Responses of lipolysis and salivary cortisol to food intake and physical activity in lean and obese children

Understanding the determinants of stress-induced eating - A qualitative study

The relationship between stress and food consumption is complex and often characterised by substantial between- and within-person variation. From a theoretical and practical perspective, more research is needed to improve our understanding of the factors that influence this relationship. The aim of this study was to identify those factors, and to derive insight into the nature of their effects on the relationship between stress and food consumption. Using semi-structured interviews, 41 adult participants (M ± SD age = 26.7 ± 6.3 yr, BMI = 22.9 ± 3.0 kg/m²) were invited to reflect on their food consumption following stressor exposure, and to elaborate on the factors that influence stress-induced eating behaviour. Reflexive thematic analyses revealed insight into the different ways in which individuals respond to stress in terms of food quantity and choices, and more significantly, highlighted a range of factors that may influence stress-induced eating behaviours. These factors included the intensity and/or nature of the stressor, aspects of prioritisation, rewarding, knowledge of and perceptions about food, normative (e.g., family, friend) influences, automated or habituated behaviours, the availability of food, and selected coping mechanisms. These findings present important directions for researchers seeking to study the variation in stress-induced eating, and may hold substantial practical value by way of informing interventions designed to alleviate unhealthy dietary responses to stress.

The effect of dairy products and non-dairy snacks on food intake, subjective appetite and cortisol levels in children: a randomized control study

Dairy snacks are available in various physical forms and their consumption is linked to improved metabolic health. The objective of this study was to determine the effect of dairy snacks of different physical forms on short-term food intake (FI), subjective appetite, and the stress hormone, cortisol, in children. Following a repeated-measures crossover design, 40 children aged 9-14 years randomly consumed 1 of 5 isoenergetic (180 kcal) snacks per study session. These snacks included solid (potato chips, cookies, and cheese), semi-solid (Greek yogurt), and fluid (2% fat milk) snacks. FI was measured 120 min after snack consumption. Subjective appetite was measured at 0 (immediately before the snack), 15, 30, 45, 60, 90, and 120 min. Salivary cortisol (n = 18) was measured after the Greek yogurt and cookie snacks at 0, 30, 60, 90, and 120 min. FI did not differ between snacks (P = 0.15). The Greek yogurt (P < 0.0001) and cheese (P = 0.0009) snacks reduced average appetite compared with the 2% fat milk snack. Salivary cortisol levels were not affected by snack (P = 0.84). This study demonstrates that dairy snacks are as effective as other popular snacks at influencing subsequent FI. However, solid and semi-solid dairy snacks are more effective at repressing subjective appetite than a fluid dairy snack. Registered at ClinicalTrials.gov (NCT02484625). Novelty: Milk, Greek yogurt and cheese have a similar effect on short-term food intake in children as popular potato chips and cookie snacks. Solid, semi-solid and liquid snacks have a similar effect on short-term food intake in children.

Associations between objective measures of physical activity, sleep and stress levels among preschool children

Background

Cortisol is often used as a biological marker for stress. When measured in urine or serum, representing a short-term measurement of the hormone, it has been associated with unfavorable sleep characteristics and both low and high physical activity levels. However, cortisol in hair represents a long-term stress measure and has been suggested as a promising new marker for chronic stress. Therefore, we aimed to examine the association between objectively measured sleep, physical activity and hair cortisol levels in preschool children.

Methods

In order to obtain objective measures of physical activity and sleep habits, 54 children aged 2–6 years wore an ActiGraph for 5 consecutive days and nights. For chronic stress measurements of each child, hair was cut from the back of the head close to the scalp for analysis of cortisol levels. Associations between measured sleep quality and quantity and level of physical activity and hair cortisol levels were estimated using linear regression analysis, presented as β. Results were adjusted for sex, age and BMI z-score.

Results

We found no significant association between log-transformed cortisol (pg/mg) and sleep duration (hours) (β = − 0.0016, p = 0.99), sleep efficiency (β = − 3.1, p = 0.18), sleep latency (β = 0.015, p = 0.16) or physical activity level (100 counts per min) (β = 0.014, p = 0.22). However, sleep latency (min) was directly associated with physical activity (counts per min) levels (β = 35.2, p = 0.02), while sleep duration (hours) (β = − 142.1, p = 0.55) and sleep efficiency (%) (β = − 4087, p = 0.26) showed no significant associations.

