Early and late nutritional windows for diabetes susceptibility

Fetal growth restriction followed by early catch-up growth impairs pancreatic islet morphology in male rats

Fetal growth restriction (FGR), followed by postnatal early catch-up growth, is associated with an increased risk of metabolic dysfunction, including type 2 diabetes in humans. This study aims to determine the effects of FGR and early catch-up growth after birth on the pathogenesis of type 2 diabetes, with particular attention to glucose tolerance, pancreatic islet morphology, and fibrosis, and to elucidate its mechanism using proteomics analysis. The FGR rat model was made by inducing mild intrauterine hypoperfusion using ameroid constrictors (ACs). On day 17 of pregnancy, ACs were affixed to the uterine and ovarian arteries bilaterally, causing a 20.9% reduction in birth weight compared to sham pups. On postnatal day 4 (P4), the pups were assigned to either the good nutrition (GN) groups with 5 pups per dam to ensure postnatal catch-up growth or poor nutrition groups with 15 pups per dam to maintain lower body weight. After weaning, all pups were fed regular chow food ad libitum (P21). Rats in both FGR groups developed glucose intolerance; however, male rats in the FGR good nutrition (FGR-GN) group also developed hypertriglyceridemia and dysmorphic pancreatic islets with fibrosis. A comprehensive and functional analysis of proteins expressed in the pancreas showed that FGR, followed by early catch-up growth, severely aggravated cell adhesion-related protein expression in male offspring. Thus, FGR and early catch-up growth caused pancreatic islet morphological abnormalities and fibrosis associated with the disturbance of cell adhesion-related protein expressions. These changes likely induce glucose intolerance and dyslipidemia in male rats.

Protein malnutrition mitigates the effects of a high-fat diet on glucose homeostasis in mice

Nutrient malnutrition, during the early stages of development, may facilitate the onset of metabolic diseases later in life. However, the consequences of nutritional insults, such as a high-fat diet (HFD) after protein restriction, are still controversial. We assessed overall glucose homeostasis and molecular markers of mitochondrial function in the gastrocnemius muscle of protein-restricted mice fed an HFD until early adulthood. Male C57BL/6 mice were fed a control (14% protein-control diet) or a protein-restricted (6% protein-restricted diet) diet for 6 weeks. Afterward, mice received an HFD or not for 8 weeks (mice fed a control diet and HFD [CH] and mice fed a protein-restricted diet and HFD [RH]). RH mice showed lower weight gain and fat accumulation and did not show an increase in fasting plasma glucose and insulin levels compared with CH mice. RH mice showed higher energy expenditure, increased citrate synthase, peroxisome-proliferator-activated receptor gamma coactivator 1-alpha protein content, and higher levels of malate and α-ketoglutarate compared with CH mice. Moreover, RH mice showed increased AMPc-dependent kinase and acetyl coenzyme-A (CoA) carboxylase phosphorylation, lower intramuscular triacylglycerol content, and similar malonyl-CoA levels. In conclusion, protein undernourishment after weaning does not potentiate fat accumulation and insulin resistance in adult young mice fed an HFD. This outcome seems to be associated with increased skeletal muscle mitochondrial oxidative capacity and reduced lipids accumulation.

The capacity-load model of non-communicable disease risk: understanding the effects of child malnutrition, ethnicity and the social determinants of health

The capacity-load model is a conceptual model developed to improve understanding of the life-course aetiology of non-communicable diseases (NCDs) and their ecological and societal risk factors. The model addresses continuous associations of both (a) nutrition and growth patterns in early life and (b) lifestyle factors at older ages with NCD risk. Metabolic capacity refers to physiological traits strongly contingent on early nutrition and growth during the first 1000 days, which promote the long-term capacity for homeostasis in the context of fuel metabolism and cardiovascular health. Metabolic load refers to components of nutritional status and lifestyle that challenge homeostasis. The higher the load, and the lower the capacity, the greater the NCD risk. The model therefore helps understand dose-response associations of both early development and later phenotype with NCD risk. Infancy represents a critical developmental period, during which slow growth can constrain metabolic capacity, whereas rapid weight gain may elevate metabolic load. Severe acute malnutrition in early childhood (stunting, wasting) may continue to deplete metabolic capacity, and confer elevated susceptibility to NCDs in the long term. The model can be applied to associations of NCD risk with socio-economic position (SEP): lower SEP is generally associated with lower capacity but often also with elevated load. The model can also help explain ethnic differences in NCD risk, as both early growth patterns and later body composition differ systematically between ethnic groups. Recent work has begun to clarify the role of organ development in metabolic capacity, which may further contribute to ethnic differences in NCD risk.

