Plasma ghrelin response following a period of acute overfeeding in normal weight men

Effects of poor maternal nutrition during gestation on ewe and offspring plasma concentrations of leptin and ghrelin

Poor maternal nutrition during gestation can negatively affect offspring growth, development, and health. Leptin and ghrelin, key hormones in energy homeostasis and appetite control, may mediate these changes. We hypothesized that restricted- and over-feeding during gestation would alter plasma concentrations of leptin and ghrelin in ewes and offspring. Pregnant ewes (n = 37) were fed 1 of 3 diets starting on d 30 ± 0.02 of gestation until necropsy at d 135 of gestation or parturition: restricted- [RES; 60% National Research Council (NRC) requirements for total digestible nutrients, n = 13], control- (CON; 100% NRC, n = 11), or over-fed (OVER; 140% NRC, n = 13). Blood samples were collected from pregnant ewes at days 20, 30, 44, 72, 100, 128, and 142 of gestation. Offspring blood samples were collected within 24 h after birth (n = 21 CON, 25 RES, 23 OVER). Plasma leptin and ghrelin concentrations were determined by RIA. Ewe data were analyzed using the MIXED procedure in SAS with ewe as the repeated subject. Offspring data were analyzed using the MIXED procedure. Correlations between BW and leptin and ghrelin concentrations were identified using PROC CORR. At d 100, RES (5.39 ± 2.58 ng/mL) had decreased leptin concentrations compared with OVER (14.97 ± 2.48 ng/mL; P = 0.008) and at d 128, RES (6.39 ± 2.50 ng/mL) also had decreased leptin concentrations compared with OVER (13.61 ± 2.47 ng/mL; P = 0.04). At d 142, RES (0.26 ± 0.04 ng/mL) had increased ghrelin concentrations compared with CON (0.15 ± 0.04 ng/mL; P = 0.04). Leptin and ghrelin concentrations were also altered between days of gestation within a dietary treatment. In CON ewes, plasma concentrations of leptin were increased at d 30 (19.28 ± 7.43 ng/mL) compared with d 44 (5.20 ± 3.10 ng/mL; P = 0.03), and the plasma concentrations of ghrelin at d 128 (0.20 ± 0.03 ng/mL) were increased compared with d 30 (0.16 ± 0.03 ng/mL; P = 0.01) and d 100 (0.17 ± 0.03 ng/mL; P = 0.04). Maternal diet did not alter plasma ghrelin or leptin concentrations in the offspring (P > 0.50). There were no strong, significant correlations between ewe BW and leptin (r < 0.33; P > 0.06) or ghrelin (r > -0.47; P > 0.001) concentrations or lamb BW and leptin or ghrelin concentrations (r > -0.32, P > 0.06). Maternal alterations in circulating leptin and ghrelin may program changes in energy balance that could result in increased adiposity in adult offspring. Alterations in energy homeostasis may be a mechanism behind the long-lasting changes in growth, body composition, development, and metabolism in the offspring of poorly nourished ewes.

The biology of human overfeeding: A systematic review

This systematic review has examined more than 300 original papers dealing with the biology of overfeeding. Studies have varied from 1 day to 6 months. Overfeeding produced weight gain in adolescents, adult men and women and in older men. In longer term studies, there was a clear and highly significant relationship between energy ingested and weight gain and fat storage with limited individual differences. There is some evidence for a contribution of a genetic component to this response variability. The response to overfeeding was affected by the baseline state of the groups being compared: those with insulin resistance versus insulin sensitivity; those prone to obesity versus those resistant to obesity; and those with metabolically abnormal obesity versus those with metabolically normal obesity. Dietary components, such as total fat, polyunsaturated fat and carbohydrate influenced the patterns of adipose tissue distribution as did the history of low or normal birth weight. Overfeeding affected the endocrine system with increased circulating concentrations of insulin and triiodothyronine frequently present. Growth hormone, in contrast, was rapidly suppressed. Changes in plasma lipids were influenced by diet, exercise and the magnitude of weight gain. Adipose tissue and skeletal muscle morphology and metabolism are substantially altered by chronic overfeeding.

Impact of sedentarism due to the COVID-19 home confinement on neuromuscular, cardiovascular and metabolic health: Physiological and pathophysiological implications and recommendations for physical and nutritional countermeasures

The COVID-19 pandemic is an unprecedented health crisis as entire populations have been asked to self-isolate and live in home-confinement for several weeks to months, which in itself represents a physiological challenge with significant health risks. This paper describes the impact of sedentarism on the human body at the level of the muscular, cardiovascular, metabolic, endocrine and nervous systems and is based on evidence from several models of inactivity, including bed rest, unilateral limb suspension, and step-reduction. Data form these studies show that muscle wasting occurs rapidly, being detectable within two days of inactivity. This loss of muscle mass is associated with fibre denervation, neuromuscular junction damage and upregulation of protein breakdown, but is mostly explained by the suppression of muscle protein synthesis. Inactivity also affects glucose homeostasis as just few days of step reduction or bed rest, reduce insulin sensitivity, principally in muscle. Additionally, aerobic capacity is impaired at all levels of the O₂ cascade, from the cardiovascular system, including peripheral circulation, to skeletal muscle oxidative function. Positive energy balance during physical inactivity is associated with fat deposition, associated with systemic inflammation and activation of antioxidant defences, exacerbating muscle loss. Importantly, these deleterious effects of inactivity can be diminished by routine exercise practice, but the exercise dose-response relationship is currently unknown. Nevertheless, low to medium-intensity high volume resistive exercise, easily implementable in home-settings, will have positive effects, particularly if combined with a 15-25% reduction in daily energy intake. This combined regimen seems ideal for preserving neuromuscular, metabolic and cardiovascular health.

Appetite-Related Responses to Overfeeding and Longitudinal Weight Change in Obesity-Prone and Obesity-Resistant Adults

OBJECTIVE

Appetite responses to 3 days of overfeeding (OF) were examined as correlates of longitudinal weight change in adults classified as obesity prone (OP) or obesity resistant (OR).

METHODS

OP (n = 22) and OR (n = 30) adults consumed a controlled eucaloric and OF diet (140% of energy needs) for 3 days, followed by 3 days of ad libitum feeding. Hunger and satiety were evaluated by visual analog scales. Ghrelin and peptide YY (PYY) levels were measured during a 24-hour inpatient visit on day 3. Body weight and composition were measured annually for 4.0 ± 1.3 years.

