Obesity and its potential mechanistic basis

Obesity: an evolutionary context

People completely lacking body fat (lipodystrophy/lipoatrophy) and those with severe obesity both show profound metabolic and other health issues. Regulating levels of body fat somewhere between these limits would, therefore, appear to be adaptive. Two different models might be contemplated. More traditional is a set point (SP) where the levels are regulated around a fixed level. Alternatively, dual-intervention point (DIP) is a system that tolerates fairly wide variation but is activated when critically high or low levels are breached. The DIP system seems to fit our experience much better than an SP, and models suggest that it is more likely to have evolved. A DIP system may have evolved because of two contrasting selection pressures. At the lower end, we may have been selected to avoid low levels of fat as a buffer against starvation, to avoid disease-induced anorexia, and to support reproduction. At the upper end, we may have been selected to avoid excess storage because of the elevated risks of predation. This upper limit of control seems to have malfunctioned because some of us deposit large fat stores, with important negative health effects. Why has evolution not protected us against this problem? One possibility is that the protective system slowly fell apart due to random mutations after we dramatically reduced the risk of being predated during our evolutionary history. By chance, it fell apart more in some people than others, and these people are now unable to effectively manage their weight in the face of the modern food glut. To understand the evolutionary context of obesity, it is important to separate the adaptive reason for storing some fat (i.e. the lower intervention point), from the nonadaptive reason for storing lots of fat (a broken upper intervention point). The DIP model has several consequences, showing how we understand the obesity problem and what happens when we attempt to treat it.

External validation of the Finnish diabetes risk score in Venezuela using a national sample: The EVESCAM

AIMS

To evaluate the performance of the Latin American Finnish Diabetes Risk Score (LA-FINDRISC) compared with the original O-FINDRISC in general population. To establish the best cut-off to detect unknown type 2 diabetes (uT2D) and prediabetes.

METHODS

The EVESCAM was a national population-based, cross-sectional, randomized cluster sampling study, which assessed 3454 adults from July 2014 to January 2017. Those with self-report of diabetes were excluded; a total of 3061 subjects were analyzed. Waist circumference adapted for Latin America was the difference between the LA-FINDRISC and the O-FINDRISC. The area under the curve (AUC), sensitivity, and specificity were calculated.

RESULTS

The prevalence of uT2D and prediabetes were 3.3% and 38.5%. The AUC with the LA-FINDRISC vs. the O-FINDRISC were: for uT2D, 0.722 vs. 0.729 in men (p=0.854) and 0.724 vs. 0.732 in women (p=0.896); for prediabetes (impaired fasting glucose [IFG] + impaired glucose tolerance [IGT], 0.590 vs. 0.587 in men (p=0.887) and 0.621 vs. 0.627 in women (p=0.777); for IFG, 0.582 vs. 0.580 in men (p=0.924) and 0.607 vs. 0.617 in women (p=0.690); for IGT, 0.691 vs. 0.692 in men (p=0.971) and 0.672 vs. 0.671 in women (p=0.974). Using the LA-FINDRISC, the best cut-offs to detect uT2D were 9 in men and 10 in women and to detect IGT was 9 in both genders.

CONCLUSION

LA-FINDRISC has similar performance than O-FINDRISC in Venezuelan adults and showed a good performance to detect uT2D and IGT, but not IFG. The best cut-offs to detect glucose alterations were established.

Diet and body fat in adolescence and early adulthood: a systematic review of longitudinal studies

Adipose tissue is a vital component of the human body, but in excess, it represents a risk to health. According to the World Health Organization, one of the main factors determining excessive body adiposity is the dietary habit. This systematic review investigated longitudinal studies that assessed the association between diet and body fat in adolescents and young adults. Twenty-one relevant papers published between 2001 and 2015 were selected. The most used method for estimating body fat was the body mass index (15 studies). Diet was most commonly assessed by estimating the consumption of food groups (cereals, milk and dairy products) and specific foods (sugar-sweetened beverages, soft drinks, fast foods, milk, etc.). Ten studies found a direct association between diet and quantity of body fat. During adolescence, adhering to a dietary pattern characterized by high consumption of energy-dense food, fast foods, sugar-sweetened beverages and soft drinks, as well as low fiber intake, appears to contribute to an increase in body fat in early adulthood. The findings of the present study suggest that the frequent consumption of unhealthy foods and food groups (higher energy density and lower nutrient content) in adolescence is associated with higher quantity of body fat in early adulthood.

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.

Psychological assessment of children and adolescents with obesity

Objective This study aimed to analyse the psychological conditions and behaviour of a group of Chinese children and adolescents with obesity, and to develop an intervention for these young patients. Methods A group of 72 patients aged from 4 to 15 years were recruited from an obesity clinic. Patients, or the parents of children younger than 12 years, filled out a series of self-report questionnaires, and the responses were recorded and analysed. Results The 72 children and adolescents with obesity had a mean age of 9.14 ± 2.18 years. The body mass index-z scores of children with obesity showed a significant positive correlation with the level of impulsive behaviour, motivational impulses, and cognitive instability (inattention). Children with obesity quickly responded with extreme emotions, and these responses were positively correlated with the degree of obesity (slight, intermediate, or severe obesity). Conclusion Children and adolescents being treated for obesity have many underlying psychological problems, including emotional instability and impulsivity, and are prone to extreme emotional-psychological problems. These difficulties are positively correlated with the degree of obesity. Therefore, clinical treatment of these problems requires not only use of medication, improved nutrition, and healthy exercise, but also addressing underlying psychologic problems.

