Appetite and gut hormone responses to moderate-intensity continuous exercise versus high-intensity interval exercise, in normoxic and hypoxic conditions

Impact of exercise training in a hypobaric/normobaric hypoxic environment on body composition and glycolipid metabolism in individuals with overweight or obesity: a systematic review and meta-analysis

Objective

This study aims to assess the impact of hypoxia training on body composition and glycolipid metabolism in excess body weight or living with obese people through meta-analysis.

Methods

Randomized controlled trials investigating the effects of hypoxia training on body composition, glucose, and lipid metabolism in excess body weight or living with obese people were systematically searched from databases including CNKI, PubMed, and Web of Science. The meta-analysis was performed by using Stata 18 and RevMan 5.4 analytic tools. The risk of bias was assessed using the Cochrane evaluation tool, and the level of certainty of evidence was determined by the GRADE framework. Between-study heterogeneity was examined using the I 2 test, and the publication bias was evaluated via the Egger test or funnel plot.

Results

A total of 32 RCTs with 1,011 participants were included. A meta-analysis of 25 RCTs was performed (499 men and 480 women, Age: 40.25 ± 15.69, BMI: 30.96 ± 3.65). In terms of body composition, the outcome indexes of body fat ratio (MD is -1.16, 95% CI -1.76 to -0.56, P = 0.00) in the hypoxia group were better than the normal oxygen group. There was no significant difference in body mass and BMI between the hypoxia group and the normal-oxygen group (P > 0.05). In terms of lipid and glucose metabolism, no significant changes were found between the hypoxia group and the normoxia group (P > 0.05). Subgroup analysis showed that training in hypoxic environment at altitude 2001-2,500 m could effectively improve body mass, TG and LDL-C (P < 0.05). The effective program to reduce body mass is to carry out moderate intensity training of 45-60 min for ≤8 weeks, ≥4 times a week (P < 0.05).

Conclusion

Hypoxic training is essential for reducing body fat ratio in excess body weight or obese people. It is recommended to carry out 45-60 min of moderate-intensity aerobic exercise for ≤8 weeks, ≥4 times a week, in a hypoxia environment of 2,001-2,500 m to lose body mass. The effects of hypoxia training and normoxia training on lipid and glucose metabolism in excess body weight or obese people are the same.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/view/CRD42024628550.

A preliminary exploration of establishing a mice model of hypoxic training

Altitude training has been widely adopted. This study aimed to establish a mice model to determine the time point for achieving the best endurance at the lowland. C57BL/6 and BALB/c male mice were used to establish a mice model of hypoxic training with normoxic training mice, hypoxic mice, and normoxic mice as controls. All hypoxic mice were placed in a chamber filled with 16% O2 and N2, and hypoxic training mice were trained for two weeks. Then mice were removed from the chamber and tested at normoxic conditions weekly at the beginning of the experiment and the second, third, fourth, and sixth weeks. The tests for endurance ability include maximal aerobic speed (MAS), Rota-rod, and grip strength. In addition, the open field, visual cliff, and Y maze were used to test cognitive abilities. Body composition and lactic acid tolerance level were also measured. For BALB/c but not C57BL/6 mice were evaluated for effectively training. Based on the average MAS of all mice, mice successfully passed the training according to the procedure: the first week (32%MAS/10min, 48%MAS/10min, and 64%MAS/10min) and second week (40%MAS/10min, 56%MAS/10min, and 72%MAS/10min). Hypoxic training mice reached peak rotarod performance on the 7th day post-training (Test 3), with significant improvements compared to Test 1, 2, 4, and 5. At Test 3, their rotarod scores significantly differed from both H and N groups, and showing a trend towards difference from NT group. Meanwhile, hypoxic mice showed significant cognitive impairment, anxiety, depression, muscle loss, and fat gain compared with hypoxic training mice after hypoxia intervation. Two consecutive weeks of 16% O2 training followed by one week of reoxygenation may be the best for endurance competition. Thus, we think a mouse model for hypoxic training was built, with Rota-rod testing as a detection indicator. Moreover, hypoxic training may alleviate the damage of hypoxia to the body.

Effects of endurance exercise under hypoxic conditions on the gastric emptying rate and intestinal cell damage

The present study examined the effects of gastric emptying rate and intestinal cell damage following a single session of endurance exercise under "hypoxic" or "normoxic" conditions at the same relative intensity. Eleven healthy males performed two trials on different days, consisting of a 60 min run on a treadmill at 70% maximal running velocity (vMax) while inspiring hypoxic (FiO2: 14.5%; HYP) or normoxic air (FiO2: 20.9%; NOR). The average running velocity was 11.4  ±  0.7 km/h in NOR and 10.8  ±  0.5 km/h in HYP, respectively. Venous blood samples were collected to evaluate plasma intestinal fatty acid binding protein (I-FABP) as an indicator of exercise-induced intestinal cell damage. The gastric emptying rate was determined by the 13C-sodium acetate breath test. Running velocities at 70% vMax and arterial oxygen saturation were significantly lower under HYP than NOR (p < 0.001). Peak heart rate and rating of perceived exertion during exercise did not differ significantly between the trials. Maximum 13C excretion time (an indication of the gastric emptying rate) was significantly delayed in the HYP (NOR: 38.5  ±  5.0 min, HYP: 45.5  ±  9.6 min; p = 0.010). Furthermore, the score of nausea increased slightly, but increased significantly after exercise only in the HYP (p = 0.04). However, exercise-induced changes in plasma I-FABP, adrenaline, and noradrenaline concentrations did not differ significantly between the two trials. These results suggest that endurance exercise under hypoxic conditions impairs digestive function in the stomach compared to exercise under normoxic conditions performed at the same relative intensity.

Effects of malnutrition on disease severity and adverse outcomes in idiopathic pulmonary arterial hypertension: a retrospective cohort study

BACKGROUND

Malnutrition is common in patients with chronic cardiovascular disease and is associated with significantly higher all-cause mortality. Approximately one-third of patients with heart failure are malnourished. However, the relationship between malnutrition and idiopathic pulmonary arterial hypertension (IPAH) remains unclear. This study aimed to clarify the prognostic value of malnutrition in patients with IPAH.

METHODS

A total of 432 consecutive participants with IPAH were included in this study between March 2013 and August 2021. Three common malnutrition assessment tools, including the geriatric nutritional risk index (GNRI), prognostic nutritional index (PNI), and controlling nutritional status (CONUT) score, were used to evaluate the nutritional status of patients with IPAH. The relationships between the malnutrition tools and long-term adverse outcomes were determined using restricted cubic splines and multivariate Cox regression models.

