Type 2 diabetes, the thrifty phenotype - an overview

Relation Between Obesity and Type 2 Diabetes: Evolutionary Insights, Perspectives and Controversies

PURPOSE OF REVIEW

Since the mid-twentieth century, obesity and its related comorbidities, notably insulin resistance (IR) and type 2 diabetes (T2D), have surged. Nevertheless, their underlying mechanisms remain elusive. Evolutionary medicine (EM) sheds light on these issues by examining how evolutionary processes shape traits and diseases, offering insights for medical practice. This review summarizes the pathogenesis and genetics of obesity-related IR and T2D. Subsequently, delving into their evolutionary connections. Addressing limitations and proposing future research directions aims to enhance our understanding of these conditions, paving the way for improved treatments and prevention strategies.

RECENT FINDINGS

Several evolutionary hypotheses have been proposed to unmask the origin of obesity-related IR and T2D, e.g., the "thrifty genotype" hypothesis suggests that certain "thrifty genes" that helped hunter-gatherer populations efficiently store energy as fat during feast-famine cycles are now maladaptive in our modern obesogenic environment. The "drifty genotype" theory suggests that if thrifty genes were advantageous, they would have spread widely, but proposes genetic drift instead. The "behavioral switch" and "carnivore connection" hypotheses propose insulin resistance as an adaptation for a brain-dependent, low-carbohydrate lifestyle. The thrifty phenotype theory suggests various metabolic outcomes shaped by genes and environment during development. However, the majority of these hypotheses lack experimental validation. Understanding why ancestral advantages now predispose us to diseases may aid in drug development and prevention of disease. EM helps us to understand the evolutionary relation between obesity-related IR and T2D. But still gaps and contradictions persist. Further interdisciplinary research is required to elucidate complete mechanisms.

Challenges in policy reforms for non-communicable diseases: the case of diabetes in Kenya

Background: The 2011 UN declaration on non-communicable diseases (NCDs) recognized their importance as a global health issue, particularly for low- and middle-income countries. The extent to which these countries address policy implementation gaps in the face of resource limitations and competing priorities remains largely unexplored.

Objective: This qualitative study presents Kenya’s experience of translating the UN declaration to national policies for diabetes prevention and control.

Methods: Policy documents published between 2006 and 2016 were analyzed. Thirty-two documents were included in the analysis. Interviews with six purposively selected policy stakeholders at multiple levels of decision-making were conducted. Emerging themes were deconstructed into a policy analysis triangle.

Results: Diabetes-specific policies already existed in Kenya before 2011, suggesting successful advocacy work by diabetes interest groups. The 2011 UN declaration subsequently coincided with a period of political transition in Kenya, opening policy windows that the diabetes community leveraged to trigger political drive against prevailing challenges. The post-declaration period reflected a transition from diabetes-specific policies to a wider NCD agenda. Most of the documents and national strategies aligned strongly with international documents, however, were based on scant local evidence. The implementation process was largely health-sector driven. The non-health sector remained largely uninvolved, contrary to global recommendations. This, in addition to fragmented health governance and weak monitoring systems, continues to undermine existing gains and efforts to fight diabetes and NCDs on a wider scale.

Conclusions: In Kenya, a major gap remains between how diabetes is addressed within the NCD policy agenda and tackling diabetes in reality, with respect to local implementation processes. More emphasis on population-wide prevention and inclusion of the non-health sector could help to cascade national efforts to the grassroots level. A concerted effort from the highest political level is needed to address overarching NCD drivers while maintaining health system improvement strategies.

Identification of late larval stage developmental checkpoints in Caenorhabditis elegans regulated by insulin/IGF and steroid hormone signaling pathways

