Thrift: a guide to thrifty genes, thrifty phenotypes and thrifty norms

A development-centric perspective on pace-of-life syndromes

Organism responses to environmental change require coordinated changes across correlated traits, so-called syndromes. For example, animals differ in their "pace-of-life syndrome" (POLS); suites of correlated life-history, behavioral and physiological traits. But standard "gene-centric" evolutionary theory cannot explain why POLSs exist because it assumes that the expression of phenotypic traits of animals is determined by genotype-specified reaction norms; it ignores that developmental processes can bias the direction of evolution so that phenotypes no longer match genotype-by-environment interactions. Here we apply a development-centric perspective to derive new POLS hypotheses that can resolve the conflict that current POLS predictions fail to explain which species/populations are resilient to environmental change.

In Search of Environmental Factors Associated With Global Differences in Birth Weight and BMI

OBJECTIVE

The "fetal origin of adult diseases hypothesis" encompasses the notion that intrauterine growth restriction (IUGR) alters fetal development trajectories. Various neonatal metrics inform IUGR, but not all contributors to IUGR have an impact on development trajectories. Chronic IUGR (twins) and slowly varying IUGR (seasonal) have little to no effect on later life trajectories. Perhaps development trajectories may evolve through other mechanisms, as for example, multiple short-lived periods of IUGR and repeated stimulation of metabolic pathways.

METHODS

Daily temperature variation could deliver a frequent IUGR as pregnant women would experience some degree of placental vasoconstriction during maximum/midday temperatures. We assessed the association with daily temperature amplitudes for globally distributed records of crude fetal growth rates (CFGR) and BMI. Paired birthweight (BW) and gestational age (GA) data permitted analyses of CFGR in 70 countries and subsequent analysis of CFGR for association with daily temperature amplitude, seasonal temperature amplitude, mean annual temperature, calorie intake per day per-1 person-1, BMI, height, and socioeconomic conditions. Analog analyses were performed for gestational age, calorie intake, BMI, and height.

RESULTS

CFGR and BMI showed a clear association with daily temperature amplitudes, which was not the case for gestational age, calorie intake, and height.

CONCLUSION

We show that daily temperature amplitudes are associated with both CFGR and BMI. These results permit a wider ecological appreciation of the hypothesis because daily temperature amplitudes inform environmental aridity and food scarcity. We discuss how scarcity, affluence, and the epidemiological environment influence the prevalence of afflictions associated with the fetal origin of adult disease hypothesis.

Developmental Programming of the Fetal Immune System by Maternal Western-Style Diet: Mechanisms and Implications for Disease Pathways in the Offspring

Maternal obesity and over/undernutrition can have a long-lasting impact on offspring health during critical periods in the first 1000 days of life. Children born to mothers with obesity have reduced immune responses to stimuli which increase susceptibility to infections. Recently, maternal western-style diets (WSDs), high in fat and simple sugars, have been associated with skewing neonatal immune cell development, and recent evidence suggests that dysregulation of innate immunity in early life has long-term consequences on metabolic diseases and behavioral disorders in later life. Several factors contribute to abnormal innate immune tolerance or trained immunity, including changes in gut microbiota, metabolites, and epigenetic modifications. Critical knowledge gaps remain regarding the mechanisms whereby these factors impact fetal and postnatal immune cell development, especially in precursor stem cells in bone marrow and fetal liver. Components of the maternal microbiota that are transferred from mothers consuming a WSD to their offspring are understudied and identifying cause and effect on neonatal innate and adaptive immune development needs to be refined. Tools including single-cell RNA-sequencing, epigenetic analysis, and spatial location of specific immune cells in liver and bone marrow are critical for understanding immune system programming. Considering the vital role immune function plays in offspring health, it will be important to understand how maternal diets can control developmental programming of innate and adaptive immunity.

Prevalence of hypertension among the indigenous population in North-East India: Is this a consequence of "nutritional transition"?

OBJECTIVES

This article aims to understand the influence of residential status on the prevalence of cardiovascular disease (CVD) risk factors among adult Angami Naga of Nagaland.

METHODS

A total number of 194 (100 rural and 94 urban) adult Angami Naga participated in the study. Blood pressure, both systolic and diastolic, was measured for each participant. Nutritional status was evaluated through body mass index. Metabolic health was measured through waist circumference, waist-hip ratio and percent body fat (%BF). Multiple regression analysis was done to examine the influence of residential status and other bio-social factors on the prevalence of obesity and hypertension.

RESULTS

Results indicate high prevalence of systolic hypertension among urban residents, in both males (29.6%_Urban vs. 20.4%_Rural ; p > .05) and females (17.4%_Urban vs. 11.6%_Rural ; p > .05), with gender inequality favoring females. Similar trend was observed in diastolic hypertension as well. On the other hand, obesity was found to be greater in rural males (8.3%_Urban vs.10.2%_Rural ; p = .002), and urban females (11.6%_Urban vs. 3.5%_Rural ; p > .05). However in %BF, only negligible percentages of urban females (2.3%_Urban vs. 0.0%_Rural ; p > .05) were found to be moderately overweight or obese and no males were found to be overweight. Further, regression analyzes indicate that age, sex, and residential status are the most important (p < .001) causal factors behind the prevalence of obesity and hypertension among the Angami Naga.

CONCLUSIONS

It was observed that elderly urban males were the most susceptible section of this community in developing CVD risk factors related vulnerabilities. However, we propose understanding this prevalence from an evolutionary approach of physiological mechanism toward nutritional transition in Angami Naga, like many other indigenous populations of northeast India.

Dietary Energy Partition: The Central Role of Glucose

Humans have developed effective survival mechanisms under conditions of nutrient (and energy) scarcity. Nevertheless, today, most humans face a quite different situation: excess of nutrients, especially those high in amino-nitrogen and energy (largely fat). The lack of mechanisms to prevent energy overload and the effective persistence of the mechanisms hoarding key nutrients such as amino acids has resulted in deep disorders of substrate handling. There is too often a massive untreatable accumulation of body fat in the presence of severe metabolic disorders of energy utilization and disposal, which become chronic and go much beyond the most obvious problems: diabetes, circulatory, renal and nervous disorders included loosely within the metabolic syndrome. We lack basic knowledge on diet nutrient dynamics at the tissue-cell metabolism level, and this adds to widely used medical procedures lacking sufficient scientific support, with limited or nil success. In the present longitudinal analysis of the fate of dietary nutrients, we have focused on glucose as an example of a largely unknown entity. Even most studies on hyper-energetic diets or their later consequences tend to ignore the critical role of carbohydrate (and nitrogen disposal) as (probably) the two main factors affecting the substrate partition and metabolism.