RESULTS

Dietary restraint and disinhibition were greater in OP than OR (mean difference: 3.5 ± 1.2 and 3.3 ± 0.9, respectively; P < 0.01) participants, and disinhibition was associated with longitudinal weight change (n = 48; r = 0.35; P = 0.02). Compared with the eucaloric diet, energy intake fell significantly in OR participants following OF (P = 0.03) but not in OP (P = 0.33) participants. Twenty-four-hour PYY area under the curve values increased with OF in OR (P = 0.02) but not in OP (P = 0.17) participants. Furthermore, changes in PYY levels with OF correlated with measured energy intake (r = -0.36; P = 0.01).

CONCLUSIONS

Baseline disinhibition and PYY responses to OF differed between OP and OR adults. Dietary disinhibition was associated with 5-year longitudinal weight gain. Differences in appetite regulation may underlie differences in propensity for weight gain.

The Effect of Short-Term Dietary Fructose Supplementation on Gastric Emptying Rate and Gastrointestinal Hormone Responses in Healthy Men

This study aimed to examine gastric emptying rate and gastrointestinal hormone responses to fructose and glucose ingestion following 3 days of dietary fructose supplementation. Using the ¹³C-breath test method, gastric emptying rates of equicaloric fructose and glucose solutions were measured in 10 healthy men with prior fructose supplementation (fructose supplement, FS; glucose supplement, GS) and without prior fructose supplementation (fructose control, FC; glucose control, GC). In addition, circulating concentrations of acylated ghrelin (GHR), glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and insulin were determined, as well as leptin, lactate, and triglycerides. Increased dietary fructose ingestion resulted in accelerated gastric emptying rate of a fructose solution but not a glucose solution. No differences in GIP, GLP-1, or insulin incremental area under curve (iAUC) were found between control and supplement trials for either fructose or glucose ingestion. However, a trend for lower ghrelin iAUC was observed for FS compared to FC. In addition, a trend of lower GHR concentration was observed at 45 min for FS compared to FC and GHR concentration for GS was greater than GC at 10 min. The accelerated gastric emptying rate of fructose following short-term supplementation with fructose may be partially explained by subtle changes in delayed postprandial ghrelin suppression.

Differential Effects of Oral and Intravenous Lipid Administration on Key Molecules Related to Energy Homeostasis

CONTEXT

The spectrum of lipid-induced changes in the secretion of hormones important in energy homeostasis has not yet been fully elucidated.

OBJECTIVE

To identify potential incretin-like effects in response to lipid administration, we examined the short-term effect of iv vs oral lipids on key molecules regulating energy homeostasis. Design, Intervention, and Participants: After a 10-hour overnight fast, 26 subjects were randomized to receive an oral lipid load, a 10% iv lipid emulsion, a 20% iv lipid emulsion, or an iv saline infusion. We obtained blood samples at 30-minute intervals for the first 2 hours and hourly thereafter for a total of 6 hours.

MAIN OUTCOME MEASURES

Circulating levels of insulin, glucose, c-peptide, free fatty acids, incretins (glucagon-like peptide-1, gastric inhibitory polypeptide), glucagon, peptide YY, ghrelin, fibroblast growth factor 21, fetuin A, irisin, omentin, and adiponectin were measured.

RESULTS

Oral lipid ingestion resulted in higher glucagon-like peptide-1, gastric inhibitory polypeptide, glucagon, and peptide YY levels, compared with the other three groups (incremental area under the curve P = .003, P < .001, P < .001, P < .001, respectively). The 20% lipid emulsion, leading to higher free fatty acid levels, resulted in greater insulin, c-peptide, and fibroblast growth factor 21 responses compared with placebo and the other two groups (incremental area under the curve P = .002, P = .005, P < .001, P < .001, respectively). Omentin, adiponectin, fetuin A, and irisin levels were not affected by either mode of lipid administration.

CONCLUSIONS

Metabolic responses to lipids depend on the route of administration. Only iv lipids trigger a dose-dependent fibroblast growth factor 21 secretion, which is nonglucagon mediated. Intravenous lipids also induce hyperinsulinemia without concurrent decreases in glucose, a phenomenon observed in insulin-resistant states. Orally administered lipids mostly affect gastrointestinal tract-secreted molecules important in glucose and energy homeostasis such as glucagon, incretins, and peptide YY.

Upper gastrointestinal sensitivity to meal-related signals in adult humans - relevance to appetite regulation and gut symptoms in health, obesity and functional dyspepsia

Both the stomach and small intestine play important roles in sensing the arrival of a meal, and its physico-chemical characteristics, in the gastrointestinal lumen. The presence of a meal in the stomach provides a distension stimulus, and, as the meal empties into the small intestine, nutrients interact with small intestinal receptors, initiating the release of gut hormones, associated with feedback regulation of gastrointestinal functions, including gut motility, and signaling to the central nervous system, modulating eating behaviours, including energy intake. Lipid appears to have particularly potent effects, also in close interaction with, and modulating the effects of, gastric distension, and involving the action of gut hormones, particularly cholecystokinin (CCK). These findings have not only provided important, and novel, insights into how gastrointestinal signals interact to modulate subjective appetite perceptions, including fullness, but also laid the foundation for an increasing appreciation of the role of altered gastrointestinal sensitivities, e.g. as a consequence of excess dietary intake in obesity, or underlying the induction of gastrointestinal symptoms in functional dyspepsia (a condition characterized by symptoms, including bloating, nausea and early fullness, amongst others, after meals, particularly those high in fat, in the absence of any structural or functional abnormalities in the gastrointestinal tract). This paper will review the effects of dietary nutrients, particularly lipid, on gastrointestinal function, and associated effects on appetite perceptions and energy intake, effects of interactions of gastrointestinal stimuli, as well as the role of altered gastrointestinal sensitivities (exaggerated, or reduced) in eating-related disorders, particularly obesity and functional dyspepsia.

Pros and cons of fatty acids in bone biology

Despite the growing interest in deciphering the causes and consequences of obesity-related disorders, the mechanisms linking fat intake to bone behaviour remain unclear. Since bone fractures are widely associated with increased morbidity and mortality, most notably in elderly and obese people, bone health has become a major social and economic issue. Consistently, public health system guidelines have encouraged low-fat diets in order to reduce associated complications. However, from a bone point of view, mechanisms linking fat intake to bone alteration remain quite controversial. Thus, after more than a decade of dedicated studies, this timely review offers a comprehensive overview of the relationships between bone and fatty acids. Using clinical evidences as a starting-point to more complex molecular elucidation, this work highlights the complexity of the system and reveals that bone alteration that cannot be solved simply by taking ω-3 pills. Fatty acid effects on bone metabolism can be both direct and indirect and require integrated investigations. Furthermore, even at the level of a single cell, one fatty acid is able to trigger several different independent pathways (receptors, metabolites…) which may all have a say in the final cellular metabolic response.

