Effect of moderate-intensity exercise session on preprandial and postprandial responses of circulating ghrelin and appetite

Endogenous Ghrelin Levels and Perception of Hunger: A Systematic Review and Meta-Analysis

BACKGROUND

Ghrelin is an orexigenic hormone primarily released by the stomach and has 2 isoforms: acylated ghrelin (AG) and de-acylated ghrelin (DAG), that appear to have different functions in humans.

OBJECTIVES

To perform a systematic review and meta-analysis of the association between plasma concentrations of total ghrelin (TG), AG, and DAG and perceptions of hunger in healthy adults.

METHODS

The following criteria were used for inclusion: 1) sample contained adults ≥18 y of age, 2) body mass index [BMI kg/m2] was ≥18.5, 3) ghrelin was sampled through blood, 4) subjective hunger was measured on a validated scale, 5) study reported a Pearson product correlation of ghrelin or had relevant figure(s) for data extraction, 6) participants were healthy with no overt disease, 7) protocols contained no physical activity or weight loss medication that suppressed appetite, 8) interventions were conducted without environmental manipulations. Moderators assessed were age, BMI, percentage of body fat (%BF), macronutrient content of test meals, energy intake (kcals), sex, and ghrelin isoform (AG, DAG, or TG).

RESULTS

The analysis included 47 studies (110 trials, n = 1799, age: 31.4 ± 12.0 y, BMI: 26.0 ± 4.75 kg/m2) and measured AG (n = 47 trials), DAG (n = 12 trials), and TG (n = 51 trials). The overall model indicated that ghrelin concentrations and perceptions of hunger were moderately correlated (r = 0.43, P < 0.001), and ghrelin isoform significantly moderated this relationship (AG: r = 0.60, P < 0.001; TG: r = 0.215, P = 0.01; DAG: r = 0.53, P = 0.695). Other significant moderators included age (b = -0.02, P = 0.01), BMI (b = -0.03, P = 0.05), %BF (b = -0.03, P = 0.05), energy intake (b = 0.0003, P = 0.04), and percentage of carbohydrates of test meals (b = 0.008, P = 0.05).

CONCLUSIONS

Ghrelin is associated with perceptions of hunger in humans, and this relationship is strengthened when AG is isolated; thus, AG may have a large impact on hunger signals in various populations. Future research should attempt to understand the role of DAG in hunger sensations.

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.

A pilot study of metabolic fitness effects of weight-supported walking in women with obesity

Background

This is an exploratory pilot study of novel technology enabling people with mobility disability to walk with minimal effort, in the “sedentary range”. The study’s premise is that impairment of the leading physical activity of daily living, walking, is a major contributor to a dysmetabolic state driving many prevalent “civilization diseases” associated with insulin resistance.

Methods

We explore within-subject changes in standard oral glucose tolerance (OGT) tests including metabotropic molecules after 22 twice-weekly, 30-minute bouts of weight-supported light-moderate physical activity in 16 non-diabetic obese, otherwise healthy, reproductive-age, volunteer women walking on an “anti-gravity” lower-body positive pressure (LBPP) treadmill.

Results

Subjects had reference base-line fasting plasma glucose and triglycerides (TG) but 2-hr OGT insulin levels of 467 ± 276 pmol • liter^-1 (mean± S.D.) indicating nascent insulin resistance, compared to post-study 308 ± 179 (p = 0.002). Fasting TG decreased from 0.80 ± 0.30 mmol • liter^-1 to 0.71 ± 0.25 (p = 0.03). Concomitantly plasma total ghrelin decreased from 69.6 ± 41.6 pmol • liter^-1 to 56.0 ± 41.3 (p = 0.008). There were no statistically significant changes in body weight or any correlations between weight change and cardiometabolic markers. However, there were robust positive correlations between changes among different classes of peptides including C-reactive protein–Interleukin 6, leptin–adiponectin, β-endorphin–oxytocin and orexin A (r ² = 0.48–0.88).

Conclusion

We conclude that brief, low-dose physical activity, walking on an anti-gravity LBPP treadmill may improve cardiometabolic risk, exhibiting favorable changes in neuro-regulatory peptides without weight loss in people with problems walking.

Exercise, Appetite and Weight Control: Are There Differences between Men and Women?

Recent years have witnessed significant research interest surrounding the interaction among exercise, appetite and energy balance, which has important implications for health. The majority of exercise and appetite regulation studies have been conducted in males. Consequently, opportunities to examine sex-based differences have been limited, but represent an interesting avenue of inquiry considering postulations that men experience greater weight loss after exercise interventions than women. This article reviews the scientific literature relating to the acute and chronic effects of exercise on appetite control in men and women. The consensus of evidence demonstrates that appetite, appetite-regulatory hormone and energy intake responses to acute exercise do not differ between the sexes, and there is little evidence indicating compensatory changes occur after acute exercise in either sex. Limited evidence suggests women respond to the initiation of exercise training with more robust compensatory alterations in appetite-regulatory hormones than men, but whether this translates to long-term differences is unknown. Current exercise training investigations do not support sex-based differences in appetite or objectively assessed energy intake, and increasing exercise energy expenditure elicits at most a partial energy intake compensation in both sexes. Future well-controlled acute and chronic exercise studies directly comparing men and women are required to expand this evidence base.