Obesity: Assessment and prevention: Module 23.2 from Topic 23 "Nutrition in obesity"

Obesity is one the major health problems of today showing an increasing prevalence among most countries. It is associated with increased risk of several diseases. The importance of early life strategies in the prevention of obesity is well established, whereas, in general, breastfed infants tend to have a lower body mass index (BMI) than formula-fed infants. There seem to be a series of behavioral and hormonal mechanisms that explain this difference. Lifestyle plays a crucial role in the development of overweight and/or obesity and targeted lifestyle modifications have an important impact on preventing obesity. In particular, sedentary behavior (viewing television, playing video games, doing cognitive work, and listening to music) and reduced overall physical activity along with shorter sleep duration promote the overconsumption of dietary macronutrients leading to obesity; at the same time physical activity or exercise in a sufficient dose seems to better facilitate long-term maintenance of new lower body weight. There is enough discussion about a potential effect of nutrients on obesity. Nevertheless, the most the crucial parameter regarding weight loss and prevention of obesity is to achieve a negative energy balance. In regard to specific diet regimes, again energy balance rather that any specific macronutrients composition and/or favoring of low glycemic index products, seems to be have a stronger effect on maintenance of lower weight after 12 months. It has to be noted, that for specific sup groups, obesity or overweight might be showing some favorable trends in survival. In particular, "obesity paradox" (OP) refers to an overall prognosis that is no worse and may even be better in some groups than non-obese patients. The OP could be explained by the fact that current classifications of obesity based on BMI may place together, in the same category, subjects with very different clinical and biochemical characteristics.

PTEN: A Thrifty Gene That Causes Disease in Times of Plenty?

The modern obesity epidemic with associated disorders of metabolism and cancer has been attributed to the presence of "thrifty genes". In the distant past, these genes helped the organism to improve energy efficiency and store excess energy safely as fat to survive periods of famine, but in the present day obesogenic environment, have turned detrimental. I propose PTEN as the likely gene as it has functions that span metabolism, cancer and reproduction, all of which are deranged in obesity and insulin resistance. The activity of PTEN can be calibrated in utero by availability of nutrients by the methylation arm of the epigenetic pathway. Deficiency of protein and choline has been shown to upregulate DNA methyltransferases (DNMT), especially 1 and 3a; these can then methylate promoter region of PTEN and suppress its expression. Thus, the gene is tuned like a metabolic rheostat proportional to the availability of specific nutrients, and the resultant "dose" of the protein, which sits astride and negatively regulates the insulin-PI3K/AKT/mTOR pathway, decides energy usage and proliferation. This "fixes" the metabolic capacity of the organism periconceptionally to a specific postnatal level of nutrition, but when faced with a discordant environment, leads to obesity related diseases.

Diverse biological processes coordinate the transcriptional response to nutritional changes in a Drosophila melanogaster multiparent population

Background

Environmental variation in the amount of resources available to populations challenge individuals to optimize the allocation of those resources to key fitness functions. This coordination of resource allocation relative to resource availability is commonly attributed to key nutrient sensing gene pathways in laboratory model organisms, chiefly the insulin/TOR signaling pathway. However, the genetic basis of diet-induced variation in gene expression is less clear.

Results

To describe the natural genetic variation underlying nutrient-dependent differences, we used an outbred panel derived from a multiparental population, the Drosophila Synthetic Population Resource. We analyzed RNA sequence data from multiple female tissue samples dissected from flies reared in three nutritional conditions: high sugar (HS), dietary restriction (DR), and control (C) diets. A large proportion of genes in the experiment (19.6% or 2471 genes) were significantly differentially expressed for the effect of diet, and 7.8% (978 genes) for the effect of the interaction between diet and tissue type (LRT, P_adj. < 0.05). Interestingly, we observed similar patterns of gene expression relative to the C diet, in the DR and HS treated flies, a response likely reflecting diet component ratios. Hierarchical clustering identified 21 robust gene modules showing intra-modularly similar patterns of expression across diets, all of which were highly significant for diet or diet-tissue interaction effects (FDR P_adj. < 0.05). Gene set enrichment analysis for different diet-tissue combinations revealed a diverse set of pathways and gene ontology (GO) terms (two-sample t-test, FDR < 0.05). GO analysis on individual co-expressed modules likewise showed a large number of terms encompassing many cellular and nuclear processes (Fisher exact test, P_adj. < 0.01). Although a handful of genes in the IIS/TOR pathway including Ilp5, Rheb, and Sirt2 showed significant elevation in expression, many key genes such as InR, chico, most insulin peptide genes, and the nutrient-sensing pathways were not observed.

Conclusions

Our results suggest that a more diverse network of pathways and gene networks mediate the diet response in our population. These results have important implications for future studies focusing on diet responses in natural populations.

The evolutionary potential of diet-dependent effects on lifespan and fecundity in a multi-parental population of Drosophila melanogaster

The nutritional conditions experienced by a population have a major role in shaping trait evolution in many taxa. Constraints exerted by nutrient limitation or nutrient imbalance can influence the maximal value that fitness components such as reproduction and lifespan attains, and organisms may shift how resources are allocated to different structures and functions in response to changes in nutrition. Whether the phenotypic changes associated with changes in nutrition represent an adaptive response is largely unknown. Further, it is unclear whether the response of fitness components to diet even has the potential to evolve in most systems. In this study, we use an admixed multi-parental population of Drosophila melanogaster reared in three different diet conditions to estimate quantitative genetic parameters for lifespan and fecundity. We find significant genetic variation for both traits in our population and show that lifespan has moderate to high heritabilities within diets. Genetic correlations for lifespan between diets were significantly less than one, demonstrating a strong genotype by diet interaction. These findings demonstrate substantial standing genetic variation in our population that is comparable to natural populations and highlights the potential for adaptation to changing nutritional environments.

Ladies first: Female and male adult height in Switzerland, 1770-1930

When investigating the well-being of a society, the living conditions of females are of special importance, not only due to the immediate impact for those directly involved, but also because of the potential intergenerational effects. Studying the dimorphism in the mean height helps to depict variation in the basic biological sex difference due to gender-related factors that potentially determine net nutrition. To expand knowledge of diachronic development in Swiss well-being conditions we investigate changes in the height of adult females born 1770-1930, and compare the series with data on contemporary males from the same sources: We employ a sample of N = 21'028 women and N = 21'329 men from passport-, convict-, maternity hospital-, and voluntary World War II army auxiliary records. The secular height trend is found both in males, from the 1870s/1880s, and in females starting with the 1840s/1850s birth cohorts. During the decades under study, mean height increased from 157 cm to 164 cm in female and 167 cm to 172 cm in male passport applicants, 154 cm to 159 cm in female and 167 cm to 169 cm in male convicts, 159 cm to 163 cm in female auxiliaries, and 155 cm to 159 cm in females giving birth in the maternity hospital of Basel. Because females seem to have started the secular trend in height earlier than their male contemporaries, the height dimorphism decreased during the second half of the 19th century. Differences between socio-economic status (SES) and data sources are found in both females and males: Women with low SES were significantly shorter than those of the other SES groups in all sources (on average 1.40 cm, p-values between 0.00 and 0.03). In men we found individuals of upper SES to be significantly taller (on average 1.96 cm, p-value = 0.00-0.10). Concerning differences between the sources, overall, passport applicants were the tallest for men as well as women; in females the individuals measured at the maternity hospital and in prison were the shortest. The variances across the datasets highlight the importance of considering different sources to depict average living conditions. Noteworthy is the finding that the diverse sources under study all show the same trajectory of increasing mean height over the course of the 19th century. In the long run, the improving net nutritional status of Swiss females may have been one of the contributors behind the general rise in well-being of the country's population from the later 19th century onwards.