Altered ghrelin secretion in mice in response to diet-induced obesity and Roux-en-Y gastric bypass

The current study examined potential mechanisms for altered circulating ghrelin levels observed in diet-induced obesity (DIO) and following weight loss resulting from Roux-en-Y gastric bypass (RYGB). We hypothesized that circulating ghrelin levels were altered in obesity and after weight loss through changes in ghrelin cell responsiveness to physiological cues. We confirmed lower ghrelin levels in DIO mice and demonstrated elevated ghrelin levels in mice 6 weeks post-RYGB. In both DIO and RYGB settings, these changes in ghrelin levels were associated with altered ghrelin cell responsiveness to two key physiological modulators of ghrelin secretion - glucose and norepinephrine. In DIO mice, increases in ghrelin cell density within both the stomach and duodenum and in somatostatin-immunoreactive D cell density in the duodenum were observed. Our findings provide new insights into the regulation of ghrelin secretion and its relation to circulating ghrelin within the contexts of obesity and weight loss.

The modulatory role of high fat feeding on gastrointestinal signals in obesity

The gastrointestinal (GI) tract is a specialized sensory system that detects and responds to constant changes in nutrient- and bacterial-derived intestinal signals, thus contributing to controls of food intake. Chronic exposure to dietary fat causes morphological, physiological and metabolic changes leading to disruptions in the regulatory feeding pathways promoting more efficient fat absorption and utilization, blunted satiation signals and excess adiposity. Accumulating evidence demonstrates that impaired gastrointestinal signals following long-term high fat consumption are, at least partially, responsible for increased caloric intake. This review focuses on the role of dietary fat in modulating oral and post-oral chemosensory signaling elements responsible for lipid detection and responses, including changes in sensitivity to satiation signals, such as GLP-1, PYY and CCK and their impact on food intake and weight gain. Furthermore, the influence of the gut microbiota on mechanisms controlling energy regulation in the face of excessive fat exposure will be explored. The profound influence of dietary fats on altering complex regulatory feeding pathways can result in dysregulation of body weight and development of obesity, while restoration or manipulation of satiation signaling may prove an effective tool in prevention and treatment of obesity.

Ghrelin and obestatin levels in children with failure to thrive and obesity

OBJECTIVES

Ghrelin and obestatin are 2 gastric hormones with opposite effects on food intake and body weight. We investigated plasma ghrelin and obestatin in children with failure to thrive (FTT) and obesity as compared with age-matched controls.

METHODS

A total of 63 children were included in the study: 13 with FTT, 17 with obesity, and 33 age-matched controls. Children fasted for at least 8 hours before specimen collection. Both hormones were measured using commercially available enzyme immunoassay kits.

RESULTS

Ghrelin and obestatin levels in children with FTT were not significantly different from that of the age-matched controls (P >0.05). In children with obesity, the total ghrelin levels were significantly lower (P = 0.0003) and the obestatin levels significantly higher (P = 0.029) compared with those in controls. In the control group, the fasting ghrelin level was significantly higher in the younger (<3 years) than in the older children (>3 years; P = 0.0004). Obestatin levels correlated positively with weight-for-age percentiles in the obese group (P = 0.011) and negatively in the control group >3 years (P = 0.019).

CONCLUSIONS

Compared with the levels in age-matched controls, fasting ghrelin and obestatin levels did not differ significantly in children with FTT. In the children with obesity, the decreased ghrelin and increased obestatin levels suggest a possible adaptive process to positive energy balance. Ghrelin had pronounced age-related changes, and obestatin was associated with the weight status. This may suggest that these 2 hormones use different mechanisms to regulate energy balance and weight.

The latest on the effect of prior exercise on postprandial lipaemia

This review examines the effect of prior exercise on postprandial triacylglycerol (pTAG) concentrations, an independent risk factor for cardiovascular diseases. Numerous studies have shown that a single bout of exercise reduces pTAG concentrations; however, several modulators such as exercise energy expenditure/deficit, mode of exercise (aerobic/resistance/high intensity/intermittent exercise or combinations), type of meal (moderate or high fat), time frame between exercise and meal and target group may individually or in conjunction influence this effect. On the other hand, at least for aerobic exercise, training reduces pTAG concentrations transiently (~2 days); therefore, exercise sessions should be frequent enough to maintain this clinically significant improvement. For the healthy population, it seems that a subject's preference and ability determine which type of exercise to undertake to attenuate pTAG concentrations; an energy expenditure of ~30 kJ/kg of body mass (or ~2-2.5 MJ) not combined with a corresponding increase in energy intake is required; for resistance or intermittent exercise, for those following a moderate rather than a high-fat diet, and for those with obesity (expressed as kJ/kg of body mass), a smaller energy expenditure is probably sufficient. More studies are needed to investigate dose-response/plateau effects, as well as the threshold of energy expenditure in those with diabetes mellitus and other high-risk populations. Finally, investigation of the underlying mechanisms may be clinically helpful in individualizing the appropriate intervention.

Serum acylated ghrelin concentrations in response to short-term overfeeding in normal weight, overweight, and obese men

Background

Ghrelin, an orexigenic gut hormone secreted primarily from the stomach, is involved in energy homeostasis. However, little data is available regarding its response to energy surplus and the development of human obesity.

Objective

The present study investigated the response of circulating acylated ghrelin to a 7-day positive energy challenge.

Design

A total of 68 healthy young men were overfed 70% more calories than required, for 1-week. Subjects were classified based on percent body fat (measured by dual-energy X-ray absorptiometry) as normal weight, overweight, and obese. Serum acylated ghrelin concentration was measured before and after the positive energy challenge. Additionally, the relationship between acylated ghrelin and obesity-related phenotypes including weight, body mass index, percent body fat, cholesterol, HDL-c, LDL-c, glucose, insulin and homeostasis model assessment of insulin resistance and β-cell function at baseline and change due to overfeeding, were assessed.

Results

Contrary to our expectations, serum acylated ghrelin was significantly increased in response to overfeeding and the increase was independent of obesity status. There was no significant difference in fasting acylated ghrelin between normal weight, overweight, and obese men at baseline. Acylated ghrelin was negatively correlated with weight and BMI for normal weight and with BMI in overweight men. Also ghrelin was correlated with change in weight and BMI in overweight (negative relationship) and obese (positive relationship) groups.