The effect of consuming low- versus high-glycemic index meals after exercise on postprandial blood lipid response following a next-day high-fat meal

Background/Objectives:

Exercise performed shortly before (that is, within half a day of) a high-fat meal is beneficial for stimulating fat oxidation after the meal and reducing postprandial triglycerides (TG). This benefit of exercise is unfortunately negated if the after-exercise food choice to replace the calories expended during exercise is one containing high-glycemic index (HGI) carbohydrates. We determined the effect of consuming low-glycemic index (LGI) carbohydrates after an exercise session on fat oxidation and TG after a subsequent high-fat meal.

Subjects/Methods:

Using a randomized, counterbalanced crossover design, 23 overweight or obese individuals (body mass index ⩾25 kg m⁻²) performed: walking exercise (90 min) at 1800 h followed by no meal (EX); exercise followed by a meal with LGI carbohydrates (that is, lentils, EX-LGI); exercise followed by a meal with HGI carbohydrates (that is, instant potatoes, white bread, EX-HGI); and a control condition with no exercise or meal. After a 10-h overnight fast, participants were given a standardized high-fat meal. Fat oxidation was estimated before and for 6 h after this meal from respiratory gas measures and TG determined from blood samples.

Results:

Fat oxidation (mean±s.d.) was higher with EX (6.9±1.7 g h⁻¹) than EX-HGI (6.3±1.6 g h⁻¹; P=0.007) and Control (5.9±1.7 g h⁻¹; P=0.00002), and EX-LGI (6.6±1.7 g h⁻¹) was higher than Control (P=0.002). TG total area under the curve was 18–32% lower with EX and EX-LGI compared with control (P=0.0005 and P=0.0001, respectively) and EX-HGI (P=0.05 and P=0.021, respectively).

Conclusions:

A meal containing HGI carbohydrates consumed after an evening exercise session cancels the beneficial effect of exercise for stimulating fat oxidation and lowering TG after a subsequent high-fat meal, whereas consuming a post-exercise meal with LGI carbohydrates retains the positive effect of exercise.

Exercise-trained men and women: role of exercise and diet on appetite and energy intake

The regulation of appetite and energy intake is influenced by numerous hormonal and neural signals, including feedback from changes in diet and exercise. Exercise can suppress subjective appetite ratings, subsequent energy intake, and alter appetite-regulating hormones, including ghrelin, peptide YY, and glucagon-like peptide 1(GLP-1) for a period of time post-exercise. Discrepancies in the degree of appetite suppression with exercise may be dependent on subject characteristics (e.g., body fatness, fitness level, age or sex) and exercise duration, intensity, type and mode. Following an acute bout of exercise, exercise-trained males experience appetite suppression, while data in exercise-trained women are limited and equivocal. Diet can also impact appetite, with low-energy dense diets eliciting a greater sense of fullness at a lower energy intake. To date, little research has examined the combined interaction of exercise and diet on appetite and energy intake. This review focuses on exercise-trained men and women and examines the impact of exercise on hormonal regulation of appetite, post-exercise energy intake, and subjective and objective measurements of appetite. The impact that low-energy dense diets have on appetite and energy intake are also addressed. Finally, the combined effects of high-intensity exercise and low-energy dense diets are examined. This research is in exercise-trained women who are often concerned with weight and body image issues and consume low-energy dense foods to keep energy intakes low. Unfortunately, these low-energy intakes can have negative health consequences when combined with high-levels of exercise. More research is needed examining the combined effect of diet and exercise on appetite regulation in fit, exercise-trained individuals.

Creating an acute energy deficit without stimulating compensatory increases in appetite: is there an optimal exercise protocol?

Recent years have witnessed significant interest from both the scientific community and the media regarding the influence of exercise on subsequent appetite and energy intake responses. This review demonstrates a consensus among the majority of scientific investigations that an acute bout of land-based endurance exercise does not stimulate any compensatory increases in appetite and energy intake on the day of exercise. Alternatively, preliminary evidence suggests that low volume, supramaximal exercise may stimulate an increase in appetite perceptions during the subsequent hours. In accordance with the apparent insensitivity of energy intake to exercise in the short term, the daily energy balance response to exercise appears to be primarily determined by the energy cost of exercise. This finding supports the conclusions of recent training studies that the energy expenditure of exercise is the strongest predictor of fat loss during an exercise programme.

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.

