The effect of increased lipid intake on hormonal responses during aerobic exercise in endurance-trained men

Metabolic and ruck performance effects of a novel, light-weight, energy-dense ketogenic bar

NEW FINDINGS

What is the central question of the study? Can a novel, energy-dense and lightweight ketogenic bar (1000 kcal) consumed 3 h before exercise modulate steady-state incline rucksack march ('ruck') performance compared to isocaloric carbohydrate bars in recreationally active, college-aged men? What is the main finding and its importance? Acute ingestion of either nutritional bar sustained ∼1 h of exhaustive rucking with a 30% of body weight rucksack. This proof-of-concept study is the first to demonstrate that carbohydrate bars and lipid bars are equally feasible for preserving ruck performance. Novel ketogenic nutrition bars may have military-relevant applications to lessen carry load without compromising exercise capacity.

ABSTRACT

Rucksack marches ('rucks') are strenuous, military-relevant exercises that may benefit from pre-event fuelling. The purpose of this investigation was to explore whether acute ingestion of carbohydrate- or lipid-based nutritional bars before rucking can elicit unique advantages that augment exercise performance. Recreationally active and healthy males (n = 29) were randomized and counterbalanced to consume 1000 kcal derived from a novel, energy-dense (percentage energy from carbohydrate/fat/protein: 5/83/12) ketogenic bar (KB), or isocaloric high-carbohydrate bars (CB; 61/23/16) 3 h before a time-to-exhaustion (TTE) ruck. Conditions were separated by a 1-week washout. The rucksack weight was standardized to 30% of bodyweight. Steady-state treadmill pace was set at 3.2 km/h (0.89 m/s) and 14% grade. TTE was the primary outcome; respiratory exchange ratio (RER), capillary ketones (R-β-hydroxybutyrate), glucose and lactate, plus subjective thirst/hunger were the secondary outcomes. Mean TTE was similar between conditions (KB: 55 ± 25 vs. CB: 54 ± 22 min; P = 0.687). The RER and substrate oxidation rates revealed greater fat and carbohydrate oxidation after the KB and CB, respectively (all P < 0.0001). Capillary R-βHB increased modestly after the KB ingestion (P < 0.0001). Neither bar influenced glycaemia. Lactate increased during the ruck independent of the condition (P < 0.0001). Thirst/fullness perceptions changed independent of the nutritional bar consumed. A novel KB nutritional bar produced equivalent TTE ruck results to the isocaloric CBs. The KB's energy density relative to CB (6.6 vs. 3.8 kcal/g) may provide a lightweight (-42% weight), pre-event fuelling alternative that does not compromise ruck physical performance.

A Sports Nutrition Perspective on the Impacts of Hypoxic High-Intensity Interval Training (HIIT) on Appetite Regulatory Mechanisms: A Narrative Review of the Current Evidence

High-intensity interval training (HIIT) and low-oxygen exposure may inhibit the secretion of appetite-stimulating hormones, suppress appetite, and inhibit dietary intake. Physiological changes affecting appetite are frequent and include appetite hormone (ghrelin, leptin, PYY, and GLP-1) effects and the subjective loss of appetite, resulting in nutritional deficiencies. This paper is a narrative review of the literature to verify the HIIT effect on appetite regulation mechanisms and discusses the possible relationship between appetite effects and the need for high-intensity exercise training in a hypoxic environment. We searched MEDLINE/PubMed and the Web of Science databases, as well as English articles (gray literature by Google Scholar for English articles) through Google Scholar, and the searched studies primarily focused on the acute effects of exercise and hypoxic environmental factors on appetite, related hormones, and energy intake. In a general normoxic environment, regular exercise habits may have accustomed the athlete to intense training and, therefore, no changes occurred in their subjective appetite, but there is a significant effect on the appetite hormones. The higher the exercise intensity and the longer the duration, the more likely exercise is to cause exercise-induced appetite loss and changes in appetite hormones. It has not been clear whether performing HIIT in a hypoxic environment may interfere with the exerciser’s diet or the nutritional supplement intake as it suppresses appetite, which, in turn, affects and interferes with the recovery efficiency after exercise. Although appetite-regulatory hormones, the subjective appetite, and energy intake may be affected by exercise, such as hypoxia or hypoxic exercise, we believe that energy intake should be the main observable indicator in future studies on environmental and exercise interventions.

Ghrelin Response to Acute and Chronic Exercise: Insights and Implications from a Systematic Review of the Literature

BACKGROUND

Ghrelin is a peptide hormone predominantly produced by the stomach. It exerts a wide range of functions including stimulating growth hormone release and regulating appetite, food intake, and glucose and lipid metabolism. Since physical exercise affects all these aspects, a particular interest is accorded to the relationship between ghrelin and exercise. This systematic review aimed to summarize the current available data on the topic for a better understanding of the relationship.