Conclusion

Our results showed that circulating acylated ghrelin was increased after a 7-day positive energy challenge regardless of adiposity status. However, acylated ghrelin was correlated with change in weight and BMI in opposing directions, in overweight and obese subjects respectively, thus dependent on obesity status.

Appetite regulation in response to sitting and energy imbalance

The impact of sitting and energy imbalance on appetite and appetite-regulating hormones (acylated ghrelin and leptin) was assessed in response to 1 day of sitting, with and without changes in energy intake. Fourteen men and women completed each of three 24-h conditions: high energy expenditure (standing) with energy balance (STAND), low energy expenditure (sitting) with energy surplus (SIT), and sitting with energy balance (SIT-BAL). Ghrelin, leptin, and appetite were measured in the fasted state and following a standardized meal. In the fasted state, there were no differences among conditions. Following the meal, ghrelin was lower in SIT than in STAND, with no change in appetite. When intake was reduced (SIT-BAL), the decrease in ghrelin when sitting was attenuated, hunger increased, and fullness decreased. SIT led to lower ghrelin concentrations in the men, whereas in the women, leptin increased. SIT-BAL led to an increase in ghrelin in the men but attenuated the leptin response, reduced ghrelin, increased hunger, and decreased fullness in the women. Because a dramatic reduction in energy expenditure was not accompanied by reduced appetite, prolonged sitting may promote excess energy intake, leading to weight gain in both men and women.

Serum peptide YY in response to short-term overfeeding in young men

BACKGROUND

Peptide YY (PYY), a gut hormone that inhibits appetite, has been linked to the development of obesity.

OBJECTIVE

This study investigated the nutritional regulation of PYY after 7 d of overfeeding (70% above normal energy requirements) in normal-weight, overweight, and obese men.

DESIGN

Sixty-nine men (aged 19-29 y) participated in the study. We analyzed the relation between fasting serum PYY before and after a 7-d overfeeding challenge in normal-weight, overweight, and obese men. In addition, we analyzed PYY with obesity-related phenotypes including weight, percentage body fat (measured by dual-energy X-ray absorptiometry), body mass index (BMI), total cholesterol, HDL, LDL, glucose, insulin, insulin resistance, and β cell function evaluated by the homeostasis model assessment of insulin resistance (HOMA-IR) and β cell function (HOMA-β) at baseline and in response to the energy surplus.

RESULTS

Fasting serum PYY concentrations at baseline were not significantly different between the normal-weight, overweight, and obese subjects on the basis of dual-energy X-ray absorptiometry or BMI. Although the PYY concentration significantly increased due to overfeeding, no differences were observed between adiposity statuses. In addition, basal PYY was negatively correlated with the changes of total cholesterol, HDL, and LDL in normal weight. In addition, the increase in PYY after overfeeding was positively correlated with HDL cholesterol and glucose in normal-weight subjects.

CONCLUSIONS

Our findings suggest that fasting PYY concentrations are not associated with adiposity status. Moreover, the 7-d overfeeding challenge significantly increased fasting PYY, which is likely a protective response to the positive energy balance.

Ghrelin gene products and the regulation of food intake and gut motility

A breakthrough using "reverse pharmacology" identified and characterized acyl ghrelin from the stomach as the endogenous cognate ligand for the growth hormone (GH) secretagogue receptor (GHS-R) 1a. The unique post-translational modification of O-n-octanoylation at serine 3 is the first in peptide discovery history and is essential for GH-releasing ability. Des-acyl ghrelin, lacking O-n-octanoylation at serine 3, is also produced in the stomach and remains the major molecular form secreted into the circulation. The third ghrelin gene product, obestatin, a novel 23-amino acid peptide identified from rat stomach, was found by comparative genomic analysis. Three ghrelin gene products actively participate in modulating appetite, adipogenesis, gut motility, glucose metabolism, cell proliferation, immune, sleep, memory, anxiety, cognition, and stress. Knockdown or knockout of acyl ghrelin and/or GHS-R1a, and overexpression of des-acyl ghrelin show benefits in the therapy of obesity and metabolic syndrome. By contrast, agonism of acyl ghrelin and/or GHS-R1a could combat human anorexia-cachexia, including anorexia nervosa, chronic heart failure, chronic obstructive pulmonary disease, liver cirrhosis, chronic kidney disease, burn, and postsurgery recovery, as well as restore gut dysmotility, such as diabetic or neurogenic gastroparesis, and postoperative ileus. The ghrelin acyl-modifying enzyme, ghrelin O-Acyltransferase (GOAT), which attaches octanoate to serine-3 of ghrelin, has been identified and characterized also from the stomach. To date, ghrelin is the only protein to be octanylated, and inhibition of GOAT may have effects only on the stomach and is unlikely to affect the synthesis of other proteins. GOAT may provide a critical molecular target in developing novel therapeutics for obesity and type 2 diabetes.

Positive energy balance is associated with accelerated muscle atrophy and increased erythrocyte glutathione turnover during 5 wk of bed rest

BACKGROUND

Physical inactivity is often associated with positive energy balance and fat gain.

OBJECTIVE

We aimed to assess whether energy intake in excess of requirement activates systemic inflammation and antioxidant defenses and accelerates muscle atrophy induced by inactivity.

DESIGN

Nineteen healthy male volunteers were studied before and at the end of 5 wk of bed rest. Subjects were allowed to spontaneously adapt to decreased energy requirement (study A, n = 10) or were provided with an activity-matched diet (study B, n = 9). Groups with higher (HEB) or lower (LEB) energy balance were identified according to median values of inactivity-induced changes in fat mass (DeltaFM, assessed by bioelectrical impedance analysis).

RESULTS

In pooled subjects (n = 19; median DeltaFM: 1.4 kg), bed rest-mediated decreases in fat-free mass (bioelectrical impedance analysis) and vastus lateralis thickness (ultrasound imaging) were significantly greater (P < 0.03) in HEB(AB) (-3.8 +/- 0.4 kg and -0.32 +/- 0.04 cm, respectively) than in LEB(AB) (-2.3 +/- 0.5 kg and -0.09 +/- 0.04 cm, respectively) subjects. In study A (median DeltaFM: 1.8 kg), bed rest-mediated increases in plasma leptin, C-reactive protein, and myeloperoxidase were greater (P < 0.04) in HEB(A) than in LEB(A) subjects. Bed rest-mediated changes of glutathione synthesis rate in eythrocytes (l-[3,3-(2)H(2)]cysteine incorporation) were greater (P = 0.03) in HEB(A) (from 70 +/- 19 to 164 +/- 29%/d) than in LEB(A) (from 103 +/- 23 to 84 +/- 27%/d) subjects.