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

Human obesity has a large genetic component, yet has many serious negative consequences. How this state of affairs has evolved has generated wide debate. The thrifty gene hypothesis was the first attempt to explain obesity as a consequence of adaptive responses to an ancient environment that in modern society become disadvantageous. The idea is that genes (or more precisely, alleles) predisposing to obesity may have been selected for by repeated exposure to famines. However, this idea has many flaws: for instance, selection of the supposed magnitude over the duration of human evolution would fix any thrifty alleles (famines kill the old and young, not the obese) and there is no evidence that hunter-gatherer populations become obese between famines. An alternative idea (called thrifty late) is that selection in famines has only happened since the agricultural revolution. However, this is inconsistent with the absence of strong signatures of selection at single nucleotide polymorphisms linked to obesity. In parallel to discussions about the origin of obesity, there has been much debate regarding the regulation of body weight. There are three basic models: the set-point, settling point and dual-intervention point models. Selection might act against low and high levels of adiposity because food unpredictability and the risk of starvation selects against low adiposity whereas the risk of predation selects against high adiposity. Although evidence for the latter is quite strong, evidence for the former is relatively weak. The release from predation ∼2-million years ago is suggested to have led to the upper intervention point drifting in evolutionary time, leading to the modern distribution of obesity: the drifty gene hypothesis. Recent critiques of the dual-intervention point/drifty gene idea are flawed and inconsistent with known aspects of energy balance physiology. Here, I present a new formulation of the dual-intervention point model. This model includes the novel suggestion that food unpredictability and starvation are insignificant factors driving fat storage, and that the main force driving up fat storage is the risk of disease and the need to survive periods of pathogen-induced anorexia. This model shows why two independent intervention points are more likely to evolve than a single set point. The molecular basis of the lower intervention point is likely based around the leptin pathway signalling. Determining the molecular basis of the upper intervention point is a crucial key target for future obesity research. A potential definitive test to separate the different models is also described.

Towards a behavioural ecology of obesity

Addressing the obesity epidemic depends on a holistic understanding of the reasons that people become and maintain excessive fat. Theories about the causes of obesity usually focus proximately or evoke evolutionary mismatches, with minimal clinical value. There is potential for substantial progress by adapting strategic body mass regulation models from evolutionary ecology to human obesity by assessing the role of information.

Epigenetic programming, early life nutrition and the risk of metabolic disease

Time separates the past from the present, during this period memory are formed - written in code and decoded to be read while other memories are erased - but when it comes to the epigenome some memories are harder to forget than others. Recent studies show chemical information is written in the context of the epigenome and codified on histone and non-histone proteins to regulate nuclear processes such as gene transcription. The genome is also subject to modification in the form of 5-methylcytosine, which has been implicated in metabolic memory. In this review, we examine some of the chemical modifications that signal early life events and explore epigenetic changes that underlie the diabetic vasculature. The fine balance between past and present is discussed, as it pertains to gestational diabetes and obesity in context to the Barker hypothesis. We also examine emerging experimental evidence suggesting the hypothalamus as a central regulator of obesity risk and explore current genomic medicine. As for how cells recall specific chemical information, we examine the experimental evidence implicating chemical cues on the epigenome, providing examples of diet during pregnancy and the increased risk of disease in offspring.

Obesity in International Migrant Populations

PURPOSE OF REVIEW

This review examines the risk of obesity in migrant groups-specifically migrants from countries with lower prevalence of obesity to countries with higher prevalence of obesity. We examine obesity prevalence within migrant groups compared with native populations and the evidence on factors that might shape obesity risk in these migrant groups.

RECENT FINDINGS

Migrants may arrive in new countries with a health advantage including generally a healthier body weight. Genetic and epi-genetic factors, as well as body size preference, socio-economic factors, and stress exposure, may play a role in increasing unhealthy weight gain in migrant populations. This unhealthy weight gain leads to similar or greater obesity risk in migrant populations compared with native populations 10-15 years after migration. Meeting the challenge of prevention and treatment of obesity in diverse populations will require greater attention to minority groups in research in the future.

Low Birthweight Increases the Likelihood of Severe Steatosis in Pediatric Non-Alcoholic Fatty Liver Disease

OBJECTIVES

Small for gestational age (SGA) is associated with an increased risk of non-alcoholic fatty liver disease (NAFLD). Our aim was to investigate the correlation of birthweight with the severity of liver damage in a large cohort of children with NAFLD.

METHODS

Two hundred and eighty-eight consecutive Caucasian Italian overweight/obese children with biopsy-proven NAFLD were included in the study. We examined the relative association of each histological feature of NAFLD with metabolic alterations, insulin-resistance, I148M polymorphism in the patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene, and birthweight relative to gestational age.

RESULTS

In the whole NAFLD cohort, 12.2% of patients were SGA, 62.8% appropriate for gestational age (AGA), and 25% large for gestational age (LGA). SGA children had a higher prevalence of severe steatosis (69%) and severe portal inflammation (14%) compared with the AGA and LGA groups. Notably, severe steatosis (>66%) was decreasing from SGA to AGA and LGA, whereas the prevalence of moderate steatosis (33-66%) was similar in three groups. The prevalence of type 1 NAFLD is higher in the LGA group with respect to the other two groups (25% vs.5.2% vs.9.4%), whereas the SGA group shows a higher prevalence of overlap type (85.8%) with respect to the LGA group (51.4%) but not compared with the AGA group (75%). At multivariable regression analysis, SGA at birth increased fourfold the likelihood of severe steatosis (odds ratio (OR) 4.0, 95% confidence interval (CI) 1.43-10.9, P=0.008) and threefold the likelihood of NAFLD Activity Score (NAS)≥5 (OR 2.98, 95% CI 1.06-8.33, P=0.037) independently of homeostasis model assessment of insulin resistance and PNPLA3 genotype. The PNPLA3-CC wild-type genotype was the strongest independent predictor of the absence of significant fibrosis (OR 0.26, 95% CI 0.13-0.52, P=<0.001).

CONCLUSIONS

In children with NAFLD, the risk of severe steatosis is increased by SGA at birth, independent of and in addition to other powerful risk factors (insulin-resistance and I148M variant of the PNPLA3 gene).