RESULTS

During a mean follow-up of 3.1 years, 158 participants experienced clinical worsening or all-cause death. Patients were stratified into the low-, intermediate- and high-risk groups based on the European Society of Cardiology (ESC) risk stratification, and the PNI (55.9 ± 5.7 vs. 54.4 ± 7.2 vs. 51.1 ± 7.1, P = 0.005) and CONUT score (2.1 ± 0.9 vs. 2.5 ± 1.2 vs. 3.3 ± 1.1, P < 0.001) identified these patient groups better than the GNRI. All three malnutrition tools were associated with well-validated variables that reflected IPAH severity, such as the World Health Organization functional class, 6-min walk distance, and N-terminal pro-brain natriuretic peptide level. The CONUT score exhibited better predictive ability than both the GNRI (ΔAUC = 0.059, P < 0.001) and PNI (ΔAUC = 0.095, P < 0.001) for adverse outcomes and significantly improved reclassification and discrimination beyond the ESC risk score. Multivariable Cox regression analysis indicated that only the CONUT score (hazard ratio = 1.363, 95% confidence interval 1.147, 1.619 per 1.0-standard deviation increment, P < 0.001) independently predicted adverse outcomes.

CONCLUSIONS

The malnutrition status was associated with disease severity in patients with IPAH. The CONUT score provided additional information regarding the risk of clinically worsening events, making it a meaningful risk stratification tool for these patients.

Impact of high-altitude acclimatization and de-acclimatization on the intestinal microbiota of rats in a natural high-altitude environment

Introduction

Intestinal microorganisms play an important role in the health of both humans and animals, with their composition being influenced by changes in the host's environment.

Methods

We evaluated the longitudinal changes in the fecal microbial community of rats at different altitudes across various time points. Rats were airlifted to high altitude (3,650 m) and acclimatized for 42 days (HAC), before being by airlifted back to low altitude (500 m) and de-acclimatized for 28 days (HADA); meanwhile, the control group included rats living at low altitude (500 m; LA). We investigated changes in the gut microbiota at 12 time points during high-altitude acclimatization and de-acclimatization, employing 16S rRNA gene sequencing technology alongside physiological indices, such as weight and daily autonomous activity time.

Results

A significant increase in the Chao1 index was observed on day 14 in the HAC and HADA groups compared to that in the LA group, indicating clear differences in species richness. Moreover, the principal coordinate analysis revealed that the bacterial community structures of HAC and HADA differed from those in LA. Long-term high-altitude acclimatization and de- acclimatization resulted in the reduced abundance of the probiotic Lactobacillus. Altitude and age significantly influenced intestinal microbiota composition, with changes in ambient oxygen content and atmospheric partial pressure being considered key causal factors of altitude-dependent alterations in microbiota composition. High-altitude may be linked to an increase in anaerobic bacterial abundance and a decrease in non-anaerobic bacterial abundance.

Discussion

In this study, the hypobaric hypoxic conditions at high-altitude increased the abundance of anaerobes, while reducing the abundance of probiotics; these changes in bacterial community structure may, ultimately, affect host health. Overall, gaining a comprehensive understanding of the intestinal microbiota alterations during high-altitude acclimatization and de-acclimatization is essential for the development of effective prevention and treatment strategies to better protect the health of individuals traveling between high- and low-altitude areas.

The beneficial effects of balloon pulmonary angioplasty for patients with chronic thromboembolic pulmonary hypertension are accompanied by increased body mass index and improved nutritional status

Although balloon pulmonary angioplasty (BPA) improves pulmonary hypertension and the prognosis of patients with chronic thromboembolic pulmonary hypertension (CTEPH), subsequent changes in body mass index (BMI), nutritional status, and appetite have not been fully investigated. This retrospective study aimed to clarify changes in BMI, nutritional status, and appetite after BPA. Fifty-two consecutive patients with CTEPH who underwent complete revascularization with BPA between July 2014 and July 2023 and were available for follow-up were evaluated. We compared the presence or absence of increased appetite, BMI change, and nutritional status before and after BPA treatment. BPA significantly improved the mean pulmonary artery pressure from 37.4 ± 8.7 mmHg to 18.7 ± 2.8 mmHg and the partial pressure of oxygen from 61.6 ± 9.3 mmHg to 82.8 ± 9.9 mmHg (both p < 0.001). Appetite was increased in 82.7% of the patients. BMI significantly increased from 23.9 ± 3.7 kg/m2 to 24.9 ± 3.7 kg/m2 (p < 0.001). As a nutritional indicator, the Geriatric Nutritional Risk Index increased from 105.3 ± 10.2 to 108.3 ± 8.3 (p < 0.001). The median Controlling Nutritional Status scores showed no significant change but the range was significantly improved from 0-9 to 0-3 (p = 0.006). In conclusion, patients with CTEPH show improved oxygenation and hemodynamics, increased BMI, and improved nutritional status following BPA. This sequence of changes may help improve patient prognosis.

Resistance and endurance training in intermittent hypoxia reduce body fat mass and blood pressure

BACKGROUND

Hypoxia is an environmental condition that occurs in sports performed at high altitude. Adaptation to hypoxia is accompanied by changes in body composition and cardiac function that could impair sport performance in altitude. These changes concern mainly to a reduction in muscle mass and an increased heart rate. In this context, a resistance training protocol in a normobaric hypoxia chamber has been implemented. Therefore, the aim of this study was to study the changes in body composition and cardiovascular variables after a training period in intermittent hypoxia.

METHODS

A single-blind experimental study was carried out for 3 weeks. Thirty-two participants were distributed in a control group resistance training in normoxia (N) at sea level and an experimental group resistance training in intermittent hypoxia (IH) between a simulated 5100-5800m during 15 sessions with a controlled diet. Anthropometry according to ISAK was used to determine body composition. Systolic and diastolic blood pressures and other cardiovascular parameters were monitored.

RESULTS

IH showed a reduction in body fat (from 8.9±1.9% to 8.2±1.7%) compared to N (from 8.4±1.5% to 8.1±1.4%) (P<0.001). In addition, significant changes in blood pressure were observed at the end compared to the beginning of the intervention in the IH (from 124.7±10.2 to 116.9±8.3 mmHg and 68.3±8.8 to 62.4±5.7 mmHg in systolic a diastolic blood pressure respectively). In addition, resting heart rate was significantly reduced in IH. However, partial oxygen saturation displayed no changes in both groups.