Dental enamel defects predict adolescent health indicators: A cohort study among the Tsimane' of Bolivia

OBJECTIVES

Bioarchaeological findings have linked defective enamel formation in preadulthood with adult mortality. We investigated how defective enamel formation in infancy and childhood is associated with risk factors for adult morbidity and mortality in adolescents.

METHODS

This cohort study of 349 Amerindian adolescents (10-17 years of age) related extent of enamel defects on the central maxillary incisors (none, less than 1/3, 1/3 to 2/3, more than 2/3) to adolescent anthropometrics (height, weight) and biomarkers (hemoglobin, glycated hemoglobin, white blood cell count, and blood pressure). Risk differences and 95% confidence intervals were estimated using multiple linear regression. Enamel defects and stunted growth were compared in their ability to predict adolescent health indicators using log-binomial regression and receiver operating characteristics (ROCs).

RESULTS

Greater extent of defective enamel formation on the tooth surface was associated with shorter height (-1.35 cm, 95% CI: -2.17, -0.53), lower weight (-0.98 kg, 95% CI: -1.70, -0.26), lower hemoglobin (-0.36 g/dL, 95% CI: -0.59, -0.13), lower glycated hemoglobin (-0.04 %A1c , 95% CI: -0.08, -0.00008), and higher white blood cell count (0.74 109 /L, 95% CI: 0.35, 1.14) in adolescence. Extent of enamel defects and stunted growth independently performed similarly as risk factors for adverse adolescent outcomes, including anemia, prediabetes/type II diabetes, elevated WBC count, prehypertension/hypertension, and metabolic health.

CONCLUSIONS

Defective enamel formation in infancy and childhood predicted adolescent health outcomes and may be primarily associated with infection. Extent of enamel defects and stunted growth may be equally predictive of adverse adolescent health outcomes.

Environmental Quality, Developmental Plasticity and the Thrifty Phenotype: A Review of Evolutionary Models

The concept of the thrifty phenotype, first proposed by Hales and Barker, is now widely used in medical research, often in contrast to the thrifty genotype model, to interpret associations between early-life experience and adult health status. Several evolutionary models of the thrifty phenotype, which refers to developmental plasticity, have been presented. These include (A) the weather forecast model of Bateson, (B) the maternal fitness model of Wells, (C) the intergenerational phenotypic inertia model of Kuzawa, and (D) the predictive adaptive response model of Gluckman and Hanson. These models are compared and contrasted, in order to assess their relative utility for understanding human ontogenetic development. The most broadly applicable model is model A, which proposes that developing organisms respond to cues of environmental quality, and that mismatches between this forecast and subsequent reality generate significant adverse effects in adult phenotype. The remaining models all address in greater detail what kind of information is provided by such a forecast. Whereas both models B and C emphasise the adaptive benefits of exploiting information about the past, encapsulated in maternal phenotype, model D assumes that the fetus uses cues about the present external environment to predict its probable adult environment. I argue that for humans, with a disproportionately long period between the closing of sensitive windows of plasticity and the attainment of reproductive maturity, backward-looking models B and C represent a better approach, and indicate that the developing offspring aligns itself with stable cues of maternal phenotype so as to match its energy demand with maternal capacity to supply. In contrast, the predictive adaptive response model D over-estimates the capacity of the offspring to predict the future, and also fails to address the long-term parent-offspring dynamics of human development. Differences between models have implications for the design of public health interventions.