METHODS

An extensive computerized search was performed in the PubMed and SPORTDiscus databases for retrieving relevant articles. The search contained the following keywords: ghrelin, appetite-related peptides, gastrointestinal peptides, gastrointestinal hormones, exercise, acute exercise, chronic exercise, training, and physical activity. Studies investigating the effects of acute/chronic exercise on circulating forms of ghrelin were included.

RESULTS

The initial search identified 840 articles. After screening, 80 articles were included. Despite a heterogeneity of studies and a variability of the findings, the review suggests that acute exercise suppresses acyl ghrelin production regardless of the participants and the exercise characteristics. Long- and very long-term exercise training programs mostly resulted in increased total and des-acyl ghrelin production. The increase is more noticeable in overweight/obese individuals, and is most likely due to weight loss resulting from the training program.

CONCLUSION

The review suggests that exercise may impact ghrelin production. While the precise mechanisms are unclear, the effects are likely due to blood flow redistribution and weight loss for acute and chronic exercise, respectively. These changes are expected to be metabolically beneficial. Further research is needed for a better understanding of the relationship between ghrelin and exercise.

Appetite and Energy Intake Regulation in Response to Acute Exercise

PURPOSE

This study aimed to determine if energy intake and appetite regulation differ in response to an acute bout of resistance exercise (REx) versus aerobic exercise (AEx).

METHODS

Physically inactive adults (n = 24, 35% ± 2% body fat, 50% female) completed three conditions: AEx (walking at 65%-70% heart rate max for 45 min), REx (1 set to failure of 12 exercises), and sedentary control (SED). Each condition was initiated in the postprandial state (35 min after breakfast). Appetite (visual analog scale for hunger, satiety, and prospective food consumption) and hormones (ghrelin, peptide YY (PYY), and glucagon-like peptide-1 (GLP-1)) were measured before and 30, 90, 120, 150, and 180 min after a standardized breakfast. Area under the curve was calculated using the trapezoid method. Ad libitum energy intake was evaluated at a lunch meal after the 180-min measurements.

RESULTS

No differences in ad libitum energy intake (REx, 991 ± 68; AEx, 937 ± 65; SED, 944 ± 76 kcal; P = 0.50) or appetite ratings (all, P > 0.05) were detected. The area under the curve for ghrelin, PYY, and GLP-1 were all lower after REx versus AEx (ghrelin: 130,737 ± 4928 for REx; 143,708 ± 7500 for AEx (P = 0.006); PYY: 20,540 ± 1177 for REx, 23,812 ± 1592 for AEx (P = 0.001); and GLP-1: 1314 ± 93 for REx, 1615 ± 110 for AEx (P = 0.013)). Neither exercise condition significantly differed from SED.

CONCLUSIONS

Acute REx lowers both orexigenic (ghrelin) and anorectic (PYY and GLP-1) gut peptides compared with acute AEx. Ad libitum energy intake did not increase compared with SED in either exercise condition, indicating both exercise modalities have appetite and energy intake suppressing effects. Future work is needed to determine if exercise of differing modalities influences chronic appetite regulation.

"A LEAP 2 conclusions? Targeting the ghrelin system to treat obesity and diabetes"

BACKGROUND

The hormone ghrelin stimulates food intake, promotes adiposity, increases body weight, and elevates blood glucose. Consequently, alterations in plasma ghrelin levels and the functioning of other components of the broader ghrelin system have been proposed as potential contributors to obesity and diabetes. Furthermore, targeting the ghrelin system has been proposed as a novel therapeutic strategy for obesity and diabetes.

SCOPE OF REVIEW

The current review focuses on the potential for targeting ghrelin and other proteins comprising the ghrelin system as a treatment for obesity and diabetes. The main components of the ghrelin system are introduced. Data supporting a role for the endogenous ghrelin system in the development of obesity and diabetes along with data that seemingly refute such a role are outlined. An argument for further research into the development of ghrelin system-targeted therapeutic agents is delineated. Also, an evidence-based discussion of potential factors and contexts that might influence the efficacy of this class of therapeutics is provided.

MAJOR CONCLUSIONS

It would not be a "leap to" conclusions to suggest that agents which target the ghrelin system - including those that lower acyl-ghrelin levels, raise LEAP2 levels, block GHSR activity, and/or raise desacyl-ghrelin signaling - could represent efficacious novel treatments for obesity and diabetes.

Ghrelin mediates exercise endurance and the feeding response post-exercise

Objective

Exercise training has several well-established health benefits, including many related to body weight, appetite control, and blood glucose homeostasis. However, the molecular mechanisms and, in particular, the hormonal systems that mediate and integrate these beneficial effects are poorly understood. In the current study, we aimed to investigate the role of the hormone ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR; ghrelin receptor), in mediating the effects of exercise on food intake and blood glucose following exercise as well as in regulating exercise endurance capacity.