CONCLUSIONS

Altogether, the training protocol in intermittent hypoxia performed in the present report allowed to adjust body weight through fat mass reduction but maintaining muscle mass. In addition, a decrease in blood pressure and basal heart rate was observed.

Appetite, Hypoxia, and Acute Mountain Sickness: A 10-Hour Normobaric Hypoxic Chamber Study

Barclay, Holly, Saptarshi Mukerji, Bengt Kayser, and Jui-Lin Fan. Appetite, hypoxia and acute mountain sickness: A 10-hour normobaric hypoxic chamber study. High Alt Med Biol. 24:329-335, 2023. Background: The effects of hypoxia and acute mountain sickness (AMS) on appetite and food preferences are moot, especially during the early phase of hypoxic exposure. We examined the effects of a 10-hour hypoxic exposure on appetite and food preference. Methods: We assessed appetite (hunger, satisfaction, fullness, perceived appetite, and lost appetite), food preferences (sweet, salty, savory, and fatty), and AMS (Lake Louise score) with questionnaires in 27 healthy individuals (13 women) across 10-hour exposures to normobaric normoxia (fraction of inspired O2 [FiO2]: 0.21) and normobaric hypoxia (FiO2: 0.12, equivalent of 5,000 m) in a randomized, single-blinded manner. Results and Conclusions: Compared with normoxia, hypoxia decreased hunger and appetite (p = 0.040 and <0.001, respectively), which was mediated by a decreased desire for sweet, salty, and fatty foods (p < 0.05 for all). AMS was associated with a decreased desire for sweet (R = -0.438, p = 0.032) and salty foods (R = -0.460, p = 0.024) and greater loss of appetite (R = -0.619, p = 0.018). Our findings suggest that acute hypoxia rapidly suppresses appetite and that AMS development further amplifies anorexia. Clinical Trial Registration Number: ACTRN12618000548235.

Effects of acute resistance exercise with different loads on appetite, appetite hormones and autonomic nervous system responses in healthy young men

Although the effect of continuous aerobic exercise on the appetite has been widely explored, the influence of resistance exercise (RE) with different variables, including training loads, training volume, and inter-set rest, on appetite responses requires further investigation. This study examined the importance of training load in RE-induced appetite regulation, with the total training volume and inter-set rest equalized. In total, 11 healthy young men (age = 23 ± 2 years, body mass index = 22 ± 2 kg/m²) were included. Participants completed 3 trials, namely moderate-load RE (MOD; 4 sets of 8 repetitions at 85% 8RM), low-load RE (LOW; 4 sets of 15 repetitions at 45% 8RM), and a control (CON; no exercise), in a randomized, crossover design. Subjective appetite ratings; concentrations of ghrelin, peptide YY (PYY), and lactate; and the autonomic nervous system activity were evaluated before exercise and 1 h after exercise. The hunger and predicted food consumption ratings, and ghrelin concentrations immediately after exercise were significantly lower in the MOD and LOW trials (p < 0.05 vs. CON). The PYY and lactate concentrations immediately after exercise were significantly higher in the MOD and LOW trials (p < 0.05 vs. CON). Heart rate variability recovery was slower in the MOD trial. These findings suggest that both moderate-load and low-load RE at equal training volumes and inter-set rest induce similar responses on hunger suppression and orexigenic signals, except for the slower recovery of autonomic modulation after moderate-load RE. Our results suggest that when individuals aim to potentiate appetite suppression after a bout of RE, both moderate- and low-load RE could be applied.

The role of exercise and hypoxia on glucose transport and regulation

Muscle glucose transport activity increases with an acute bout of exercise, a process that is accomplished by the translocation of glucose transporters to the plasma membrane. This process remains intact in the skeletal muscle of individuals with insulin resistance and type 2 diabetes mellitus (T2DM). Exercise training is, therefore, an important cornerstone in the management of individuals with T2DM. However, the acute systemic glucose responses to carbohydrate ingestion are often augmented during the early recovery period from exercise, despite increased glucose uptake into skeletal muscle. Accordingly, the first aim of this review is to summarize the knowledge associated with insulin action and glucose uptake in skeletal muscle and apply these to explain the disparate responses between systemic and localized glucose responses post-exercise. Herein, the importance of muscle glycogen depletion and the key glucoregulatory hormones will be discussed. Glucose uptake can also be stimulated independently by hypoxia; therefore, hypoxic training presents as an emerging method for enhancing the effects of exercise on glucose regulation. Thus, the second aim of this review is to discuss the potential for systemic hypoxia to enhance the effects of exercise on glucose regulation.

Changes in body mass, appetite-related hormones, and appetite sensation in women during 4 days of hypobaric hypoxic exposure equivalent to 3,500-m altitude

Altitude exposure may suppress appetite and hence provide a viable weight-loss strategy. While changes in food intake and availability as well as physical activity may contribute to altered appetite at altitude, herein we aimed to investigate the isolated effects of hypobaric hypoxia on appetite regulation and sensation. Twelve healthy women (age: 24.0 ± 4.2 years, body mass: 60.6 ± 7.0 kg) completed two 4-day sojourns in a hypobaric chamber, one in normoxia [P_B = 761 mmHg, 262 m (NX)] and one in hypobaric hypoxia [P_B = 493 mmHg (HH)] equivalent to 3,500-m altitude. Energy intake was standardized 4 days prior and throughout both sojourns. Plasma concentrations of leptin, acylated ghrelin, cholecystokinin (CCK), and cytokine growth differentiation factor 15 (GDF15) were determined every morning. Before and after breakfast, lunch, and dinner, appetite was assessed using visual analog scales. Body mass was significantly decreased following HH but not NX (-0.71 ± 0.32 kg vs. -0.05 ± 0.54 kg, condition: P < 0.001). Compared to NX, acylated ghrelin decreased throughout the HH sojourn (condition × time: P = 0.020), while leptin was higher throughout the entire HH sojourn (condition: P < 0.001). No differences were observed in CCK and GDF15 between the sojourns. Feelings of satiety and fullness were higher (condition: P < 0.001 and P = 0.013, respectively), whereas prospective food consumption was lower in HH than in NX (condition: P < 0.001). Our findings suggest that hypoxia exerts an anorexigenic effect on appetite-regulating hormones, suppresses subjective appetite sensation, and can induce weight loss in young healthy women. Among the investigated hormones, acylated ghrelin and leptin most likely explain the observed HH-induced appetite suppression.NEW & NOTEWORTHY This study investigated the effects of hypoxia on appetite regulation in women while strictly controlling for diet, physical activity, menstrual cycle, and environmental conditions. In young women, 4 days of altitude exposure (3,500 m) decreases body weight and circulating acylated ghrelin levels while preserving leptin concentrations. In line with the hormonal changes, altitude exposure induces alterations in appetite sensation, consisting of a decreased feeling of hunger and prospective food intake and an increased feeling of fullness and satiety.