CONCLUSIONS

Positive energy balance during inactivity is associated with greater muscle atrophy and with activation of systemic inflammation and of antioxidant defenses. Optimizing caloric intake may be a useful strategy for mitigating muscle loss during period of chronic inactivity.

Characterization of ghrelin in pedigreed baboons: evidence for heritability and pleiotropy

BACKGROUND

Ghrelin is an orexigenic hormone that is produced primarily in the stomach, and stimulates food intake via its receptors situated in the hypothalamus.

OBJECTIVE

The purpose of this study was to characterize baboon ghrelin cDNA and investigate the genetic influence on the variation in plasma ghrelin levels in baboons.

METHODS AND PROCEDURES

The sample consisted of 376 baboons (263 females, 113 males) from a pedigreed colony at the Southwest Foundation for Biomedical Research, San Antonio, Texas. Ghrelin cDNA was cloned by reverse-transcription polymerase chain reaction (RT-PCR) and sequenced. Real-time RT-PCR was performed to quantify mRNA from the collected tissues. Genetic contribution to plasma ghrelin was estimated using a variance components method implemented in SOLAR.

RESULTS

The baboon coding region and predicted amino acid sequence for ghrelin showed 97 and 96% sequence identity with humans, respectively. Maximum expression of ghrelin mRNA was detected in hypothalamus and stomach. Mean +/- s.e. plasma levels of ghrelin were 3,406 +/- 99 pg/ml. A significant heritability was observed for plasma ghrelin (h(2)= 0.25, P < 0.001). A genome-wide scan revealed the evidence of suggestive linkage for a locus affecting plasma ghrelin on chromosome 9q22 (between markers D9S910 and D9S261, logarithm of the odds (LOD) score = 2.3). Significant genetic correlations (P < 0.001) among ghrelin, body weight, and leptin were observed.

DISCUSSION

These results indicate a significant genetic component in the variation of plasma ghrelin in baboons and reveal a high degree of similarity between baboon and human ghrelin with respect to its cDNA and its correlation with other obesity traits.

Effects of short-term exercise and energy surplus on hormones related to regulation of energy balance

Energy surplus raises circulating concentrations of leptin and insulin while lowering plasma ghrelin. Exercise has the opposite effects. The purpose of this study was to determine whether exercise counters the hormonal effects of energy surplus independent of changes in energy balance. To do that, we assessed plasma concentrations of leptin, insulin, and ghrelin at baseline, after overfeeding, and after overfeeding plus exercise. Baseline (B) leptin and insulin concentrations and ghrelin area under the curve were measured during an oral glucose challenge in 9 healthy, active subjects (6 male, 3 female) after 2 days in energy balance without exercise. Measurements were repeated after subjects were overfed by +3213 +/- 849 kJ/d for 3 more sedentary days (OF). In the third condition, the same net energy surplus (+3125 +/- 933 kJ/d) was generated for 24 hours by doubling the overfeeding (+6284 +/- 1669 kJ/d) and countering it with a bout of exercise (expenditure = 3063 +/- 803 kJ); and measurements were made the next day (OF + EX). Compared with B, leptin went up (5.8 +/- 8.2 to 7.6 +/- 10.6 ng/mL) after OF, but was not significantly higher after OF + EX (7.1 +/- 10.2 ng/mL). Compared with B, insulin was +36% and +43% higher after OF and OF + EX, respectively. In contrast, ghrelin area under the curve did not change after OF but was significantly lower (-14%) than B or OF after OF + EX (indicating greater suppression). These data suggest that the effect of short-term exercise on fasting leptin and insulin depends on energy balance but the ghrelin response may be partially mediated by effects of exercise independent of energy balance.

A high-fat diet raises fasting plasma CCK but does not affect upper gut motility, PYY, and ghrelin, or energy intake during CCK-8 infusion in lean men

There is evidence from studies in animals that the effects of both fat and CCK on gastrointestinal function and energy intake are attenuated by consumption of a high-fat diet. In humans, the effects of exogenous CCK-8 on antropyloroduodenal motility, plasma CCK, peptide YY (PYY), and ghrelin concentrations, appetite, and energy intake are attenuated by a high-fat diet. Ten healthy lean males consumed isocaloric diets (~15,400 kJ per day), containing either 44% (high-fat, HF) or 9% (low-fat, LF) fat, for 21 days in single-blind, randomized, cross-over fashion. Immediately following each diet (i.e., on day 22), subjects received a 45-min intravenous infusion of CCK-8 (2 ng.kg(-1).min(-1)), and effects on antropyloroduodenal motility, plasma CCK, PYY, ghrelin concentrations, hunger, and fullness were determined. Thirty minutes after commencement of the infusion, subjects were offered a buffet-style meal, from which energy intake (in kilojoules) was quantified. Body weight was unaffected by the diets. Fasting CCK (P < 0.05), but not PYY and ghrelin, concentrations were greater following the HF, compared with the LF, diet. Infusion of CCK-8 stimulated pyloric pressures (P < 0.01) and suppressed antral and duodenal pressures (P < 0.05), with no difference between the diets. Energy intake also did not differ between the diets. Short-term consumption of a HF diet increases fasting plasma CCK concentrations but does not affect upper gut motility, PYY and ghrelin, or energy intake during CCK-8 infusion, in a dose of 2 ng.kg(-1).min(-1), in healthy males.

Serum retinol-binding protein 4 concentrations in response to short-term overfeeding in normal-weight, overweight, and obese men

BACKGROUND

Retinol-binding protein 4 (RBP4) is a novel adipokine that induces insulin resistance in mice. Studies in humans have shown a correlation between serum RBP4 and insulin resistance in obese subjects and in subjects with type 2 diabetes. Few data are available regarding the nutritional regulation of RBP4.

OBJECTIVE

The study investigated the relation of RBP4 with phenotypes of glucose and lipid metabolism at baseline and in response to a 7-d overfeeding protocol in young men.

DESIGN

Sixty-five men participated in the study. Subjects were classified on the basis of body mass index (BMI; kg/m(2)) as normal-weight (</=24.9) or as overweight or obese (>/=25.0). Serum RBP4, interleukin-6, visfatin, glucose, insulin, total cholesterol, HDL cholesterol, and LDL cholesterol (calculated), and triacylglycerols were measured. Insulin resistance and beta cell function were assessed by using the homeostasis model. Percentage body fat was measured by using dual-energy X-ray absorptiometry.