Analysis of Positive Selection at Single Nucleotide Polymorphisms Associated with Body Mass Index Does Not Support the "Thrifty Gene" Hypothesis

The "thrifty gene hypothesis" suggests genetic susceptibility to obesity arises because of positive selection for alleles that favored fat deposition and survival during famines. We used public domain data to locate signatures of positive selection based on derived allele frequency, genetic diversity, long haplotypes, and differences between populations at SNPs identified in genome-wide association studies (GWASs) for BMI. We used SNPs near the lactase (LCT), SLC24A5, and SLC45A2 genes as positive controls and 120 randomly selected SNPs as negative controls. We found evidence for positive selection (p < 0.05) at nine out of 115 BMI SNPs. However, five of these involved positive selection for the protective allele (i.e., for leanness). The widespread absence of signatures of positive selection, combined with selection favoring leanness at some alleles, does not support the suggestion that obesity provided a selective advantage to survive famines, or any other selective advantage.

The metabolic syndrome: an emerging risk state for cardiovascular disease

The common clustering of glucose intolerance, insulin resistance, abdominal adiposity, elevated blood pressure, and low HDL cholesterol is referred to as metabolic syndrome. Individuals with this syndrome have an increased risk of developing cardiovascular disease (CVD). The World Health Organisation and the National Cholesterol Education Programme’s Adult Treatment Panel III (NCEP-ATP III) have outlined specific diagnostic criteria for the diagnosis of the metabolic syndrome to help in the Identification of this syndrome in clinical practice. While the WHO criteria were specifically developed for use in research, the NCEP criteria are useful in clinical diagnosis of the metabolic syndrome. The metabolic syndrome is amenable to lifestyle modifications such as increased physical activity, weight loss, and possibly intake of low-glycemic foods. Drug therapy may be used to treat individual components of the syndrome such as elevated blood pressure and dyslipidemia. To control elevated glucose levels (when there is failure of lifestyle modification), medications such as metformin, thiazolidinedione derivatives and alpha glucosidase inhibitors may be used.

Predation risk modulates diet-induced obesity in male C57BL/6 mice

OBJECTIVE

In this study, the behavioral and physiological changes induced by experimentally varying the risk of predation in male mice fed a high-fat diet were examined. In particular, the study aimed to assess whether the risk of being predated modulates the body weight gain, providing an ecological context for the obesity resistance observed in many species of small mammals.

METHODS

Body weight, food intake, physical activity, and core body temperature of 35 male C57BL/6 mice were monitored for 20 days, while feeding a high-fat diet. A third of the animals were exposed to elevated risk of predation through exposure to the sounds of nocturnal predatory birds, and these were compared to animals exposed to a neutral noise or silence.

RESULTS

Male mice exposed to predation risk had significantly lower weight gain than the neutral or silent groups. Reduced food intake and increased physical activity were the main proximal factors explaining this effect. The risk of predation also induced changes in boldness.

CONCLUSIONS

This study provides evidence supporting the role of predation risk on body weight gain of small mammals.

Metabolic vs. hedonic obesity: a conceptual distinction and its clinical implications

Body weight is determined via both metabolic and hedonic mechanisms. Metabolic regulation of body weight centres around the 'body weight set point', which is programmed by energy balance circuitry in the hypothalamus and other specific brain regions. The metabolic body weight set point has a genetic basis, but exposure to an obesogenic environment may elicit allostatic responses and upward drift of the set point, leading to a higher maintained body weight. However, an elevated steady-state body weight may also be achieved without an alteration of the metabolic set point, via sustained hedonic over-eating, which is governed by the reward system of the brain and can override homeostatic metabolic signals. While hedonic signals are potent influences in determining food intake, metabolic regulation involves the active control of both food intake and energy expenditure. When overweight is due to elevation of the metabolic set point ('metabolic obesity'), energy expenditure theoretically falls onto the standard energy-mass regression line. In contrast, when a steady-state weight is above the metabolic set point due to hedonic over-eating ('hedonic obesity'), a persistent compensatory increase in energy expenditure per unit metabolic mass may be demonstrable. Recognition of the two types of obesity may lead to more effective treatment and prevention of obesity.

Rs7206790 and rs11644943 in FTO gene are associated with risk of obesity in Chinese school-age population

To evaluate the associations between candidate FTO single nucleotide polymorphisms (SNPs) and obesity, a case-control study was conducted among Chinese school-age children, which included 500 obese cases and 500 matched controls (age, gender and location). We selected 24 candidate FTO tag-SNPs via bio-informatics analysis and performed genotyping using SNPScan technology. Results indicated that rs7206790 and rs11644943 were significantly associated with obesity among school-age children in both additive and recessive models (P<0.05) after adjusting confounders. Comparing rs7206790 CC and CG genotype of carriers, those carrying the GG genotype had an increased risk of obesity (adjusted odds ratio [OR], 3.76; 95% Confidence interval [CI], 1.24–11.43). Carriers of the AA allele of rs11644943 had a lower risk of obesity (adjusted OR, 0.16; 95% CI, 0.04–0.72) compared with those of the T allele (TT and TA). These two SNPs (rs7206790 and rs11644943) were not Linkage Disequilibrium (LD) with previous reported obesity-associated SNPs. Under the recessive model adjusted for age and gender and location, rs7206790 GG allele carriers had significantly increased BMIs (P = 0.012), weight (P = 0.012), waist circumferences (WC) (P = 0.045) and hip circumferences (HC) (P = 0.033). Conversely, rs11644943 AA allele carriers had significantly decreased BMIs (P = 0.006), WC (P = 0.037) and Waist-to-height ratios (WHtR) (P = 0.012). A dose-response relationship was found between the number of risk alleles in rs7206790, rs11644943 and rs9939609 and the risk of obesity. The Genetic Risk Score (GRS) of the reference group was 3; in comparison, those of 2, 4, and ≥5 had ORs for obesity of 0.24 (95%CI, 0.05–1.13), 1.49 (95%CI, 1.10–2.01), and 5.20 (95%CI, 1.75–15.44), respectively. This study confirmed the role of FTO variation on genetic susceptibility to obesity. We reported two new obesity-related FTO SNPs (rs7206790 and rs11644943) among Chinese school-age children.