Organisms in the wild develop with varying food availability. During periods of nutritional scarcity, development may slow or arrest until conditions improve. The ability to modulate developmental programs in response to poor nutritional conditions requires a means of sensing the changing nutritional environment and limiting tissue growth. The mechanisms by which organisms accomplish this adaptation are not well understood. We sought to study this question by examining the effects of nutrient deprivation on Caenorhabditis elegans development during the late larval stages, L3 and L4, a period of extensive tissue growth and morphogenesis. By removing animals from food at different times, we show here that specific checkpoints exist in the early L3 and early L4 stages that systemically arrest the development of diverse tissues and cellular processes. These checkpoints occur once in each larval stage after molting and prior to initiation of the subsequent molting cycle. DAF-2, the insulin/insulin-like growth factor receptor, regulates passage through the L3 and L4 checkpoints in response to nutrition. The FOXO transcription factor DAF-16, a major target of insulin-like signaling, functions cell-nonautonomously in the hypodermis (skin) to arrest developmental upon nutrient removal. The effects of DAF-16 on progression through the L3 and L4 stages are mediated by DAF-9, a cytochrome P450 ortholog involved in the production of C. elegans steroid hormones. Our results identify a novel mode of C. elegans growth in which development progresses from one checkpoint to the next. At each checkpoint, nutritional conditions determine whether animals remain arrested or continue development to the next checkpoint.

Organisms in the wild often face long periods in which food is scarce. This may occur due to seasonal effects, loss of territory, or changes in predator-to-prey ratio. During periods of scarcity, organisms undergo adaptations to conserve resources and prolong survival. When nutrient deprivation occurs during development, physical growth and maturation to adulthood is delayed. These effects are also observed in malnourished individuals, who are smaller and reach puberty at later ages. Developmental arrest in response to nutrient scarcity requires a means of sensing changing nutrient conditions and coordinating an organism-wide response. How this occurs is not well understood. We assessed the developmental response to nutrient withdrawal in the nematode worm Caenorhabditis elegans. By removing food in the late larval stages, a period of extensive tissue formation, we have uncovered previously unknown checkpoints that occur at precise times in development. Diverse tissues and cellular processes arrest at the checkpoints. Insulin-like signaling and steroid hormone signaling regulate tissue arrest following nutrient withdrawal. These pathways are conserved in mammals and are linked to growth processes and diseases. Given that the pathways that respond to nutrition are conserved in animals, it is possible that similar checkpoints may also be important in human development.

Diet, genetics, and disease: a focus on the middle East and north Africa region

The Middle East and North Africa (MENA) region suffers a drastic change from a traditional diet to an industrialized diet. This has led to an unparalleled increase in the prevalence of chronic diseases. This review discusses the role of nutritional genomics, or the dietary signature, in these dietary and disease changes in the MENA. The diet-genetics-disease relation is discussed in detail. Selected disease categories in the MENA are discussed starting with a review of their epidemiology in the different MENA countries, followed by an examination of the known genetic factors that have been reported in the disease discussed, whether inside or outside the MENA. Several diet-genetics-disease relationships in the MENA may be contributing to the increased prevalence of civilization disorders of metabolism and micronutrient deficiencies. Future research in the field of nutritional genomics in the MENA is needed to better define these relationships.

South Pacific Islanders resist type 2 diabetes: comparison of aerobic and resistance training

The purpose of this study was to evaluate the effectiveness of two exercise modalities for improving glycosylated hemoglobin (HbA1c) and associated clinical outcomes in Polynesian adults diagnosed with type 2 diabetes and visceral obesity. Twenty-six adults were randomized to receive resistance training or aerobic training, 3×/week, for 16 weeks. Dependent variables collected before and after intervention included: diabetes markers including HbA1c, blood lipids, relevant cytokines (C-reactive protein, adiponectin), and anthropometric and hemodynamic indices. Eighteen participants (72% female; age: 49.3 ± 5.3 years; waist circumference: 128.7 ± 18.7 cm) completed the intervention and follow-up assessments. Body mass index in the whole cohort at baseline indicated Class III (morbid) obesity (43.8 ± 9.5 kg/m(2)). Compliance to training was 73 ± 19 and 67 ± 18% in the aerobic and resistance training groups, respectively. HbA1c remained elevated in both groups after training. Aerobic training reduced systolic and diastolic blood pressure and increased serum triglycerides (all P < 0.05). No other exercise-induced adaptations were noted within or between groups. Post hoc analysis using pooled data indicated that higher adherence to training (≥75% attendance, n = 8) significantly reduced waist circumference (P < 0.001) and tended to reduce body weight and fasting insulin (all P ≤ 0.11) versus lower adherence (<75% attendance, n = 10). In conclusion, this study did not demonstrate an improvement in HbA1c with exercise in morbidly obese Polynesian people. Future investigations involving exercise regimens that are more practicable and which involve greater frequency and duration of training may be required to induce significant and clinically meaningful adaptations in this unique diabetes population.