Conclusions

In our study, a high physical activity level was associated with poorer sleep habits. Neither sleep quality nor physical activity were related to long term cortisol exposure. These results are among the first to study associations between objectively measured sleep, physical activity and chronic cortisol levels among preschool children. More and larger studies are therefore needed.

Cortisol secretion pattern in overweight/obese and normal-weight infants: a cross-sectional study

Background The salivary circadian diurnal cortisol plays an important role in growth and development. Inappropriate levels may induce changes associated with an increased risk of obesity later in life. It is unknown if there are differences in cortisol secretion pattern between overweight/obese infants when compared with theirs peers in infancy. Thus, this study aimed to compare the salivary cortisol secretion pattern in overweight/obese and normal-weight infants. Methods Thirty-three (overweight/obese = 17 and normal weight = 16) infants between 6 and 24 months of age had saliva samples collected upon awakening (T1), 30 min after waking (T2), at 12:00 am or before the baby's meal (T3), and prior to bedtime (T4). Highly sensitive enzyme immunoassays were used for cortisol analyses. Results Salivary cortisol levels were similar between the groups: T1 (p = 0.22; 95% confidence interval [CI]: -5.65, 1.37), T2 (p = 0.24; 95% CI: -8.23, 2.17), T3 (p = 0.95; 95% CI: -3.16, 2.96), and T4 (p = 0.81; 95% CI: -1.39, 1.08); and no differences were observed between area under the curve (AUC) (p = 0.80; 95% CI: -4.58-13.66). The cortisol level reduced in T4 (95% CI: 1.35-2.96) compared to T1 (95% CI: 5.15-8.49) and T2 in the overweight/obese group (p < 0.001; 95% CI: 6.02-11.04). In the normal-weight group, the cortisol reduced in T3 (95% CI: 2.86-8.18) compared to T1 (95% CI: 5.64-12.28) and decreased until T4 (p = 0.001; 95% CI: 1.25-3.37). Conclusions The overweight/obese infant group presented a different pattern of cortisol secretion, although cortisol levels did not differ between the control group.

A Role for Exercise in Attenuating Unhealthy Food Consumption in Response to Stress

It is well established that both acute and chronic stress can be detrimental to health and wellbeing by directly increasing the risk of several chronic diseases and related health problems. In addition, stress may contribute to ill-health indirectly via its downstream effects on individuals’ health-related behaviour, such as promoting the intake of unhealthy palatable foods high in fat and sugar content. This paper reviews (a) the research literature on stress-models; (b) recent research investigating stress-induced eating and (c) the potential physiological and psychological pathways contributing to stress-induced eating. Particular attention is given to (d) the role of physical exercise in attenuating acute stress, with exploration of potential mechanisms through which exercise may reduce unhealthy food and drink consumption subsequent to stressor exposure. Finally, exercise motivation is discussed as an important psychological influence over the capacity for physical exercise to attenuate unhealthy food and drink consumption after exposure to stressors. This paper aims to provide a better understanding of how physical exercise might alleviate stress-induced unhealthy food choices.

Exercise Effects on Adipose Tissue Postprandial Lipolysis and Blood Flow in Children

Poor suppression of lipolysis and blunted increase in blood flow after meal ingestion in obese adults may indicate resistance to the antilipolytic action of insulin. Exercise may be used to normalize lipolytic responses to food intake by increasing insulin sensitivity.

PURPOSE

To determine if acute bouts of aerobic exercise and/or excise training alter lipolytic and blood flow responses to food intake in lean (LN) and obese (OB) children.

METHODS

Sixty-five children (9-11 yr) were randomized into acute exercise (EX: 16 LN and 28 OB) or control (CON: 9 LN and 12 OB) groups that exercised (EX), or rested (CON) between standardized breakfast and lunch. Microdialysis probes were inserted into the subcutaneous abdominal adipose tissue to monitor interstitial glycerol (lipolysis) and blood flow. Changes in interstitial glycerol and nutritive flow were calculated from dialysate samples before and after each meal. A subgroup (OB = 15 and LN = 9) from the acute exercise group underwent 16 wk of aerobic exercise training.

