In the target article, Nettle et al. integrate different domains of research from epidemiology, animal studies, and human psychology to explain eating behavior in humans. We are especially intrigued by the speculations the authors make about the implications of the insurance hypothesis for understanding the etiology of eating disorders, particularly anorexia nervosa. Here, we wish to highlight research from the field of body representations, which we believe has interesting connections with, and implications for, the insurance hypothesis.
Given that it forms the core of the insurance hypothesis, Nettle et al. appropriately focus on the role of food insecurity in shaping eating behavior. However, their model includes one other important variable, which receives less attention, namely, the current fat reserves of the organism. Consider two scenarios. In the first scenario, the probability of finding food equals 0.5, and the organism has substantial current fat reserves (3 units). In the second scenario, the probability of finding food also equals 0.5, but the current reserves are now lower (1 unit). In the model proposed by Nettle et al., these two scenarios would result in a very different eating behavior, even when food insecurity (i.e., the probability of finding food) stayed the same. Thus, to decide whether fat storage is beneficial, an organism must be able not only to predict the food supply, but also to accurately evaluate its current reserves. In other words, to act optimally, the organism needs to know its own body size. It needs a body image.
The distinction between actual levels of fat reserves and the mental representation thereof would be largely academic if body representations were largely veridical. In fact, however, there is substantial evidence for large distortions of body representation in many neurological and psychiatric conditions, most pertinently in the present context in eating disorders such as anorexia (e.g., Bruch Reference Bruch1978; Cash & Deagle Reference Cash and Deagle1997), as well as in obesity (e.g., Powell et al. Reference Powell, de Lemos, Banks, Ayers, Rohatgi, Khera, McGuire, Berry, Albert, Vega, Grundy and Das2010). In the case of anorexia, moreover, body image distortions are a strong predictor of poor prognosis for recovery (Casper et al. Reference Casper, Halmi, Goldberg, Eckert and Davis1979) and of relapse following recovery (Fairburn et al. Reference Fairburn, Peveler, Jones, Hope and Doll1993; Keel et al. Reference Keel, Dorer, Franko, Jackson and Herzog2005).
Recent research has suggested that even healthy people maintain highly distorted body representations (for review, see Longo Reference Longo2017). For example, perceptual abilities such as tactile distance perception (Longo & Haggard Reference Longo and Haggard2011; Taylor-Clarke et al. Reference Taylor-Clarke, Jacobsen and Haggard2004) and position sense (Longo & Haggard Reference Longo and Haggard2010; Longo et al. Reference Longo, Long and Haggard2012) appear to rely on highly distorted representations of body size and shape. Similarly, distortions have also been found in explicit judgments of body part length (Longo & Haggard Reference Longo and Haggard2012) and even in judgments about the spatial configuration of body landmarks (Fuentes et al. Reference Fuentes, Longo and Haggard2013; Longo Reference Longo2015). Further, a clear pattern of body image distortions has been shown in normal-weight adolescent girls, with a tendency to overestimate body width and underestimate body length (Halmi et al. Reference Halmi, Goldberg and Cunningham1977).
Thus, distorted body representations appear to be a normal part of human cognition, as well as being central to serious clinical conditions involving disordered eating. We believe these findings have interesting and important implications for the model proposed by Nettle et al. We speculate that a distorted body image may be an intervening variable mediating the relationship between perceived food scarcity and eating behavior. More specifically, distortions of body image may function to modulate eating behavior: Perceiving oneself as thin may motivate increased consumption, whereas perceiving oneself as fat may discourage consumption.
If both food insecurity and perceived fat reserves (body image) are important contributors to eating behavior, what is the relationship between these two factors? One possibility is that body image and food insecurity are independent of each other, have different causes, and affect eating behavior separately. In this case, body image may modulate the effect of food insecurity influence on fat storage. For example, people who perceive themselves as fat will not eat (or will eat less) even when the food supply is insecure. In the target article, Nettle et al. predict that anorexia occurs when a person's estimate of food security is unusually high, and they propose that introducing food insecurity may promote weight gain in anorexia patients. However, if body image is independent of perceived food insecurity, this proposed treatment may prove inadequate.
Alternatively, body image may be shaped by environmental cues and serve as an intervening variable mediating the relationship between perceived food scarcity and eating behavior. In this case, perceiving the supply of food as secure should lead people to perceive themselves as fat, whereas perceiving the supply of food as scarce should lead people to perceive themselves as thin. In this case, the treatment proposed by Nettle et al. would affect not only eating behavior but also body image. To our knowledge, no research has specifically investigated the relationship between body image and perceived food insecurity. This opens a new possible line of future research and provides a potential way of empirically testing the implications of the insurance hypothesis.