If Body Fatness is Under Physiological Regulation, Then How Come We Have an Obesity Epidemic?

Life involves a continuous use of energy, but food intake, which supplies that energy, is episodic. Feeding is switched on and off by a complex array of predominantly gut-derived peptides (and potentially nutrients) that initiate and terminate feeding bouts. Energy is stored as glucose and glycogen to overcome the problem of the episodic nature of intake compared with the continuous demand. Intake is also adjusted to meet immediate changes in demands. Most animals also store energy as fat. In some cases, this serves the purpose of storing energy in anticipation of a known future shortfall (e.g., hibernation, migration, or reproduction). Other animals, however, store fat in the absence of such anticipated needs, and in this case the fat appears to be stored in preparation for unpredictable catastrophic shortfalls in supply. Fat storage, however, brings disadvantages as well as advantages, in particular an increased risk of predation. Hence, many animals seem to have evolved a dual intervention point system preventing them from storing too little or too much fat. The physiological basis of the lower intervention point is well established, but the upper intervention point is much less studied. Human obesity can potentially be understood in an evolutionary context as due to drift in the upper intervention point following release from predation 2 million years ago (the drifty gene hypothesis) combined with a stimulus in modern society to overconsume calories, possibly attempting to satisfy intake of a limiting micro- or macro-nutrient like protein (the protein leverage hypothesis).

Evolutionary perspectives on the obesity epidemic: adaptive, maladaptive, and neutral viewpoints

The prevalence of obesity in modern societies has two major contributory factors-an environmental change that has happened in historical times and a genetic predisposition that has its origins in our evolutionary history. Understanding both aspects is complex. From an evolutionary perspective, three different types of explanation have been proposed. The first is that obesity was once adaptive and enabled us to survive (or sustain fecundity) through periods of famine. People carrying so-called thrifty genes that enabled the efficient storage of energy as fat between famines would be at a selective advantage. In the modern world, however, people who have inherited these genes deposit fat in preparation for a famine that never comes, and the result is widespread obesity. The key problem with this, and any other adaptive scenario, is to understand why, if obesity was historically so advantageous, many people did not inherit these thrifty genes and in modern society are able to remain slim, despite the environmental change favoring fat storage. The second type of explanation is that obesity is not adaptive and may never even have existed in our evolutionary past, but it is favored today as a maladaptive by-product of positive selection on some other trait. An example of this type of explanation is the suggestion that obesity results from variation in brown adipose tissue thermogenesis. Finally, a third class of explanation is that most mutations in the genes that predispose us to obesity are neutral and have been drifting over evolutionary time--so-called drifty genes, leading some individuals to be obesity prone and others obesity resistant. In this article, I review the current evidence for and against these three different scenarios and conclude that the thrifty gene hypothesis is untenable but the other two ideas may provide a cogent explanation of the modern obesity phenomenon.

Maternal dietary fat affects the LT muscle fatty acid composition of progeny at weaning and finishing stages in pigs

The present study was conducted to investigate whether maternal dietary fat affects the fatty acid composition of the longissimus thoracis (LT) muscle in offspring pigs at weaning and finishing stages. Fourteen sows were randomly assigned to a control or a high fat (HF) group. The HF sows received a diet containing 8% corn oil starting seven days before farrowing until weaning. The results showed that a high-fat diet significantly increased the contents of serum-lipid-related indexes in the sows. Although the triglyceride content did not change, the C18:2n-6 content was higher in the colostrum and in the LT muscle of offspring pigs at both investigated stages. The total n-6 content and the n-6/n-3 ratio generally increased. This study demonstrated that maternal dietary fat during lactation affects the fatty acid composition of the LT muscle of progeny at weaning, and can have persistent effects in later life.

Compliance with physical exercise: using a multidisciplinary approach within a dose-dependent exercise study of moderately overweight men

AIMS

Sixty-one healthy, sedentary, moderately overweight young men participated in a randomised controlled trial to examine the effects of two different doses of endurance exercise on health behaviour and exercise compliance.

METHODS

Participants were randomised to a sedentary control group, a moderate (MOD; 300 kcal/day) or a high-dose (HIGH; 600 kcal/day) endurance exercise group for 12 weeks. A sub-set of the subjects were interviewed using pre-determined, qualitative questions to elucidate physical activity and health behaviour. In combination with the Theory of Planned Behaviour (TPB), a post hoc thematic analysis was conducted to connect qualitative and quantitative data in a joint analysis.

RESULTS

Of the subjects interviewed, exercise compliance expressed as 95% CI was [96.8; 103%] in the MOD group and [82.9; 99.6%] in the HIGH group. The different doses of daily exercise equally improved various metabolic health parameters. The MOD group was untroubled by the exercise load and had a positive attitude towards exercise. The HIGH group expressed increased fatigue, less positivity and perceived exercise as time-consuming. The MOD group described themselves as more energetic, and thereby may have increased physical activity levels in areas of their everyday lives that were not related to the intervention.

CONCLUSIONS

A multidisciplinary approach provided explanations for similar effects of two different doses of exercise. This could not have been determined via either qualitative or quantitative methodology alone. The preconditions of the TBP were fulfilled, and it represents a methodological model to explain the high degree of compliance and motivation to exercise.