do Monte BG, Watanabe IM, Cunha J, Peripato AC. A link between thrifty phenotype and maternal care across two generations of intercrossed mice

Maternal effects are causal influences from mother to offspring beyond genetic information, and have lifelong consequences for multiple traits. Previously, we reported that mice whose mothers did not nurse properly had low birth weight followed by rapid fat accumulation and disturbed development of some organs. That pattern resembles metabolic syndromes known collectively as the thrifty phenotype, which is believed to be an adaptation to a stressful environment which prepares offspring for reduced nutrient supply. The potential link between maternal care, stress reactivity, and the thrifty phenotype, however, has been poorly explored in the human and animal literature: only a couple of studies even mention (much less, test) these concepts under a cohesive framework. Here, we explored this link using mice of the parental inbred strains SM/J and LG/J–who differ dramatically in their maternal care–and the intercrossed generations F1 and F2. We measured individual differences in 15 phenotypes and used structural equation modeling to test our hypotheses. We found a remarkable relationship between thrifty phenotype and lower quality of maternal behaviors, including nest building, pup retrieval, grooming/licking, and nursing. To our knowledge, this is the first study to show, in any mammal, a clear connection between the natural variation in thrifty phenotype and maternal care. Both traits in the mother also had a substantial effect on survival rate in the F3 offspring. To our surprise, however, stress reactivity seemed to play no role in our models. Furthermore, the strain of maternal grandmother, but not of paternal grandmother, affected the variation of maternal care in F2 mice, and this effect was mediated by thrifty phenotype in F2. Since F1 animals were all genetically identical, this finding suggests that maternal effects pass down both maternal care and thrifty phenotype in these mice across generations via epigenetic transmission.

Understanding the role of maternal diet on kidney development; an opportunity to improve cardiovascular and renal health for future generations

The leading causes of mortality and morbidity worldwide are cardiovascular disease (high blood pressure, high cholesterol and renal disease), cancer and diabetes. It is increasingly obvious that the development of these diseases encompasses complex interactions between adult lifestyle and genetic predisposition. Maternal malnutrition can influence the fetal and early life environment and pose a risk factor for the future development of adult diseases, most likely due to impaired organogenesis in the developing offspring. This then predisposes these offspring to cardiovascular disease and renal dysfunction in adulthood. Studies in experimental animals have further illustrated the significant impact maternal diet has on offspring health. Many studies report changes in kidney structure (a reduction in the number of nephrons in the kidney) in offspring of protein-deprived dams. Although the early studies suggested that increased blood pressure was also present in offspring of protein-restricted dams, this is not a universal finding and requires clarification. Importantly, to date, the literature offers little to no understanding of when in development these changes in kidney development occur, nor are the cellular and molecular mechanisms that drive these changes well characterised. Moreover, the mechanisms linking maternal nutrition and a suboptimal renal phenotype in offspring are yet to be discerned—one potential mechanism involves epigenetics. This review will focus on recent information on potential mechanisms by which maternal nutrition (focusing on malnutrition due to protein restriction, micronutrient restriction and excessive fat intake) influences kidney development and thereby function in later life.

Short- and long-term reproductive effects of prenatal and lactational growth restriction caused by maternal diabetes in male rats

BACKGROUND

A suboptimal intrauterine environment may have a detrimental effect on gonadal development and thereby increases the risk for reproductive disorders and infertility in adult life. Here, we used uncontrolled maternal diabetes as a model to provoke pre- and perinatal growth restriction and evaluate the sexual development of rat male offspring.

METHODS

Maternal diabetes was induced in the dams through administration of a single i.v. dose of 40 mg/kg streptozotocin, 7 days before mating. Female rats presenting glycemic levels above 200 mg/dL after the induction were selected for the experiment. The male offspring was analyzed at different phases of sexual development, i.e., peripuberty, postpuberty and adulthood.

RESULTS

Body weight and blood glucose levels of pups, on the third postnatal day, were lower in the offspring of diabetic dams compared to controls. Maternal diabetes also provoked delayed testicular descent and preputial separation. In the offspring of diabetic dams the weight of reproductive organs at 40, 60 and 90 days-old was lower, as well as sperm reserves and sperm transit time through the epididymis. However the plasma testosterone levels were not different among experimental groups.

