Food insecurity as a driver of obesity in humans: The insurance hypothesis

Abstract

Short abstract-Common sense says that obesity is the consequence of too much food. Adaptive reasoning says something rather different: individuals should store fat when access to food is insecure, to buffer themselves against future shortfall. Applied to humans, this principle suggests that food insecurity should be a risk factor for overweight and obesity. We provide a meta-analysis of the extensive epidemiological literature, finding that food insecurity robustly predicts high body weight, but only amongst women in high-income countries. We discuss the relevance of food insecurity to understanding the global obesity problem.Long abstract-Integrative explanations of why obesity is more prevalent in some sectors of the human population than others are lacking. Here, we outline and evaluate one candidate explanation, the insurance hypothesis (IH). The IH is rooted in adaptive evolutionary thinking: the function of storing fat is to provide a buffer against shortfall in the food supply. Thus, individuals should store more fat when they receive cues that access to food is uncertain. Applied to humans, this implies that an important proximate driver of obesity should be food insecurity rather than food abundance per se. We integrate several distinct lines of theory and evidence that bear on this hypothesis. We present a theoretical model that shows it is optimal to store more fat when food access is uncertain, and we review the experimental literature from non-human animals showing that fat reserves increase when access to food is restricted. We provide a meta-analysis of 125 epidemiological studies of the association between perceived food insecurity and high body weight in humans. There is a robust positive association, but it is restricted to adult women in high-income countries. We explore why this could be in light of the IH and our theoretical model. We conclude that whilst the IH alone cannot explain the distribution of obesity in the human population, it may represent a very important component of a pluralistic explanation. We also discuss insights it may offer into the developmental origins of obesity, dieting-induced weight gain, and Anorexia Nervosa.

A marker of biological ageing predicts adult risk preference in European starlings, Sturnus vulgaris

“…Telomere length was measured via qPCR from blood samples taken on day 5 and day 56, with mean telomere length in each sample expressed relative to a known single-copy gene (the T/S ratio), as detailed by Nettle et al (2017). We calculated developmental telomere attrition (henceforth ΔTL) as the change in T/S ratio between day 5 and day 56, standardized using the method of Verhulst et al (2013).…”

The evolution of body fatness: trading off disease and predation risk

“…There is some limited support for the idea that increased stochasticity drives elevated fat storage Cao et al, 2009;Zhang et al, 2012;Zhu et al, 2014); however, other studies suggest the reverse (Monarca et al, 2015b). In humans, this idea is generally called the 'food insecurity' hypothesis, or the 'hunger-obesity' paradigm (Nettle et al, 2017;Dhurandhar, 2016), i.e. poverty leads to greater food insecurity, which engages mechanisms ancestrally linked to starvation risk and food unpredictability, to elevate fat storage.…”

“…It has been implied that for this model to work predation must be reduced to zero (Higginson et al, 2016;Nettle et al, 2017); however, this is not a necessary condition -only that predation falls to a low enough level that it is no longer a significant force for differential selection on body weight. For example, predation might continue unabated on children or the elderly but such predatory activity would be irrelevant for selection on body weight: as is the case for mortality in famines (Speakman, 2007a,b).…”

“…It has been suggested that the reason for storing fat in these situations is to provide a source of energy that would cover any period of unanticipated failure in the food supply, i.e. as a hedge against the risk of starvation (McNamara and Houston, 1990;McNamara et al, 2005); with respect to fat storage in humans, this is also called the food unpredictability hypothesis or the food insurance hypothesis (Nettle et al, 2017). The potential of fat as a reserve to endure periods of catastrophic food supply failure (i.e.…”

Reply to VI Kraak

“…Twenty-five percent of the variation in prevalence of adult obesity in the United States is associated with levels of poverty (6). There are many studies using a range of different methods which support the suggestion that such a link is potentially causal (7)(8)(9). For people in poverty, whether fast-food and full-service restaurants offer healthy options or not is irrelevant, because this sector of society cannot afford to dine out at any form of restaurant more than very occasionally as a special treat.…”