Genetic Dissection of Nutrition-Induced Plasticity in Insulin/Insulin-Like Growth Factor Signaling and Median Life Span in a Drosophila Multiparent Population

The nutritional environments that organisms experience are inherently variable, requiring tight coordination of how resources are allocated to different functions relative to the total amount of resources available. A growing body of evidence supports the hypothesis that key endocrine pathways play a fundamental role in this coordination. In particular, the insulin/insulin-like growth factor signaling (IIS) and target of rapamycin (TOR) pathways have been implicated in nutrition-dependent changes in metabolism and nutrient allocation. However, little is known about the genetic basis of standing variation in IIS/TOR or how diet-dependent changes in expression in this pathway influence phenotypes related to resource allocation. To characterize natural genetic variation in the IIS/TOR pathway, we used >250 recombinant inbred lines (RILs) derived from a multiparental mapping population, the Drosophila Synthetic Population Resource, to map transcript-level QTL of genes encoding 52 core IIS/TOR components in three different nutritional environments [dietary restriction (DR), control (C), and high sugar (HS)]. Nearly all genes, 87%, were significantly differentially expressed between diets, though not always in ways predicted by loss-of-function mutants. We identified cis (i.e., local) expression QTL (eQTL) for six genes, all of which are significant in multiple nutrient environments. Further, we identified trans (i.e., distant) eQTL for two genes, specific to a single nutrient environment. Our results are consistent with many small changes in the IIS/TOR pathways. A discriminant function analysis for the C and DR treatments identified a pattern of gene expression associated with the diet treatment. Mapping the composite discriminant function scores revealed a significant global eQTL within the DR diet. A correlation between the discriminant function scores and the median life span (r = 0.46) provides evidence that gene expression changes in response to diet are associated with longevity in these RILs.

How to get the most bang for your buck: the evolution and physiology of nutrition-dependent resource allocation strategies

All organisms use resources to grow, survive and reproduce. The supply of these resources varies widely across landscapes and time, imposing ultimate constraints on the maximal trait values for allocation-related traits. In this review, we address three key questions fundamental to our understanding of the evolution of allocation strategies and their underlying mechanisms. First, we ask: how diverse are flexible resource allocation strategies among different organisms? We find there are many, varied, examples of flexible strategies that depend on nutrition. However, this diversity is often ignored in some of the best-known cases of resource allocation shifts, such as the commonly observed pattern of lifespan extension under nutrient limitation. A greater appreciation of the wide variety of flexible allocation strategies leads directly to our second major question: what conditions select for different plastic allocation strategies? Here, we highlight the need for additional models that explicitly consider the evolution of phenotypically plastic allocation strategies and empirical tests of the predictions of those models in natural populations. Finally, we consider the question: what are the underlying mechanisms determining resource allocation strategies? Although evolutionary biologists assume differential allocation of resources is a major factor limiting trait evolution, few proximate mechanisms are known that specifically support the model. We argue that an integrated framework can reconcile evolutionary models with proximate mechanisms that appear at first glance to be in conflict with these models. Overall, we encourage future studies to: (i) mimic ecological conditions in which those patterns evolve, and (ii) take advantage of the 'omic' opportunities to produce multi-level data and analytical models that effectively integrate across physiological and evolutionary theory.

Food Aversions and Cravings during Pregnancy on Yasawa Island, Fiji

Women often experience novel food aversions and cravings during pregnancy. These appetite changes have been hypothesized to work alongside cultural strategies as adaptive responses to the challenges posed by pregnancy (e.g., maternal immune suppression). Here, we report a study that assessed whether data from an indigenous population in Fiji are consistent with the predictions of this hypothesis. We found that aversions focus predominantly on foods expected to exacerbate the challenges of pregnancy. Cravings focus on foods that provide calories and micronutrients while posing few threats to mothers and fetuses. We also found that women who experience aversions to specific foods are more likely to crave foods that meet nutritional needs similar to those provided by the aversive foods. These findings are in line with the predictions of the hypothesis. This adds further weight to the argument that appetite changes may function in parallel with cultural mechanisms to solve pregnancy challenges.

An adaptive response to uncertainty can lead to weight gain during dieting attempts

BACKGROUND AND OBJECTIVES

Peoples' attempts to lose weight by low calorie diets often result in weight gain because of over-compensatory overeating during lapses. Animals usually respond to a change in food availability by adjusting their foraging effort and altering how much energy reserves they store. But in many situations the long-term availability of food is uncertain, so animals may attempt to estimate it to decide the appropriate level of fat storage.

METHODOLOGY

We report the results of a conceptual model of feeding in which the animal knows whether food is currently abundant or limited, but does not know the proportion of time, there will be an abundance in the long-term and has to learn it.

RESULTS

If the food supply is limited much of the time, such as during cycles of dieting attempts, the optimal response is to gain a lot of weight when food is abundant.

CONCLUSIONS AND IMPLICATIONS

This implies that recurring attempts to diet, by signalling to the body that the food supply is often insufficient, will lead to a greater fat storage than if food was always abundant. Our results shed light on the widespread phenomenon of weight gain during weight cycling and indicate possible interventions that may reduce the incidence of obesity.

From Undernutrition to Overnutrition: The Evolution of Overweight and Obesity among Young Men in Switzerland since the 19th Century

OBJECTIVE

The global obesity epidemic continues, new approaches are needed to understand the causes. We analyzed data from an evolutionary perspective, stressing developmental plasticity.

METHODS

We present diachronical height, weight, and BMI data for 702,902 Swiss male conscripts aged 18-20 years, a representative, standardized and unchanged data source.

RESULTS

From 1875 to 1879, the height distribution was slightly left-skewed; 12.1% of the conscripts were underweight, overweight and obesity were rare. The BMI-to-height relationship was positive but not linear, and very short conscripts were particularly slim. Since the 1870s, Swiss conscripts became taller, a trend that markedly slowed in the 1990s. In contrast, weight increased in two distinct steps at the end of the 1980s and again after 2002. Since 2010, BMI did not increase but stabilized at a high level.

CONCLUSIONS

The body of young men adapted differently to varying living conditions over time: First, less investment in height and weight under conditions of undernutrition and food uncertainty; second, more investment in height under more stable nutritional conditions; third, development of obesity during conditions of plateaued height growth, overnutrition, and decreasing physical activity. This example contributes to the evaluation of hypotheses on human developmental plasticity.

Costs of Foraging Predispose Animals to Obesity-Related Mortality when Food Is Constantly Abundant

Obesity is an important medical problem affecting humans and animals in the developed world, but the evolutionary origins of the behaviours that cause obesity are poorly understood. The potential role of occasional gluts of food in determining fat-storage strategies for avoiding mortality have been overlooked, even though animals experienced such conditions in the recent evolutionary past and may follow the same strategies in the modern environment. Humans, domestic, and captive animals in the developed world are exposed to a surplus of calorie-rich food, conditions characterised as ‘constant-glut’. Here, we use a mathematical model to demonstrate that obesity-related mortality from poor health in a constant-glut environment should equal the average mortality rate in the ‘pre-modern’ environment when predation risk was more closely linked with foraging. It should therefore not be surprising that animals exposed to abundant food often over-eat to the point of ill-health. Our work suggests that individuals tend to defend a given excessive level of reserves because this level was adaptive when gluts were short-lived. The model predicts that mortality rate in constant-glut conditions can increase as the assumed health cost of being overweight decreases, meaning that any adaptation that reduced such health costs would have counter-intuitively led to an increase in mortality in the modern environment. Taken together, these results imply that efforts to reduce the incidence of obesity that are focussed on altering individual behaviour are likely to be ineffective because modern, constant-glut conditions trigger previously adaptive behavioural responses.

