Conjectures on some curious connections among social status, calorie restriction, hunger, fatness, and longevity

Impact of sustained calorie restriction and weight cycling on body composition in high-fat diet-fed male and female C57BL/6J mice

OBJECTIVE

The objective of this study was to investigate body composition changes with weight cycling (WC) among adult C57BL/6J mice with diet-induced obesity.

METHODS

A total of 555 single-housed mice were fed a high-fat diet ad libitum (AL) from 8 to 43 weeks of age. The 200 heaviest mice of each sex were randomized to the following four groups: ever obese (EO, continued AL feeding); obese weight loser (OWL, calorie-restricted); obese weight loser moderate (OWLM, body weight halfway between EO and OWL); and WC (diet restricted to OWL followed by AL refeeding cycles). Body weight and composition data were collected. Linear regression was used to calculate residuals between predicted and observed fat mass. Linear mixed models were used to compare diet groups.

RESULTS

Although weight loss and regain resulted in changes in body weight and composition, fat mass, body weight, and relative body fat were not significantly greater for the WC group compared with the EO group. During long-term calorie restriction, males (but not females) in the OWLM group remained relatively fatter than the EO group.

CONCLUSIONS

WC did not increase body weight or relative fat mass for middle-aged, high-fat diet-fed adult mice. However, long-term moderate calorie restriction resulted in lower body weight but greater "relative" fat in male mice.

Sex and Race Differences in Obesity-Related Genetic Susceptibility and Risk of Cardiometabolic Disease in Older US Adults

Importance

The fat mass and obesity-associated gene (FTO) is associated with obesity phenotypes, but the association is inconsistent across populations. Within-population differences may explain some of the variability observed.

Objective

To investigate sex differences in the association between FTO single-nucleotide variants (SNVs) and obesity traits among self-identified non-Hispanic Black and non-Hispanic White US adults, to examine whether the SNVs were associated with cardiometabolic diseases, and to evaluate whether obesity mediated the association between FTO SNVs and cardiometabolic diseases.

Design, Setting, and Participants

This cross-sectional study used data from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a US population-based cohort study with available genetic data (assayed in 2018) and phenotypic data at baseline (enrolled 2003-2007). Participants were aged 45 to 98 years at baseline. Data were analyzed from October 2021 to October 2022.

Exposures

Eleven SNVs in the FTO gene present among both Black and White participants.

Main Outcomes and Measures

Objectively measured obesity indicators (body mass index and waist-to-height ratio), objectively measured and/or self-reported cardiometabolic diseases (hypertension, stroke history, heart disease, and diabetes), and self-reported social-economic and psychosocial status.

Results

A total of 10 447 participants (mean [SD] age, 64.4 [9.7] years; 5276 [55.8%] women; 8743 [83.7%] Black and 1704 [16.3%] White) were included. In the White group, 11 FTO SNVs were significantly associated with obesity, hypertension, and diabetes using linear models (eg, body mass index: β = 0.536; 95% CI, 0.197-0.875), but none of the FTO SNVs were associated with obesity traits in the Black group. White males had a higher risk of obesity while White females had a higher risk of hypertension and diabetes. However, 1 FTO SNV (rs1121980) was associated with a direct increase in the risk of heart disease in Black participants not mediated by obesity (c' = 0.145 [SE, 0.0517]; P = .01).

Conclusions and Relevance

In this cross-sectional study of obesity phenotypes and their association with cardiometabolic diseases, the tested FTO SNVs reflected sex differences in White participants. Different patterns of associations were observed among self-identified Black participants. Therefore, these results could inform future work discovering risk alleles or risk scores unique to Black individuals or further investigating genetic risk in all US residents.

Low subjective social status is associated with daily selection of fewer healthy foods and more high-fat/high sugar foods

