Insurance Hypothesis Research Articles

Children respond to food restriction by increasing food consumption.

Consistent with the insurance hypothesis, research shows that when children experience restricted access to food, they display increased intake when restrictions are lifted. This effect appears more robust for girls compared to boys, and for children with lower levels of inhibitory control. The insurance hypothesis has potentially important implications for parental feeding practices.

Adaptive principles of weight regulation: Insufficient, but perhaps necessary, for understanding obesity.

We reflect on the major issues raised by a thoughtful and diverse set of commentaries on our target article. We draw attention to the need to differentiate between ultimate and proximate explanation; the insurance hypothesis (IH) needs to be understood as an ultimate-level argument, although we welcome the various suggestions made about proximate mechanisms. Much of this response is concerned with clarifying the interrelationships between adaptationist explanations like the IH, constraint explanations, and dysfunction explanations, in understanding obesity. We also re-examine the empirical evidence base, concurring that it is equivocal and only partially supportive. Several commentators offer additional supporting evidence, whereas others propose alternative explanations for the evidence we reviewed and suggest ways that our current knowledge could be strengthened. Finally, we take the opportunity to clarify some of the assumptions and predictions of our formal model.

A life-history theory perspective on obesity.

We extend Nettle et al.'s insurance hypothesis (IH) argument, drawing upon life-history theory (LHT), a developmental evolutionary perspective that documents downstream consequences of early-life exposure to unpredictable environments. We discuss novel evidence consistent with both IH and LHT, suggesting that early-life exposure to unpredictable environments is associated with reduced engagement in weight management behaviors and a greater probability of adulthood obesity.

Episodic memory as an explanation for the insurance hypothesis in obesity

In evaluating the insurance hypothesis as an explanation for obesity, we propose one missing piece of the puzzle. Our suggested explanation for why individuals report food insecurity is that an individual may have an impaired episodic ability to plan for the future.

A game theory appraisal of the insurance hypothesis: Specific polymorphisms in the energy homeostasis network as imprints of a successful minimax strategy.

The existence of specific polymorphisms in genes of key hormones of the energy homeostasis network that have been shown to predispose to obesity and the so-called metabolic syndrome provides further biological support for the proposed insurance hypothesis. In a broader sense, such polymorphisms can be understood as biological imprints of an evolutionarily successful minimax strategy employed by ancient Homo sapiens subpopulations in a one-player game against nature.

Future Research Directions for the Insurance Hypothesis regarding Food Insecurity and Obesity.

This commentary discusses Nettle et al.'s "The Insurance Hypothesis" linking food insecurity to a high body mass index (BMI). Discussion about how the relationship between race/ethnicity and obesity in the United States is consistent with this hypothesis is presented. Potential ways forward to elucidate the validity of this hypothesis in humans through rigorous controlled trials is highlighted.

Mapping multiple drivers of human obesity.

The insurance hypothesis is a reasonable explanation for the current obesity epidemic. One alternative explanation is that the marketing of high-sugar foods, especially sugar-sweetened beverages, drives the rise in obesity. Another prominent hypothesis is that obesity spreads through social influence. We offer a framework for estimating the extent to which these different models explain the rise in obesity.

Committed to the insurance hypothesis of obesity.

Can ideas about the regulation of body mass in birds be used to explain the breakdown of regulation associated with obesity and anorexia in humans? There is no evidence to think so. Medicine can always benefit from the application of evolutionary ecology ideas, but we must be prepared to dismiss these ideas when they just do not fit the data.

Anti-fat discrimination in marriage more clearly explains the poverty–obesity paradox

The target article proposes the insurance hypothesis as an explanation for higher levels of obesity among food-insecure women living in high-income countries. An alternative hypothesis based on anti-fat discrimination in marriage can also account for such correlations between poverty and obesity and is more consistent with finer-grained analyses by marital status, gender, and age.

Epidemiological foundations for the insurance hypothesis: Methodological considerations.

Nettle et al. evaluate evidence for the insurance hypothesis, which links obesity with the perception of food scarcity. Epidemiological findings in this area have generally been weak and inconsistent. The present commentary examines three key methodological issues arising from the literature on the association between obesity and the perception of food scarcity in humans, with suggestions for future epidemiological research.

Predicting human adiposity – sometimes – with food insecurity: Broaden the model for better accuracy

The target article explores the role of food insecurity as a contemporary risk factor for human overweight and obesity. The authors provide conditional support for the insurance hypothesis among adult women from high-income countries. We consider the potential contribution of additional factors in producing variation in adiposity patterns between species and across human contexts.

Using food insecurity in health prevention to promote consumer's embodied self-regulation.

Health messages designed to address obesity are typically focused on the long-term benefits of eating healthy food. However, according to the insurance hypothesis, obese people are food insecure, and this causes them to be overly concerned about short-term consumption. As such, it is necessary to rethink public health messaging and consider how to reduce short-term insecurity by eating healthy food.

Expanding the insurance hypothesis of obesity with physiological cues.

Food insecurity relates to fat storage, but cannot explain fat storage in excess of levels optimal for buffering-that is, obesity. However, factors related to food unpredictability in the past, including stress, disease, micronutrient content of food, and physical activity, may cue physiological processes that change intake or fat deposition even in the absence of actual food unpredictability.

Eating and body image: Does food insecurity make us feel thinner?

Body image distortions are common in healthy individuals and a central aspect of serious clinical conditions, such as eating disorders. This commentary explores the potential implications of body image and its distortions for the insurance hypothesis. In particular, we speculate that body image may be an intervening variable mediating the relationship between perceived food scarcity and eating behavior.