A Human Thrifty Phenotype Associated With Less Weight Loss During Caloric Restriction

Successful weight loss is variable for reasons not fully elucidated. Whether effective weight loss results from smaller reductions in energy expenditure during caloric restriction is not known. We analyzed whether obese individuals with a "thrifty" phenotype, that is, greater reductions in 24-h energy expenditure during fasting and smaller increases with overfeeding, lose less weight during caloric restriction than those with a "spendthrift" phenotype. During a weight-maintaining period, 24-h energy expenditure responses to fasting and 200% overfeeding were measured in a whole-room indirect calorimeter. Volunteers then underwent 6 weeks of 50% caloric restriction. We calculated the daily energy deficit (kilocalories per day) during caloric restriction, incorporating energy intake and waste, energy expenditure, and daily activity. We found that a smaller reduction in 24-h energy expenditure during fasting and a larger response to overfeeding predicted more weight loss over 6 weeks, even after accounting for age, sex, race, and baseline weight, as well as a greater rate of energy deficit accumulation. The success of dietary weight loss efforts is influenced by the energy expenditure response to caloric restriction. Greater decreases in energy expenditure during caloric restriction predict less weight loss, indicating the presence of thrifty and spendthrift phenotypes in obese humans.

Can evidence from genome-wide association studies and positive natural selection surveys be used to evaluate the thrifty gene hypothesis in East Asians?

Body fat deposition and distribution differ between East Asians and Europeans, and for the same level of obesity, East Asians are at higher risks of Type 2 diabetes (T2D) and other metabolic disorders. This observation has prompted the reclassifications of body mass index thresholds for the definitions of “overweight” and “obese” in East Asians. However, the question remains over what evolutionary mechanisms have driven the differences in adiposity morphology between two population groups that shared a common ancestor less than 80,000 years ago. The Thrifty Gene hypothesis has been suggested as a possible explanation, where genetic factors that allowed for efficient food-energy conversion and storage are evolutionarily favoured by conferring increased chances of survival and fertility. Here, we leveraged on the existing findings from genome-wide association studies and large-scale surveys of positive natural selection to evaluate whether there is currently any evidence to support the Thrifty Gene hypothesis. We first assess whether the existing genetic associations with obesity and T2D are located in genomic regions that are reported to be under positive selection, and if so, whether the risk alleles sit on the extended haplotype forms. In addition, we interrogate whether these risk alleles are the derived forms that differ from the ancestral alleles, and whether there is significant evidence of population differentiation at these SNPs between East Asian and European populations. Our systematic survey did not yield conclusive evidence to support the Thrifty Gene hypothesis as a possible explanation for the differences observed between East Asians and Europeans.

Why Is It So Difficult to Lose Weight?

Obesity is notoriously difficult to treat. Effective treatment has been encumbered by traditional assumptions about the cause of the disease. Obesity is typically considered a manifestation of the patient’s dietary misconduct, a simple lack of willpower, or the inability to modify dysfunctional eating habits. Abundant evidence suggests that eating behavior is much more complex than patient choice alone. Eating and the system of regulating eating and body weight are largely controlled by complex signals from multiple organ systems that monitor food intake, gastrointestinal function, and energy storage and send multiple messages to the brain. The brain coordinates the physiological messages and creates additional signals about eating, appetite, hunger, and satiety. Multiple survival, environmental, and genetic factors become part of a biological regulatory system that controls eating and body weight. The system appears to be unstable and often becomes dysfunctional, particularly in an environment of abundant food and calories. Despite the difficulty in modifying the regulatory system, opportunities for management of the disease do exist. Comprehensive lifestyle management can be useful, as can selective pharmacotherapy and bariatric surgery. Public policy changes will likely be helpful in changing community understanding of the disease and its management.

Brown adipose tissue: endocrine determinants of function and therapeutic manipulation as a novel treatment strategy for obesity

Introduction

Recent observation of brown adipose tissue (BAT) being functional in adult humans provides a rationale for its stimulation to increase energy expenditure through ‘adaptive thermogenesis’ for an anti-obesity strategy. Many endocrine dysfunctions are associated with changes in metabolic rate that over time may result in changes in body weight. It is likely that human BAT plays a role in such processes.

Review

In this brief review article, we explore the endocrine determinants of BAT activity, and discuss how these insights may provide a basis for future developments of novel therapeutic strategies for obesity management.

A review of electronic and print data comprising original and review articles retrieved from PubMed search up to December 2013 was conducted (Search terms: brown adipose tissue, brown fat, obesity, hormone). In addition, relevant references from the articles were screened for papers containing original data.

Conclusion

There is promising data to suggest that targeting endocrine hormones for BAT modulation can yield a cellular bioenergetics answer for successful prevention and management of human obesity. Further understanding of the physiological link between various endocrine hormones and BAT is necessary for the development of new therapeutic options.

Electronic supplementary material

The online version of this article (doi:10.1186/s40608-014-0013-5) contains supplementary material, which is available to authorized users.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Metabolic remodeling of white adipose tissue in obesity

Adipose tissue metabolism is a critical regulator of adiposity and whole body energy expenditure; however, metabolic changes that occur in white adipose tissue (WAT) with obesity remain unclear. The purpose of this study was to understand the metabolic and bioenergetic changes occurring in WAT with obesity. Wild-type (C57BL/6J) mice fed a high-fat diet (HFD) showed significant increases in whole body adiposity, had significantly lower V̇(O₂), V̇(CO₂), and respiratory exchange ratios, and demonstrated worsened glucose and insulin tolerance compared with low-fat-fed mice. Metabolomic analysis of WAT showed marked changes in lipid, amino acid, carbohydrate, nucleotide, and energy metabolism. Tissue levels of succinate and malate were elevated, and metabolites that could enter the Krebs cycle via anaplerosis were mostly diminished in high-fat-fed mice, suggesting altered mitochondrial metabolism. Despite no change in basal oxygen consumption or mitochondrial DNA abundance, citrate synthase activity was decreased by more than 50%, and responses to FCCP were increased in WAT from mice fed a high-fat diet. Moreover, Pgc1a was downregulated and Cox7a1 upregulated after 6 wk of HFD. After 12 wk of high-fat diet, the abundance of several proteins in the mitochondrial respiratory chain or matrix was diminished. These changes were accompanied by increased Parkin and Pink1, decreased p62 and LC3-I, and ultrastructural changes suggestive of autophagy and mitochondrial remodeling. These studies demonstrate coordinated restructuring of metabolism and autophagy that could contribute to the hypertrophy and whitening of adipose tissue in obesity.