Socioeconomic status has been related to poorer eating behaviors, potentially due to feeling of lower status relative to peers. Despite experimental evidence that temporarily feeling of lower status can contribute to greater caloric intake, it remains unclear how feeling of lower social status relate to eating behavior in daily life. This study aimed to test whether lower subjective social status (SSS)-the feeling of having relatively lower social status-in American society and relative to college peers were related to daily food selection. A sample of 131 young adults (Mage = 20.3, SD = 0.8; 60% female; 46% Latinos; 34% European American; 15% Asian American; 5% of other ethnicities) reported their SSS in society and in college and completed 15 daily reports regarding the number of daily servings they had of fruits, vegetables, fried foods, fast foods, desserts, and sugary drinks. Multilevel models with days nested within individuals were used to test whether low SSS in society or college related to daily food intake. Next, we examined whether associations were driven by young adults' perceived stress and daily stressors. Analyses controlled for age, gender, ethnicity, family and personal income, and parents' education to test the unique associations between subjective status and food intake. Whereas SSS in society was not related to food intake, young adults with lower SSS in their college consumed fewer daily servings of healthy foods and more daily servings of high-fat/high-sugar foods. Although lower college SSS was related to greater perceived stress, perceived stress and daily stressors were consistently unrelated to daily food intake. Findings suggested that lower SSS in local environments (e.g., college) may impact young adults' daily food choices through processes beyond heightened stress.

Objective and subjective socioeconomic status associated with metabolic syndrome severity among African American adults in Jackson Heart Study

PURPOSE

To assess independent associations between objective socioeconomic status (OSS) and subjective social status (SSS) with metabolic syndrome (MetS) severity and indicators among African American (AA) adults in the Jackson Heart Study (JHS) at baseline (2000-2004) and eight-year follow-up (2009-2013).

METHODS

Participants included 1724 AA adults from the JHS cohort (64.4 % women; mean age 53.4 ± 11.8). Associations of OSS (annual household income and school years completed) and SSS (measured with MacArthur Scales) with sex- and race/ethnic-specific MetS severity Z-score were examined after adjustment for demographics and MetS risk factors (i.e., nutrition, physical activity, smoking status, alcohol consumption, and depressive symptoms) at baseline and eight-year follow-up.

PRINCIPAL RESULTS

Independent of OSS, demographic, psychosocial, and lifestyle factors, individuals with lower US-society SSS had more severe MetS at baseline. A significant interaction existed between sex and US-society SSS such that women with lower perceived social status had more severe MetS severity at baseline, and for every one unit increase in US-society SSS, MetS severity Z-score is estimated to decrease by 0.04. Components of MetS driving the relationship between US-society SSS and MetS severity at baseline were the inverse associations of SSS with glucose levels and the positive associations of SSS with HDL-C. Physical activity was independently associated with MetS severity at baseline, but not at eight-year follow-up.

MAJOR CONCLUSIONS

Though subjective and objective measures of social status are independently associated with cardiometabolic risk factors and MetS severity among AA adults, SSS may be a stronger predictor of MetS severity than OSS, particularly among women. SSS should be considered in conjunction with OSS when exploring social determinants of cardiometabolic health.

Evolutionary considerations on social status, eating behavior, and obesity

Lower socioeconomic status (SES) is consistently related to higher obesity risk, especially in women living in developed countries such as the United States and Western Europe. Prevailing theories to describe this relationship have focused primarily on proximate level factors such as the generally poorer food environment (e.g. relative lack of healthy food options and higher concentrations of fast food restaurants) found in lower vs. higher SES neighborhoods and the higher financial costs associated with purchasing healthy, nutrient-dense foods compared to unhealthy, energy-dense foods. These factors are hypothesized to preclude the purchase of these foods by lower SES individuals. Unfortunately, public health interventions aimed at improving the food environment of lower SES communities and to provide financial resources for purchasing healthy foods have had limited success in reducing overall energy intake and body weight. Some evidence suggests these interventions may even exacerbate obesity. More recent hypotheses have shifted the focus to ultimate (or adaptive) factors that view increased energy intake and accrual of body fat among individuals of lower social status as adaptive strategies to protect against potential prolonged food scarcity. The purpose of this review is integrate past research at the proximate and ultimate levels with a consideration of how social status and SES during development (in utero through adolescence) may moderate the relationships between social status, eating behavior, and obesity. Utilizing an evolutionary framework that incorporates life history theory can lead to more integrative and thorough interpretations of past research and allow researchers to better elucidate the complex set of environmental, physiological, psychological, and behavioral factors that influence obesity risk among individuals of lower social status.

