The work of Nettle et al. on the drivers of obesity impressively integrates theory and data from multiple disciplines, including behavioral ecology, evolutionary biology, and differential psychology. It addresses a pressing public health issue, as the prevalence of obesity is rising worldwide (Ng et al. Reference Ng, Fleming, Robinson, Thomson, Graetz, Margono, Mullany, Biryukov, Abbafati, Abera, Abraham, Abu-Rmeileh, Achoki, AlBuhairan, Alemu, Alfonso, Ali, Ali, Guzman, Ammar, Anwari, Banerjee, Barquera, Basu, Bennett, Bhutta, Blore, Cabral, Nonato, Chang, Chowdhury, Courville, Criqui, Cundiff, Dabhadkar, Dandona, Davis, Dayama, Dharmaratne, Ding, Durrani, Esteghamati, Farzadfar, Fay, Feigin, Flaxman, Forouzanfar, Goto, Green, Gupta, Hafezi-Nejad, Hankey, Harewood, Havmoeller, Hay, Hernandez, Husseini, Idrisov, Ikeda, Islami, Jahangir, Jassal, Jee, Jeffreys, Jonas, Kabagambe, Khalifa, Kengne, Khader, Khang, Kim, Kimokoti, Kinge, Kokubo, Kosen, Kwan, Lai, Leinsalu, Li, Liang, Liu, Logroscino, Lotufo, Lu, Ma, Mainoo, Mensah, Merriman, Mokdad, Moschandreas, Naghavi, Naheed, Nand, Narayan, Nelson, Neuhouser, Nisar, Ohkubo, Oti, Pedroza, Prabhakaran, Roy, Sampson, Seo, Sepanlou, Shibuya, Shiri, Shiue, Singh, Singh, Skirbekk, Stapelberg, Sturua, Sykes, Tobias, Tran, Trasande, Toyoshima, van de Vijver, Vasankari, Veerman, Velasquez-Melendez, Vlassov, Vollset, Vos, Wang, Wang, Weiderpass, Werdecker, Wright, Yang, Yatsuya, Yoon, Yoon, Zhao, Zhou, Zhu, Lopez, Murray and Gakidou2014). However, we think that Nettle et al.’s presentation of psychological theories of obesity is somewhat incomplete and that the explanation of the observed pattern of effects may benefit from a closer integration of current research on self-regulation and self-control.

For many people, restricting food intake represents a typical self-control dilemma. For example, a dieter might feel tempted to eat a delicious dessert although she is trying to lose weight. Thus, the dieter is torn between two motives (Fujita Reference Fujita2011): one that presses for a smaller, more concrete, and proximal reward (i.e., eating the dessert now), and the other that presses for a larger, more abstract, and remote reward (i.e., losing weight). Several studies have shown that conditions of uncertainty are highly relevant for self-control dilemmas such as the one described above, because uncertainty exacerbates temporal discounting – the tendency to prefer smaller immediate over larger delayed rewards (Kidd et al. Reference Kidd, Palmeri and Aslin2013; Mischel Reference Mischel1961; Mischel & Grusec Reference Mischel and Grusec1967). In fact, it has been argued that this decreased motivation for long-term rewards under conditions of uncertainty can be highly adaptive (De Ridder & De Wit Reference De Ridder, De Wit, De Ridder and De Wit2006; Mischel Reference Mischel2014).

In addition to this motivational explanation of why people sometimes prefer immediate rewards over larger delayed rewards, there can also be situations in which people lack the ability to inhibit impulses (Hofmann et al. Reference Hofmann, Friese and Wiers2008). For example, Friese et al. (Reference Friese, Hofmann and Wänke2008) have demonstrated that impulsive influences on eating behavior are particularly increased when cognitive load (i.e., the amount of mental effort being used in the working memory) is high. In a similar vein, cognitive load has been demonstrated to disinhibit dieters’ eating behavior (Ward & Mann Reference Ward and Mann2000) and to promote unhealthy choices (Shiv & Fedorikhin Reference Shiv and Fedorikhin2002). Thus, high cognitive load may undermine people's control capacities such that impulses that are normally held in check “break through” and have an increased impact on eating and drinking behavior (Hofmann et al. Reference Hofmann, Friese and Wiers2008; Wiers et al. Reference Wiers, Ames, Hofmann, Krank and Stacy2010).