Mechanisms for Combined Hypoxic Conditioning and Divergent Exercise Modes to Regulate Inflammation, Body Composition, Appetite, and Blood Glucose Homeostasis in Overweight and Obese Adults: A Narrative Review

Obesity is a major global health issue and a primary risk factor for metabolic-related disorders. While physical inactivity is one of the main contributors to obesity, it is a modifiable risk factor with exercise training as an established non-pharmacological treatment to prevent the onset of metabolic-related disorders, including obesity. Exposure to hypoxia via normobaric hypoxia (simulated altitude via reduced inspired oxygen fraction), termed hypoxic conditioning, in combination with exercise has been increasingly shown in the last decade to enhance blood glucose regulation and decrease the body mass index, providing a feasible strategy to treat obesity. However, there is no current consensus in the literature regarding the optimal combination of exercise variables such as the mode, duration, and intensity of exercise, as well as the level of hypoxia to maximize fat loss and overall body compositional changes with hypoxic conditioning. In this narrative review, we discuss the effects of such diverse exercise and hypoxic variables on the systematic and myocellular mechanisms, along with physiological responses, implicated in the development of obesity. These include markers of appetite regulation and inflammation, body conformational changes, and blood glucose regulation. As such, we consolidate findings from human studies to provide greater clarity for implementing hypoxic conditioning with exercise as a safe, practical, and effective treatment strategy for obesity.

Influence of acute and chronic intermittent hypoxic-hyperoxic exposure prior to aerobic exercise on cardiovascular risk factors in geriatric patients-a randomized controlled trial

Background: Intermittent hypoxic-hyperoxic exposure (IHHE) and aerobic training have been proposed as non-pharmacological interventions to reduce age-related risk factors. However, no study has yet examined the effects of IHHE before aerobic exercise on cardiovascular risk factors in the elderly. Therefore, the aim of this study was to investigate the acute and chronic effects of IHHE prior to aerobic cycling exercise on blood lipid and lipoprotein concentrations as well as blood pressure in geriatric patients. Methods: In a randomized, controlled, and single-blinded trial, thirty geriatric patients (72-94 years) were assigned to two groups: intervention (IG; n = 16) and sham control group (CG; n = 14). Both groups completed 6 weeks of aerobic cycling training, 3 times a week for 20 min per day. The IG and CG were additionally exposed to IHHE or sham IHHE (i.e., normoxia) for 30 min prior to aerobic cycling. Blood samples were taken on three occasions: immediately before the first, ∼10 min after the first, and immediately before the last session. Blood samples were analyzed for total (tCh), high-density (HDL-C), and low-density lipoprotein cholesterol (LDL-C), and triglyceride (Tgl) serum concentration. Resting systolic (SBP) and diastolic blood pressure (DBP) was assessed within 1 week before, during (i.e., at week two and four), and after the interventions. Results: The baseline-adjusted ANCOVA revealed a higher LDL-C concentration in the IG compared to the CG after the first intervention session (ηp 2 = 0.12). For tCh, HDL-C, Tgl, and tCh/HDL-C ratio there were no differences in acute changes between the IG and the CG (ηp 2 ≤ 0.01). With regard to the chronic effects on lipids and lipoproteins, data analysis indicated no differences between groups (ηp 2 ≤ 0.03). The repeated measures ANOVA revealed an interaction effect for SBP (ηp 2 = 0.06) but not for DBP (ηp 2 ≤ 0.01). Within-group post-hoc analysis for the IG indicated a reduction in SBP at post-test (d = 0.05). Conclusion: Applying IHHE prior to aerobic cycling seems to be effective to reduce SBP in geriatric patients after 6 weeks of training. The present study suggests that IHHE prior to aerobic cycling can influence the acute exercise-related responses in LDL-C concentration but did not induce chronic changes in basal lipid or lipoprotein concentrations.

Effects of Six Weeks of Hypoxia Exposure on Hepatic Fatty Acid Metabolism in ApoE Knockout Mice Fed a High-Fat Diet

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease with a characteristic of abnormal lipid metabolism. In the present study, we employed apolipoprotein E knockout (ApoE KO) mice to investigate the effects of hypoxia exposure on hepatic fatty acid metabolism and to test whether a high-fat diet (HFD) would suppress the beneficial effect caused by hypoxia treatment. ApoE KO mice were fed a HFD for 12 weeks, and then were forwarded into a six-week experiment with four groups: HFD + normoxia, normal diet (ND) + normoxia, HFD + hypoxia exposure (HE), and ND + HE. The C57BL/6J wild type (WT) mice were fed a ND for 18 weeks as the baseline control. The hypoxia exposure was performed in daytime with normobaric hypoxia (11.2% oxygen, 1 h per time, three times per week). Body weight, food and energy intake, plasma lipid profiles, hepatic lipid contents, plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and molecular/biochemical makers and regulators of the fatty acid synthesis and oxidation in the liver were measured at the end of interventions. Six weeks of hypoxia exposure decreased plasma triglycerides (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) contents but did not change hepatic TG and non-esterified fatty acid (NEFA) levels in ApoE KO mice fed a HFD or ND. Furthermore, hypoxia exposure decreased the mRNA expression of Fasn, Scd1, and Srebp-1c significantly in the HFD + HE group compared with those in the HFD + normoxia group; after replacing a HFD with a ND, hypoxia treatment achieved more significant changes in the measured variables. In addition, the protein expression of HIF-1α was increased only in the ND + HE group but not in the HFD + HE group. Even though hypoxia exposure did not affect hepatic TG and NEFA levels, at the genetic level, the intervention had significant effects on hepatic metabolic indices of fatty acid synthesis, especially in the ND + HE group, while HFD suppressed the beneficial effect of hypoxia on hepatic lipid metabolism in male ApoE KO mice. The dietary intervention of shifting HFD to ND could be more effective in reducing hepatic lipid accumulation than hypoxia intervention.