The obesity syndrome and acanthosis nigricans. Acanthosis nigricans is a common cosmetic problem providing epidemiological clues to the obesity syndrome, the insulin-resistance syndrome, the thrifty metabolism, dyslipidaemia, hypertension and diabetes mellitus type II

Obesity and its consequences are arguably the chief public health problems facing the developed world. Obesity causes many fatal diseases, in particular cerebrovascular and cardiovascular disease. Acanthosis nigricans (AN) is a common cosmetic disability in pigmented ethnic groups. It may present with periorbital darkening or darkening of the neck or knuckles as well as acrochordons (skin tags) around eyelids, neck or axillae. The more classical AN of axillae and groins is less often a cosmetic disability, although it is an important physical sign. AN is very common in pigmented populations throughout the world, irrespective of domicile. It is rare in whites. AN is closely associated with all the features of the insulin-resistance syndrome (IRS), especially obesity. AN and IRS share a similar prevalence and epidemiology. IRS (also known as syndrome X or the deadly quartet) is characterized by insulin resistance (IR) and its associated conditions, including obesity, dyslipidaemia, hypertension and diabetes mellitus (DM) type II. The sequelae of IRS are cardiovascular and cerebrovascular disease. The origins of insulin resistance and its sequel, IRS, are debated. Insulin resistance can result from obesity. Also obesity usually presents before AN, hypertension or DM II. For these reasons it may be more helpful to recognize instead an obesity syndrome. The obesity syndrome is characterized by a genetically determined thrifty metabolism that protects subjects in famine conditions but which, in conditions of plenty, leads to weight gain with all its consequences, including hyperlipidaemia, hypertension, IR with DM II, and, in due course, cerebrovascular and cardiovascular disease. In pigmented races, AN is an important early manifestation of the obesity syndrome. AN helps identify persons at particular risk of developing the obesity syndrome, dyslipidaemia, hypertension and IR with DM II. Recognition of AN, therefore, offers important opportunities for health screening and preventative medicine.

Separate and combined effects of nutrition during juvenile and sexual development on female life-history trajectories: the thrifty phenotype in a cockroach

We have yet to understand fully how conditions during different periods of development interact to influence life-history structure. Can the negative effects of poor juvenile nutrition be overcome by a good adult diet, or are life-history strategies set by early experience? Here, we tested the influence and interaction of different nutritional quality during juvenile and sexual development on female resource allocation physiology, life history and courtship behaviour in the cockroach, Nauphoeta cinerea. Nymphs were raised on either a good-quality or poor-quality diet. After adult eclosion, females were either switched to the opposite diet or remained on their original diet. We assessed mating behaviour and lifetime reproductive success for half of the females from each treatment. We evaluated reproductive investment, somatic investment and resource reallocation from reproduction to the soma via oocyte apoptosis in the remaining females. We found that poor juvenile conditions resulted in a fat phenotype with slow juvenile growth and short reproductive lifespan that could not be retrieved with a change in diet. Good juvenile conditions resulted in the converse, but again fixed, phenotype in adulthood. Thus, juvenile nutrition sets adult patterns of resource allocation.

Impact of genetic and epigenetic factors from early life to later disease

There is ample evidence that subtle changes in the early environment, not restricted to the fetal period but expanded to the plastic phase of early development, influence adulthood disease appearance. There is also evidence that genetic background resulting from our evolution is an important contributor to susceptibility to perinatal imprinting. However, rapid adjustment and optimization, at times necessary for survival, require a type of plasticity that the genome sequence alone cannot achieve. Without changing the genomic backbone, epigenetic modulation, in reaction to a given environment, results in functional adaptation of the genomic response. Evolutionally acquired genomic susceptibilities and environmentally induced epigenomic modulations occurring early in life impact on later development of human diseases.