Development of food intake controls: neuroendocrine and environmental regulation of food intake during early life

This article is part of a Special Issue "Energy Balance". The development of neuroendocrine regulation of food intake during early life has been shaped by natural selection to allow for optimal growth and development rates needed for survival. In vertebrates, neonates or early larval forms typically exhibit "feeding drive," characterized by a developmental delay in 1) responsiveness of the hypothalamus to satiety signals (e.g., leptin, melanocortins) and 2) sensitivity to environmental cues that suppress food intake. Homeostatic regulation of food intake develops once offspring transition to later life history stages when growth is slower, neuroendocrine systems are more mature, and appetite becomes more sensitive to environmental or social cues. Across vertebrate groups, there is a tremendous amount of developmental plasticity in both food intake regulation and stress responsiveness depending on the environmental conditions experienced during early life history stages or by pregnant/brooding mothers. This plasticity is mediated through the organizing effects of hormones acting on the food intake centers of the hypothalamus during development, which alter epigenetic expression of genes associated with ingestive behaviors. Research is still needed to reveal the mechanisms through which environmental conditions during development generate and maintain these epigenetic modifications within the lifespan or across generations. Furthermore, more research is needed to determine whether observed patterns of plasticity are adaptive or pathological. It is clear, however, that developmental programming of food intake has important effects on fitness, and therefore, has ecological and evolutionary implications.

Link between insulin resistance and hypertension: What is the evidence from evolutionary biology?

Insulin resistance and hypertension are considered as prototypical "diseases of civilization" that are manifested in the modern environment as plentiful food and sedentary life. The human propensity for insulin resistance and hypertension is a product, at least in part, of our evolutionary history. Adaptation to ancient lifestyle characterized by a low sodium, low-calorie food supply and physical stress to injury response has driven our evolution to shape and preserve a thrifty genotype, which is favorite with energy-saving and sodium conservation. As our civilization evolved, a sedentary lifestyle and sodium- and energy-rich diet, the thrifty genotype is no longer advantageous, and may be maladaptive to disease phenotype, such as hypertension, obesity and insulin resistance syndrome. This article reviews human evolution and the impact of the modern environment on hypertension and insulin resistance.

Factors affecting insulin-regulated hepatic gene expression

Obesity has become a major concern of public health. A common feature of obesity and related metabolic disorders such as noninsulin-dependent diabetes mellitus is insulin resistance, wherein a given amount of insulin produces less than normal physiological responses. Insulin controls hepatic glucose and fatty acid metabolism, at least in part, via the regulation of gene expression. When the liver is insulin-sensitive, insulin can stimulate the expression of genes for fatty acid synthesis and suppress those for gluconeogenesis. When the liver becomes insulin-resistant, the insulin-mediated suppression of gluconeogenic gene expression is lost, whereas the induction of fatty acid synthetic gene expression remains intact. In the past two decades, the mechanisms of insulin-regulated hepatic gene expression have been studied extensively and many components of insulin signal transduction pathways have been identified. Factors that alter these pathways, and the insulin-regulated hepatic gene expression, have been revealed and the underlying mechanisms have been proposed. This chapter summarizes the recent progresses in our understanding of the effects of dietary factors, drugs, bioactive compounds, hormones, and cytokines on insulin-regulated hepatic gene expression. Given the large amount of information and progresses regarding the roles of insulin, this chapter focuses on findings in the liver and hepatocytes and not those described for other tissues and cells. Typical insulin-regulated hepatic genes, such as insulin-induced glucokinase and sterol regulatory element-binding protein-1c and insulin-suppressed cytosolic phosphoenolpyruvate carboxyl kinase and insulin-like growth factor-binding protein 1, are used as examples to discuss the mechanisms such as insulin regulatory element-mediated transcriptional regulation. We also propose the potential mechanisms by which these factors affect insulin-regulated hepatic gene expression and discuss potential future directions of the area of research.

Novel "thrifty" models of increased eating behaviour

The thrifty genotype and phenotype hypotheses were developed to explain the rapid increase in diabetes and obesity in developed countries around the world. Most subsequent "thrifty" research has focused on the early developmental origins of the metabolic syndrome and cardio-metabolic disease. The goal of this manuscript is to review an emerging line of research that uses a similar thrifty framework to understand the early developmental origins of eating-related phenotypes that have primary relevance to many psychiatric disorders. Given the important role of environmental adversity in various psychiatric disorders that involve overeating, and their early age of onset, it is likely that several thrifty mechanisms are relevant in this regard. Understanding the early origins of increased eating behaviour based on a thrifty model might point the way to highly targeted preventative interventions during critical periods of development, and provide a new way of addressing these common and difficult to treat disorders.

Roles of Vitamin A Metabolism in the Development of Hepatic Insulin Resistance

The increase in the number of people with obesity- and noninsulin-dependent diabetes mellitus has become a major public health concern. Insulin resistance is a common feature closely associated with human obesity and diabetes. Insulin regulates metabolism, at least in part, via the control of the expression of the hepatic genes involved in glucose and fatty acid metabolism. Insulin resistance is always associated with profound changes of the expression of hepatic genes for glucose and lipid metabolism. As an essential micronutrient, vitamin A (VA) is needed in a variety of physiological functions. The active metablite of VA, retinoic acid (RA), regulates the expression of genes through the activation of transcription factors bound to the RA-responsive elements in the promoters of RA-targeted genes. Recently, retinoids have been proposed to play roles in glucose and lipid metabolism and energy homeostasis. This paper summarizes the recent progresses in our understanding of VA metabolism in the liver and of the potential transcription factors mediating RA responses. These transcription factors are the retinoic acid receptor, the retinoid X receptor, the hepatocyte nuclear factor 4α, the chicken ovalbumin upstream promoter-transcription factor II, and the peroxisome proliferator-activated receptor β/δ. This paper also summarizes the effects of VA status and RA treatments on the glucose and lipid metabolism in vivo and the effects of retinoid treatments on the expression of insulin-regulated genes involved in the glucose and fatty acid metabolism in the primary hepatocytes. I discuss the roles of RA production in the development of insulin resistance in hepatocytes and proposes a mechanism by which RA production may contribute to hepatic insulin resistance. Given the large amount of information and progresses regarding the physiological functions of VA, this paper mainly focuses on the findings in the liver and hepatocytes and only mentions the relative findings in other tissues and cells.

Diet and our genetic legacy in the recent anthropocene: a Darwinian perspective to nutritional health

Nutrient-gene research tends to focus on human disease, although such interactions are often a by-product of our evolutionary heritage. This review explores health in this context, reframing genetic variation/epigenetic phenomena linked to diet in the framework of our recent evolutionary past. This "Darwinian/evolutionary medicine" approach examines how diet helped us evolve among primates and to adapt (or fail to adapt) our metabolome to specific environmental conditions leading to major diseases of civilization. This review presents updated evidence from a diet-gene perspective, portraying discord that exists with respect to health and our overall nutritional, cultural, and activity patterns. While Darwinian theory goes beyond nutritional considerations, a significant component within this concept does relate to nutrition and the mismatch between genes, modern diet, obesogenic lifestyle, and health outcomes. The review argues that nutritional sciences should expand knowledge on the evolutionary connection between food and disease, assimilating it into clinical training with greater prominence.