Mechanism of hyperphagia contributing to obesity in brain-derived neurotrophic factor knockout mice

Global-heterozygous and brain-specific homozygous knockouts (KOs) of brain-derived neurotrophic factor (BDNF) cause late- and early-onset obesity, respectively, both involving hyperphagia. Little is known about the mechanism underlying this hyperphagia or whether BDNF loss from peripheral tissues could contribute to overeating. Since global-homozygous BDNF-KO is perinatal lethal, a BDNF-KO that spared sufficient brainstem BDNF to support normal health was utilized to begin to address these issues. Meal pattern and microstructure analyses suggested overeating of BDNF-KO mice was mediated by deficits in both satiation and satiety that resulted in increased meal size and frequency and implicated a reduction of vagal signaling from the gut to the brain. Meal-induced c-Fos activation in the nucleus of the solitary tract, a more direct measure of vagal afferent signaling, however, was not decreased in BDNF-KO mice, and thus was not consistent with a vagal afferent role. Interestingly though, meal-induced c-Fos activation was increased in the dorsal motor nucleus of the vagus nerve (DMV) of BDNF-KO mice. This could imply that augmentation of vago-vagal digestive reflexes occurred (e.g., accommodation), which would support increased meal size and possibly increased meal number by reducing the increase in intragastric pressure produced by a given amount of ingesta. Additionally, vagal sensory neuron number in BDNF-KO mice was altered in a manner consistent with the increased meal-induced activation of the DMV. These results suggest reduced BDNF causes satiety and satiation deficits that support hyperphagia, possibly involving augmentation of vago-vagal reflexes mediated by central pathways or vagal afferents regulated by BDNF levels.

A mathematical model of weight loss under total starvation: evidence against the thrifty-gene hypothesis

The thrifty-gene hypothesis (TGH) posits that the modern genetic predisposition to obesity stems from a historical past where famine selected for genes that promote efficient fat deposition. It has been previously argued that such a scenario is unfeasible because under such strong selection any gene favouring fat deposition would rapidly move to fixation. Hence, we should all be predisposed to obesity: which we are not. The genetic architecture of obesity that has been revealed by genome-wide association studies (GWAS), however, calls into question such an argument. Obesity is caused by mutations in many hundreds (maybe thousands) of genes, each with a very minor, independent and additive impact. Selection on such genes would probably be very weak because the individual advantages they would confer would be very small. Hence, the genetic architecture of the epidemic may indeed be compatible with, and hence support, the TGH. To evaluate whether this is correct, it is necessary to know the likely effects of the identified GWAS alleles on survival during starvation. This would allow definition of their advantage in famine conditions, and hence the likely selection pressure for such alleles to have spread over the time course of human evolution. We constructed a mathematical model of weight loss under total starvation using the established principles of energy balance. Using the model, we found that fatter individuals would indeed survive longer and, at a given body weight, females would survive longer than males, when totally starved. An allele causing deposition of an extra 80 g of fat would result in an extension of life under total starvation by about 1.1-1.6% in an individual with 10 kg of fat and by 0.25-0.27% in an individual carrying 32 kg of fat. A mutation causing a per allele effect of 0.25% would become completely fixed in a population with an effective size of 5 million individuals in 6000 selection events. Because there have probably been about 24,000 famine events since the evolution of hominins 4 million years ago, there has been ample time even for genes with only very minor impacts on adiposity to move to fixation. The observed polymorphic variation in the genes causing the predisposition to obesity is incompatible with the TGH, unless all these single nucleotide polymorphisms (SNPs) arose in the last 900,000 years, a requirement we know is incorrect. The TGH is further weakened by the observation of no link between the effect size of these SNPs and their prevalence, which would be anticipated under the TGH model of selection if all the SNPs had arisen in the last 900,000 years.

Set points, settling points and some alternative models: theoretical options to understand how genes and environments combine to regulate body adiposity

The close correspondence between energy intake and expenditure over prolonged time periods, coupled with an apparent protection of the level of body adiposity in the face of perturbations of energy balance, has led to the idea that body fatness is regulated via mechanisms that control intake and energy expenditure. Two models have dominated the discussion of how this regulation might take place. The set point model is rooted in physiology, genetics and molecular biology, and suggests that there is an active feedback mechanism linking adipose tissue (stored energy) to intake and expenditure via a set point, presumably encoded in the brain. This model is consistent with many of the biological aspects of energy balance, but struggles to explain the many significant environmental and social influences on obesity, food intake and physical activity. More importantly, the set point model does not effectively explain the 'obesity epidemic'--the large increase in body weight and adiposity of a large proportion of individuals in many countries since the 1980s. An alternative model, called the settling point model, is based on the idea that there is passive feedback between the size of the body stores and aspects of expenditure. This model accommodates many of the social and environmental characteristics of energy balance, but struggles to explain some of the biological and genetic aspects. The shortcomings of these two models reflect their failure to address the gene-by-environment interactions that dominate the regulation of body weight. We discuss two additional models--the general intake model and the dual intervention point model--that address this issue and might offer better ways to understand how body fatness is controlled.

The effect of maternal omega-3 long-chain polyunsaturated fatty acid (n-3 LCPUFA) supplementation during pregnancy and/or lactation on body fat mass in the offspring: a systematic review of animal studies

Dietary n-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) reduce adipogenesis and lipogenesis in adult rodents, but it is not clear whether an increased n-3 LCPUFA supply during the perinatal period influences body fat mass in the offspring. This systematic review aimed to evaluate the existing evidence from animal studies, which have addressed this question. Medline was searched for relevant articles. Studies were included if they involved maternal n-3 PUFA or LCPUFA supplementation and measured fat mass in the offspring. The design and quality of each study was assessed. Only four animal studies met our inclusion criteria. Three studies reported a lower fat mass in offspring of n-3 LCPUFA supplemented dams, however only one of these studies confined the intervention to the perinatal period. The dose of n-3 PUFA, the nature of the control treatment, the approaches used and outcomes assessed differed between studies. This review highlights the paucity of robust animal data as to the effect of increased n-3 LCPUFA exposure during the perinatal period alone, on body fat mass in the offspring and calls for further studies.