RESULTS

No significant differences were found in serum RBP4 between the 2 groups at baseline. Likewise, no significant differences were observed in fasting serum RBP4 in response to overfeeding. Baseline RBP4 was negatively correlated with the change in insulin resistance in normal-weight subjects, independent of age and BMI. No significant correlation was found between serum RBP4 and visfatin, interleukin-6, or any other variables measured.

CONCLUSIONS

Short-term overfeeding did not induce significant changes in RBP4. Baseline RBP4 concentrations may predict insulin resistance when exposed to a positive energy challenge in normal-weight men.

Ghrelin enhances in vivo skeletal muscle but not liver AKT signaling in rats

OBJECTIVE

Ghrelin administration can induce fat weight gain and hyperglycemia (potentially through ghrelin-induced hepatic glucose production), but plasma ghrelin is positively associated with whole-body insulin sensitivity (mainly reflecting muscle insulin action) being increased in lean individuals or after diet-induced weight loss and reduced in obesity or after diet-induced weight gain. To investigate potential mechanisms, we measured in vivo effects of sustained ghrelin administration at a non-orexigenic dose on skeletal muscle and liver insulin signaling at the AKT level and adipokine expression changes.

RESEARCH METHODS AND PROCEDURES

Young-adult male rats received 4-day, twice daily subcutaneous ghrelin (200 mug/injection) or saline. We measured skeletal muscle (mixed, gastrocnemius; oxidative, soleus) and liver protein levels of activated [phosphorylated (P)] and total (T) AKT and glycogen synthase kinase (GSK; reflecting AKT-dependent GSK inactivation) and epididymal adipose tissue adipokine mRNA.

RESULTS

Ghrelin increased body weight (+1.4%) and blood glucose (both p < 0.05 vs. saline) but not food intake, plasma insulin, or free fatty acids. Ghrelin, however, enhanced P/T/AKT and P/T/GSK ratios and glucose transporter-4 mRNA in soleus (p < 0.05), but not in gastrocnemius, muscle. In contrast, ghrelin reduced hepatic P/T-AKT and P/T-GSK. No alterations occurred in adiponectin, leptin, or resistin transcripts or plasma adiponectin.

DISCUSSION

Despite moderate weight gain and in the absence of insulin-free fatty acid changes, sustained ghrelin administration enhanced oxidative muscle AKT activation. Reduced liver AKT signaling could potentially contribute to concomitant blood glucose increments. These findings support ghrelin as a novel tissue-specific modulator of lean tissue AKT signaling with insulin-sensitizing effects in skeletal muscle but not in liver in vivo.

Small-molecule ghrelin receptor antagonists improve glucose tolerance, suppress appetite, and promote weight loss

Ghrelin, through action on its receptor, GH secretagogue receptor type 1a (GHS-R1a), exerts a variety of metabolic functions including stimulation of appetite and weight gain and suppression of insulin secretion. In the present study, we examined the effects of novel small-molecule GHS-R1a antagonists on insulin secretion, glucose tolerance, and weight loss. Ghrelin dose-dependently suppressed insulin secretion from dispersed rat islets. This effect was fully blocked by a GHS-R1a antagonist. Consistent with this observation, a single oral dose of a GHS-R1a antagonist improved glucose homeostasis in an ip glucose tolerance test in rat. Improvement in glucose tolerance was attributed to increased insulin secretion. Daily oral administration of a GHS-R1a antagonist to diet-induced obese mice led to reduced food intake and weight loss (up to 15%) due to selective loss of fat mass. Pair-feeding experiments indicated that weight loss was largely a consequence of reduced food intake. The impact of a GHS-R1a antagonist on gastric emptying was also examined. Although the GHS-R1a antagonist modestly delayed gastric emptying at the highest dose tested (10 mg/kg), delayed gastric emptying does not appear to be a requirement for weight loss because lower doses produced weight loss without an effect on gastric emptying. Consistent with the hypothesis that ghrelin regulates feeding centrally, the anorexigenic effects of potent GHS-R1a antagonists in mice appeared to correspond with their brain exposure. These observations demonstrate that GHS-R1a antagonists have the potential to improve the diabetic condition by promoting glucose-dependent insulin secretion and promoting weight loss.

Modulation by high-fat diets of gastrointestinal function and hormones associated with the regulation of energy intake: implications for the pathophysiology of obesity

The presence of fat in the small intestine slows gastric emptying, stimulates the release of many gastrointestinal hormones, and suppresses appetite and energy intake as a result of the digestion of fats into free fatty acids; the effects of free fatty acids are, in turn, dependent on their chain length. Given these effects of fat, it is paradoxical that high dietary fat intakes have been linked to increased energy intake and body weight and are considered to play a significant role in the pathogenesis of obesity. However, increasing evidence indicates that a chronic increase in dietary fat is associated with an attenuation of the feedback signals arising from the small intestine induced by fat, with a consequent relative acceleration of gastric emptying, modulation of gastrointestinal hormone secretion, and attenuation of the suppression of energy intake. This review addresses the gastrointestinal factors involved in the regulation of appetite and energy intake, with a particular focus on 1) the gastrointestinal mechanisms triggered by small intestinal fat that modulate energy intake, 2) the potential role of a high dietary fat intake in the development of obesity, and 3) implications for the prevention and management of obesity.

Tryptophan enhances ghrelin expression and secretion associated with increased food intake and weight gain in weanling pigs

These studies were conducted to determine whether ghrelin, a 28-amino acid peptide produced mainly by the stomach, was involved in tryptophan-mediated appetite stimulation in swine. In experiment 1, 36 crossbred (Long WhitexLarge White) barrows were used in a 2x3 factorial design to determine the effects of food intake (ad libitum versus limit fed) and tryptophan level (0.12%, 0.19% and 0.26%) on growth performance as well as ghrelin expression, plasma insulin, ghrelin and leptin levels. Ad libitum fed pigs gained more weight, but had poorer feed conversion than limit fed pigs. Weight gain, food intake and feed conversion all improved with increased ingestion of dietary tryptophan. Ad libitum feeding increased plasma insulin. Plasma insulin was unaffected by the level of dietary tryptophan. However, plasma leptin was significantly lower in pigs fed 0.19% tryptophan compared to those fed 0.12% tryptophan. Plasma ghrelin levels and ghrelin mRNA level in gastric fundus and duodenun was significantly higher in pigs fed 0.19% and 0.26% tryptophan diet compared with pigs fed 0.12%. In the second experiment, 18 crossbred barrows were divided into three treatments involving oral infusion of saline, tryptophan (40mg/kg BW) or 5-hydroxytryptophan (40mg/kg BW). Plasma ghrelin levels at 20, 40 and 60min after infusion of tryptophan were higher than after saline and 5-hydroxytryptophan infusion, 5-hydroxytryptophan infusion induced lower food intake than saline infusion, and tryptophan infusion increased food intake 2, 8 and 24h after infusion. In conclusion, oral tryptophan ingestion increased ghrelin expression in gastric fundus and plasma ghrelin level.