RESULTS

Poor suppression of lipolysis and a blunted increase in adipose tissue nutritive blood flow in response to breakfast was associated with BMI percentile (r = 0.3, P < 0.05). These responses were normalized at lunch in the OB in the EX (P < 0.05), but not in OB in the CON. Sixteen weeks of exercise training did not improve meal-induced blood flow and marginally altered the antilipolytic response to the two meals (P = 0.06).

CONCLUSIONS

Daily bouts of acute aerobic exercise should be used to improve the antilipolytic and nutritive blood flow response to a subsequent meal in obese children.

Novel method for detection of reactive oxygen species in vivo in human skeletal muscle

Excessive production of reactive oxygen species (ROS) are implicated in the pathogenesis of numerous disease states. However, direct measurement of in vivo ROS in humans has remained elusive due to limited access to appropriate tissue beds and the inherently short half-lives and high reactivity of ROS. Herein, we describe a novel technique by which to measure in vivo ROS in human skeletal muscle. Microdialysis probes were inserted into the vastus lateralis of eight healthy volunteers. Amplex Ultrared, a highly specific fluorogenic substrate for hydrogen peroxide (H(2)O(2)), and horseradish peroxidase (HRP), were perfused through microdialysis probes, and outflowing dialysate was collected and fluorescence was measured. Extracellular H(2)O(2) that crossed the microdialysis membrane was measured via fluorescence of the dialysate. Superoxide dismutase (SOD) was then added to the inflowing perfusion media to convert any superoxide crossing the microdialysis membrane to H(2)O(2) within the microdialysis probe. Fluorescence significantly increased (P=0.005) upon SOD addition. These data demonstrate the feasibility of measuring both in vivo H(2)O(2) and superoxide in the extracellular environment of human skeletal muscle, providing a technique with a potential application to a wide range of circulatory and metabolic studies of oxidative stress.

Combined food intake and exercise unmask different hormonal responses in lean and obese children

Our purpose was to investigate the effect of obesity in prepubertal children on the hormonal response to exercise performed under different conditions of nutrient availability. Prepubertal obese (age, 10.3 ± 1.8 years; %body fat, 36.1 ± 6.1; n = 9) and lean (age, 9.2 ± 1.6 years; %body fat, 22.2 ± 4.1; n = 7) children completed 2 experimental sessions in which they performed a 30 min of cycling exercise at 50% of their maximal aerobic power either 1 h (T1h) or 3 h (T3h) after a standardized breakfast. Plasma insulin-like growth factor 1 (IGF-1), IGF binding protein 1 (IGFBP-1), and IGFBP-3 levels were assessed at baseline and after exercise. Urine was collected during the sessions, and catecholamine and glucocorticoid excretions were analyzed. A significant time effect was observed for IGFBP-1; postexercise levels decreased in lean and obese children (p ≤ 0.001). IGF-1 and IGFBP-3 were not affected by obesity or food intake combined with exercise. In lean children, urinary excretion rates of epinephrine, norepinephrine, cortisol, and cortisone were significantly higher during the sessions than during the overnight resting period; in obese children, only epinephrine in T1h was significantly increased (p ≤ 0.05 for all). Our study indicates that the activity of the hypothalamic–pituitary–adrenal axis and sympathetic adrenal medullary axis was similar in lean and obese children, based on measurement under resting conditions, but response to exercise performed in postprandial conditions was altered in obese children for both axes. In addition, exercise in the postprandial state elicited a decrease in IGFBP-1 plasma levels, whereas IGF-1 and IGFBP-3 levels were not significantly altered.

Diurnal cortisol rhythms in Tsimane' Amazonian foragers: new insights into ecological HPA axis research