Methods

We used two mouse models of treadmill running to characterize the changes in plasma ghrelin with exercise. We also assessed the role of the ghrelin system to influence food intake and blood glucose after exercise, exercise endurance, and parameters potentially linked to responses to exercise. Mice lacking GHSRs (GHSR-null mice) and wild-type littermates were studied.

Results

An acute bout of exercise transiently elevated plasma acyl-ghrelin. Without the action of this increased ghrelin on GHSRs (as in GHSR-null mice), high intensity interval exercise markedly reduced food intake compared to control mice. The effect of exercise to acutely raise blood glucose remained unmodified in GHSR-null mice. Exercise-induced increases in plasma ghrelin positively correlated with endurance capacity, and time to exhaustion was reduced in GHSR-null mice as compared to wild-type littermates. In an effort to mechanistically explain their reduced exercise endurance, exercised GHSR-null mice exhibited an abrogated sympathoadrenal response, lower overall insulin-like growth factor-1 levels, and altered glycogen utilization.

Conclusions

Exercise transiently increases plasma ghrelin. GHSR-null mice exhibit decreased food intake following high intensity interval exercise and decreased endurance when submitted to an exercise endurance protocol. These data suggest that an intact ghrelin system limits the capacity of exercise to restrict food intake following exercise, although it enhances exercise endurance.

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High intensity exercise transiently increases plasma ghrelin.

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Without ghrelin action on its receptors (growth hormone secretagogue receptors), exercise markedly reduces food intake.

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An intact ghrelin system enhances exercise endurance.

A 3-day high-fat/low-carbohydrate diet does not alter exercise-induced growth hormone response in healthy males

OBJECTIVE

The purpose of the present study was to examine the effects of 3 days isoenergetic high-fat/low-carbohydrate diet (HF-LC) relative to low-fat/high-carbohydrate diet (LF-HC) on the exercise-induced growth hormone (GH) response in healthy male subjects.

DESIGN

Ten healthy young males participated in this study. Each subject consumed the HF-LC (18±1% protein, 61±2% fat, 21±1% carbohydrate, 2720 kcal per day) for 3 consecutive days after consuming the LF-HC (18±1% protein, 20±1% fat, 62±1% carbohydrate, 2755 kcal per day) for 3 consecutive days. After each dietary intervention period, the hormonal and metabolic responses to an acute exercise (30 min of continuous pedaling at 60% of V˙O2max) were compared. The intramyocellular lipid (IMCL) contents in the vastus lateralis, soleus, and tibialis anterior were evaluated by proton magnetic resonance spectroscopy.

RESULTS

Serum GH concentrations increased significantly during the exercise after both the HF-LC and LF-HC periods (P<0.05). However, the exercise-induced GH response was not significantly different between the two periods. Fat utilization and lipolytic responses during the exercise were enhanced significantly after the HF-LC period compared with the LF-HC period. IMCL content did not differ significantly in any portion of muscle after the dietary interventions.

CONCLUSIONS

We could not show that short-term HF-LC consumption changed significantly exercise-induced GH response or IMCL content in healthy young males.

Effects of resistance exercise training on acyl-ghrelin and obestatin levels in hemodialysis patients

BACKGROUND

Patients undergoing hemodialysis (HD) present altered levels of appetite hormones such as acyl-ghrelin (orexigenic) and obestatin (anorexigenic), which may contribute to anorexia. Physical exercise may affect these hormones and improve appetite in these patients.

OBJECTIVES

The objective of this study is to evaluate the effects of a resistance exercise program in appetite hormones, body composition, and nutritional status in HD patients.

DESIGN

Intervention study with the control group.

SUBJECTS

Fifty-two patients on regular HD program were enrolled into two groups: 37 patients performed exercises (56.7% male, 45 ± 12.8 years, 57 (9-192) months on HD) and 15 patients comprised the control group (66.7% men, 50 ± 10.6 years, 57 (11-153) months on HD).

MEASUREMENTS

Exercise program (performed with elastic bands and ankle cuffs in both lower limbs) was supervised three times a week during 6 months (72 sessions). Patients had their blood drawn in a regular HD day after overnight fasting, before and after 6 months of exercise program. Obestatin, acyl-ghrelin, routine biochemical parameters, quality of life, and anthropometric data were collected and analyzed before and after 6 months.

RESULTS

After 6 months of exercise, obestatin levels reduced [from 3.0 ng/mL (2.3-3.4) to 1.9 ng/mL (0.6-3.4)] and acyl-ghrelin levels increased [from 21.5 pg/mL (1.3-77.7) to 37.2 pg/mL (16.7-94.1)] and the control group presented no significant differences in both plasma levels of hormones. Body composition and physical functional assessed by SF-36 and albumin levels (3.7 ± 0.3 to 3.9 ± 0.2, p < 0.05) improved after exercises.

CONCLUSION

Six months of resistance exercises contributed to changes in plasma appetite hormones, body composition, and nutritional status in hemodialysis patients.