Social Status and Adolescent Physical Activity: Expanding the Insurance Hypothesis to Incorporate Energy Expenditure

Low social status (SS) is a determinant of poor health status and is associated with increased disease burden. Obesity affects 20.6% of American adolescents, most of whom are from low-SS families. Contributors to the development of obesity among adolescents include sedentary behavior and low levels of physical activity. Environmental determinants-infrastructure, policy, and social relationships-influence engagement in physical activity and are affected by SS. Significant declines in physical activity have been documented during adolescence, and adolescents of low SS engage in significantly less physical activity per week than those with high SS. This article briefly reviews the literature on the relationship between SS and physical activity in adolescents and introduces a proposed biological mechanism that may explain that relationship. Characterizing the effects that SS can have on physical activity may help tailor clinical interventions and public health campaigns seeking to improve adolescent physical activity and weight management, thus increasing their effectiveness. This may be particularly beneficial for underserved populations.

Mind over matter. The impact of subjective social status on health outcomes and health behaviors

Recent insights have shown subjective status to impact health and health behavior. It is however unclear how this exactly happens. In this study we explore two mechanisms: this of a direct, mediating effect of subjective status explaining the impact of material class on health outcomes and behavior and an indirect, moderating impact on the relationship between material class and health outcomes and behavior. To test this empirically we conduct two studies, focusing on Great-Britain, using survey-data from the English Longitudinal Study of Ageing (N: 2709-3448) and the Whitehall II-study (N: 6275-6467). Our linear and logistic regression analyses show subjective status has a mainly direct impact on health outcomes and has both a direct, mediating and indirect, moderating impact on health behavior. In the conclusion of our article we reflect on the theoretical reasons why subjective status has a direct impact in certain cases, while playing an indirect role in other cases.

Subjective social status is associated with compensation for large meals - A prospective pilot study

OBJECTIVES

Subjective social status (SSS) is known to be inversely associated with obesity. Our objective was to determine if SSS is associated with eating behaviors that would predispose to weight gain, specifically, with inadequate compensation for excess energy consumed during a single large meal. Therefore, we conducted a pilot study to determine the association of SSS with 24-h energy balance, 24-h and post-lunch energy intake, changes in body composition and changes in adjusted resting energy expenditure on days when a high-energy lunch was consumed in free-living human subjects.

METHOD

Female participants (7 normal weight and 10 overweight) consumed 60% of' estimated 24-h energy requirements as a lunchtime meal in the laboratory for 14 days. Subjective social status was measured at baseline using the MacArthur Scale. Remote Food Photography Method was used to record food intake outside of the lab on days 1-2, 7-8, and 12-13. Associations of 24-h energy balance, 24-h and post-lunch energy intake, changes in adjusted resting energy expenditure and changes in percent body fat (measured by dual x-ray absorptiometry) with SSS were studied.

RESULTS

Mean (standard deviation) age and BMI were 36.29 (8.25) years and 26.43 (2.32) kg/m², respectively. Lower SSS was significantly associated with positive energy balance (p for trend 0.002), and higher post-lunch energy intake (p = 0.02) when controlled for age and initial body mass index.

CONCLUSIONS

Our pilot data show that lower SSS is associated with higher post-lunch energy intake, which is indicative of poor energy compensation following a large meal. Over a longer time period, this could result in fat mass gain. Studies that are of longer duration and well-powered are warranted to confirm our findings.

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.

Low subjective socioeconomic status stimulates orexigenic hormone ghrelin - A randomised trial

Recent evidence suggests that lower perceived socioeconomic status is linked to increased appetite and intake of greater calories. Yet, whether insecurity of socioeconomic resources directly influences regulatory systems of appetite and energy intake is not known. Considering psychological states, mindsets and beliefs have shown to meaningfully affect physiological responses to food, the present study tested the hypothesis that low subjective socioeconomic status (SSS) will have a direct influence on physiological responses, such as appetite-related hormones (ghrelin, pancreatic polypeptide and insulin). Forty-eight healthy males were randomly (crossover, counterbalanced) assigned, to two experimental conditions where participants were either experimentally induced to feel low SSS or not (control; CON). Feelings of low SSS resulted in an increase in active ghrelin (an orexigenic hormone) following the SSS manipulation compared with baseline, while no change in active ghrelin was observed in CON. Furthermore, participants reported lower fullness and satiety following low SSS compared with CON. Our findings demonstrate that SSS may influence hunger regulation and appetite, and suggest that physiological systems regulating energy balance (i.e. caloric resources) may also be sensitive to perceived deprivation or imbalances in critical non-food resources (socioeconomic resources).

Body Mass Index and Subjective Social Status: The Coronary Artery Risk Development in Young Adults Study

OBJECTIVE

Subjective social status (SSS), or perceived social status, may explain, in part, the relationship between socioeconomic status (SES) and obesity. The objective of this study was to test whether SSS mediates the relationship between two indicators of SES (income and education) and body mass index (BMI).

