.

First, these types of people are more open-minded when it comes to eating and so they eat a wider variety of foods. A study of almost 2,000 Estonians found that open people were less likely to eat a traditional diet (e.g. meat, potatoes, bread) and more likely to eat a healthy diet (e.g. fresh fruit and vegetables, cereals, fish).

Similarly, the same researcher found that open Scots were more likely to eat a Mediterranean-style diet (e.g. pasta, oil, vinegar, poultry) and less likely to eat a convenience diet (e.g. canned vegetables, meat pies, sausage rolls).

Other papers have found openness to experience to predict consumption of healthy foodstuffs like fruit and vegetables, and nuts, red wine and fiber.

The second reason may be that open people, being more intellectually curious, are more cognizant of what they eat. Indeed, openness has been related to higher levels of cognitively restrained eating and to healthy eating beyond just a varied diet, such as avoiding foods flavored with fats. In fact, one paper found that openness was the most consistent predictor of healthy eating behaviors.

Conscientiousness

Perhaps the next most consistent predictor of healthy eating is conscientiousness. This trait has always had a strong relationship with health — it is, for instance, a consistent negative predictor of mortality — and it’s no surprise that it is related to diet, too.

In a meta-analysis of several large-scale longitudinal studies, conscientiousness was found to be the only significant predictor of obesity, with conscientious people being at lower risk and having a higher chance of reverting to non-obesity. Similarly, another paper found that conscientiousness was the only trait to significantly predict BMI (negatively). Several other papers have linked the trait to health indices such as waist size and triglycerides.

In terms of eating, conscientiousness has been associated with a diet high in fruit and fiber and low in fat and salt; increased intake of fruit and vegetables; an avoidance of fats and the tendency to swap high-fat foods for low-fat foods; a lower propensity toward binge eating; and reduced alcohol consumption.

These findings are ostensibly explained by the higher-order cognitive functions associated with conscientiousness. Conscientious people are better able to plan their diet and refrain from indulgence. As an example, the trait has been found to predict cognitive dietary restraint.

Extroversion

Third, the literature suggests that extroversion is a liability when it comes to healthy eating. For example, the trait is associated with higher BMI. One longitudinal study found that weight gain over two years was predicted by extroversion alone.

Extroversion is typified by a sensitivity to rewards and an approach-focus, and it is easy to see how indulgent foods play their part here. Brain imaging research has shown that those higher in reward sensitivity exhibit higher activation in their brain’s reward circuitry when shown appetizing, as opposed to bland, food. Meanwhile, reward sensitivity has been related to overeating and weight gain.

It is hardly surprising, therefore, that extroverts are less likely to avoid meat fats (e.g. burgers, steaks), that extroverts like sweet foods and that extroversion correlates with increased alcohol consumption.

However, these findings are not always consistent, suggesting that extraversion may be a less significant predictor of dietary behaviors than other traits.

On the other hand, one reason for these inconsistent findings may be the interaction between multiple personality traits. In a review of the neuroscience literature on dietary behavior and personality, researchers demonstrate that obesity is related to lower activity in the lateral prefrontal regions, which are associated with self-control (i.e., conscientiousness), higher reactivity of the reward circuitry (i.e. extraversion), and a weaker link between the two.

People with higher reward circuitry benefit from the moderating role of the prefrontal regions. In other words, extroverts may be able to resist unhealthy dietary behaviors when they have high levels of conscientiousness.

In support of this, one study found that low conscientious individuals reported more snacking between meals during a stressful period than during a non-stressful period, and another study found that emotional eating was linked to lower conscientiousness.

Agreeableness

The relationship between agreeableness and healthy eating is perhaps the least pronounced. However, it is significant. Low agreeableness has indeed been linked to a higher BMI in midlife and to a greater increase in BMI across the lifespan.

The reason for this is likely to be that agreeable people are more likely to “stick to the rules” when it comes to their diet. For example, agreeableness has been correlated positively with vegetable consumption among teenagers, negatively with alcohol consumption, and positively with a diet high in fruit and fiber and low in fat and salt. Agreeable people, being warm and kind, also have more positive attitudes toward healthy diets.

While some researchers found a correlation between agreeableness and obesity, the authors suggested that this may simply be because agreeable people are more honest in their self-reporting. However, in the aforementioned Scottish study, agreeableness did in fact correlate with the convenience diet (e.g. sausage rolls, meat pies, etc.). It’s feasible that agreeable people are more susceptible to unhealthy foods when they are socially expected.

Neuroticism

Those higher on neuroticism have been found to have higher BMI in a number of studies, and they suffer from diet-related health problems such as metabolic syndrome.

The explanation for this can be found in emotional eating, which has been linked to neuroticism. Emotional eating has its roots in psychosomatic theory — that is, people eat in response to negative emotions such as anxiety, in order to reduce these feelings and instead induce feelings of comfort and safety.

So, because neurotic people are more likely to feel negative emotions, they feel a stronger urge to comfort-eat. No wonder that people high in neuroticism consume more sugar and fats, eat less fruit, keep eating after they are full, binge eat and find it hard to avoid food flavored with fat (e.g. butter, cream).

Interestingly, Schaefer, Knuth & Rumpel (2011) report that theirs is the only fMRI study to have found neuroticism to be positively correlated with activity in the brain’s reward circuits. The stimuli used in the research were chocolate bars; the authors suggest that these are more rewarding for neurotic people since they use them as comfort foods.

However, neuroticism has also been associated with unhealthy eating on the other end of the spectrum. Studies have found high levels of the trait among those classified as underweight and those with eating disorders such as anorexia. The likely explanation is that neurotic people have lower self-esteem and feel greater pressure to refrain from eating. Indeed, several studies have correlated neuroticism with restrained eating.

What to Do?

So how can we use this information to shed a few pounds and fit into our bikinis — or mankinis? Although personality traits are largely stable over a lifetime, there are some short-term fixes. For example, introducing some conscientiousness by eating in a tidier room has been found to make people 47 percent more likely to choose an apple, over some chocolate, for a snack.

Beyond the role of personality, Brian Wansink’s Mindless Eating identifies a number of fascinating nudges which can help us eat less. For example, we eat less food off of red plates, we eat less food from smaller containers, and we eat less food when there is less variety to it (e.g. fewer flavors).