Peak oxygen uptake test in the assessment of growth hormone deficiency

This study aimed at evaluating a peak oxygen uptake test as a simple diagnostic tool to assess growth-hormone deficiency (GHD) in adults. Based on the findings of multiple growth hormone (GH) samplings after the exercise, a single GH sample taken 15 min postexercise revealed high accuracy in the diagnosis of GHD in the present study. A standardized peak oxygen uptake test may, therefore, provide an accurate alternative to more invasive tests of GHD.

Acute aerobic exercise differentially alters acylated ghrelin and perceived fullness in normal-weight and obese individuals

Adiposity alters acylated ghrelin concentrations, but it is unknown whether adiposity alters the effect of exercise and feeding on acylated ghrelin responses. Therefore, the purpose of this study was to determine whether adiposity [normal-weight (NW) vs. obese (Ob)] influences the effect of exercise and feeding on acylated ghrelin, hunger, and fullness. Fourteen NW and 14 Ob individuals completed two trials in a randomized counterbalanced fashion, including a prior exercise trial (EX) and a no exercise trial (NoEX). During the EX trial, the participants performed 1 h of treadmill walking (55–60% peak O2 uptake) during the evening, 12 h before a 4-h standardized mixed meal test. Frequent blood samples were taken and analyzed for acylated ghrelin, and a visual analog scale was used to assess perceived hunger and fullness. In NW individuals, EX, compared with NoEX, reduced fasting acylated ghrelin concentrations by 18% ( P = 0.03), and, in response to feeding, the change in acylated ghrelin ( P = 0.02) was attenuated by 39%, but perceived hunger and fullness were unaltered. In Ob individuals, despite no changes in fasting or postprandial acylated ghrelin concentrations with EX, postprandial fullness was attenuated by 46% compared with NoEX ( P = 0.05). In summary, exercise performed the night before a meal suppresses acylated ghrelin concentrations in NW individuals without altering perceived hunger or fullness. In Ob individuals, despite no changes in acylated ghrelin concentrations, EX reduced the fullness response to the test meal. Acylated ghrelin and perceived fullness responses are differently altered by acute aerobic exercise in NW and Ob individuals.

Exercise and ghrelin. A narrative overview of research

Since its discovery in 1999, ghrelin has been implicated in a multiplicity of physiological activities. Most notably, ghrelin has an important influence on energy metabolism and after the identification of its potent appetite stimulating effects ghrelin has been termed the 'hunger hormone'. Exercise is a stimulus which has a significant impact on energy homeostasis and consequently a substantial body of research has investigated the interaction between exercise and ghrelin. This narrative review provides an overview of research relating to the acute and chronic effects of exercise on circulating ghrelin (acylated, unacylated and total). To enhance study comparability, the scope of this review is limited to research undertaken in adult humans and consequently studies involving children and animals are not discussed. Although there is significant ambiguity within much of the early research, our review suggests that acute exercise transiently interferes with the production of acylated ghrelin. Furthermore, the consensus of evidence indicates that exercise training does not influence circulating ghrelin independent of weight loss. Additional research is needed to verify and extend the available literature, particularly by uncovering the mechanisms governing acute exercise-related changes and characterising responses in other populations such as females, older adults, and the obese.

The influence of vigorous running and cycling exercise on hunger perceptions and plasma acylated ghrelin concentrations in lean young men

Vigorous running suppresses plasma acylated ghrelin concentrations but the limited literature on cycling suggests that acylated ghrelin is unchanged, perhaps because body mass is supported during cycling. It is important from a research and applied perspective to determine whether acylated ghrelin and hunger responses are exercise-mode specific. This study sought to examine this. Eleven recreationally active males fasted overnight and completed three 4-h trials: control, running, and cycling, in a random order. Participants rested throughout the control trial and ran or cycled at 70% of mode-specific maximal oxygen uptake for the first hour during exercise trials, resting thereafter. Hunger was measured every 0.5 h using visual analogue scales. Eight venous blood samples were collected to determine acylated ghrelin concentrations and a standardised meal was consumed at 3 h. Compared with the control trial, acylated ghrelin concentrations were suppressed to a similar extent at 0.5 and 1 h during the running (p < 0.005) and cycling (p < 0.001) trials. Area under the curve values for ghrelin concentration over time were lower during exercise trials versus control (Control: 606 ± 379; Running: 455 ± 356; Cycling: 448 ± 315 pg·mL(-1)·4 h(-1); mean ± SD, p < 0.05). Hunger values did not differ significantly between trials but an interaction effect (p < 0.05) indicated a tendency for hunger to be suppressed during exercise. Thus, at similar relative exercise intensities, plasma acylated ghrelin concentrations are suppressed to a similar extent during running and cycling.