Effects of Intermittent Hypoxia-Hyperoxia on Performance- and Health-Related Outcomes in Humans: A Systematic Review

BACKGROUND

Intermittent hypoxia applied at rest or in combination with exercise promotes multiple beneficial adaptations with regard to performance and health in humans. It was hypothesized that replacing normoxia by moderate hyperoxia can increase the adaptive response to the intermittent hypoxic stimulus.

OBJECTIVE

Our objective was to systematically review the current state of the literature on the effects of chronic intermittent hypoxia-hyperoxia (IHH) on performance- and health-related outcomes in humans.

METHODS

PubMed, Web of Science™, Scopus, and Cochrane Library databases were searched in accordance with PRISMA guidelines (January 2000 to September 2021) using the following inclusion criteria: (1) original research articles involving humans, (2) investigation of the chronic effect of IHH, (3) inclusion of a control group being not exposed to IHH, and (4) articles published in peer-reviewed journals written in English.

RESULTS

Of 1085 articles initially found, eight studies were included. IHH was solely performed at rest in different populations including geriatric patients (n = 1), older patients with cardiovascular (n = 3) and metabolic disease (n = 2) or cognitive impairment (n = 1), and young athletes with overtraining syndrome (n = 1). The included studies confirmed the beneficial effects of chronic exposure to IHH, showing improvements in exercise tolerance, peak oxygen uptake, and global cognitive functions, as well as lowered blood glucose levels. A trend was discernible that chronic exposure to IHH can trigger a reduction in systolic and diastolic blood pressure. The evidence of whether IHH exerts beneficial effects on blood lipid levels and haematological parameters is currently inconclusive. A meta-analysis was not possible because the reviewed studies had a considerable heterogeneity concerning the investigated populations and outcome parameters.

CONCLUSION

Based on the published literature, it can be suggested that chronic exposure to IHH might be a promising non-pharmacological intervention strategy for improving peak oxygen consumption, exercise tolerance, and cognitive performance as well as reducing blood glucose levels, and systolic and diastolic blood pressure in older patients with cardiovascular and metabolic diseases or cognitive impairment. However, further randomized controlled trials with adequate sample sizes are needed to confirm and extend the evidence. This systematic review was registered on the international prospective register of systematic reviews (PROSPERO-ID: CRD42021281248) ( https://www.crd.york.ac.uk/prospero/ ).

Weight Loss and Fat Metabolism during Multi-Day High-Altitude Sojourns: A Hypothesis Based on Adipocyte Signaling

Several publications and random observations have reported weight loss in high-altitude sojourners of both sexes. This could be a result of multiple adaptations, which hypoxia and mountaineering provoke on a cellular and organic level. Several publications have discussed the effect on appetite-regulating hormones to be one of the main contributing factors. We aimed to review the available data and show the current state of knowledge regarding nutritional aspects in high altitude with a special focus on fatty dietary forms. To reach this aim we conducted a literature search via PubMed according to the PRISMA 2020 protocol to identify relevant studies. We found that very few studies cover this field with scientifically satisfying evidence. For final analysis, reviews as well as papers that were not clearly related to the topic were excluded. Six articles were included discussing hormonal influences and the impact of exercise on appetite regulation as well as genetic factors altering metabolic processes at altitude. Leptin expression seems to be the biggest contributor to appetite reduction at altitude with an initial increase followed by a decrease in the course of time at high altitude. Its expression is greatly dependent on the amount of white adipose tissue. Since the expression of leptin is associated with an increased β-oxidation of fatty acids, a high-fat diet could be advantageous at a certain time point in the course of high-altitude sojourns.

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.

A High-Protein, Low Glycemic Index Diet Suppresses Hunger but Not Weight Regain After Weight Loss: Results From a Large, 3-Years Randomized Trial (PREVIEW)

Background: Previous studies have shown an increase in hunger during weight-loss maintenance (WLM) after diet-induced weight loss. Whether a combination of a higher protein, lower glycemic index (GI) diet and physical activity (PA) can counteract this change remains unclear. Aim: To compare the long-term effects of two diets [high protein (HP)-low GI vs. moderate protein (MP)-moderate GI] and two PA programs [high intensity (HI) vs. moderate intensity (MI)] on subjective appetite sensations during WLM after ≥8% weight loss (WL). Methods: Data derived from the 3-years PREVIEW randomized intervention study. An 8-weeks WL phase using a low-energy diet was followed by a 148-weeks randomized WLM phase. For the WLM phase, participants were assigned to one of the four groups: HP-MI, HP-HI, MP-MI, and MP-HI. Available data from 2,223 participants with overweight or obesity (68% women; BMI ≥ 25 kg/m²). Appetite sensations including satiety, hunger, desire to eat, and desire to eat something sweet during the two phases (at 0, 8 weeks and 26, 52, 104, and 156 weeks) were assessed based on the recall of feelings during the previous week using visual analogue scales. Differences in changes in appetite sensations from baseline between the groups were determined using linear mixed models with repeated measures. Results: There was no significant diet × PA interaction. From 52 weeks onwards, decreases in hunger were significantly greater in HP-low GI than MP-moderate GI (P _{time × diet} = 0.018, P _dietgroup = 0.021). Although there was no difference in weight regain between the diet groups (P _{time × diet} = 0.630), hunger and satiety ratings correlated with changes in body weight at most timepoints. There were no significant differences in appetite sensations between the two PA groups. Decreases in hunger ratings were greater at 52 and 104 weeks in HP-HI vs. MP-HI, and greater at 104 and 156 weeks in HP-HI vs. MP-MI. Conclusions: This is the first long-term, large-scale randomized intervention to report that a HP-low GI diet was superior in preventing an increase in hunger, but not weight regain, during 3-years WLM compared with a MP-moderate GI diet. Similarly, HP-HI outperformed MP-HI in suppressing hunger. The role of exercise intensity requires further investigation. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT01777893.

The hypoxia response and nutritional peptides

Hypoxia controls metabolism at several levels, e.g., via mitochondrial ATP production, glucose uptake and glycolysis. Hence it is likely that hypoxia also affects the action and/or production of many peptide hormones linked to food intake and appetite control. Many of those are produced in the gastrointestinal tract, endocrine pancreas, adipose tissue, and selective areas in the brain which modulate and concert their actions. However, the complexity of the hypoxia response and the links to peptides/hormones involved in food intake and appetite control in the different organs are not well known. This review summarizes the role of the hypoxia response and its effects on major peptides linked to appetite regulation, nutrition and metabolism.