Epidemiological and nutrition transition in developing countries: impact on human health and development

Whereas common infectious and parasitic diseases such as malaria and the HIV/AIDS pandemic remain major unresolved health problems in many developing countries, emerging non-communicable diseases relating to diet and lifestyle have been increasing over the last two decades, thus creating a double burden of disease and impacting negatively on already over-stretched health services in these countries. Prevalence rates for type 2 diabetes mellitus and CVD in sub-Saharan Africa have seen a 10-fold increase in the last 20 years. In the Arab Gulf current prevalence rates are between 25 and 35% for the adult population, whilst evidence of the metabolic syndrome is emerging in children and adolescents. The present review focuses on the concept of the epidemiological and nutritional transition. It looks at historical trends in socio-economic status and lifestyle and trends in nutrition-related non-communicable diseases over the last two decades, particularly in developing countries with rising income levels, as well as the other extreme of poverty, chronic hunger and coping strategies and metabolic adaptations in fetal life that predispose to non-communicable disease risk in later life. The role of preventable environmental risk factors for obesity and the metabolic syndrome in developing countries is emphasized and also these challenges are related to meeting the millennium development goals. The possible implications of these changing trends for human and economic development in poorly-resourced healthcare settings and the implications for nutrition training are also discussed.

Diabetes mellitus in the Hispanic/Latino population: an increasing health care challenge in the United States

The prevalence of diabetes in the U.S. Hispanic population has grown to epidemic proportions. The prevalence of diagnosed diabetes in Hispanics is 1.9 times higher than that in Caucasians. Diabetes is diagnosed at an earlier age, and, for a multiplicity of reasons, Hispanics suffer from higher rates of diabetic complications and mortality. The etiology for the higher prevalence of diabetes and its complications is not clear, but it is thought to be related to genetic and environmental factors. In this manuscript, we review recent epidemiologic information on the prevalence, pathophysiology, and complications of diabetes, as well as the recommendations for the management of Hispanics with type 2 diabetes.

LPIN2 is associated with type 2 diabetes, glucose metabolism, and body composition

OBJECTIVE

To identify the type 2 diabetes gene located at chromosome 18p11.

RESEARCH DESIGN AND METHODS

We investigated the region in a young genetically isolated population by genotyping 34 single nucleotide polymorphisms (SNPs) in 78 case subjects and 101 control subjects. Two SNPs were selected and followed up in two cohorts. The first cohort came from a general Dutch population. In this cohort, association with type 2 diabetes was investigated using 616 type 2 diabetic case subjects and 2,890 control subjects; association with oral glucose tolerance test data was performed in 361 normoglycemic people. Association with fat distribution was studied in the second replication cohort, consisting of 836 people from the genetically isolated population.

RESULTS

At the initial step, we found that the common C allele of SNP rs3745012 was associated with type 2 diabetes (odds ratio 2.01, P = 0.03). This SNP is located at the 3' untranslated region of the LPIN2 gene, which is a plausible candidate for type 2 diabetes and obesity. In the cohort from the general Dutch population, we demonstrated that rs3745012 interacts with BMI in determination of type 2 diabetes: whereas in subjects with high BMI, the common C allele is associated with type 2 diabetes, the same allele exhibits a neutral or protective effect in lean subjects (P = 0.05 overall effect, P = 0.02 interaction). Most remarkably, rs3745012 strongly affected composite insulin sensitivity index (P = 0.006 for overall effect, P = 0.004 for interaction). In the second replication cohort, we found that the allele C of rs3745012 increases trunk-to-legs fat mass ratio (P = 0.001) and may affect other fat-related measurements.

CONCLUSIONS

rs3745012 SNP of the LPIN2 gene is associated with type 2 diabetes and fat distribution.

Intrauterine programming of physiological systems: causes and consequences

The intrauterine conditions in which the mammalian fetus develops have an important role in regulating the function of its physiological systems later in life. Changes in the intrauterine availability of nutrients, oxygen, and hormones program tissue development and lead to abnormalities in adult cardiovascular and metabolic function in several species. The timing, duration, severity, and type of insult during development determines the specific physiological outcome. Intrauterine programming of physiological systems occurs at the gene, cell, tissue, organ, and system levels and causes permanent structural and functional changes, which can lead to overt disease, particularly with increasing age.

Racializing narratives: obesity, diabetes and the "Aboriginal" thrifty genotype

This post-colonial reading of narratives of obesity, diabetes, and the hypothesized "thrifty genotype" ascribed to Aboriginal peoples shows how scientific and popular texts support the belief in biological "race." Although the scientific consensus is that "race" is not a empirical category, many scientists use it without comment as a "crude proxy" for presumed genetic differences. The division between science and the social sciences/humanities protects such confusing practices from full scientific and social critique, something interdisciplinary research teams, science studies and improved peer review could provide.