Effects of resistance exercise and obesity level on ghrelin and cortisol in men

Resistance exercise (RE) is increasingly recommended by health organizations as a weight management tool. The purpose of this study was to examine the effects of an acute high-volume, whole-body RE protocol on the glucoregulatory and ghrelin response in sedentary obese and lean men. Five World Health Organization (WHO) class 1 obese (body mass index [BMI], 30.00-34.99) (age, 21.6 ± 2.5 years; height, 176.3 ± 3.7 cm; body mass, 97.8 ± 8.58 kg; body fat, 34.7% ± 2.95%), 5 WHO 2 (BMI, 35-39.99)/WHO 3 (BMI, ≥40) obese (age, 20.0 ± 1.4 years; height, 177.7 ± 5.15 cm; body mass, 120.8 ± 10.49 kg; body fat, 40.5% ± 5.82 %), and 9 lean men (age, 20.1 ± 2.1 years; height, 177.8 ± 8.7 cm; body mass, 71.7 ± 5.8 kg; body fat, 14.7% ± 3.54 %) completed an acute RE testing protocol (6 exercises, 3 sets of 10 repetitions at 85%-95% 10-repetition maximum with 120- and 90-second rest periods); and blood samples were collected pre-, mid-, and immediately postexercise and during recovery (+50, +70, and +110). Resistance exercise produced differences over time in cortisol, insulin, and glucose. Group differences were observed for ghrelin, with the WHO class 2/3 group having significantly greater ghrelin levels than the lean group (d = 0.28, P = .009) and the WHO class 1 group (d = 0.39, P = .002). Higher ghrelin was significantly associated with lower cortisol only in obese individuals. In addition, higher growth hormone was associated with lower ghrelin in lean individuals. Results suggest that glucoregulatory homeostasis is altered with increasing levels of obesity and that these alterations may mediate the response of cortisol and ghrelin in response to RE.

Influence of running and walking on hormonal regulators of appetite in women

Nine female runners and ten walkers completed a 60 min moderate-intensity (70% VO(2)max) run or walk, or 60 min rest in counterbalanced order. Plasma concentrations of the orexogenic peptide ghrelin, anorexogenic peptides peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and appetite ratings were measured at 30 min interval for 120 min, followed by a free-choice meal. Both orexogenic and anorexogenic peptides were elevated after running, but no changes were observed after walking. Relative energy intake (adjusted for cost of exercise/rest) was negative in the meal following running (-194 ± 206 kcal) versus walking (41 ± 196 kcal) (P = 0.015), although both were suppressed (P < 0.05) compared to rest (299 ± 308 and 284 ± 121 kcal, resp.). The average rate of change in PYY and GLP-1 over time predicted appetite in runners, but only the change in GLP-1 predicted hunger (P = 0.05) in walkers. Results provide evidence that exercise-induced alterations in appetite are likely driven by complex changes in appetite-regulating hormones rather than change in a single gut peptide.

Exercise-induced GH secretion in the assessment of GH deficiency in adult individuals

OBJECTIVE

The role of exercise testing in the assessment of GH deficiency (GHD) in adult patients is currently unclear. This study aimed at evaluating the diagnostic value of exercise-induced GH levels in the detection of severe GHD in adult patients.

METHODS

Fourteen patients confirmed to have severe GHD according to current guidelines and 20 healthy control individuals (CI) exercised for 120  min at 50-60% of their individual VO2(max). GH was measured before and every 30  min throughout exercise. The diagnostic value of predicting GHD was assessed by performing receiver operating characteristics (ROC) analysis for each time point of GH assessment. To optimise comparability within the study population a sub-analysis with ten individuals specifically matched for gender, age, body mass index and waist was performed.

RESULTS

Exercise-induced GH secretion was significantly lower in patients with GHD than in CI (P<0.001). Area under the ROC curve (AUC(ROC)) was 0.954±0.033, 0.993±0.009, 0.989±0.012 and 0.992±0.009 for the overall population and 0.870±0.086, 0.980±0.024, 0.970±0.034 and 0.978±0.027 for the matched individuals at 30, 60, 90 and 120  min of exercise respectively. At 60  min of exercise a cut off GH value of 2.4  ng/ml translates into a sensitivity of 100% and a specificity of 95 and 90% in the diagnosis of GHD for the overall population and matched individuals respectively.

CONCLUSION

GH assessment during a standardised aerobic exercise of moderate intensity is a reliable test with high diagnostic accuracy in predicting severe GHD in adult individuals. Based on the current findings exercise duration of 60  min appears to be sufficient for diagnostic purposes.

A review of weight control strategies and their effects on the regulation of hormonal balance

The estimated prevalence of obesity in the USA is 72.5 million adults with costs attributed to obesity more than 147 billion dollars per year. Though caloric restriction has been used extensively in weight control studies, short-term success has been difficult to achieve, with long-term success of weight control being even more elusive. Therefore, novel approaches are needed to control the rates of obesity that are occurring globally. The purpose of this paper is to provide a synopsis of how exercise, sleep, psychological stress, and meal frequency and composition affect levels of ghrelin, cortisol, insulin GLP-1, and leptin and weight control. We will provide information regarding how hormones respond to various lifestyle factors which may affect appetite control, hunger, satiety, and weight control.

