Human food selection and its relation to the global obesity epidemic is a complex, multifaceted problem. As Nettle et al. discuss, this complicated public health challenge requires multiple explanations. The authors present a compelling case for food insecurity as a contributor to weight gain and increases in obesity, but note the need for specification as to how this mechanism operates. Here, I argue that a variety of unconscious psychological mechanisms either underlie the relation between food insecurity and weight gain or co-occur as an independent contributor to obesity, in addition to the authors’ model. A growing body of research in social and developmental psychology highlights that people's explicit preferences do not always match up with their implicit associations – attitudes that people may not even realize they hold (Greenwald & Banaji Reference Greenwald and Banaji1995). In the strongest case, such attitudes even reflect stereotypes with which a person actively disagrees. For example, even those who explicitly endorse egalitarian views and believe that people from all backgrounds are equally American implicitly endorse connections between social group membership and national identity (i.e., “American = White?” by Devos & Banaji Reference Devos and Banaji2005). These associations are importantly related to behavior, including discrimination in hiring, heath care, and judicial decisions (Chapman et al. Reference Chapman, Kaatz and Carnes2013; McConnell & Leibold Reference McConnell and Leibold2001; Rachlinski et al. Reference Rachlinski, Johnson, Wistrich and Guthrie2009; Rudman & Glick Reference Rudman and Glick2001). Similarly, a variety of implicit processes may underlie human eating behavior or illuminate why food insecurity and weight gain are related. Just as implicit social attitudes may differ from people's explicit beliefs about social groups and stereotypes, conscious food-related goals or preferences may bear little resemblance to the unconscious mechanisms that influence what and how much people eat and the relation between food intake and weight gain.

For instance, living in chronically stressful environments alters regulation of the hypothalamic-pituitary-adrenal (HPA) axis. In turn, hormonal shifts are related to changes in appetite, preferences for comfort foods, and changes in metabolism that can contribute to weight gain (Knutson et al. Reference Knutson, Spiegel, Penev and Van Cauter2007; Lumeng et al. Reference Lumeng, Miller, Peterson, Kaciroti, Sturza, Rosenblum and Vazquez2014). These findings point to a complex biobehavioral network that affects not only what people choose to eat (e.g., a comforting food at the end of a stressful day), but also how the body processes those foods and signals the need to eat again by altering the balancing of appetite-inhibiting and appetite-signaling hormones. Chronically stressful environments, which are replete with psychosocial stress, are often also characterized by food insecurity. Therefore, weight gain in food-insecure environments may actually represent a complex network of stress-related reactions, in which food insecurity is just one symptom of a broader environment of stress. Additionally, some foods – specifically those that would contribute to weight gain and are readily available in high-income countries – may have addictive properties. In studies of rats, overconsumption of palatable high-fat foods triggered addiction-like behaviors and neural responses, and was not disrupted by conditioned electric shocks (Johnson & Kenny Reference Johnson and Kenny2010). Foods that are similarly high in fat, sugar, and salt are readily available to humans, who demonstrate patterns of neural response to these food cues that are similar to neural circuitry observed in drug addiction (Gearhardt et al. Reference Gearhardt, Grilo, DiLeone, Brownell and Potenza2011). In addition to an instinct to increase consumption when faced with food insecurity, the propensity to eat foods that contribute to weight gain is very difficult to overcome.

In addition to these biobehavioral pathways, eating is a highly social experience (Liberman et al. Reference Liberman, Woodward, Sullivan and Kinzler2016; Rozin Reference Rozin2005; Shutts et al. Reference Shutts, Kinzler and DeJesus2013). From an early age, food consumption and preferences are influenced by social input. Children eat more of foods that are labeled with socially relevant symbols, including familiar brands and characters (Roberto et al. Reference Roberto, Baik, Harris and Brownell2010; Robinson et al. Reference Robinson, Borzekowski, Matheson and Kraemer2007). From infancy through adulthood, people eat more when surrounded by other people or when receiving positive social feedback from caregivers (Lumeng & Hillman Reference Lumeng and Hillman2007; Lumeng et al. Reference Lumeng, Patil and Blass2007; Salvy et al. Reference Salvy, Jarrin, Paluch, Irfan and Pliner2007; Reference Salvy, De La Haye, Bowker and Hermans2012). Additionally, social modeling influences food selection across the life span, as people tend to prefer the foods their peers and social in-group members eat (Birch Reference Birch1980; Cruwys et al. Reference Cruwys, Bevelander and Hermans2015; Frazier et al. Reference Frazier, Gelman, Kaciroti, Russell and Lumeng2012; Hendy & Raudenbush Reference Hendy and Raudenbush2000; Shutts et al. Reference Shutts, Kinzler, McKee and Spelke2009; Reference Shutts, Banaji and Spelke2010). These contextual influences may unconsciously guide adults and children toward particular food choices, including eating more food than they would otherwise or selecting foods that contribute to weight gain, for reasons beyond their own preferences or goals.

The social and biobehavioral pathways outlined here suggest that unconscious psychological mechanisms alter human eating behavior, as well as the body's response to food in the absence of any changes in food intake. Food insecurity is an important indicator that an individual lives in a stressful environment. Along with social influences on food selection, these environments play an important role in food selection, weight gain, and the development of obesity. Finally, implicit in many studies of obesity is that individuals are to blame for their outcomes. When Nettle et al. use phrases such as “decision-making mechanisms” (e.g., sect. 1, para. 1) to describe human eating behavior, this language implies that their model characterizes a deliberate, conscious process. Obesity is highly stigmatized – obese and overweight individuals face discrimination and negative social consequences (Carr & Friedman Reference Carr and Friedman2005; Puhl & Brownell Reference Puhl and Brownell2001; Schwartz et al. Reference Schwartz, Chambliss, Brownell, Blair and Billington2003). In the case of childhood obesity, practice guidelines imply that parents are to blame not only for not adequately encouraging their children to eat healthy foods and avoid unhealthy foods, but also for improperly restricting their children's eating and pressuring their children to eat (Barlow Reference Barlow2007; Pesch et al. Reference Pesch, Appugliese, Kaciroti, Rosenblum, Miller and Lumeng2016). These issues highlight that people are often blamed for their own weight gain or their children's weight gain, despite the myriad unconscious processes that influence eating behavior and the body's response to food. To productively understand the development of obesity and effective prevention strategies, considering both conscious decisions and underlying psychological mechanisms is critical.