Although a growing body of research has documented important pathways by which the HPA axis mediates the interface between the psychosocial world and individual health, there is a paucity of data from nonwestern populations, particularly from those populations with distinct nutritional and infectious disease ecologies. The specific objectives of this study are: (1) to document variation in diurnal cortisol rhythms among the Tsimane', a remote population in the Bolivian Amazon, (2) to explore this variation by age and by gender, and (3) to compare diurnal rhythms from this study to other population based studies of cortisol conducted in industrialized nations. Salivary cortisol samples were collected twice daily, immediately upon waking and before bed, for three consecutive days from 303 participants (age 1.6-82 years, 1564 samples) in conjunction with the Tsimane' Amazonian Panel Study (TAPS). Cortisol rhythms showed strong age effects across the developmental span, with basal levels and slopes increasing into adulthood, although individuals older than 60 years demonstrated a precipitous flattening of the diurnal slope. Cortisol profiles were elevated in adult females compared to their age-matched male counterparts, and diurnal slopes, as well as mean cortisol concentrations among the Tsimane' were the lowest reported in any population based study of HPA axis function. Although the within-population variation in cortisol profiles was consistent with the established correlates of time of day, age, and sex, the between-population comparisons revealed dramatically lower levels of HPA activity among the Tsimane'. This study provides a benchmark against which to reference cortisol levels from industrialized populations, and expands the range of documented variation in HPA axis function in a nonwestern context.

Effect of time interval between food intake and exercise on substrate oxidation during exercise in obese and lean children

BACKGROUND & AIMS

Exercise induces adaptations in fat metabolism favourable to the treatment of obesity. However, time interval between meal and exercise alters substrate bioavailability and oxidation during exercise. The aim of this study was therefore to investigate the effect of time interval between food intake and exercise on substrate oxidation rates in obese and lean children.

METHODS

The metabolic responses to exercise of nine obese children (10.3 ± 1.8 years; %body fat: 36.1 ± 6.1) and seven lean children (9.2 ± 1.6 years; %body fat: 22.2 ± 4.1) were compared 1 h (time interval 1, TI1) and 3 h (TI3) after a standardized breakfast.

RESULTS

Despite significantly lower plasma glucose and insulin concentrations and large effect size suggesting a higher plasma FFA availability (lean, 1.43, obese 0.98), fat oxidation was not significantly increased in TI3 compared to TI1 in both lean and obese children. Fat oxidation contributed marginally to energy expenditure during exercise (<20%) in both conditions and groups but was moderately increased during TI3 compared to TI1 in lean children (effect size: 0.54).

CONCLUSIONS

The low contribution of fat oxidation to energy expenditure during exercise in obese and lean children fed 3 h before exercise questions the efficacy of moderate intensity exercise to favourably affect fat balance.

Concentrations of salivary testosterone, cortisol, and immunoglobulin A after supra-maximal exercise in female adolescents

The aim of this study was to examine the effect of supra-maximal exercise on circulating concentrations of salivary testosterone, salivary cortisol, and salivary immunoglobulin A in female adolescents. Nineteen apparently healthy females aged 15-16 years participated in this study. All participants completed 668 s sprints, interspersed with 30 s recovery intervals on a cycle ergometer. Salivary testosterone, cortisol, and immunoglobulin A samples were taken before and 5 min after exercise. Experimental procedures continued over two mornings, at least 3 h after a light breakfast. Participants refrained from performing any strenuous physical activity for at least 24 h prior to the exercise test. None of the participants were engaged in a structured training programme. The group mean (± s) for peak power output was 562 ± 113.0 W. Female adolescents recruited for this study showed no changes in salivary testosterone, cortisol or immunoglobulin A following repeated bouts of supra-maximal cycling (P > 0.05). To date, there has been a paucity of information concerning adolescents' hormonal and mucosal immune function responses to supra-maximal exercise. Our data provide further guidance with regard to physical activities and sports prescription for female adolescents. Further research, on a larger sample of females, is required to elucidate the physiological significance of these findings.

Metabolic flexibility and obesity in children and youth

The concept of metabolic flexibility describes the ability of skeletal muscle to switch between the oxidation of lipid as a fuel during fasting periods to the oxidation of carbohydrate during insulin stimulated period. Alterations in energy metabolism in adults with obesity, insulin resistance and/or type 2 diabetes induce a state of impaired metabolic flexibility, or metabolic inflexibility. Despite the increase in the prevalence of type 2 diabetes in obese children and youth, less is known about the factors involved in the development of metabolic inflexibility in the paediatric population. Metabolic flexibility is conditioned by nutrient partitioning in response to feeding, substrate mobilization and delivery to skeletal muscle during fasting or exercising condition, and skeletal muscle oxidative capacity. Our aim in this review was to identify among these factors those making obese children at risk of metabolic inflexibility. The development of ectopic rather than peripheral fat storage appears to be a factor strongly linked with a reduced metabolic flexibility. Tissue growth and maturation are determinants of impaired energy metabolism later in life but also as a promising way to reverse metabolic inflexibility given the plasticity of many tissues in youth. Finally, we have attempted to identify perspectives for future investigations of metabolic flexibility in obese children that will improve our understanding of the genesis of metabolic diseases associated with obesity.