Peripheral signals of energy homeostasis as possible markers of training stress in athletes: a review

The importance of physical exercise in regulating energy balance and ultimately body mass is widely recognized. There have been several investigative efforts in describing the regulation of the energy homeostasis. Important in this regulatory system is the existence of several peripheral signals that communicate the status of body energy stores to the hypothalamus including leptin, adiponectin, ghrelin, interleukin-6, interleukin-1β, and tumor necrosis factor-α--different cytokines and other peptides that affect energy homeostasis. In certain circumstances, all these peripheral signals may be used to reveal the condition of the athlete as the result of several months of prolonged exercise training. These hormone and cytokine concentrations characterize a physical stress condition in which different hormone and cytokine responses are apparently linked to changes in physical performance. The possibility to use these peripheral signals as markers of training stress (and possible overreaching/overtraining) in elite athletes should be considered. These measured hormone and cytokine levels could also be used to characterize the physical stress of single exercise session, as the hormone and cytokine response to exercise may actually be a response to the concurrent energy deficit. In summary, different peripheral signals of energy homeostasis may be sensitive to changes in specific training stress and may be useful for predicting the onset of possible overreaching/overtraining in athletes.

Significant lowering of plasma ghrelin but not des-acyl ghrelin in response to acute exercise in men

Ghrelin, an acylated peptide produced predominantly in the stomach, stimulates feeding and growth hormone (GH) secretion via interaction with the GH secretagogue receptor. Ghrelin molecules are present in two major endogenous forms, an acylated form (ghrelin) and a des-acylated form (des-acyl ghrelin). Recent studies indicated that aerobic exercise did not change plasma total ghrelin levels, however, dynamics of circulating ghrelin and des-acyl ghrelin during aerobic exercise remains unclear. The purpose of this study is to examine the effects of moderate intensity exercise on plasma ghrelin and des-acyl ghrelin concentrations, and to investigate the relationship between ghrelin molecules and other hormonal and metabolic parameters during exercise. Nine healthy males (25.2 ± 0.5 years) exercised for 60 min at 50% of their maximal oxygen consumptions. We measured the plasma concentrations of ghrelin, des-acyl ghrelin, GH, norepinephrine (NE), epinephrine (E), dopamine (DA), insulin, and glucose. Plasma ghrelin level significantly decreased during exercise, whereas plasma des-acyl ghrelin and total ghrelin levels did not change. Plasma NE, E, DA and GH levels were significantly increased during exercise. Plasma insulin level significantly decreased during exercise, and plasma glucose levels remained steady during exercise. NE, E, DA, and GH were correlated negatively with plasma ghrelin levels. These findings suggest that acute moderate exercise may suppress ghrelin release from the stomach, decrease ghrelin O-acyltransferase activity, and/or activate ghrelin utilization in peripheral tissues and that exercise-induced ghrelin suppression may be mediated by activated adrenergic system.

Influence of brisk walking on appetite, energy intake, and plasma acylated ghrelin

PURPOSE

This study examined the effect of an acute bout of brisk walking on appetite, energy intake, and the appetite-stimulating hormone-acylated ghrelin.

METHODS

Fourteen healthy young males (age 21.9 +/- 0.5 yr, body mass index 23.4 +/- 0.6 kg x m(-2), (.)VO2max 55.9 +/- 1.8 mL x kg(-1) x min(-1); mean +/- SEM) completed two 8-h trials (brisk walking and control) in a randomized counterbalanced fashion. The brisk walking trial commenced with 60 min of subjectively paced brisk walking on a level-motorized treadmill after which participants rested for 7 h. Participants rested for the duration of the control trial. Ad libitum buffet meals were offered twice during main trials (1.5-2 and 5-5.5 h). Appetite (hunger, fullness, satisfaction, and prospective food consumption) was assessed at 30-min intervals throughout. Levels of acylated ghrelin, glucose, insulin, and triacylglycerol were determined from plasma.

RESULTS

Sixty minutes of brisk walking (7.0 +/- 0.1 km x h(-1) yielded a net (exercise minus resting) energy expenditure of 2008 +/- 134 kJ, yet it did not significantly influence appetite, energy/macronutrient intake, or the plasma concentration of acylated ghrelin either during or after exercise(P > 0.05). Participants did not compensate for energy expended during walking, therefore a deficit in energy was induced (1836 kJ, 439 kcal) relative to control.

CONCLUSIONS

This study demonstrates that, despite inducing a moderate energy deficit, an acute bout of subjectively paced brisk walking does not elicit compensatory responses in acylated ghrelin, appetite, or energy intake. This finding lends support for a role of brisk walking in weight management.