Gonadectomy and high dietary fat but not high dietary carbohydrate induce gains in body weight and fat of domestic cats

A high concentration of dietary carbohydrate is suggested to increase the risk of obesity and diabetes mellitus in domestic cats. To evaluate this, food intake, body weight, fat mass and circulating adiposity-related factors were determined in twenty-four sexually mature (9-12 months) cats assigned to four six-cat dietary groups balanced for body weight and sex. The effect of dietary fat in exchange for carbohydrate at 9, 25, 44 and 64 % of metabolisable energy (ME) in a purified diet of constant protein:ME ratio was studied 13 weeks before and 17 weeks after gonadectomy (GX). Body weight did not significantly change among the cats before GX except for an increase of 17 (sem 5) % in cats given the highest-fat diet. Following GX, all groups gained body weight, and body fat mass was positively correlated (r 0.50; P < 0.04) with dietary fat percentage. Post-GX weight gains were much greater for females (+39 (sem 5) %) than males (+10 (sem 4) %). Plasma ghrelin concentration negatively correlated (P < 0.02) with dietary fat percentage and, before GX, was greater (P < 0.05) in females than males. Plasma insulin concentration increased with weight gain induced by high dietary fat. Plasma glucose, TAG and leptin concentrations were not affected by dietary fat percentage, GX or weight gain. These data provide evidence that in cats, high dietary fat, but not carbohydrate, induces weight gain and a congruent increase in insulin, while GX increases sensitivity to weight gain induced by dietary fat.

Twenty-four-hour ghrelin is elevated after calorie restriction and exercise training in non-obese women

OBJECTIVE

The purpose of this study was to determine whether chronic energy deficiency achieved with caloric restriction combined with exercise is associated with changes in the 24-hour profile of ghrelin in non-obese, pre-menopausal women.

RESEARCH METHODS AND PROCEDURES

Twelve non-obese (BMI = 18 to 25 kg/m(2)), non-exercising women (age, 18 to 24 years) were randomly assigned to a non-exercising control group or a diet and exercise group. The 3-month diet and exercise intervention yielded a daily energy deficit of -45.7 +/- 12.4%. Serial measurements were made of body composition, energy balance, and feelings of fullness. Repeated blood sampling over 24 hours to measure ghrelin occurred before and after the study.

RESULTS

Significant decreases in body weight, body fat, and feelings of fullness were observed in only the energy-deficit group (p < 0.05); significant changes in the following ghrelin features were found in only the deficit group (p < 0.05): elevations in baseline (+353 +/- 118 pg/mL), lunch peak (+370 +/- 102 pg/mL), dinner peak (+438 +/- 149 pg/mL), nocturnal rise (+269 +/- 77 pg/mL), and nocturnal peak (+510 +/- 143 pg/mL). In addition, we found a larger dinner decline (-197 +/- 52 pg/mL) and negative correlations between changes in the ghrelin dinner profile and changes in body weight (R = 0.784), 24-hour intake (R = 0.67), energy deficiency (R = 0.762), and feelings of fullness (R = 0.648; p < 0.05).

DISCUSSION

Changes in ghrelin concentrations across the day after weight loss are closely associated with other physiological adaptations to energy deficiency, further supporting the role of ghrelin as a countermeasure to restore energy balance.

Serum visfatin concentrations are positively correlated with serum triacylglycerols and down-regulated by overfeeding in healthy young men

BACKGROUND

Visfatin is an insulin-mimicking adipokine. Visfatin is elevated in obesity and type 2 diabetes. However, its role in glucose and lipid metabolism in healthy humans is unclear.

OBJECTIVE

The objective was to investigate the correlations of visfatin with phenotypes of glucose, lipids, and body composition and the responses of visfatin to short-term overfeeding in healthy young men.

DESIGN

Sixty-one healthy young men were recruited from the Newfoundland population. Serum visfatin, interleukin 6, glucose, insulin, total cholesterol, HDL cholesterol, LDL cholesterol, and triacylglycerol concentrations were measured with an autoanalyzer, and percentage body fat (%BF) and percentage trunk fat (%TF) were measured with dual-energy X-ray absorptiometry. Insulin resistance and beta cell function were assessed with the homeostasis model. All measurements were completed at baseline and after a 7-d overfeeding protocol exceeding the baseline requirement by 70%. Subjects were classified on the basis of %BF as lean (<21%), overweight (21-25.9%), or obese (>or=26%).

RESULTS

Multiple regression analysis showed that triacylglycerols correlated with fasting serum visfatin (P < 0.001). Moreover, serum visfatin decreased 19% overall-23% in lean, 9% in overweight, and 18% in obese subjects (P < 0.0001)-after the overfeeding protocol. None of the variables measured, including interleukin 6, were associated with the reduction in visfatin. In contrast with the findings in mice, visfatin concentrations before and after overfeeding did not correlate with glucose, insulin, insulin resistance, beta cell function, %BF, or %TF.

CONCLUSIONS

Visfatin is down-regulated by overfeeding. Under physiologic conditions, visfatin does not appear to control glucose metabolism but may play a regulatory role in lipid metabolism.

Overfeeding-induced weight gain suppresses plasma ghrelin levels in rats

The elevation of plasma ghrelin associated with weight loss has been taken as evidence of a role for ghrelin in the adaptive response to body weight change. However, there has been no clear experimental evidence that circulating ghrelin is suppressed by weight gain. We investigate this issue using a model of involuntary (intra-gastric gavage) overfeeding-induced obesity. Rats were first maintained at normal body weight with 4 daily tube-feedings of liquid diet (2.11 kcal/ml), each delivered at a volume of 9 ml. Gavage volume was then increased to 13 ml/feeding for 2 weeks, during which rats gained 25% of their initial body weight. Fasting plasma ghrelin levels and the response to 9- and 13-ml intra-gastric load sizes were measured during the weight-stable and overfed conditions. We found that: 1) weight gain decreased circulating ghrelin levels; 2) this response could not be attributed to additional food in the gastrointestinal tract; 3) the ghrelin response to nutrient loads was diminished in the obese vs normal-weight conditions. Having discounted diet composition and differences in gastric contents at the time of blood sampling, the decrease in ghrelin levels with overfeeding can be unambiguously attributed to physiological correlates of weight gain.