In the target article, Nettle et al. integrate different domains of research from epidemiology, animal studies, and human psychology to explain eating behavior in humans. We are especially intrigued by the speculations the authors make about the implications of the insurance hypothesis for understanding the etiology of eating disorders, particularly anorexia nervosa. Here, we wish to highlight research from the field of body representations, which we believe has interesting connections with, and implications for, the insurance hypothesis.
Given that it forms the core of the insurance hypothesis, Nettle et al. appropriately focus on the role of food insecurity in shaping eating behavior. However, their model includes one other important variable, which receives less attention, namely, the current fat reserves of the organism. Consider two scenarios. In the first scenario, the probability of finding food equals 0.5, and the organism has substantial current fat reserves (3 units). In the second scenario, the probability of finding food also equals 0.5, but the current reserves are now lower (1 unit). In the model proposed by Nettle et al., these two scenarios would result in a very different eating behavior, even when food insecurity (i.e., the probability of finding food) stayed the same. Thus, to decide whether fat storage is beneficial, an organism must be able not only to predict the food supply, but also to accurately evaluate its current reserves. In other words, to act optimally, the organism needs to know its own body size. It needs a body image.
The distinction between actual levels of fat reserves and the mental representation thereof would be largely academic if body representations were largely veridical. In fact, however, there is substantial evidence for large distortions of body representation in many neurological and psychiatric conditions, most pertinently in the present context in eating disorders such as anorexia (e.g., Bruch Reference Bruch1978; Cash & Deagle Reference Cash and Deagle1997), as well as in obesity (e.g., Powell et al. Reference Powell, de Lemos, Banks, Ayers, Rohatgi, Khera, McGuire, Berry, Albert, Vega, Grundy and Das2010). In the case of anorexia, moreover, body image distortions are a strong predictor of poor prognosis for recovery (Casper et al. Reference Casper, Halmi, Goldberg, Eckert and Davis1979) and of relapse following recovery (Fairburn et al. Reference Fairburn, Peveler, Jones, Hope and Doll1993; Keel et al. Reference Keel, Dorer, Franko, Jackson and Herzog2005).
Recent research has suggested that even healthy people maintain highly distorted body representations (for review, see Longo Reference Longo2017). For example, perceptual abilities such as tactile distance perception (Longo & Haggard Reference Longo and Haggard2011; Taylor-Clarke et al. Reference Taylor-Clarke, Jacobsen and Haggard2004) and position sense (Longo & Haggard Reference Longo and Haggard2010; Longo et al. Reference Longo, Long and Haggard2012) appear to rely on highly distorted representations of body size and shape. Similarly, distortions have also been found in explicit judgments of body part length (Longo & Haggard Reference Longo and Haggard2012) and even in judgments about the spatial configuration of body landmarks (Fuentes et al. Reference Fuentes, Longo and Haggard2013; Longo Reference Longo2015). Further, a clear pattern of body image distortions has been shown in normal-weight adolescent girls, with a tendency to overestimate body width and underestimate body length (Halmi et al. Reference Halmi, Goldberg and Cunningham1977).
Thus, distorted body representations appear to be a normal part of human cognition, as well as being central to serious clinical conditions involving disordered eating. We believe these findings have interesting and important implications for the model proposed by Nettle et al. We speculate that a distorted body image may be an intervening variable mediating the relationship between perceived food scarcity and eating behavior. More specifically, distortions of body image may function to modulate eating behavior: Perceiving oneself as thin may motivate increased consumption, whereas perceiving oneself as fat may discourage consumption.
If both food insecurity and perceived fat reserves (body image) are important contributors to eating behavior, what is the relationship between these two factors? One possibility is that body image and food insecurity are independent of each other, have different causes, and affect eating behavior separately. In this case, body image may modulate the effect of food insecurity influence on fat storage. For example, people who perceive themselves as fat will not eat (or will eat less) even when the food supply is insecure. In the target article, Nettle et al. predict that anorexia occurs when a person's estimate of food security is unusually high, and they propose that introducing food insecurity may promote weight gain in anorexia patients. However, if body image is independent of perceived food insecurity, this proposed treatment may prove inadequate.
Alternatively, body image may be shaped by environmental cues and serve as an intervening variable mediating the relationship between perceived food scarcity and eating behavior. In this case, perceiving the supply of food as secure should lead people to perceive themselves as fat, whereas perceiving the supply of food as scarce should lead people to perceive themselves as thin. In this case, the treatment proposed by Nettle et al. would affect not only eating behavior but also body image. To our knowledge, no research has specifically investigated the relationship between body image and perceived food insecurity. This opens a new possible line of future research and provides a potential way of empirically testing the implications of the insurance hypothesis.