Elevated sialic acid, but not CRP, predicts features of the metabolic syndrome independently of BMI in women

AIMS

C-reactive protein (CRP) is a predictor of many diseases including type II diabetes and cardiovascular disease. Fewer studies have similarly shown sialic acid (SA) to be a predictor of obesity-related diseases, but importantly SA shows less intra-individual variability than CRP and acts as an integrated marker of the activity of a number of acute-phase proteins. This study examines the association between both CRP and SA with individual and combined features of the metabolic syndrome.

SUBJECTS

In all, 257 women with a body mass index (BMI) ranging from 25.1 to 54.5 kg/m2 (geometric mean 33.1+/-5.8 kg/m2) and aged 19-71 y (mean 45.6+/-12.1 y) were studied. Subjects had no symptoms of intercurrent infection, known diabetes, treated dyslipidaemia, a chronic inflammatory condition, liver disease or malignancy.

RESULTS

Linear regression demonstrates that both CRP and SA were positively associated with weight, BMI, insulin resistance, dyslipidaemia and hypertension. There was a highly significant (P<0.0001) positive association of both SA and CRP with none, one, two, three or four features of the metabolic syndrome. For a 1 s.d. (4.0 mg/l) increase in CRP, there was a significant increased risk when comparing the odds of having metabolic syndrome (defined as three or more individual features) compared with the remainder of the population (odds ratio=1.7, P<0.0001), but this was not significant after adjustment for BMI. However, for a 1 s.d. (0.34 mmol/l) increase in SA, the odds of having metabolic syndrome compared with those without metabolic syndrome was 2.5 (P<0.0001), and persisted after additional adjustment for BMI (adjusted odds ratio=1.9, P<0.0001).

CONCLUSIONS

While SA and CRP are both univariately associated with individual features of the metabolic syndrome, SA, but not CRP, is significantly associated with the metabolic syndrome, independent of BMI. We conclude that SA identifies a subgroup of overweight individuals with an inflammatory phenotype, who are at the greatest risk of metabolic syndrome.

Type 2 diabetes in South Asians: a pathophysiologic focus on the Asian-Indian epidemic

There is a high prevalence of type 2 diabetes mellitus and coronary artery disease among urban and migrant Asian Indians, despite the absence of traditional risk factors. Evidence exists that Asian Indians are more insulin resistant than white persons and that insulin resistance may play an important role in the pathogenesis of these diseases. Increased visceral fat in Asian Indians is associated with increased generalized obesity, which is not apparent from their nonobese body mass index. Increased visceral fat is related to dyslipidemia and increased frequency of insulin resistance and may account for the increased prevalence of diabetes mellitus and cardiovascular disease in Asian Indians. In addition, early protein energy deprivation, as indicated by low weight at birth and at 1 year of age, may induce a state of vulnerability to the development of type 2 diabetes in later life, especially if the quantitative and qualitative aspects of nutrition and altered lifestyles during adult years pose an additional challenge.

Genómica de la regulación del peso corporal: mecanismos moleculares que predisponen a la obesidad

Obesity has become a worldwide public health problem which affects millions of people. Substantial progress has been made in elucidating the pathogenesis of energy homeostasis over the past few years. The fact that obesity is under strong genetic control has been well established. Twin, adoption and family studies have shown that genetic factors play a significant role in the pathogenesis of obesity. Human monogenic obesity is rare in large populations. The most common form of obesity is considered to be a polygenic disorder. New treatments are currently required for this common metabolic disease and type 2 diabetes. The identification of physiological and biochemical factors that underlie the metabolic disturbances observed in obesity is a key step in developing better therapeutic outcomes. The discovery of new genes and pathways involved in the pathogenesis of such a disease is critical to this process. However, identification of genes that contribute to the risk of developing the disease represents a significant challenge since obesity is a complex disease with many genetic and environmental causes. A number of diverse approaches have been used to discover and validate potential new genes for obesity. To date, DNA-based approaches using candidate genes and genome-wide linkage analysis have not had a great success in identifying genomic regions or genes involved in the development of these diseases. Recent advances in the ability to evaluate linkage analysis data from large family pedigrees (using variance components-based linkage analysis) show great promise in robustly identifying genomic regions associated with the development of obesity. Studying rare mutations in humans and animal models has provided fundamental insight into a complex physiological process, and has complemented population-based studies that seek to reveal primary causes. Remarkable progress has been made in both fronts and the pace of advance is likely to accelerate as functional genomics and the human genome project expand and mature. Approaches based on Mendelian and quantitative genetics may well converge, and ultimately lead to more rational and selective therapies.