CONCLUSIONS

It is difficult to isolate the effects directly from diabetes and those from IUGR. Although the exposure to hyperglycemic environment during prenatal life and lactation delayed the onset of puberty in male rats, the IUGR, in the studied model, did not influenced the structural organization of the male gonads of the offspring at any point during sexual development. However the decrease in sperm reserves in epididymal cauda and the acceleration in sperm transit time in this portion of epididymis may lead to an impairment of sperm quality and fertility potential in these animals. Additional studies are needed in attempt to investigate the fertility of animals with intrauterine growth restriction by maternal diabetes and possible multigenerational effects.

In utero protein restriction causes growth delay and alters sperm parameters in adult male rats

BACKGROUND

Recent studies have supported the concept of "fetal programming" which suggests that during the intrauterine development the fetus may be programmed to develop diseases in adulthood. The possible effects of in utero protein restriction on sexual development of rat male offspring were evaluated in the present study.

METHODS

Pregnant Wistar rats were divided into two experimental groups: one group treated with standard chow (SC, n = 8, 17% protein) and the other group treated with hypoproteic chow (HC, n = 10, 6% protein) throughout gestation. After gestation the two experimental groups received standard chow. To evaluate the possible late reproductive effects of in utero protein restriction, the male offspring of both groups were assessed at different phases of sexual development: prepubertal (30 days old); peripubertal (60 days old); adult (90 days old). Student's t-test and Mann-Whitney test were utilized. Differences were considered significant when p < 0.05.

RESULTS

We found that in utero protein restriction reduced the body weight of male pups on the first postnatal day and during the different sexual development phases (prepubertal, peripubertal and adult). During adulthood, Sertoli cell number, sperm motility and sperm counts in the testis and epididymal cauda were also reduced in HC. Furthermore, the numbers of sperm presenting morphological abnormalities and cytoplasmic drop retention were higher in HC.

CONCLUSIONS

In conclusion, in utero protein restriction, under these experimental conditions, causes growth delay and alters male reproductive-system programming in rats, suggesting impairment of sperm quality in adulthood.

Cafeteria diet-induced insulin resistance is not associated with decreased insulin signaling or AMPK activity and is alleviated by physical training in rats

Excess energy intake via a palatable low-fat diet (cafeteria diet) is known to induce obesity and glucose intolerance in rats. However, the molecular mechanisms behind this adaptation are not known, and it is also not known whether exercise training can reverse it. Male Wistar rats were assigned to 12-wk intervention groups: chow-fed controls (CON), cafeteria diet (CAF), and cafeteria diet plus swimming exercise during the last 4 wk (CAF(TR)). CAF feeding led to increased body weight (16%, P < 0.01) and increased plasma glucose (P < 0.05) and insulin levels (P < 0.01) during an IVGTT, which was counteracted by training. In the perfused hindlimb, insulin-stimulated glucose transport in red gastrocnemius muscle was completely abolished in CAF and rescued by exercise training. Apart from a tendency toward an approximately 20% reduction in both basal and insulin-stimulated Akt Ser(473) phosphorylation (P = 0.051) in the CAF group, there were no differences in insulin signaling (IR Tyr(1150/1151), PI 3-kinase activity, Akt Thr(308), TBC1D4 Thr(642), GSK3-alpha/beta Ser(21/9)) or changes in AMPKalpha1 or -alpha2, GLUT4, Munc18c, or syntaxin 4 protein expression or in phosphorylation of AMPK Thr(172) among the groups. In conclusion, surplus energy intake of a palatable but low-fat cafeteria diet resulted in obesity and insulin resistance that was rescued by exercise training. Interestingly, insulin resistance was not accompanied by major defects in the insulin-signaling cascade or in altered AMPK expression or phosphorylation. Thus, compared with previous studies of high-fat feeding, where insulin signaling is significantly impaired, the mechanism by which CAF diet induces insulin resistance seems different.