Influence of resistance and aerobic exercise on hunger, circulating levels of acylated ghrelin, and peptide YY in healthy males

Resistance (muscle strengthening) exercise is a key component of exercise recommendations for weight control, yet very little is known about the effects of resistance exercise on appetite. We investigated the effects of resistance and aerobic exercise on hunger and circulating levels of the gut hormones acylated ghrelin and peptide YY (PYY). Eleven healthy male students: age 21.1 +/- 0.3 yr, body mass index 23.1 +/- 0.4 kg/m(2), maximum oxygen uptake 62.1 +/- 1.8 ml.kg(-1).min(-1) (means +/- SE) undertook three, 8-h trials, 1) resistance exercise: a 90-min free weight lifting session followed by a 6.5-h rest period, 2) aerobic exercise: a 60-min run followed by a 7-h rest period, 3) control: an 8-h rest, in a randomized crossover design. Meals were provided 2 and 5 h into each trial. Hunger ratings and plasma concentrations of acylated ghrelin and PYY were measured throughout. Two-way ANOVA revealed significant (P < 0.05) interaction effects for hunger, acylated ghrelin, and PYY, indicating suppressed hunger and acylated ghrelin during aerobic and resistance exercise and increased PYY during aerobic exercise. A significant trial effect was observed for PYY, indicating higher concentrations on the aerobic exercise trial than the other trials (8 h area under the curve: control 1,411 +/- 110, resistance 1,381 +/- 97, aerobic 1,750 +/- 170 pg/ml 8 h). These findings suggest ghrelin and PYY may regulate appetite during and after exercise, but further research is required to establish whether exercise-induced changes in ghrelin and PYY influence subsequent food intake.

Increases in ghrelin and decreases in leptin without altering adiponectin during extreme weight loss in male competitive bodybuilders

The aim of this study was to investigate responses of ghrelin, leptin, and adiponectin to a weight reduction period of 10 weeks in male subjects with high lean body mass and low body fat values. Fourteen male bodybuilders (7 competitors: 28.3 +/- 10.3 years, 175.3 +/- 5.4 cm, 82.2 +/- 9.3 kg; 7 controls: 22.4 +/- 3.0 years, 182.4 +/- 6.9 cm, 85.3 +/- 10.5 kg) participated in this study. The subjects were tested 3 times: 11 weeks (TEST1), 5 weeks (TEST2), and 3 days (TEST3) before the national championships. Testing procedure included dual-energy x-ray absorptiometry scan; calculation of daily energy intake and expenditure; and venous blood sampling for fasting ghrelin, leptin, and adiponectin. In the competitors' group, a significant (P < .05) 4.1-kg loss of body fat was observed that resulted in 6.5% +/- 1.5% of the body fat at the end of the study. Ghrelin increased significantly by 20.4% by TEST2. By TEST3, ghrelin was further increased by 6% (P > .05). The pattern of leptin was opposite, with a significant 27.7% decrease at TEST2 and no further decrease at TEST3 (P > .05). No significant change was observed in adiponectin concentration during the study. In the control group, no significant changes in biochemical parameters were observed. In conclusion, ghrelin concentration significantly increases, but is suppressed in conditions of limited energy availability that is accompanied by significant body mass loss in male subjects with initial low body fat values.

Exercise-induced suppression of acylated ghrelin in humans

Ghrelin is an orexigenic hormone secreted from endocrine cells in the stomach and other tissues. Acylation of ghrelin is essential for appetite regulation. Vigorous exercise induces appetite suppression, but this does not appear to be related to suppressed concentrations of total ghrelin. This study examined the effect of exercise and feeding on plasma acylated ghrelin and appetite. Nine male subjects aged 19-25 yr participated in two, 9-h trials (exercise and control) in a random crossover design. Trials began at 0800 in the morning after an overnight fast. In the exercise trial, subjects ran for 60 min at 72% of maximum oxygen uptake between 0800 and 0900. After this, they rested for 8 h and consumed a test meal at 1100. In the control trial, subjects rested for 9 h and consumed a test meal at 1100. Area under the curve values for plasma acylated ghrelin concentration (assessed from venous blood samples) were lower over the first 3 h and the full 9 h of the exercise trial compared with the control trial: 317+/-135 vs. 510+/-186 pg.ml(-1).3 h and 917+/-342 vs. 1,401+/-521 pg.ml(-1).9 h (means+/-SE) respectively (P<0.05). Area under the curve values for hunger (assessed using a visual scale) were lower over the first 3 h of the exercise trial compared with the control trial (P=0.013). These findings demonstrate that plasma acylated ghrelin concentration and hunger are suppressed during running.

Regulation of appetite in lean and obese adolescents after exercise: role of acylated and desacyl ghrelin

CONTEXT

Increased physical activity is an integral part of weight loss programs in adolescents. We hypothesized that exercise could affect appetite-regulating hormones and the subjective desire to eat, which could partly explain the poor success rate of the existing interventions.