Using a novel computer-based approach to assess the acute effects of exercise on appetite-related measures

Measuring food intake using standard buffet meals can be complicated by sensory and external cues which can alter energy intake. The present study was designed to examine the effects of acute exercise on non-metabolic factors related to appetite and food intake using a computer-based assessment. Twenty-seven men and women participated in two sessions in random order: 60-min walking on the treadmill (exercise trial; EX) or seated rest (control trial; CON). Subjective hunger and fullness, food liking, food utility, and ideal portion size were assessed before and immediately after exercise or rest, and hourly for 2 h. The findings showed that an acute bout of moderate intensity exercise had an anorexigenic effect; characterised by diminished hunger (-17.4%, p=0.004) and lower prospective ideal portion size (-7.7%, p=0.003) compared to no exercise. This novel, computer-based assessment, is a useful alternative to buffet meals setting and allows for the determination of non-metabolic factors associated with feeding behaviour in relation to exercise.

Lifestyle factors and ghrelin: critical review and implications for weight loss maintenance

Ghrelin, the only known appetite-stimulating hormone in humans, may be one factor involved in increased appetite, cravings and food intake following weight loss. Innovative strategies for suppressing ghrelin and decreasing appetite during weight loss maintenance are needed. Recent research has highlighted relationships between ghrelin, stress and lifestyle factors. The purposes of the current review are to (i) describe the current status of knowledge about ghrelin and lifestyle factors; (ii) critically examine research in this area, highlighting inconsistencies and methodological issues and (iii) discuss future directions and implications for obesity treatment. Based on Literature search using PsycINFO and Medline databases, we reviewed experimental studies on relationships between ghrelin, stress, exercise and sleep. Ghrelin levels are positively related to stress hormones, and stress management interventions including exercise and sleep may help to reduce acylated ghrelin and corresponding appetite. Behavioural interventions may offer a practical, cost-effective alternative for reducing or stabilizing ghrelin levels after initial weight loss. Adding behavioural techniques designed to reduce ghrelin to traditional weight loss maintenance protocols may help individuals to maintain weight loss. Future directions for investigating relationships between ghrelin and behavioural factors, examining the efficacy of behavioural programmes in reducing ghrelin and improving weight loss maintenance are discussed.

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.

The impact of physical exercise on the gastrointestinal tract

PURPOSE OF REVIEW

Physical exercise can be both beneficial and harmful for the gastrointestinal tract in a dose-effect relationship between its intensity and health. Mild-to-moderate intensity exercises play a protective role against colon cancer, diverticular disease, cholelithiasis and constipation, whereas acute strenuous exercise may provoke heartburn, nausea, vomiting, abdominal pain, diarrhea and even gastrointestinal bleeding. This review focuses on mechanisms involved in those symptoms and their associations with type of exercises in humans.

RECENT FINDINGS

One quarter to one half of elite athletes are hampered by the gastrointestinal symptoms that may deter them from participation in training and competitive events. Vigorous exercise-induced gastrointestinal symptoms are often attributed to altered motility, mechanical factor or altered neuroimmunoendocrine secretions. Training, lifestyle modifications, meal composition, adequate hydration and avoidance of excessive use of some medications are the recommendations.

SUMMARY

Strenuous exercise and dehydrated states would be the causes of gastrointestinal symptoms referred by 70% of the athletes. Gut ischemia would be the main cause of nausea, vomiting, abdominal pain and (bloody) diarrhea. The frequency is almost twice as high during running than during other endurance sports as cycling or swimming and 1.5-3.0 times higher in the elite athletes than the recreational exercisers.

Influence of acute exercise with and without carbohydrate replacement on postprandial lipid metabolism

Acute exercise, undertaken on the day before an oral fat tolerance test (OFTT), typically reduces postprandial triglycerides (TG) and increases high-density lipoprotein-cholesterol (HDL-C). However, the benefits of acute exercise may be overstated when studies do not account for compensatory changes in dietary intake. The objective of this study was to determine the influence of acute exercise, with and without carbohydrate (CHO) replacement, on postprandial lipid metabolism. Eight recreationally active young men underwent an OFTT on the morning after three experimental conditions: no exercise [control (Con)], prolonged exercise without CHO replacement (Ex-Def) and prolonged exercise with CHO replacement to restore CHO and energy balance (Ex-Bal). The exercise session in Ex-Def and Ex-Bal consisted of 90 min cycle ergometry at 70% peak oxygen uptake (V̇o2peak) followed by 10 maximal 1-min sprints. CHO replacement was achieved using glucose solutions consumed at 0, 2, and 4 h postexercise. Muscle glycogen was 40 ± 4% ( P < 0.05) and 94 ± 3% ( P = 0.24) of Con values on the morning of the Ex-Def and Ex-Bal OFTT, respectively. Postprandial TG were 40 ± 14% lower and postprandial HDL-C, free fatty acids, and 3-hydroxybutyrate were higher in Ex-Def compared with Con ( P < 0.05). Most importantly, these exercise effects were not evident in Ex-Bal. Postprandial insulin and glucose and the homeostatic model assessment of insulin resistance (HOMAIR) were not significantly different across trials. There was no relation between the changes in postprandial TG and muscle glycogen across trials. In conclusion, the influence of acute exhaustive exercise on postprandial lipid metabolism is largely dependent on the associated CHO and energy deficit.