Intrauterine growth restriction as a potential risk factor for disease onset in adulthood

Intrauterine growth restriction (IUGR) is a risk factor for cardiovascular disease, type 2 diabetes mellitus, and obesity in adulthood. Several studies on diverse geographic and ethnic cohorts have provided evidence that being born small for gestational age (SGA) increases adult disease risk through various pathways of metabolic dysregulation. Unfavorable influences in the fetal environment may program metabolic homeostasis in later life affecting blood pressure, glucose tolerance and lipid regulation. Fetal restricted protein supply may impair the development of the kidney and reduce the nephron number, which is involved in blood pressure regulation. Moreover, children exposed to IUGR may exhibit postnatal rapid catch-up growth, altered body composition, increased visceral adiposity and low adiponectin levels which predispose to cardiovascular disease and type 2 diabetes mellitus in adulthood. Impairment in fetal pancreatic development and subsequent insulin signalling deficits due to IUGR may also be involved in the pathogenesis of these conditions. This review summarizes some of the hypotheses that have been put forward to explain the association between fetal growth restriction and subsequent metabolic dysregulation that may increase adult disease risk.

Murine aortic reactivity is programmed equally by maternal low protein diet or late gestation dexamethasone

OBJECTIVE

In rats, maternal low protein diet induces growth restriction, increases fetal glucocorticoid exposure and programs cardiovascular and endocrine dysfunction in adult offspring. We hypothesized that both maternal low protein diet and late gestation dexamethasone program murine offspring to develop hypertension, vascular dysfunction, and glucose intolerance.

METHODS

An iso-caloric low protein diet (LP) was provided to dams from E0 to E19. Additional dams received a normal protein diet without (NP) or with either dexamethasone (NP-Dex, 0.1 mg/kg/d sc) or normal saline (NP-NS) from E10 to E18.

RESULTS

Offspring of dams given LP weighed less at 10 days than NP offspring, while Dex administration did not alter pup weight. At 4 months, all four groups had similar systolic blood pressures and no detectable differences were evoked by oral L-NAME. Offspring of LP mice had impaired glucose clearance that was directly correlated with their weight at 10 days. Aortic rings from offspring of both LP and NP-Dex exposed dams had impaired vasodilatation to acetylcholine.

CONCLUSIONS

These findings demonstrate that both maternal low protein diet and late gestation dexamethasone program murine offspring to develop endothelial dysfunction in the absence of hypertension, while only maternal LP impaired perinatal growth and glucose clearance in adult offspring.

KEYWORDS

Acetylcholine; blood pressure; developmental biology; fetal programming

Prenatal and perinatal zinc restriction: effects on body composition, glucose tolerance and insulin response in rat offspring

Maternal undernutrition increases the risk of adult chronic diseases, such as obesity and type 2 diabetes. This study evaluated the effect of maternal zinc restriction in predisposing the offspring to adiposity and altered insulin response in later life. Seventy-day-old female Wistar/NIN rats received a control (ZnC) or zinc-restricted (ZnR) diet for 2 weeks. Following mating with control males, a subgroup of the ZnR dams were rehabilitated with ZnC diet from parturition. Half the offspring born to the remaining ZnR dams were weaned onto the ZnC diet and the other half continued on the ZnR diet throughout their life. Body composition, glucose tolerance, insulin response and plasma lipid profile were assessed in male and female offspring at 3 and 6 months of age. The ZnR offspring weighed less than control offspring at birth and weaning and continued so until 6 months of age. Rehabilitation regimens corrected the body weights of male but not female offspring. Maternal zinc restriction increased the percentage of body fat and decreased lean mass, fat-free mass and fasting plasma insulin levels in both male and female offspring at 6 months of age. Also, glucose-induced insulin secretion was decreased in female but not male offspring. Despite the differences in fasting insulin and the area under the curve for insulin, the fasting glucose and the area under the curve for glucose were in general comparable among offspring of different groups. Rehabilitation from parturition or weaning partly corrected the changes in the percentage of body fat but had no such effect on other parameters. Changes in plasma lipid profile were inconsistent among the offspring of different groups. Thus chronic maternal zinc restriction altered the body composition and impaired the glucose-induced insulin secretion in the offspring.