Metabolic effects of ghrelin and its potential implications in uremia

Ghrelin is a recently described hormone secreted by the stomach. Ghrelin administration in ad-libitum-fed rodents was shown to increase appetite as well as body weight and body fat content, showing metabolic effects of ghrelin in vivo and suggesting its involvement in the pathogenesis of obesity. However, plasma ghrelin concentration was shown to be inversely correlated with body weight and body fat in people and rodents. Increased plasma ghrelin concentration was also reported during diet-induced weight loss and in malnourished states. These findings suggest that circulating ghrelin is regulated by nutritional state and body fat with a feedback mechanism opposing changes in body composition, with a potential key adaptive role during calorie restriction. Plasma ghrelin concentration was shown to be increased in advanced renal failure and hemodialysis patients. The known metabolic effects of ghrelin and the potential implications of hyperghrelinemia in kidney disease will be discussed in this article.

Ghrelin and the short- and long-term regulation of appetite and body weight

Ghrelin, an acylated upper gastrointestinal peptide, is the only known orexigenic hormone. Considerable evidence implicates ghrelin in mealtime hunger and meal initiation. Circulating levels decrease with feeding and increase before meals, achieving concentrations sufficient to stimulate hunger and food intake. Preprandial ghrelin surges occur before every meal on various fixed feeding schedules and also among individuals initiating meals voluntarily without time- or food-related cues. Ghrelin injections stimulate food intake rapidly and transiently, primarily by increasing appetitive feeding behaviors and the number of meals. Preprandial ghrelin surges are probably triggered by sympathetic nervous output. Postprandial suppression is not mediated by nutrients in the stomach or duodenum, where most ghrelin is produced. Rather, it results from post-ingestive increases in lower intestinal osmolarity (information probably relayed to the foregut via enteric nervous signaling), as well as from insulin surges. Consequently, ingested lipids suppress ghrelin poorly compared with other macronutrients. Beyond a probable role in meal initiation, ghrelin also fulfills established criteria for an adiposity-related hormone involved in long-term body-weight regulation. Ghrelin levels circulate in relation to energy stores and manifest compensatory changes in response to body-weight alterations. Ghrelin crosses the blood-brain barrier and stimulates food intake by acting on several classical body-weight regulatory centers, including the hypothalamus, hindbrain, and mesolimbic reward system. Chronic ghrelin administration increases body weight via diverse, concerted actions on food intake, energy expenditure, and fuel utilization. Congenital ablation of the ghrelin or ghrelin-receptor gene causes resistance to diet-induced obesity, and pharmacologic ghrelin blockade reduces food intake and body weight. Ghrelin levels are high in Prader-Willi syndrome and low after gastric bypass surgery, possibly contributing to body-weight alterations in these settings. Extant evidence favors roles for ghrelin in both short-term meal initiation and long-term energy homeostasis, making it an attractive target for drugs to treat obesity and/or wasting disorders.

The physiology and potential clinical applications of ghrelin, a novel peptide hormone

Ghrelin, a peptide hormone originally identified as the endogenous ligand of the growth hormone secretagogue receptor, is secreted primarily from the stomach and secondarily from the small intestine and colon. Ghrelin may also be expressed in the pancreatic islets, hypothalamus, pituitary, and several tissues in the periphery. The growth hormone secretagogue receptor is widely expressed, suggesting diverse physiologic roles for ghrelin. A growing body of evidence suggests that, in addition to its predictable effect on growth hormone secretion, ghrelin has an important role in the short-term regulation of appetite and the long-term regulation of energy balance and glucose homeostasis. Recent studies have implicated ghrelin in the regulation of gastrointestinal, cardiovascular, and immune function and have suggested a role for ghrelin in bone physiology. The identification of obestatin, a novel peptide hormone derived from the same gene as ghrelin, has recently added further complexity to ghrelin physiology. Obestatin appears to have actions opposite of ghrelin on energy homeostasis and gastrointestinal function. Despite the rapid progress, many questions remain unanswered, including the regulation of ghrelin and obestatin secretion, the downstream pathways that mediate their effects, and their precise physiologic endocrine and paracrine roles. This review presents data on ghrelin structure, expression, and function, with emphasis placed on human studies, highlighting areas that require future investigation and providing speculation about potential clinical applications of ghrelin agonists or antagonists.

Regulation of Ghrelin in Physiologic and Pathophysiologic States

Ghrelin, a ligand for the growth hormone secretagogue receptor, is an orexigenic hormone produced in the gastrointestinal tract. In humans and other animals, circulating ghrelin levels fluctuate over the course of the day in relation to food intake. If circulating ghrelin plays a role in determining food intake from meal to meal, it will be important to understand the factors that regulate plasma ghrelin levels in relation to feeding. Circulating ghrelin levels also appear to reflect body weight changes over the longer term, raising the possibility that ghrelin functions as an adiposity signal. This review discusses some of the factors known to affect ghrelin levels, including nutrient stimulation of the gastrointestinal tract, diet composition, and weight loss. We also consider potential hormonal and neural mediators of the effects of nutrients and weight change on ghrelin levels.

Preprandial ghrelin is not affected by macronutrient intake, energy intake or energy expenditure

Background

Ghrelin, a peptide secreted by endocrine cells in the gastrointestinal tract, is a hormone purported to have a significant effect on food intake and energy balance in humans. The influence of factors related to energy balance on ghrelin, such as daily energy expenditure, energy intake, and macronutrient intake, have not been reported. Secondly, the effect of ghrelin on food intake has not been quantified under free-living conditions over a prolonged period of time. To investigate these effects, 12 men were provided with an ad libitum cafeteria-style diet for 16 weeks. The macronutrient composition of the diets were covertly modified with drinks containing 2.1 MJ of predominantly carbohydrate (Hi-CHO), protein (Hi-PRO), or fat (Hi-FAT). Total energy expenditure was measured for seven days on two separate occasions (doubly labeled water and physical activity logs).

Results

Preprandial ghrelin concentrations were not affected by macronutrient intake, energy expenditure or energy intake (all P > 0.05). In turn, daily energy intake was significantly influenced by energy expenditure, but not ghrelin.

Conclusion

Preprandial ghrelin does not appear to be influenced by macronutrient composition, energy intake, or energy expenditure. Similarly, ghrelin does not appear to affect acute or chronic energy intake under free-living conditions.