METHODS

A cross-sectional, structural equation path analysis was applied to the Coronary Artery Risk Development in Young Adults (CARDIA) study (n = 2,624). The analysis tested whether SSS (MacArthur scale), education, and income were associated with BMI at the year 20 examination (adjusting for sex, age, and race), and it was hypothesized that the associations of education and income with BMI would be at least partly mediated by SSS.

RESULTS

SSS had a significant direct effect on BMI (-0.21, P = 0.018). Education had a significant direct relationship with SSS (0.11, P < 0.001) and a small but significant indirect relationship with BMI through SSS (-0.02, P = 0.022). Although income did not have a significant direct relationship with BMI, it did have a significant indirect relationship through SSS (b = -0.05, P = 0.019).

CONCLUSIONS

Results are consistent with the hypothesized model in which SSS partially mediates the relationship between SES indicators and BMI.

Complementary Hypotheses on Contributors to the Obesity Epidemic

Increased rates of obesity have occurred within virtually every race, age, sex, ethnicity, and economic group. Despite substantial punditry on the issue, the exact reasons are incompletely known. The two most common factors cited as contributing to the obesity epidemic, and those whose causal influence on increasing obesity levels in the population are often presumed unequivocally, are food marketing practices and institutionally driven reductions in physical activity. These have been called "the big two." This Perspective builds on previous writings in this area to introduce additional factors that may contribute to the obesity epidemic. It is emphasized that there may be other factors working in combination with the big two, influencing body fatness through effects on energy intake, energy expenditure, and/or nutrient partitioning.

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.

Social status and energy intake: a randomized controlled experiment

While the inverse association between socioeconomic status (SES) and obesity in high gross domestic product countries is well established using observational data, the extent to which the association is due to a true causal effect of SES and, if so, the mechanisms of this effect remain incompletely known. To assess the influence of social status on obesity via energy intake, we randomized individuals to a higher or lower social status and observed subsequent energy intake. College students between the ages of 18 and 25 were randomized to social status and were operationalized as being a leader or follower in a partner activity as purportedly determined by a (bogus) test of leadership ability. Investigators were blinded to treatment assignment. Immediately after being told their leadership assignment, paired participants were provided with platters of food. Energy intake was objectively measured in kilocalories (kcal) consumed, and paired t-tests were used to test for significant differences in intake between leaders and followers. A total of 60 participants were included in the final analysis (males = 28, females = 32). Overall, no difference in energy intake was observed between leaders and followers, consuming an average of 575.3 and 579.8 kcal, respectively (diff = 4.5 kcal, P = 0.94). The null hypothesis of no effect of social status, operationalized as assignment to a leadership position in a small-group activity, on energy intake was not rejected.

Caloric restriction in lean and obese strains of laboratory rat: effects on body composition, metabolism, growth and overall health

NEW FINDINGS

What is the central question of this study? How do lean and obese rats respond physiologically to caloric restriction? What is the main finding and its importance? Obese rats show marked benefits compared with lean animals. Reduced body fat is associated with improved longevity with caloric restriction (CR) in rodents. Little is known regarding effects of CR in genetically lean versus obese strains. Long-Evans (LE) and Brown Norway (BN) rats make an ideal comparison for a CR study because the percentage body fat of young adult LE rats is double that of BN rats. Male LE and BN rats were either fed ad libitum (AL) or were calorically restricted to 80 or 90% of their AL weight. The percentages of fat, lean and fluid mass were measured non-invasively at 2- to 4-week intervals. Metabolic rate and respiratory quotient were measured after 3, 6, 9 and 12 months of CR. Overall health was scored monthly. The percentage of fat of the LE strain decreased with CR, whereas the percentage of fat of the BN strain remained above the AL group for several months. The percentage of lean mass increased above the AL for both strains subjected to CR. The percentage of fluid was unaffected by CR. The average metabolic rate over 22 h of the BN rats subjected to CR was reduced, whereas that of LE rats was increased slightly above the AL group. The respiratory quotient of BN rats was decreased with CR. Overall health of the CR LE group was significantly improved compared with that of the AL group, whereas health of the CR BN rats was impaired compared with the AL group. Overall, the lean BN and obese LE strains differ markedly in fat utilization and metabolic response to prolonged CR. There appears to be little benefit of CR in the lean strain.