Ameliorative Effect of Ananas comosus on Cobalt Chloride-Induced Hypoxia in Caco2 cells via HIF-1α, GLUT 1, VEGF, ANG and FGF

In the present study, protective effects of Ananas comosus i.e., pineapple pulp (PA) against cobalt chloride (CoCl₂)‑induced hypoxia in Caco-2 cells were evaluated. PA reduces levels of lipid peroxidation, reactive oxygen and nitrogen species. It was proved to be cytoprotective and increased anti-oxidant activity against CoCl₂-induced hypoxia. The inference drawn from this experiment was CoCl₂-induced hypoxia that regulates hypoxia-inducible factor-1 (HIF-1), a transcription factor. It was also confirmed that PA pre-treatment inhibited the expression of HIF-1α, thereby downregulating the hypoxia-associated gene/protein expressions such as GLUT-1, VEGF, ANG and FGF. Finally, supplementation of PA could help in snow-balling the digestive hormones like leptin and CCK in hypoxic conditions. Therefore, this report provides substantial proof of reducing the hypoxia-induced loss of appetite at high-altitude environments. Graphical Abstract.

[Into thin air - Altitude training and hypoxic conditioning: From athlete to patient]

INTRODUCTION

Hypoxic exposure should be considered as a continuum, the effects of which depend on the dose and individual response to hypoxia. Hypoxic conditioning (HC) represents an innovative and promising strategy, ranging from improved human performance to therapeutic applications.

STATE OF THE ART

With the aim of improving sports performance, the effectiveness of hypoxic exposure, whether natural or simulated, is difficult to demonstrate because of the large variability of the protocols used. In therapeutics, the benefits of HC are described in many pathological conditions such as obesity or cardiovascular pathologies. If the HC benefits from a strong preclinical rationale, its application to humans remains limited.

PERSPECTIVES

Advances in training and acclimation will require greater personalization and precise periodization of hypoxic exposures. For patients, the harmonization of HC protocols, the identification of biomarkers and the development and subsequent validation of devices allowing a precise control of the hypoxic stimulus are necessary steps for the development of HC.

CONCLUSIONS

From the athlete to the patient, HC represents an innovative and promising field of research, ranging from the improvement of human performance to the prevention and treatment of certain pathologies.

Hypoxia, energy balance, and obesity: An update

Because of the enduring rise in the prevalence of obesity worldwide, there is continued interest in hypoxia as a mechanism underlying the pathophysiology of obesity and its comorbidities and as a potential therapeutic adjunct for the management of the disease. Lifelong exposure to altitude is accompanied by a lower risk for obesity, whereas altitude sojourns are generally associated with a loss of body mass. A negative energy balance upon exposure to hypoxia can be due to a combination of changes in determinants of energy expenditure (resting metabolic rate and physical activity energy expenditure) and energy intake (appetite). Over the past 15 years, the potential therapeutic interest of hypobaric or normobaric hypoxic exposure in individuals with obesity-to lower body mass and improve health status-has become an active field of research. Various protocols have been implemented, using actual altitude sojourns or intermittent normobaric hypoxic exposures, at rest or in association with physical activity. Although several studies suggest benefits on body mass and cardiovascular and metabolic variables, further investigations are required before recommending hypoxic exposure in obesity management programs. Future studies should also better clarify the effects of hypoxia on appetite, the intestinal microbiota, and finally on overall energy balance.

Effects of Ramadan Intermittent Fasting on Gut Hormones and Body Composition in Males with Obesity

We studied the effects of Ramadan intermittent fasting (RIF) on gut hormones (leptin, glucagon-like peptide-1 (GLP-1), peptide YY (PYY), cholecystokinin (CCK), and ghrelin) in males with obesity. Thirty sedentary males were randomly allocated to either an experimental group (EG, n = 15) or a control group (CG, n = 15). The EG group completed their Ramadan fasting rituals (30 days), whereas the CG continued with their normal daily habits. Blood samples were collected at four time points: 24 h before the start of Ramadan (T0), on the 15th day of Ramadan (T1), the day after the end of Ramadan (T2) and 21 days after Ramadan (T3). There were significant pre-to-post improvements for leptin (p = 0.01, d = 1.52), GLP-1 (p = 0.022, d = 0.75), PYY (p = 0.031, d = 0.69) and CCK (p = 0.027, d = 0.81) in the EG, with no interaction effect for ghrelin (p = 0.74; d = 0.008). No significant changes (p > 0.05) occurred in plasma volume variations (ΔPV) after RIF in both EG (−0.03 ± 0.01%) and CG (0.06 ± 0.07%). RIF represents an effective strategy to modify appetite-regulating hormones, leading to improved body composition indices and reduced obesity.

Appetite and energy intake responses to breakfast consumption and carbohydrate supplementation in hypoxia

PURPOSE

The purpose of experiment one was to determine the appetite, acylated ghrelin and energy intake response to breakfast consumption and omission in hypoxia and normoxia. Experiment two aimed to determine the appetite, acylated ghrelin and energy intake response to carbohydrate supplementation after both breakfast consumption and omission in hypoxia.

METHODS

In experiment one, twelve participants rested and exercised once after breakfast consumption and once after omission in normobaric hypoxia (4300 m: F_iO₂ ~11.7%) and normoxia. In experiment two, eleven participants rested and exercised in normobaric hypoxia (4300 m: F_iO₂ ~11.7%), twice after consuming a high carbohydrate breakfast and twice after breakfast omission. Participants consumed both a carbohydrate (1.2g·min^-1 glucose) and a placebo beverage after breakfast consumption and omission. Measures of appetite perceptions and acylated ghrelin were taken at regular intervals throughout both experiments and an ad-libitum meal was provided post-exercise to quantify energy intake.

RESULTS

Breakfast consumption had no significant effect on post exercise energy intake or acylated ghrelin concentrations, despite reductions in appetite perceptions. As such, breakfast consumption increased total trial energy intake compared with breakfast omission in hypoxia (7136 ± 2047 kJ vs. 5412 ± 1652 kJ; p = 0.02) and normoxia (9276 ± 3058 vs. 6654 ± 2091 kJ; p < 0.01). Carbohydrate supplementation had no effect on appetite perceptions or acylated ghrelin concentrations after breakfast consumption or omission. As such, carbohydrate supplementation increased total energy intake after breakfast consumption (10222 ± 2831 kJ vs. 7695 ± 1970 kJ p < 0.01) and omission (8058 ± 2574 kJ vs. 6174 ± 2222 kJ p = 0.02).