Effect of long-chain polyunsaturated fatty acid supplementation during pregnancy or lactation on infant and child body composition: a systematic review

BACKGROUND

n-3 (omega-3) Long-chain polyunsaturated fatty acids (LC-PUFAs) inhibit fat cell differentiation and fat storage in adults, and this has led to the hypothesis that maternal n-3 LC-PUFA supplementation may reduce fat mass in children.

OBJECTIVE

The objective of this systematic review was to evaluate the effect of n-3 LC-PUFA supplementation in pregnancy or lactation on infant and child body composition in randomized controlled trials.

DESIGN

MEDLINE and EMBASE databases were searched for relevant articles. Human trials that supplemented the maternal diet with n-3 LC-PUFAs during pregnancy or lactation and assessed either body fat mass or body mass index in children were included. Trials had to be randomized in design. The quality of all included studies was assessed against set criteria, and results of eligible trials were compared.

RESULTS

There were only 3 human trials (4 publications) that met our inclusion criteria. There was considerable disparity in study design and trial quality. The results were variable and showed positive, negative, or neutral effects of maternal n-3 LC-PUFA supplementation on body fat mass in children.

CONCLUSIONS

This systematic review highlights the paucity of robust data from human studies to evaluate the effect of increased n-3 LC-PUFA exposure during the perinatal period on body fat mass in offspring. Further studies are required in which the intervention is confined to the perinatal period and that are sufficiently powered, have appropriate controls, have adequate blinding of participants and investigators, and have high retention rates.

Perspective on biomaterials used in the surgical treatment of morbid obesity

Morbid obesity is defined as having a body mass index greater than or equal to 40.0 kg m(-2), or 37.0 kg m(-2) with comorbidities. Bariatric surgery remains the most effective treatment for morbid obesity. Bariatric procedures such as sleeve gastrectomy, vertical banded gastroplasty and adjustable gastric banding all generate excess body-weight loss typically over 3-5 years. The biomaterials used during these procedures, namely silicone, polypropylene, expanded polytetrafluoroethylene and titanium, are all non-degradable biomaterials. Hence, their presence in vivo exceeds the functional requirement of an implant to treat morbid obesity. Accordingly, research into non-invasive and reversible surgical procedures has increased, particularly in light of the dramatic increase in paediatric obesity. Tissue engineering is an alternative approach to treat morbid obesity, as it incorporates both engineering and biological principles into the design and development of an implant to surgically treat morbid obesity. It is hypothesized that a biodegradable polymer to treat morbid obesity could be developed to effectively promote excess weight loss. The aim of this review is to discuss morbid obesity with regards to its aetiology, prevalence and current modalities of treatment. Specifically, the shortcomings of the biomaterials currently used to surgically treat morbid obesity shall be reviewed, and alternative biomaterials shall be proposed.

The Thrsp null mouse (Thrsp(tm1cnm)) and diet-induced obesity

We created a Thrsp (Spot 14 or S14) null mouse (Thrsp(tm1cnm)) to study the role of Thrsp in de novo lipid synthesis. The Thrsp null mouse exhibits marked deficiencies in de novo lipogenesis in the lactating mammary gland. We now report the Thrsp gene deletion affects body weight and glucose tolerance associated with increased insulin sensitivity. By post-natal day 150 the rate of first generation C57BL/6J backcross Thrsp null mouse weight gain slowed compared to wild type animals. This was due to changes in body fat mass. We studied mice backcrossed for 5 and 11 generations. The weight difference between the null and wild type adult mice diminished with progressive backcross generations. In conclusion the Thrsp gene is involved in the regulation of diet-induced obesity and deletion of Thrsp leads to an improvement in age associated glucose tolerance.

Maternal anthropometry is associated with the body mass index and waist:height ratio of offspring at 23 years of age

Obesity is considered a public health problem worldwide. Evidence from epidemiologic studies has shown that early undernutrition may be a determinant of obesity later in life. Longitudinal studies are scarce in the setting of low- and middle-income countries. In Pelotas, southern Brazil, a birth cohort has been followed since 1982. Between 2004 and 2005, 4297 members of this cohort were interviewed. The aim of this study is to describe the association between maternal anthropometry and offspring BMI and waist:height ratio (WHtR) at 23 y of age in individuals from the 1982 Pelotas birth cohort. Independent variables included maternal prepregnancy BMI and maternal height, obtained in 1982. The BMI and WHtR of the offspring at 23 y of age were the outcomes. The analysis was stratified by sex and restricted to those cohort members belonging to the lower income group. Multivariable linear regression was adjusted for potential confounding or mediating factors according to a hierarchical framework. For each unit of maternal prepregnancy BMI, the offspring BMI increased 0.65 and 0.63 kg/m(2) in men and women, respectively (P < 0.001). Maternal prepregnancy BMI was directly associated with offspring WHtR in both sexes (P < 0.001). On the other hand, maternal height was not associated with offspring BMI or WHtR. In conclusion, our study suggests that maternal anthropometry is associated with the offspring BMI and WHtR at 23 y of age.