The value of biodiversity for the functioning of tropical forests: insurance effects during the first decade of the Sabah biodiversity experiment.

One of the main environmental threats in the tropics is selective logging, which has degraded large areas of forest. In southeast Asia, enrichment planting with seedlings of the dominant group of dipterocarp tree species aims to accelerate restoration of forest structure and functioning. The role of tree diversity in forest restoration is still unclear, but the ‘insurance hypothesis’ predicts that in temporally and spatially varying environments planting mixtures may stabilize functioning owing to differences in species traits and ecologies. To test for potential insurance effects, we analyse the patterns of seedling mortality and growth in monoculture and mixture plots over the first decade of the Sabah biodiversity experiment. Our results reveal the species differences required for potential insurance effects including a trade-off in which species with denser wood have lower growth rates but higher survival. This trade-off was consistent over time during the first decade, but growth and mortality varied spatially across our 500 ha experiment with species responding to changing conditions in different ways. Overall, average survival rates were extreme in monocultures than mixtures consistent with a potential insurance effect in which monocultures of poorly surviving species risk recruitment failure, whereas monocultures of species with high survival have rates of self-thinning that are potentially wasteful when seedling stocks are limited. Longer-term monitoring as species interactions strengthen will be needed to more comprehensively test to what degree mixtures of species spread risk and use limited seedling stocks more efficiently to increase diversity and restore ecosystem structure and functioning.

Morpho-environmental strategies in the genus Ononis L. (subsections Natrix and Viscosae) in Western Mediterranean

Very similar morphologies have always been pointed out for subsections Natrix and Viscosae of the genus Ononis L. Morphological, environmental and biogeographic approaches do not show significant differences between taxa of both subsections, and only life form was pointed out as biological descriptor to explain taxonomic and ecological strategies for these taxa: Natrix is composed by perennial life forms, while Viscosae is solely represented by annual life forms. The discussion of results was conducted through the insurance hypothesis, according to which resilient or resistant behaviours, here represented by taxonomic diversity and morpho-environmental variability, described the ecological strategies for these taxa. In this way, wider morpho-environmental variability induced more responses (higher taxonomic diversity and life forms), i.e. more resilience. On contrary, the narrower morpho-environmental variability induced less taxonomic diversity and only perennial life forms, i.e. more resistance. Two future climate change scenarios were also used to confirm these resilience and resistance strategies for both subsections.

Plankton Community Stability and Its Relationship with Phytoplankton Species Richness in Lake Nansihu, China

The relationship between biodiversity and ecosystem functioning is a central issue in ecology. The insurance hypothesis suggests that biodiversity could improve community productivity and reduce the temporal variability of main ecosystem processes. In the present study, we used a plankton community that was investigated from 2011 to 2014 in Lake Nansihu to test this hypothesis and explore the mechanisms involved. As a result, 138 phytoplankton and 76 zooplankton species were identified in the lake, and their biomasses showed apparent seasonal variations. The average temporal stability index of zooplankton taxa was significantly higher than that of phytoplankton. Complex relationships were observed between the species richness and temporal stability of different phytoplankton taxa: a unimodal relationship for both Cyanophyta and Bacillariophyta; a strong concave relationship for Euglenophyta; and no apparent relationship for both Chlorophyta and total phytoplankton. These relationships were primarily controlled by the portfolio effect; while the effects of overyielding and species asynchrony were relatively weak. Phytoplankton species richness had a significant positive influence on the temporal stability indices of protozoa, Rotifera and total zooplankton, while its influence on Cladocera and copepods was not significant. The dominant mechanisms were found to be ‘trophic overyielding’ and a weak ‘trophic portfolio effect’; however, ‘trophic species asynchrony’ played a minor role. These results demonstrated that the effects of diversity on community stability can be complex in natural ecosystems. In addition, the diversity of phytoplankton not only influenced its own temporal stability, but also affected the stability of zooplankton through trophic interactions.

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

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 although 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.

Do migratory warblers carry excess fuel reserves during migration for insurance or for breeding purposes?

ABSTRACT Migration is energetically costly, and many passerines prepare for and maintain migration with hyperphagia and increased fuel or fat reserves. During spring migration, as they approach their breeding grounds, passerines may deposit fat in excess of what is needed to complete migration. Individuals may carry excess fuel reserves as insurance against potentially poor environmental conditions in early spring (insurance hypothesis). If this is true, individuals arriving early at northern stopover locations or their breeding grounds should have greater energy reserves than later arrivals. Alternatively, passerines may arrive in spring with excess fat to help offset the demands of breeding (breeding performance hypothesis). Given the energetic requirements of egg production, females may arrive with greater reserves than males if excess fat directly or indirectly offsets breeding costs. We analyzed the energetic condition of 12 warbler species mist-netted during migration from 1999 to 2012 at Braddock B...

Land use imperils plant and animal community stability through changes in asynchrony rather than diversity.

Human land use may detrimentally affect biodiversity, yet long-term stability of species communities is vital for maintaining ecosystem functioning. Community stability can be achieved by higher species diversity (portfolio effect), higher asynchrony across species (insurance hypothesis) and higher abundance of populations. However, the relative importance of these stabilizing pathways and whether they interact with land use in real-world ecosystems is unknown. We monitored inter-annual fluctuations of 2,671 plant, arthropod, bird and bat species in 300 sites from three regions. Arthropods show 2.0-fold and birds 3.7-fold higher community fluctuations in grasslands than in forests, suggesting a negative impact of forest conversion. Land-use intensity in forests has a negative net impact on stability of bats and in grasslands on birds. Our findings demonstrate that asynchrony across species—much more than species diversity alone—is the main driver of variation in stability across sites and requires more attention in sustainable management.