Importantly, cognitive load is often chronically high among people with scarce resources, and the cognitive load caused by poverty might directly explain its connection to unhealthy impulsive behaviors (Mani et al. Reference Mani, Mullainathan, Shafir and Zhao2013; Shah et al. Reference Shah, Mullainathan and Shafir2012; Vohs Reference Vohs2013). By experimentally inducing concerns about financial decisions in a series of four laboratory experiments, Mani et al. (Reference Mani, Mullainathan, Shafir and Zhao2013) found that thinking about financial challenges reduces cognitive performance among poor but not among rich participants. In a similar vein, a field study by the same authors among Indian sugarcane farmers demonstrated diminished cognitive function of farmers in times of poverty (pre-harvest) compared to times of wealth (post-harvest). These results suggests that poverty (as well as other forms of scarcity) can cause cognitive costs, and poverty's cognitive burden – in terms of reducing available processing resources – takes a heavy mental toll on behavioral regulation (Vohs Reference Vohs2013).

The psychology of self-control, together with insights from the psychology of scarcity, may also explain why the food insecurity–obesity link is stronger for women in high-income countries as demonstrated by Nettle et al.: Globally, women suffer a greater burden of poverty than do men (Gornick & Boeri Reference Gornick, Boeri, Brady and Burton2016; Pearce Reference Pearce1978). As a consequence, they also suffer a greater cognitive burden, which may undermine their control capacities for impulsive influences on eating behavior. Moreover, many high-income countries are characterized by the ubiquity of cheap, energy-dense foods (Drewnowski & Specter Reference Drewnowski and Specter2004; French et al. Reference French, Story and Jeffery2001; Hill & Peters Reference Hill and Peters1998; Hill et al. Reference Hill, Wyatt, Reed and Peters2003; Rao et al. Reference Rao, Afshin, Singh and Mozaffarian2013), and the relationship between the energy density and the energy cost of foods is often inverse, implying that healthier foods and diets are more expensive than less healthy options (Drewnowski & Specter Reference Drewnowski and Specter2004; Rao et al. Reference Rao, Afshin, Singh and Mozaffarian2013). The high availability and low costs of energy-dense foods, combined with the cognitive burden that poverty imposes on many people (especially women), may thus account for the observed pattern of increased energy intake. It is noteworthy that questionnaires on food insecurity (Kendall et al. Reference Kendall, Olson and Frongillo1995; Nord et al. Reference Nord, Andrews and Carlson2009; Radimer et al. Reference Radimer, Olson, Greene, Campbell and Habicht1992) used in Nettle et al.’s meta-analysis seem to tap into these cognitive aspects (e.g., worry) of insufficient food supply, which explains why the inclusion of income or socioeconomic position does not change the results of their analysis.

Finally, we believe that the current methods for testing the food insurance hypothesis are limited. We agree that more longitudinal evidence is necessary to test whether changes in food insecurity lead to changes in body weight, as suggested by Nettle et al. Future research on food insecurity and human obesity would, however, also profit from more rigorous experimental tests of the underlying processes (e.g., cognitive load) of the food insecurity–obesity link. As in studies testing the basics tenets of self-control (e.g., Friese et al. Reference Friese, Hofmann and Wänke2008) and research on scarcity and cognitive functioning (e.g., Mani et al. Reference Mani, Mullainathan, Shafir and Zhao2013), controlled laboratory experiments and field studies are needed to test whether food insecurity is causally related to overconsumption and, eventually, obesity.