Thrifty genes for obesity, an attractive but flawed idea, and an alternative perspective: the 'drifty gene' hypothesis

Almost 50 years ago Neel proposed a hypothesis to explain the prevalence of obesity and diabetes in modern society--the 'thrifty gene' hypothesis. The fundamental basis of the hypothesis was that, in our early evolutionary history, genes, that promoted efficient fat deposition would have been advantageous because they allowed their holders to survive at periods of famine. In modern society, such genes are disadvantageous because they promote fat deposition in preparation for a famine that never comes, and the result is widespread obesity and diabetes. In recent years I, and others, have questioned some of the fundamental assumptions of this hypothesis--particularly focusing on whether differential survival of lean against obese in famines provides sufficient selective pressure for the spread of so-called 'thrifty genes'. These arguments have been criticized because famines not only affect survival but also fecundity, and obese people would be expected to sustain fecundity longer in the face of food shortages. In this paper, I show that the reduced fecundity argument is flawed because famines are almost universally followed by periods of enhanced fecundity, which offsets the decline observed during the famine itself. The net effect of famines on fecundity is consequently insufficient to rescue the thrifty gene idea. Elsewhere, I have suggested an alternative scenario that subsections of the population have a genetic predisposition to obesity due to an absence of selection, combined with genetic drift. The scenario presented earlier was based on evidence from prehistory concerning the release of our ancestors from heavy predation pressure around 2 million years ago. I suggest here that this is one of a number of potential scenarios based on random genetic drift that may explain the specific aetiology of the obesity epidemic. Together, these alternatives, based on central notion that genetic drift rather than positive selection was a dominant factor, may be called the 'drifty gene' hypothesis.

Maternal nutrition and the programming of obesity: The brain

The increasing incidence of obesity in the developed and developing world in the last decade has led to a need to define our understanding of the physiological mechanisms which can predispose individuals to weight gain in infancy, childhood and adulthood. There is now a considerable body of evidence which has shown that the pathway to obesity may begin very early in life, and that exposure to an inappropriate level of nutrition during prenatal and/or early postnatal development can predispose individuals to obesity in later life The brain is at the heart of the regulation of appetite and food preferences, and it is increasingly being recognized that the development of central appetitive structures is acutely sensitive to the nutritional environment both before and immediately after birth. This review will summarize the body of work which has highlighted the critical role of the brain in the early origins of obesity and presents some perspectives as to the potential application of these research findings in the clinical setting.

Congenital and environmental factors associated with adipocyte dysregulation as defects of insulin resistance

The metabolic syndrome refers to insulin resistance and its associated cluster of related cardiovascular metabolic risk factors including type 2 diabetes, hypertension, dyslipidemia and central obesity. Although many hypotheses and facts have been proposed to explain the interaction between genetic and environmental causes of this syndrome, the primary etiology of the metabolic syndrome is adipose tissue dysregulation. Firstly, the thrifty genotype and phenotype hypothesis may explain the endemic increase in type 2 diabetes and cardiovascular disease in developing countries and elucidates the congenital susceptibility and environmental triggering of the metabolic syndrome. Secondly, over-nutrition leads to fatty acid (FA) accumulation in adipocytes and to an overflow to ectopic fat storage organs. This causes functional changes in adipocytes shifting the intra-cellular metabolic pathway toward insulin resistance. Thirdly, obese subjects exhibit increased fat cell size and over-secretion of biologic adipocytokines. Fourthly, failure to adequately develop adipose tissue mass, as seen in lipodystrophy cases, causes severe insulin resistance and diabetes. Lastly, similar to human type 2 diabetes, Psammonys obesus, a desert rat which feeds mainly on low-calorie vegetation, develops the metabolic syndrome when given a diet of calorie rich food. The above evidence indicates adipocyte dysregulation and secretion of FA as well as certain molecules from overloaded adipocytes/adipokines contribute to the pathogenesis of impaired insulin secretion and insulin resistance, endothelial dysfunction, a pro-inflammatory state and promote progression of atherosclerosis. The metabolic syndrome is a modern disease resulting adipocyte dysmetabolism resulting from the paradox of the slow human evolution combined with rapid environmental changes.

A nonadaptive scenario explaining the genetic predisposition to obesity: the "predation release" hypothesis

The "thrifty gene hypothesis" suggests we evolved genes for efficient food collection and fat deposition to survive periods of famine and that now that food is continuously available, these genes are disadvantageous because they make us obese in preparation for a famine that never comes. However, famines are relatively infrequent modern phenomena that involve insufficient mortality for thrifty genes to propagate. I suggest here that early hominids would have been subjected to stabilizing selection for body fatness, with obesity selected against by the risk of predation. Around two million years ago predation was removed as a significant factor by the development of social behavior, weapons, and fire. The absence of predation led to a change in the population distribution of body fatness due to random mutations and drift. Because this novel hypothesis involves random drift, rather than directed selection, it explains why, even in Western society, most people are not obese.

Obesity epidemic in India: intrauterine origins?

The epidemic of ‘obesity’ in India is not appreciated because BMI underestimates the adiposity of Indians. Specific adiposity measurements are necessary for recognition of the adiposity of ‘thin’ Indians. The origin of this adiposity is only beginning to be understood. In addition to a possible genetic predisposition, intrauterine ‘programming’ might be responsible, although in the ‘thrifty phenotype’ hypothesis the adiposity of the ‘thin’ fetus has not been appreciated. Dutch men who faced ‘winter hunger’ during the first trimester of their in utero life have become more obese as adults. Low birth weight predicts central obesity in some studies, including studies in urban children. It has also been shown that small and thin Indian newborns (weight 2·7?kg and ponderal index 2·4?kg\m3) have poor muscle and visceral mass but higher adiposity for a given weight compared with white Caucasian babies. This body composition is influenced by maternal adiposity before pregnancy and by aspects of maternal nutritional intake and circulating nutrient concentrations during pregnancy. There are no strong paternal determinants of adiposity at birth. Adiposity may be an integral part of the orchestrated adjustments made to support ‘brain preservation’ during intrauterine growth, because brain tissue is predominantly fat. Increased nutrition in the face of a genetic predisposition or multigenerational undernutrition increases maternal insulin resistance in late pregnancy and promotes fetal adiposity even in absence of marked hyperglycaemia. Further research is necessary to define the role of specific nutrients and metabolites in the intrauterine processes promoting adiposity before maternal interventions to curtail the epidemic of obesity and diabetes are planned.