OBJECTIVE

The objective of this study was to investigate prospectively the effects of exercise on acylated ghrelin (AG) and desacyl ghrelin (DG) concentrations and on appetite.

SETTING

The setting for this study was a tertiary care center.

PARTICIPANTS

Normal-weight [NW; body mass index (mean +/- se), 20.7 +/- 0.5 kg/m2] and overweight (OW; body mass index, 32.4 +/- 1.7) male adolescents (n = 17/group, age 15.3 +/- 0.2 yr) were studied.

INTERVENTION

Those studied participated in 5 consecutive days of aerobic exercise (1 h/d).

MAIN OUTCOME

Changes in AG and DG concentrations and in appetite during a test meal were studied.

RESULTS

Exercise did not significantly affect insulin sensitivity or body weight. Fasting total (AG and DG) ghrelin concentrations were lower in OW (600 +/- 33 pg/ml) compared with NW (764 +/- 33 pg/ml, P < 0.05) boys and were not affected by exercise. In contrast, there was a differential effect of exercise on both AG and DG (P <or= 0.019). AG significantly increased after exercise, and this increase was greater in NW compared with OW adolescents (P < 0.05). Higher AG concentrations were correlated with an increase in markers of appetite (P < 0.05).

CONCLUSION

Exercise differentially affects AG and DG in NW and OW male adolescents. Our data suggest that total ghrelin does not adequately reflect AG and DG concentrations and that the influence of exercise-induced hormonal changes should be considered to ensure success in weight management.

Plasma ghrelin responses to acute sculling exercises in elite male rowers

The regulatory effect of ghrelin on growth hormone (GH) is limited in describing ghrelin response to acute submaximal exercise intensities in elite athletes. We investigated the effects of a single sculling exercise performed above and below the individual anaerobic threshold (IAT) on total ghrelin concentration in highly trained male rowers. Nine elite male rowers (20.1 +/- 3.7 years; 190.0 +/- 5.2 cm; 89.6 +/- 4.6 kg; %body fat: 9.9 +/- 2.5%) volunteered for this study. Single scull rowing was performed below and above IAT using a mean of 5 bpm above and below the heart rate of the IAT during graded exercise test. Ghrelin, leptin, GH, insulin, and glucose were measured before, immediately after, and after 30 min of recovery. Plasma ghrelin concentration did not increase significantly in either exercise but was approaching significance after 30 min of recovery (P = 0.051) when the constant load sculling was performed at the intensity above the IAT. There were no changes in plasma leptin levels. GH increased significantly immediately after exercise and remained elevated during the 30 min of recovery in both exercise conditions, while insulin decreased significantly immediately after exercise and remained significantly lower after the 30 min of recovery in both exercise intensities. Baseline ghrelin was not correlated with the body composition, physical performance, or blood biochemical data. There was no significant relationship between plasma ghrelin and other blood variables immediately after the 30 min of recovery in both exercise tests and changes in ghrelin were not related to blood biochemical variables after the exercise tests. The acute constant load sculling exercise above or below IAT that increased GH concentrations did not significantly increase the circulating plasma ghrelin levels.

Intramyocellular lipid stores increase markedly in athletes after 1.5 days lipid supplementation and are utilized during exercise in proportion to their content

Intramyocellular lipids (IMCL) and muscle glycogen provide local energy during exercise (EX). The objective of this study was to clarify the role of high versus low IMCL levels at equal initial muscle glycogen on fuel selection during EX. After 3 h of depleting exercise, 11 endurance-trained males consumed in a crossover design a high-carbohydrate (7 g kg(-1) day(-1)) low-fat (0.5 g kg(-1) day(-1)) diet (HC) for 2.5 days or the same diet with 3 g kg(-1) day(-1) more fat provided during the last 1.5 days of diet (four meals; HCF). Respiratory exchange, thigh muscle substrate breakdown by magnetic resonance spectroscopy, and plasma FFA oxidation ([1-(13)C]palmitate) were measured during EX (3 h, 50% W (max)). Pre-EX IMCL concentrations were 55% higher after HCF. IMCL utilization during EX in HCF was threefold greater compared with HC (P < 0.001) and was correlated with aerobic power and highly correlated (P < 0.001) with initial content. Glycogen values and decrements during EX were similar. Whole-body fat oxidation (Fat(ox)) was similar overall and plasma FFA oxidation smaller (P < 0.05) during the first EX hour after HCF. Myocellular fuels contributed 8% more to whole-body energy demands after HCF (P < 0.05) due to IMCL breakdown (27% Fat(ox)). After EX, when both IMCL and glycogen concentrations were again similar across trials, a simulated 20-km time-trial showed no difference in performance between diets. In conclusion, IMCL concentrations can be increased during a glycogen loading diet by consuming additional fat for the last 1.5 days. During subsequent exercise, IMCL decrease in proportion to their initial content, partly in exchange for peripheral fatty acids.