Cortisol levels in pregnancy as a psychobiological predictor for birth weight

Antenatal maternal stress is thought to negatively affect fetal development, birth outcomes, and infant's development. Glucocorticoids are suggested to be a common link between prenatal stressors and infant's health. However, data on these mechanisms are rare and sometimes conflicting. The objective of this study was to examine the effects of maternal distress during pregnancy on fetal development and birth weight in humans prospectively. This study focuses on cortisol as one mediating the mechanism of the association between maternal distress and birth outcomes. Pregnancy-related and general distress was measured in 81 women with uncomplicated, singleton pregnancies. The rise of salivary cortisol on awakening (CAR) was assessed in weeks 13-18 and 35-37 postmenstrual age of pregnancy. Mothers completed a structured interview, the perceived stress scale, a widely used psychological instrument that provided a global measure of perceived stress, as well as the Prenatal Distress Questionnaire, a self-report questionnaire designed to assess worries and anxiety in pregnancy. Pre-, peri-, and postnatal medical risk factors as well as birth characteristics were extracted from medical records routinely kept by the attending obstetricians. Hierarchical multiple regressions indicate that maternal cortisol levels explained 19.8% of the variance in birth weight and 9% of the variance in body length at birth, even after controlling for gestational age, parity, pre-pregnancy BMI, smoking, and infant's sex. Newborns of mothers with higher cortisol levels in pregnancy had lower birth weights and were shorter at birth. An ANCOVA for repeated measures indicated that, after controlling for covariates, pregnancy-related as well as general distress in pregnancy did not influence cortisol levels after awakening (area under the curve). No significant associations between perceived stress and anthrometric measures at birth were found. In conclusion, maternal cortisol levels in pregnancy influence intrauterine growth and may be a better predictor for birth outcome than perceived stress.

Fat and carbohydrate metabolism during submaximal exercise in children

During exercise, the contribution of fat and carbohydrate to energy expenditure is largely modulated by the intensity of exercise. Age, a short- or long-term diet enriched in carbohydrate or fat substrate stores, training and gender are other factors that have also been found to affect this balance. These factors have been extensively studied in adults from the perspective of improving performance in athletes, or from a health perspective in people with diseases. During the last decade, lifestyle changes associated with high-energy diets rich in lipid and reduced physical activity have contributed to the increase in childhood obesity. This lifestyle change has emerged as a serious health problem favouring the early development of cardiovascular diseases, insulin resistance or type 2 diabetes mellitus. Increasing physical activity levels in young people is important to increase energy expenditure and promote muscle oxidative capacity. Therefore, it is surprising that the regulation of balance between carbohydrate and lipid use during exercise has received much less attention in children than in adults. In this review, we have focused on the factors that affect carbohydrate and lipid metabolism during exercise and have identified areas that may be relevant in explaining the higher contribution of lipid to energy expenditure in children when compared with adults. Low muscle glycogen content is possibly associated with a low activity of glycolytic enzymes and high oxidative capacity, while lower levels of sympathoadrenal hormones are likely to favour lipid metabolism in children. Changes in energetic metabolism occurring during adolescence are also dependent on pubertal events with an increase in testosterone in boys and estrogen and progesterone in girls. The profound effects of ovarian hormones on carbohydrate and fat metabolism along with their effects on oxidative enzymes could explain that differences in substrate metabolism have not always been observed between girls and women. Finally, although the regulatory mechanisms of fat and carbohydrate balance during exercise are quite well identified, there are a lack of data specific to children and most of the evidences reported in this review were drawn from studies in adults. Isotope tracer techniques and nuclear magnetic resonance will allow non-invasive investigation of the metabolism of the different substrate sources in skeletal muscle.