Characterization of obesity in Japanese monkeys (Macaca fuscata) in a pedigreed colony

BACKGROUND

Japanese monkey, Macaca fuscata, is recognized as the monkey species inhabiting the northernmost area in the world, and thus likely to possess unique fat-depositing mechanisms to resist cold weather in winter. We report that obese females are present in the Wakasa group of Japanese monkey reared in an open enclosure of the Primate Research Institute, Kyoto University.

METHODS AND RESULTS

Eight of 12 females were categorized as obese, showing percentage body fat of over 22%. The levels of serum leptin (mean +/- SD, 4.9 +/- 2.3 ng/ml) measured in these obese monkeys were significantly higher than those of non-obese peers of the same group (n = 4; 1.2 +/- 0.5 ng/ml) and another Japanese monkey group (Takahama, n = 14; 0.8 +/- 0.25 ng/ml); however, serum levels of adiponectin, insulin, glucose, hemoglobin A1c, and fructosamine did not differ between obese and non-obese monkeys. Few serum lipid parameters such as triglyceride and cholesterol showed lower levels in obese monkeys than their non-obese peers.

CONCLUSIONS

These results show that these obese monkeys in the Wakasa group have not developed obesity-related diseases/disorders such as diabetes. In the Wakasa group, the frequency of obese individuals was high in some maternal lineages, suggesting that genetic factors responsible for obesity may have been inherited in these lineages.

Thrifty genes for obesity and the metabolic syndrome--time to call off the search?

Over the last 50 years there has been a major epidemic of obesity and associated co-morbidities, the so-called 'metabolic syndrome', mostly in the western world but with an increasingly global dimension. The development of such chronic diseases has a strong genetic component, yet the timescale of their increase cannot reflect a population genetic change. Consequently, the most accepted model is that obesity and its sequelae are a result of a gene-environment interaction, an ancient genetic selection to deposit fat efficiently that is maladaptive in modern society. Why we have this genetic predisposition has been a matter of much speculation. Following the seminal contribution of Neel, there has been a broad consensus that over evolutionary time we have been exposed to regular periods of famine, during which fatter individuals would have enjoyed a selective advantage by their greater survival. Consequently, individuals with genes promoting the efficient deposition of fat during periods between famines ('thrifty genes') would be favoured. In the modern environment this genetic predisposition prepares us for a famine that never comes, and an epidemic of obesity with all the attendant chronic illnesses follows. In this review I present details of the evidence supporting the famine hypothesis and then show that this idea has five fundamental flaws. In essence, famines are a relatively modern phenomenon and occur only about once every 100-150 years. Consequently, most human populations have only experienced at most 100 famine events in their evolutionary history. Famines involve increases in total mortality that only rarely exceed 10% of the population. Moreover, most people in famines die of disease rather than starvation and the age distribution of mortality during famine would not result in differential mortality between lean and obese individuals. A simple genetic model shows that famines provide insufficient selective advantage over an insufficient time period for a thrifty gene to have any penetration in the modern human population. Over the 40 or so years since Neel proposed the thrifty gene hypothesis, no convincing candidates for these genes have been discovered. My analysis suggests that perhaps it is time to call off the search.

Increased body fat in mice with a targeted mutation of the paternally expressed imprinted gene Peg3

Peg3 encodes a C2H2 type zinc finger protein that is implicated in a novel physiological pathway regulating core body temperature, feeding behavior, and obesity in mice. Peg3+/- mutant mice develop an excess of abdominal, subcutaneous, and intra-scapular fat, despite a lifetime of lower food intake than wild-type animals. However, they start life with reduced fat reserves and are slower to enter puberty. These mice maintain a lower core body temperature, fail to respond to a cold challenge, and have lower metabolic activity as measured by oxygen consumption. Plasma leptin levels are significantly higher than in wild types, and Peg3+/- mice appear to have developed leptin resistance. Administration of exogenous leptin resulted in a significant reduction in food intake in wild-type mice that was not observed in Peg3+/- mutants. This mutation, which is strongly expressed in hypothalamic tissue during development, has the capacity to regulate multiple events relating to energy homeostasis.

A life course perspective: understanding food choices in time, social location, and history

A life course perspective provides a framework for understanding how food choices develop in changing temporal, social, and historical contexts. This article describes the application of life course concepts to food choices, including trajectories, transitions, turning points, lives in place and time, and timing of events in lives. A life course approach to food choice can contribute to understanding the social and biological pathways of health risk and resilience over the life span. Life course analysis is a useful research and practice tool because of the many ways in which foods, the individuals choosing them, and food choice environments are changing.

Poor fetal growth followed by rapid postnatal catch-up growth leads to premature death

It is widely accepted that individuals with a low birth weight are at increased risk of developing type 2 diabetes, insulin resistance and cardiovascular disease. This risk is amplified if the poor fetal growth is followed by rapid postnatal catch-up growth. We have shown recently that poor fetal growth, resulting from maternal protein restriction, followed by postnatal catch-up growth is associated with reduced average longevity in mice. Here, we show that in addition to reduced average longevity, mice which have been growth restricted in utero and then grown rapidly during the lactation period have a reduced maximum longevity. Maximum longevity of these mice was, further, reduced when the animals were weaned onto an obesity-inducing cafeteria-style diet. This reduced maximum longevity was associated with early age-related weight loss. These results demonstrate that maternal nutrition during critical periods of development has a major impact on quantity as well as quality of life.

Programming of obesity and cardiovascular disease

BACKGROUND

There is evidence that malnutrition in early life induces a growth retardation leading, in adult life, to manifest components of the metabolic syndrome. However, the impact on obesity seems less clearly established.