The thrifty phenotype hypothesis: thrifty offspring or thrifty mother?

Medical research is increasingly focusing on the contribution of nutritional programming to disease in later life. Programming is a process whereby a stimulus during a critical window of time permanently affects subsequent structure, function or developmental schedule of the organism. The thrifty phenotype hypothesis is widely used to interpret such studies, with early growth restriction seen as adaptation to environmental deprivation. However, such permanent adjustment is less beneficial than maintaining flexibility so as to recover from early growth deficits if the environment improves. Thus, the existing thrifty phenotype hypothesis fails to explain why plasticity is lost so early in development in species with extended growth. One explanation is that the developing organism simply cannot maintain phenotypic plasticity throughout the period of organ growth. This article adds a life history perspective, arguing that programming of the offspring may in some species benefit maternal fitness more than it does that of individual offspring. Closing the critical window early in development allows the preservation of maternal strategy in offspring phenotype, which in humans benefits the mother by constraining offspring demand after weaning. The offspring gains by being buffered against environmental fluctuations during the most sensitive period of development, allowing coherent adaptation of organ growth to the state of the environment. The critical window is predicted to close when offspring physiology becomes independent of maternal physiology, the timing of which depends on offspring trait. Because placental nutrition and lactation buffer against short-term environmental fluctuations, maternal strategy is predicted to derive from long-term experience, encapsulated in maternal size and nutritional status. Such an approach implies that public health programmes for improving birth weight may be more effective if they target maternal development rather than nutrition during pregnancy. Equally, aggressive nutritional management of infants born small or pre-term may induce the very environmental fluctuations that are naturally softened by maternal nutrition.

Glucotoxicity and beta-cell failure in type 2 diabetes mellitus

Type 2 diabetes mellitus is increasing worldwide with a trend of declining age of onset. It is characterized by insulin resistance and a progressive loss of beta-cell function. The ability to secrete adequate amounts of insulin is determined by the functional integrity of beta-cells and their overall mass. Glucose, the main regulator of insulin secretion and production, exerts negative effects on beta-cell function when present in excessive amounts over a prolonged period. The multiple metabolic aberrations induced by chronic hyperglycemia in the beta-cell include increased sensitivity to glucose, increased basal insulin release, reduced response to stimulus to secrete insulin, and a gradual depletion of insulin stores. Inadequate insulin production during chronic hyperglycemia results from decreased insulin gene transcription due to hyperglycemia-induced changes in the activity of beta-cell specific transcription factors. Hyperglycemia may negatively affect beta-cell mass by inducing apoptosis without a compensatory increase in beta-cell proliferation and neogenesis. The detrimental effect of excessive glucose concentrations is referred to as 'glucotoxicity'. The present review discusses the role of glucotoxicity in beta-cell dysfunction in type 2 diabetes mellitus.

Single nucleotide polymorphisms of thrifty genes for energy metabolism: evolutionary origins and prospects for intervention to prevent obesity-related diseases

The "thrifty" genotype and phenotype that save energy are detrimental to the health of people living in affluent societies. Individual differences in energy metabolism are caused primarily by single nucleotide polymorphisms (SNPs), some of which promote the development of obesity/type 2 diabetes mellitus. In this review, four major questions are addressed: (1) Why did regional differences in energy metabolism develop during evolution? (2) How do genes respond to starvation and affluence? (3) Which SNPs correspond to the hypothetical "thrifty genes"? (4) How can we cope with disease susceptibility caused by the "thrifty" SNPs? We examined mtDNA and genes for energy metabolism in people who live in several parts of Asia and the Pacific islands. We included 14 genes, and the SNP frequencies of PPAR gamma 2, LEPR, and UCP3-p and some other genes differ significantly between Mongoloids and Caucasoids. These differences in SNPs may have been caused by natural selection depending on the types of agriculture practiced in different regions. Interventions to counteract the adverse effects of "thrifty" SNPs have been partially effective.