Measurement and meaning of salivary cortisol: a focus on health and disease in children

Measurement of salivary cortisol can provide important information about hypothalamic-pituitary-adrenal (HPA) axis activity under normal conditions and in response to stress. However, there are many variables relating to the measurement of cortisol in saliva which may introduce error and therefore may render difficult the comparison and interpretation of data between, and within, laboratories. This review addresses the effects of gender, age, time and location of sampling, units of measurement, assay conditions and compliance with the protocol, all of which have the potential to impact upon the precision, accuracy and reliability of salivary cortisol measurements in the literature. Some of these factors are applicable to both adults and children, but the measurement of salivary cortisol in children introduces aspects of unique variability which demand special attention. The specific focus of this review is upon the somewhat neglected area of methodological variability of salivary cortisol measurement in children. In addition to these methodological issues, the review highlights the use of salivary cortisol measurements to provide information about HPA axis dysfunction associated with psycho- and patho-physiological conditions in children. Novel applications for salivary cortisol measurements in future research into HPA axis activity in children are also discussed.

Truncal distribution of fat mass, metabolic profile and hypothalamic-pituitary adrenal axis activity in prepubertal obese children

OBJECTIVE

To investigate whether truncal distribution of fat mass (TDFM) is associated with variations of the hypothalamic-pituitary-adrenocortical (HPA) axis activity in prepubertal obese children.

STUDY DESIGN

TDFM, assessed with dual energy X-ray absorptiometry and a comprehensive set of measures of HPA axis activity and reactivity have been studied in 45 prepubertal obese children aged 6 to 11 years (girls) and 6 to 13 years (boys).

RESULTS

After adjustment for whole body fat mass (%) (WBFM), TDFM correlated positively with insulin (r = 0.50, 95% CI [0.23; 0.70]) and homeostasis model assessment of insulin resistance (r = 0.52, 95% CI [0.25; 0.71]). When adjusted for WBFM, TDFM correlated positively with morning plasma cortisol (r = 0.38, 95% CI [0.15; 0.64]) in the total population. TDFM correlated negatively with the rise of salivary cortisol after a standard meal (r = -0.43, 95% CI [-0.71; -0.02]), obviously in girls. When adjusted for WBFM and TDFM, morning plasma cortisol correlated positively with total cholesterol (r = 0.41, 95% CI [0.11; 0.65]) and triglyceride (r = 0.44, 95% CI [0.14; 0.67]). The rise of salivary cortisol after a standard meal was negatively (r = -0.56, 95% CI [-0.85; -0.01]) and positively (r = 0.74, 95% CI [0.16; 0.94]) correlated with homeostasis model assessment of insulin resistance in boys and girls, respectively.

CONCLUSIONS

Association exists in prepubertal obese children between TDFM and markers of HPA axis activity. These data suggest that HPA axis could be involved early in life in obesity associated with pejorative metabolic profile.

Differential expression of aquaporin 7 in adipose tissue of lean and obese high fat consumers

Aquaporin 7 (AQP7) is an aquaglyceroprotein responsible for the secretion and uptake of glycerol from the adipocyte. The modulation of the expression of this membrane transport protein might play an important role in the susceptibility to the development of obesity. The aim of the present study was to compare the AQP7 gene expression in subcutaneous abdominal fat in lean vs. obese high fat intakers with a similar daily physical activity pattern. Twelve young men, 6 lean (BMI=23.2+/-0.4kg/m(2)) and 6 obese (35.0+/-1.1kg/m(2)) with a similar habitual dietary intake of fat (45.5+/-2.5 vs. 43.5+/-1.7% daily energy from fat for lean and obese, respectively) and physical activity (16.0+/-5.7 vs. 17.2+/-5.1 METsh/week for lean and obese, respectively), were recruited. Subcutaneous abdominal fat biopsies were obtained and total RNA was extracted and purified. Pools of RNA from lean and obese individuals were probed into Affymetrix GeneChip Human U133A. The microarray analysis revealed that AQP7 gene was down-regulated in obese compared to lean subjects. The results of the microarray analysis were confirmed by real-time PCR studies. In summary, our data show that the AQP7 gene is differentially expressed in adipose tissue of lean and obese individuals. The down-regulation of the AQP7 gene could be implicated in the susceptibility to obesity by reducing glycerol release and promoting the accumulation of lipids in the adipose tissue.