OBJECTIVE

To review the effects of foetal and postnatal malnutrition on the programming of obesity in the context of the metabolic syndrome, as well as the link between central obesity and cardiovascular diseases.

METHODS

Included in the review were recent papers exploring the mechanisms linking maternal nutrition with impaired foetal growth and later obesity, cardiovascular disease, hypertension and diabetes in humans and animals.

RESULTS

The programming of obesity during foetal and early postnatal life depends of the timing of maternal malnutrition as well as the postnatal environment. Obesity arises principally in offspring submitted to malnutrition during early stages of gestation and which presented early catch-up growth. The programming may involve the dysregulation of appetite control or the hormonal environment leading to a context favourable to obesity development (hypersecretion of corticosteroids, hyperinsulinaemia and hyperleptinaemia and anomalies in the IGF axis). Adipose tissue secretes actively several factors implicated in inflammation, blood pressure, coagulation and fibrinolysis. The programmed development of intra-abdominal obesity after early growth restriction may thus favour higher prevalence of hypertension and cardiovascular diseases.

CONCLUSIONS

Abdominal obesity appears in malnourished offspring and is aggravated by early catch-up growth. Higher rates of intra-abdominal obesity observed after growth restriction may participate to hypertension and create atherothrombotic conditions leading to the development of cardiovascular diseases.

A mechanism underlying mature-onset obesity: evidence from the hyperphagic phenotype of brain-derived neurotrophic factor mutants

Mice deficient in brain-derived neurotrophic factor (BDNF) develop mature-onset obesity, primarily due to overeating. To gain insight into the mechanism of this hyperphagia, we characterized food intake, body weight, meal pattern, and meal microstructure in young and mature mice fed balanced or high-fat diets. Hyperphagia and obesity occurred in mature but not young BDNF mutants fed a balanced diet. This hyperphagia was mediated by increased meal number, which was associated with normal meal size, meal duration, and satiety ratio. In contrast, the high-fat diet induced premature development of hyperphagia and obesity in young BDNF mutants and a similar magnitude hyperphagia in mature mutants. This hyperphagia was supported by increased meal size and was accompanied by a reduced satiety ratio. Thus the mechanism underlying hyperphagia was present before significant weight gain, but whether it occurred, and whether meal frequency or meal size was altered to support it, was modulated by a process associated with aging and by diet properties. Meal pattern changes associated with the balanced diet suggested meal initiation, and the oropharyngeal positive feedback that drives feeding, were enhanced and might have contributed to overeating in BDNF mutants, whereas negative feedback was normal. Consistent with this hypothesis, meal microstructure revealed that all hyperphagic mutant groups exhibited increased intake rates at meal onset. Therefore, the central nervous system targets of BDNF actions may include orosensory brain stem neurons that process and transmit positive feedback or forebrain neurons that modulate its strength.

Increasing trends of obesity in Sweden between 1996/97 and 2000/01

BACKGROUND

During the last two decades, obesity has reached epidemic proportions in industrialised societies such as Sweden.

OBJECTIVE

The first aim of this study is to examine whether the body mass index (BMI) and obesity increased between 1996/97 and 2000/01 in different subgroups in the Swedish population. The second aim is to examine whether there were any differences in BMI between subgroups of the population, characterised by age, gender, educational status, smoking habits, degree of urbanisation, and country of birth. The third aim is to examine whether BMI increased between the two periods after adjustment for all the explanatory variables.

METHODS

This study is based on two cross-sectional, random samples of the entire population aged 16-84 y, the first from 1996/97 including 5622 men and 5940 women and the second from 2000/01 including 5515 men and 5838 women. To investigate the possible change in obesity between the two periods, a logistic model adjusted for age was applied, after stratification by gender. To study the relationship between BMI and the explanatory variables, and the possible change in the subgroups of the population between the two periods, a linear regression model was used.

RESULTS

The total BMI mean increased by 0.4 units from 1996/97 to 2000/01 for both men and women. The prevalence of obesity also increased to about 10% in 2000/01. In some subgroups, the prevalence of obesity was especially high, for example, men and women aged 55-74 y, men with middle educational status, women with low educational status, former smokers, and Finnish-born men and women.

CONCLUSIONS

These findings illustrate that both BMI and obesity increased in the Swedish population between 1996/97 and 2000/01. This increase in BMI and obesity is most likely due to environmental factors, such as diet and a sedentary lifestyle. Health interventions need to target both certain subgroups and the whole population.

Birth size, early childhood growth, and adolescent obesity in a Brazilian birth cohort

DESIGN

Cross-sectional visit to a subsample of a population-based birth cohort.

SAMPLE

A total of 1076 adolescents aged 14-16 y; 51% males.

MEASUREMENTS

Weight, height, subscapular and triceps skinfolds were used for assessing overweight and obesity in adolescence, using WHO-recommended criteria. Anthropometric status in early life was measured through birthweight and through weight and length/height at average ages of 20 and 43 months.

RESULTS

All analyses were adjusted for socioeconomic and maternal confounding factors. Birthweight and attained size (Z-scores of weight-for-age, height-for-age and weight-for-height) at 20 and 43 months were associated linearly and positively with overweight and obesity in adolescence. Four in each five obese adolescents were not overweight in childhood. Rapid weight gain, both between birth and 20 months, and between 20 and 43 months, was also associated with adolescent overweight and with obesity. Rapid height gain between 20 and 43 months was associated with overweight only. Most associations were stronger for boys.

CONCLUSIONS

Birth size, attained size in childhood and particularly growth velocity in early life were associated with increased prevalence of obesity and overweight in Brazilian adolescents. On the other hand, the vast majority of overweight or obese adolescents were not overweight children. Early interventions are undoubtedly important, but population-based strategies aimed at improving diets and physical activity appear to have greater long-term potential than measures targeted at overweight children.