The thrifty phenotype as an adaptive maternal effect

Human diseases in adulthood are increasingly associated with growth patterns in early life, implicating early-life nutrition as the underlying mechanism. The thrifty phenotype hypothesis proposed that early-life metabolic adaptations promote survival, with the developing organism responding to cues of environmental quality by selecting an appropriate trajectory of growth. Recently, some authors have proposed that the thrifty phenotype is also adaptive in the longer-term, by preparing the organism for its likely adult environment. However, windows of plasticity close early during human development, and subsequent environmental changes may result in the selected trajectory becoming inappropriate, leading to adverse effects on health. This paradox generates uncertainty as to whether the thrifty phenotype is indeed adaptive for the offspring in humans. The thrifty phenotype should not be considered a dichotomous concept, rather it refers to the capacity of all offspring to respond to environmental information during early ontogenetic development. This article argues that the thrifty phenotype is the consequence of three different adaptive processes - niche construction, maternal effects, and developmental plasticity - all of which in humans are influenced by our large brains. While developmental plasticity represents an adaptation by the offspring, both niche construction and parental effects are subject to selection on parental rather than offspring fitness. The three processes also operate at different paces. Human offspring do not become net calories-producers until around 18 years of age, such that the high energy costs of the human brain are paid primarily by the mother, even after weaning. The evolutionary expansion of human brain volume occurred in environments characterised by high volatility, inducing strong selective pressure on maternal capacity to provision multiple offspring simultaneously. The thrifty phenotype is therefore best considered as a manipulation of offspring phenotype for the benefit of maternal fitness. The information that enters offspring phenotype during early development does not predict the likely future environment of the offspring, but rather reflects the mother's own developmental experience and the quality of the environment during her own maturation. Offspring growth trajectory thus becomes aligned with long-term maternal capacity to provision. In contemporary populations, the sensitivity of offspring development to maternal phenotype exposes the offspring to adverse effects, through four distinct pathways. The offspring may be exposed to (1) poor maternal metabolic control (e.g. gestational diabetes), (2) maternally derived toxins (e.g. maternal smoking), or (3) low maternal social status (e.g. small size). Adverse consequences of these effects may then be exacerbated by (4) exposure either to the "toxic" western environment in postnatal life, in which diet and physical activity levels are mismatched with metabolic experience in utero, or at the other extreme to famine. The rapid emergence of the epidemic of the metabolic syndrome in the 20th Century reflects the rapid acceleration in the pace of niche construction relative to the slower physiological combination of developmental plasticity and parental effects.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

A new method for quantifying encephalization in the growing individual

Here we describe a new method for quantifying encephalization in the growing individual and provide a worked example of the methods. The new method is based on the use of conditional SD scores derived from brain and body growth references. These encephalization SD scores control for age, sex and body size effects on brain size, and therefore, control for the confounds associated with allometry as well as growth differences between the brain and body and between the sexes. The methods also control for distribution skewness. Encephalization SD scores derived from pre- and post-natal data may be directly compared and changes in SD score over time assessed. These methods may be applied to a broad range of data where relative size during growth is to be quantified. Derived SD scores may also be applied to correlation and regression analyses where statistical relationships with other variables are of interest.

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.

Fructose feeding in the suckling-weaning transition in rats: effects on hyperlipidemia in adulthood