CONCLUSION

Both breakfast consumption and carbohydrate supplementation provide beneficial dietary interventions for increasing energy intake in hypoxic conditions.

Detraining effect on overweight/obese women after high-intensity interval training in hypoxia

PURPOSE

Promising benefits on fat mass and biochemical components may be reported after applying programs of cyclic hypoxia and HIIT.

AIM

To investigate the effect of a month of detraining on cardiometabolic risk markers after active hypoxia exposure.

METHODS

Participants included 59 overweight/obese women, who started a 12-week program of 36 sessions, and were randomly divided into four groups: (a) aerobic interval training in hypoxia (AitH; FiO₂  = 17.2%; n = 13), (b) aerobic interval training in normoxia (AitN; n = 15), (c) sprint interval training in hypoxia (SitH; FiO₂  = 17.2%; n = 15), and (d) sprint interval training in normoxia (SitN; n = 18). Body composition, anthropometric, and biochemical parameters were assessed at baseline (A), after 36 training sessions (B) and after 4 weeks of detraining (C).

RESULTS

Hypoxia conditions showed a significant positive effect on waist circumference (P = 0.01), WHR (P = 0.04), and percentage of trunk fat mass (P < 0.001). The percentage of trunk fat continued to decrease significantly after training cessation in both AitH and SitH groups.

CONCLUSION

After 4 weeks of detraining with a previous 12 weeks of high-intensity interval training under cyclic normobaric hypoxia, the percentage of fat mass located in the trunk decreases significantly and this effect was not observed in the normoxia groups.

Post-Exercise Appetite and Ad Libitum Energy Intake in Response to High-Intensity Interval Training versus Moderate- or Vigorous-Intensity Continuous Training among Physically Inactive Middle-Aged Adults

High-intensity interval training (HIIT) is considered a time-efficient exercise strategy for weight management. However, data regarding the acute appetite and energy intake responses to HIIT versus continuous training remain inconclusive. This study investigated the ad libitum energy intake and appetite responses to a single session of HIIT versus moderate-intensity continuous training (MICT) and vigorous-intensity continuous training (VICT). Using a randomized crossover design, 11 middle-aged physically inactive men (45.7 ± 7.4 years, 23.5 ± 2.1 kg m^-2) participated in three treadmill trials at 7-day intervals. HIIT comprised 10 1-min periods at 100% VO_2max interspersed with 1-min periods of active recovery. MICT comprised a 40-min session at 65% VO_2max, while VICT comprised a 20-min session at 80% VO_2max. After each trial, the participants consumed an ad libitum buffet meal for which the energy intake was recorded. The participants' perceived appetite was assessed before and after exercise sessions using the Visual Analogue Scale (VAS). No significant differences in post-exercise ad libitum energy intake were observed between trials (HIIT: 645 ± 262.9 kcal; MICT: 614.7 ± 271.2 kcal; VICT: 623.1 ± 249.0 kcal, p > 0.05). Although the perceived appetite responses exhibited a significant main effect of time (p < 0.01), no group differences were observed (p > 0.05). In summary, these findings suggest that the interval or continuous nature of exercise has no significant effect on appetite responses in physically inactive middle-aged adults, at least during the short-term post-exercise period.

Is Oxygen Uptake Measurement Enough to Estimate Energy Expenditure During High-Intensity Intermittent Exercise? Quantification of Anaerobic Contribution by Different Methods

Purpose: The aim of the present study was to compare the contributions of the anaerobic pathway as determined by two different methods and energy expenditure during a typical high-intensity intermittent exercise (HIIE) protocol.

Methods: A descriptive research design was utilized in which thirteen physically active men performed six experimental sessions consisting of an incremental test (session 1), submaximal tests at 40, 50, 60, 70, 75, 80, 85, 90% of velocity associated with maximum oxygen uptake (vV˙O_2max) with two intensities per session (sessions 2–5), and the HIIE protocol (session 6; 10 efforts of 1 min at vV˙O_2max interspersed by 1 min of passive recovery). The estimation of anaerobic energy system contribution was calculated by: (a) the excess post-exercise oxygen consumption plus delta lactate method and (b) the accumulated oxygen deficit method using the difference between predicted oxygen demand from the submaximal tests of varying intensities and accumulated oxygen uptake during HIIE. Estimation of aerobic energy system contribution was calculated through the measurement of oxygen consumption during activity. Total EE during the entire HIIE protocol (efforts + recovery) and for the efforts only were calculated from each method.

Results: For efforts + recovery and efforts only, anaerobic contribution was similar for both methods, and consequently total EE was also equivalent (p = 0.230 for both comparisons). During efforts + recovery, aerobic:anaerobic energy system contribution was (68 ± 4%: 32 ± 4%), while efforts only was (54 ± 5%: 46 ± 5%) with both situations demonstrating greater aerobic than anaerobic contribution (p < 0.001 for both).

Conclusion: Anaerobic contribution seems to be relevant during HIIE and must to be taken into account during total EE estimation; however, the type of method employed did not change the anaerobic contribution or total EE estimates.

Exposure and Exercise Training in Hypoxic Conditions as a New Obesity Therapeutic Modality: A Mini Review

Obesity is an important health problem caused by positive energy balance. Generally, low calorie dietary intake combined with regular exercise is the most common modality to lose bodily fat in obese people. Although this is the first modality of choice for obesity treatment, it needs to be applied to obese patients for at least 12 weeks or more and it does not provide consistent results because it is difficult to suppress increased appetite due to exercise. Recently, many researchers have been applying hypoxic conditions for the treatment of obesity, as many studies show that people residing in high altitudes have a lower percentage of body fat and fewer obesity-related illnesses than people living at sea level. Hypoxic therapy treatment, including hypoxic exposure or hypoxic exercise training, is recommended as a way to treat and prevent obesity by suppression of appetite, increasing basal metabolic rate and fat oxidation, and minimizing side effects. Hypoxic therapy inhibits energy intake and appetite-related hormones, and enhances various cardiovascular and metabolic function parameters. These observations indicate that hypoxic therapy is a new treatment modality for inducing fat reduction and promoting metabolic and cardiovascular health, which may be an important and necessary strategy for the treatment of obesity. As such, hypoxic therapy is now used as a general medical practice for obesity treatment in many developed countries. Therefore, hypoxic therapy could be a new, practical, and useful therapeutic modality for obesity and obesity-related comorbidities.