Age-associated epigenetic drift: implications, and a case of epigenetic thrift?

It is now well established that the genomic landscape of DNA methylation (DNAm) gets altered as a function of age, a process we here call ‘epigenetic drift’. The biological, functional, clinical and evolutionary significance of this epigenetic drift, however, remains unclear. We here provide a brief review of epigenetic drift, focusing on the potential implications for ageing, stem cell biology and disease risk prediction. It has been demonstrated that epigenetic drift affects most of the genome, suggesting a global deregulation of DNAm patterns with age. A component of this drift is tissue-specific, allowing remarkably accurate age-predictive models to be constructed. Another component is tissue-independent, targeting stem cell differentiation pathways and affecting stem cells, which may explain the observed decline of stem cell function with age. Age-associated increases in DNAm target developmental genes, overlapping those associated with environmental disease risk factors and with disease itself, notably cancer. In particular, cancers and precursor cancer lesions exhibit aggravated age DNAm signatures. Epigenetic drift is also influenced by genetic factors. Thus, drift emerges as a promising biomarker for premature or biological ageing, and could potentially be used in geriatrics for disease risk prediction. Finally, we propose, in the context of human evolution, that epigenetic drift may represent a case of epigenetic thrift, or bet-hedging. In summary, this review demonstrates the growing importance of the ‘ageing epigenome’, with potentially far-reaching implications for understanding the effect of age on stem cell function and differentiation, as well as for disease prevention.

Rotating shift-work as an independent risk factor for overweight Italian workers: a cross-sectional study

Background

A job-related factor is attracting a growing interest as a possible determinant of body weight gain in shift-workers.

Objective

The aim of the study was to reinvestigate the issue of overweight between rotating shift workers and daytime workers, taking into consideration possible confounding covariate factors.

Methods

This is a cross-sectional study, conducted by reviewing data from subjects participating in an occupational surveillance program in 2008. Participants answered a self-administered questionnaire to retrieve information about socio-demographic factors and working conditions (job schedule type, job-related physical activity, time in job), subjective health status, health care visits during the previous year, and lifestyle factors (dietary habits, leisure time physical activity, alcohol consumption). Participants underwent a medical examination for measurement of BMI, and acquisition of medical history.

Results

Compared to daytime workers (N = 229), rotating shift workers (N = 110) displayed higher BMI (mean BMI was 27.6±3.9 and 26.7±3.6 for shift workers, and daytime workers, respectively; p<0.05). Logistic regression analysis allowed to highlight the role of rotating shift-work as an independent risk factor for increased body weight (OR 1.93, 95%CI 1.01–3.71), being aged between 35 and 54 years was a major determinant of increased BMI (OR 2.39, 95%CI 1.14–5.00). In addition, family history of obesity was the strongest determinant of overweight/obesity (OR 9.79, 95%CI 1.28–74.74). Interestingly, no significant association was found between overweight and other potentially relevant factors, such as diet quality and food choices, alcohol consumption, levels of occupational and leisure-time physical activity.

Conclusions

Present findings seem to support the notion that rotating shift work is an independent risk factor for overweight, regardless of workers' dietary habits and physical activity levels.

Developmental programming: impact of prenatal testosterone excess on insulin sensitivity, adiposity, and free fatty acid profile in postpubertal female sheep

Prenatal T excess causes reproductive and metabolic disruptions including insulin resistance, attributes of women with polycystic ovary syndrome. This study tested whether increases in visceral adiposity, adipocyte size, and total free fatty acids underlie the insulin resistance seen in prenatal T-treated female sheep. At approximately 16 months of age, insulin resistance and adipose tissue partitioning were determined via hyperinsulinemic euglycemic clamp and computed tomography, respectively, in control and prenatal T-treated females. Three months later, adipocyte size and free fatty acid composition were determined. Results revealed that at the postpubertal time points tested, insulin sensitivity was increased, visceral adiposity and adipocyte size in both the sc and the visceral compartments were reduced, and circulating palmitic acid was increased in prenatal T-treated females relative to controls. In parallel studies, 20-month-old prenatal T-treated females tended to have increased basal insulin to glucose ratio. Relative to earlier findings of reduced insulin sensitivity of prenatal T-treated females during early life and adulthood, these findings of increased insulin sensitivity and reduced adiposity postpubertally are suggestive of a period of developmental adaptation. The disruption observed in free fatty acid metabolism a few months later correspond to a time point when the insulin sensitivity indices of prenatal T-treated animals appear to shift toward insulin resistance. In summary, current findings of improved insulin sensitivity and reduced visceral adiposity in postpubertal prenatal T-treated sheep relative to our earlier findings of reduced insulin sensitivity during early postnatal life and adulthood are indicative of a period of developmental adaptation.

Endocannabinoids and obesity

A safe and effective antiobesity drug is needed to combat the global obesity epidemic. The discovery of cannabinoids from medicinal herbs has revealed the endocannabinoid system (ECS) in animals and humans, which regulates various physiological activities such as feeding, thermogenesis, and body weight (BW). Although cannabinoid receptors 1 (CB1) antagonists have shown antiobesity efficacies in animal models and in the clinic, they failed to establish as a treatment due to their psychological side effects. Recent studies indicate that CB1 in various peripheral tissues may mediate some of the therapeutic effects of CB1 antagonists, such as improved lipid and glucose homeostasis. It rationalizes the development of compounds with limited brain penetration, for minimizing the side effects while retaining the therapeutic efficacies. A survey of the literature has revealed some controversies about how the ECS affects obesity. This review summarizes the research progresses and discusses some future perspectives.

Ethnic variability in adiposity, thrifty phenotypes and cardiometabolic risk: addressing the full range of ethnicity, including those of mixed ethnicity

Ethnic groups vary in cardiometabolic risk, but the underlying mechanisms remain unclear. Several components of body composition variability (fat/lean ratio, fat distribution, lean mass composition and metabolism, and adipose tissue biology) are increasingly linked with cardiometabolic risk and vary substantially across ethnic groups. Constituents of lean mass are proposed to contribute to 'metabolic capacity', a generic trait favouring the maintenance of homeostasis. Adiposity is proposed to contribute to 'metabolic load', which at higher levels challenges metabolic homeostasis, elevating cardiometabolic risk. Ethnic differences in body composition, representing different load-capacity ratios, may therefore contribute to ethnic variability in cardiometabolic risk. Ecological and evolutionary factors potentially contributing to ethnic variability in body composition are explored. In contemporary populations, clinicians encounter an increasing range of ethnicity, along with many individuals of mixed-ethnic ancestry. Increasing understanding of the contribution of body composition to cardiometabolic risk may reduce the need to treat ethnic groups as qualitatively different. A conceptual model is proposed, treating insulin sensitivity and stroke risk as composite functions of body composition variables. Operationalizing this model may potentially improve the ability to assess cardiovascular risk across the full ethnicity spectrum, and to predict cardiometabolic consequences of excess weight gain.

The evolution of human adiposity and obesity: where did it all go wrong?