The sucking-weaning transition is characterized by high rates of growth and development and may be a sensitive period during which dietary intake could program metabolism to increase the risk of cardiovascular disease and diabetes in adulthood. Intake of a high fructose (FR) diet is known to induce hypertriglyceridemia and insulin resistance in rats when they are consuming this diet. We examined whether a FR diet fed early in life produces detrimental changes in lipid and glucose metabolism that persist to adulthood. Weanling rats were fed 65% FR (wt/wt), a purified control diet (CNTL) or standard chow (CHOW) for 5 weeks. Beyond 9 weeks of age, all rats were fed CHOW. During FR feeding, plasma triglycerides (TG) were significantly elevated in the FR group (FR = 217 +/- 20; CNTL = 163 +/- 17; chow = 156 +/- 10). At 21 wks of age, TG's were similar in rats fed FR or CNTL versus CHOW at weaning (p > 0.87). Hepatic fatty acid synthase (FAS) activity was elevated in FR and CNTL groups vs. CHOW (65 +/- 7, 72 +/- 6 vs. 48 +/- 4 nmol NADPH/mg protein/min, p < 0.01). There were no differences in indices of glucose homeostasis at 21 weeks of age. Early exposure to a diet high in simple sugars (FR or CNTL) and/or low in fiber during the suckling-weaning transition may contribute to modest dyslipidemia later in life. Together, changes observed in this study may increase the risk of cardiovascular disease in adulthood.

Programming of intermediary metabolism

Studies of animal models were carried out to explore mechanisms that might underlie epidemiological findings linking indices of poor early (fetal and early postnatal) growth to an increased risk of developing poor glucose tolerance, including the metabolic syndrome, in adult life. Adult obesity was also seen to play an important role in adding to these risks. We proposed the 'thrifty phenotype' hypothesis to provide a conceptual and mechanistic framework that could be tested by experimentation in animal models. Our main approach has been to feed a reduced protein diet to pregnant and/or lactating rat dams as a means of reducing growth in the fetal and/or preweaning stages of pup growth. Animals were weaned onto either a normal diet or an obesity-inducing highly palatable, cafeteria-style diet. Alterations in intermediary metabolism were noted in the rats with early growth restriction, which provide support for our hypothesis and clues to the mechanism.

Sir David Cuthbertson Medal Lecture. The impact of dietary protein restriction on insulin secretion and action

The goal of this review is to develop the hypothesis, and review the evidence, that protein restriction, through synergistic effects on multiple organ systems predisposes to loss of normal regulation of fuel homeostasis that plays the central role in the development of type 2 (non-insulin-dependent) diabetes mellitus. The ability of insulin to regulate glucose production and disposal varies between individuals. These differences, together with the various compensatory mechanisms that are invoked to attempt to normalize fuel homeostasis, are of fundamental importance in the development and clinical course of type 2 diabetes mellitus. Protein deprivation impacts on both insulin secretion and insulin action. These effects may persist even when a diet containing adequate protein is presented subsequently. Data are presented that suggest that protein restriction results in an impaired ability of pancreatic beta-cells to compensate adequately for the defect in insulin action in insulin-resistant individuals. This persistent impairment of insulin secretion resulting from protein restriction predisposes to loss of glucoregulatory control and impaired insulin action after the subsequent imposition of a diabetogenic challenge. This inability to maintain the degree of compensatory hyperinsulinaemia necessary to prevent loss of glucose tolerance may have relevance to the increased incidence of diabetes on changing from a nutritionally-poor diet to a Western diet, and to the hypothesis that some cases of type 2 diabetes in adulthood may be related to poor early nutrition.

The long-term consequences of intra-uterine protein malnutrition for glucose metabolism

Our initial observations, in epidemiological studies, linking indices of poor early (fetal and infant) growth to the subsequent development of poor glucose tolerance and the insulin resistance syndrome in adult life, have been confirmed in studies in a wide variety of populations around the world. These findings led us 5 years ago to propose the 'thrifty phenotype' hypothesis. Tests of this hypothesis in an animal model in which the pregnant and/or lactating rat dams are fed on an isoenergetic diet containing just under half the normal protein content are consistent with the ideas put forward. They have also allowed us to refine the hypothesis in the light of the new data as follows: (1) the growth of the fetus (and possibly infant) is quantitatively and qualitatively altered by its nutritional environment (which may include maternal diet-dependent changes in maternal hormones); (2) these changes serve to select between the growth rates of different tissues according to priorities which differ between males and females (nutritional thrift) and to alter organ function to constitute a thrifty offspring adapted to survival in poor nutritional circumstances (thrifty phenotype); (3) an individual so constituted suffers adverse consequences in adult life if he/she experiences good or supranormal nutrition; (4) both poor insulin secretion and insulin resistance can result from these adaptive processes; (5) the adverse consequences include loss of glucose tolerance and hypertension. The precise outcome of growth retardation during early life may vary according to the type and timing of the factors responsible for the retardation. It remains to be determined to what extent these potentially adverse effects can be delayed or prevented by a suitable postnatal diet. Experiments in animal models are largely consistent with the concepts proposed from human epidemiological studies. They show that the metabolism of the liver, muscle and adipose tissue may be programmed by maternal nutrition during gestation and lactation. The combination of early growth restriction and subsequent adult obesity reproduced in the rat are the main features of the insulin resistance syndrome.