Because obesity is associated with diverse chronic diseases, little attention has been directed to the multiple beneficial functions of adipose tissue. Adipose tissue not only provides energy for growth, reproduction and immune function, but also secretes and receives diverse signaling molecules that coordinate energy allocation between these functions in response to ecological conditions. Importantly, many relevant ecological cues act on growth and physique, with adiposity responding as a counterbalancing risk management strategy. The large number of individual alleles associated with adipose tissue illustrates its integration with diverse metabolic pathways. However, phenotypic variation in age, sex, ethnicity and social status is further associated with different strategies for storing and using energy. Adiposity therefore represents a key means of phenotypic flexibility within and across generations, enabling a coherent life-history strategy in the face of ecological stochasticity. The sensitivity of numerous metabolic pathways to ecological cues makes our species vulnerable to manipulative globalized economic forces. The aim of this article is to understand how human adipose tissue biology interacts with modern environmental pressures to generate excess weight gain and obesity. The disease component of obesity might lie not in adipose tissue itself, but in its perturbation by our modern industrialized niche. Efforts to combat obesity could be more effective if they prioritized 'external' environmental change rather than attempting to manipulate 'internal' biology through pharmaceutical or behavioral means.

Learned food-cue stimulates persistent feeding in sated rats

Cues that predict food can stimulate appetite and feeding independent of physiological hunger. How long such effects might last is currently unknown. Here we began to characterize long-term effects in a rodent model of cue-potentiated feeding. Rats were conditioned to associate a tone with food pellets distinct from their regular laboratory chow, and then were tested along with controls for food consumption following tone presentations. In Experiment 1, rats were tested under sated or food-deprived conditions to determine whether fasting would augment cue-driven feeding. Rats in the control group regulated intake based on physiological state, while conditioned rats consumed similar large amounts of food regardless. Experiment 2 tested the durability of cue-potentiated feeding to repeated testing in sated rats. We observed robust cue-potentiated feeding during the first two tests, while in the third and fourth tests both groups ate similar large amounts of pellets. In both experiments the conditioned tone-cue induced binge-like consumption of the cued food and persistent feeding for the duration of 4-h tests. Rats then failed to adjust daily chow consumption to account for their increased intake post-cue. In summary, brief cue priming stimulated substantial intake in sated states that was behaviorally uncompensated for by homeostatic mechanisms.

Obesity and type 2 diabetes: which patients are at risk?

An estimated 72.5 million American adults are obese, and the growing US obesity epidemic is responsible for substantial increase in morbidity and mortality, as well as increased health care costs. Obesity results from a combination of personal and societal factors, but is often viewed as a character flaw rather than a medical condition. This leads to stigma and discrimination towards obese individuals and decreases the likelihood of effective intervention. Conditions related to obesity are increasingly common, such as metabolic syndrome, impaired fasting glucose (IFG) and impaired glucose tolerance (IGT), all of which indicate high risk for type 2 diabetes (T2DM). This paper reviews the progression from obesity to diabetes, identifying physiological changes that occur along this path as well as opportunities for patient identification and disease prevention. Patients with prediabetes (defined as having IFG, IGT or both) and/or metabolic syndrome require interventions designed to preserve insulin sensitivity and β-cell function, both of which start to deteriorate prior to T2DM diagnosis. Lifestyle modification, including both healthy eating choices and increased physical activity, is essential for weight management and diabetes prevention. Although sustained weight loss is often considered by patients and physicians as being impossible to achieve, effective interventions do exist. Specifically, the Diabetes Prevention Program (DPP) and programs modelled along its parameters have shown repeated successes, even with long-term maintenance. Recent setbacks in the development of medications for weight loss further stress the importance of lifestyle management. By viewing obesity as a metabolic disorder rather than a personal weakness, we can work with patients to address this increasingly prevalent condition and improve long-term health outcomes.

[Evolutionary endocrinology: a pending matter]

Twenty years have passed since the foundational article of what is now known as evolutionary medicine (EM) was published. This young medical discipline examines, following Darwinian principles, susceptibility to certain diseases and how we react to them. In short, EM analyzes the final cause of the disease from a historical perspective. Over the years, EM has been introduced in various medical areas in very different ways. While it has found a role in some fields such as infectious diseases and oncology, its contribution in other areas has been quite limited. In endocrinology, EM has only gained prominence as a basis for the so-called "diseases of civilization", including diabetes mellitus and obesity. However, many experts suggest that it may have a much higher potential. The aim of this paper is to provide a view about what evolutionary medicine is. Some examples of how EM may contribute to progress of our specialty are also given. There is no doubt that evolution enriches medicine, but medicine also offers knowledge to evolution.

Gene-diet interactions in childhood obesity

Childhood overweight and obesity have reached epidemic proportions worldwide, and the increase in weight-associated co-morbidities including premature type 2 diabetes mellitus (T2DM) and atherosclerotic cardiovascular disease will soon become major healthcare and economic problems. A number of studies now indicate that the childhood obesity epidemic which has emerged during the past 30 years is a complex multi-factorial disease resulting from interaction of susceptibility genes with an obesogenic environment. This review will focus on gene-diet interactions suspected of having a prominent role in promoting childhood obesity. In particular, the specific genes that will be presented (FTO, MC4R, and NPC1) have recently been associated with childhood obesity through a genome-wide association study (GWAS) and were shown to interact with nutritional components to increase weight gain. Although a fourth gene (APOA2) has not yet been associated with childhood obesity, this review will also present information on what now represents the best characterized gene-diet interaction in promoting weight gain.

Obesity and energy balance: is the tail wagging the dog?

The scientific study of obesity has been dominated throughout the twentieth century by the concept of energy balance. This conceptual approach, based on fundamental thermodynamic principles, states that energy cannot be destroyed, and can only be gained, lost or stored by an organism. Its application in obesity research has emphasised excessive appetite (gluttony), or insufficient physical activity (sloth), as the primary determinants of excess weight gain, reflected in current guidelines for obesity prevention and treatment. This model cannot explain why weight accumulates persistently rather than reaching a plateau, and underplays the effect of variability in dietary constituents on energy and intermediary metabolism. An alternative model emphasises the capacity of fructose and fructose-derived sweeteners (sucrose, high-fructose corn syrup) to perturb cellular metabolism via modification of the adenosine monophosphate (AMP)/adenosine triphosphate (ATP) ratio, activation of AMP kinase and compensatory mechanisms, which favour adipose tissue accretion and increased appetite while depressing physical activity. This conceptual model implicates chronic hyperinsulinaemia in the presence of a paradoxical state of 'cellular starvation' as a key driver of the metabolic modifications inducing chronic weight gain. We combine evidence from in vitro and in vivo experiments to formulate a perspective on obesity aetiology that emphasises metabolic flexibility and dietary composition rather than energy balance. Using this model, we question the direction of causation of reported associations between obesity and sleep duration or childhood growth. Our perspective generates new hypotheses, which can be tested to improve our understanding of the current obesity epidemic, and to identify novel strategies for prevention or treatment.