Foetal nutrition, foetal growth restriction and health later in life

Retarded intrauterine growth has been linked to increased risk of perinatal mortality and morbidity, sudden infant death and poorer health later in life. The independent variables used in these studies are mainly neonatal size parameters, such as weight, ponderal index and ratios of head and abdominal measures. These are, in terms of foetal development and growth, crude parameters. This paper discusses the concepts of growth retardation used in most clinical and epidemiological studies. It is again emphasized that small for gestational age (SGA) and intrauterine growth retardation (IUGR) are different concepts. SGA is a size parameter that may or may not reflect restricted foetal growth and is therefore of limited value. Even IUGR, defined as retarded foetal growth rate, may be a too crude a criterion to select foetuses with short- and long-term health risks. Other biophysical measurements, such as foetal blood flow patterns and biochemical parameters, may be helpful in a better selection of these foetuses and infants. Furthermore, different causes of IUGR, e.g. poor maternal nutrition versus insufficient placental function, may not have the same effects on the foetus. The discrepancies in the results of studies on the relationship between IUGR or foetal malnutrition and short- and long-term health risks may be explained by the crudeness of the independent variables used. In the future, research on the biology of the developing human foetus should be more focused in the studies of the relationship between the intrauterine environment and nutrition and risk of poor health later in life.

Inadequate vitamin D status: does it contribute to the disorders comprising syndrome 'X'?

Environmental factors are important in the aetiology of glucose intolerance, type II diabetes and IHD. The lack of vitamin D, which is necessary for adequate insulin secretion, relates demographically to increased risk of myocardial infarction. These disorders are connected, degenerative vascular disease increasing with glucose intolerance and diabetes and, with its risk factors, comprising syndrome 'X'. Evidence is presented suggesting that vitamin D deficiency may be an avoidable risk factor for syndrome 'X', adding another preventative measure to current recommendations which are aimed at reducing the worldwide epidemic of these disorders. Experimentally, vitamin D deficiency progressively reduces insulin secretion; glucose intolerance follows and becomes irreversible. Relationships between vitamin D status, glucose tolerance and 30 min insulin secretion during oral glucose tolerance tests are reported in British Asians; insulin secretion, but not glycaemia, improving with short-term supplementation. Studies showing reduction in blood pressure and in risk of heart attack and diabetes with exercise (usually outdoor), rarely consider the role of vitamin D status. Glycaemia and insulin secretion in elderly European men, however, relate to vitamin D status, independent of season or physical activity. Prolonged supplementation can improve glycaemia. Hypertension improves with vitamin D treatment with or without initial deficiency. Vitamin D status and climate are reviewed as risk factors for myocardial infarction; the risk reducing with altitude despite increasing cold. Glycaemia and fibrinogenaemia improve with insulin secretion increases in summer. Variation in vitamin D requirements could arise from genetic differences in vitamin D processing since bone density can vary with vitamin D-receptor genotype. Vitamin D receptors are present in islet beta cells and we report insulin secretion in healthy Asians differing profoundly with the Apa I genotype, being independent of vitamin D status. Those at risk of vitamin D deficiency include the elderly, those living indoors or having a covered-up style of dress, especially dark-skinned immigrants, and pregnant women, and these are groups recognized as being at increased risk of diabetes.