Appetite, food intake and gut hormone responses to intense aerobic exercise of different duration

The purpose of the study is to investigate the effect of acute bouts of high-intensity aerobic exercise of differing durations on subjective appetite, food intake and appetite-associated hormones in endurance-trained males. Twelve endurance-trained males (age = 21 ± 2 years; BMI = 21.0 ± 1.6 kg/m²; VO_2max = 61.6 ± 6.0 mL/kg/min) completed four trials, within a maximum 28 day period, in a counterbalanced order: resting (REST); 15 min exercise bout (15-min); 30 min exercise bout (30-min) and 45 min exercise bout (45-min). All exercise was completed on a cycle ergometer at an intensity of ~76% VO_2max Sixty minutes post exercise, participants consumed an ad libitum meal. Measures of subjective appetite and blood samples were obtained throughout the morning, with plasma analyzed for acylated ghrelin, total polypeptide tyrosine-tyrosine (PYY) and total glucagon-like peptide 1 (GLP-1) concentrations. The following results were obtained: Neither subjective appetite nor absolute food intake differed between trials. Relative energy intake (intake - expenditure) was significantly greater after REST (2641 ± 1616 kJ) compared with both 30-min (1039 ± 1520 kJ) and 45-min (260 ± 1731 kJ), and significantly greater after 15-min (2699 ± 1239 kJ) compared with 45-min (condition main effect, P < 0.001). GLP-1 concentration increased immediately post exercise in 30-min and 45-min, respectively (condition × time interaction, P < 0.001). Acylated ghrelin was transiently suppressed in all exercise trials (condition × time interaction, P = 0.011); the greatest, most enduring suppression, was observed in 45-min. PYY concentration was unchanged with exercise. In conclusion, high-intensity aerobic cycling lasting up to 45 min did not suppress subjective appetite or affect absolute food intake, but did reduce relative energy intake, in well-trained endurance athletes. Findings question the role of appetite hormones in regulating subjective appetite in the acute post-exercise period.

A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity

Interval training (including high-intensity interval training [HIIT] and sprint interval training [SIT]) is promoted in both scientific and lay media as being a superior and time-efficient method for fat loss compared with traditional moderate-intensity continuous training (MICT). We evaluated the efficacy of HIIT/SIT when directly compared with MICT for the modulation of body adiposity. Databases were searched to 31 August 2016 for studies with exercise training interventions with minimum 4-week duration. Meta-analyses were conducted for within-group and between-group comparisons for total body fat percentage (%) and fat mass (kg). To investigate heterogeneity, we conducted sensitivity and meta-regression analyses. Of the 6,074 studies netted, 31 were included. Within-group analyses demonstrated reductions in total body fat (%) (HIIT/SIT: -1.26 [95% CI: -1.80; -0.72] and MICT: -1.48 [95% CI: -1.89; -1.06]) and fat mass (kg) (HIIT/SIT: -1.38 [95% CI: -1.99; -0.77] and MICT: -0.91 [95% CI: -1.45; -0.37]). There were no differences between HIIT/SIT and MICT for any body fat outcome. Analyses comparing MICT with HIIT/SIT protocols of lower time commitment and/or energy expenditure tended to favour MICT for total body fat reduction (p = 0.09). HIIT/SIT appears to provide similar benefits to MICT for body fat reduction, although not necessarily in a more time-efficient manner. However, neither short-term HIIT/SIT nor MICT produced clinically meaningful reductions in body fat.

Changes in appetite, energy intake, body composition, and circulating ghrelin constituents during an incremental trekking ascent to high altitude

Purpose

Circulating acylated ghrelin concentrations are associated with altitude-induced anorexia in laboratory environments, but have never been measured at terrestrial altitude. This study examined time course changes in appetite, energy intake, body composition, and ghrelin constituents during a high-altitude trek.

Methods

Twelve participants [age: 28(4) years, BMI 23.0(2.1) kg m⁻²] completed a 14-day trek in the Himalayas. Energy intake, appetite perceptions, body composition, and circulating acylated, des-acylated, and total ghrelin concentrations were assessed at baseline (113 m, 12 days prior to departure) and at three fixed research camps during the trek (3619 m, day 7; 4600 m, day 10; 5140 m, day 12).

Results

Relative to baseline, energy intake was lower at 3619 m (P = 0.038) and 5140 m (P = 0.016) and tended to be lower at 4600 m (P = 0.056). Appetite perceptions were lower at 5140 m (P = 0.027) compared with baseline. Acylated ghrelin concentrations were lower at 3619 m (P = 0.046) and 4600 m (P = 0.038), and tended to be lower at 5140 m (P = 0.070), compared with baseline. Des-acylated ghrelin concentrations did not significantly change during the trek (P = 0.177). Total ghrelin concentrations decreased from baseline to 4600 m (P = 0.045). Skinfold thickness was lower at all points during the trek compared with baseline (P ≤ 0.001) and calf girth decreased incrementally during the trek (P = 0.010).

Conclusions

Changes in plasma acylated and total ghrelin concentrations may contribute to the suppression of appetite and energy intake at altitude, but differences in the time course of these responses suggest that additional factors are also involved. Interventions are required to maintain appetite and energy balance during trekking at terrestrial altitudes.

Hypoxia-Related Hormonal Appetite Modulation in Humans during Rest and Exercise: Mini Review

Obesity is associated with numerous chronic ailments and represents one of the major health and economic issues in the modernized societies. Accordingly, there is an obvious need for novel treatment approaches. Recently, based on the reports of reduced appetite and subsequent weight loss following high-altitude sojourns, exposure to hypoxia has been proposed as a viable weight-reduction strategy. While altitude-related appetite modulation is complex and not entirely clear, hypoxia-induced alterations in hormonal appetite modulation might be among the key underlying mechanisms. The present paper summarizes the up-to-date research on hypoxia/altitude-induced changes in the gut and adipose tissue derived peptides related to appetite regulation. Orexigenic hormone ghrelin and anorexigenic peptides leptin, glucagon-like peptide-1, peptide YY, and cholecystokinin have to-date been investigated as potential modulators of hypoxia-driven appetite alterations. Current evidence suggests that hypoxia can, especially acutely, lead to decreased appetite, most probably via reduction of acylated ghrelin concentration. Hypoxia-related short and long-term changes in other hormonal markers are more unclear although hypoxia seems to importantly modulate leptin levels, especially following prolonged hypoxic exposures. Limited evidence also suggests that different activity levels during exposures to hypoxia do not additively affect hormonal appetite markers. Although very few studies have been performed in obese/overweight individuals, the available data indicate that hypoxia/altitude exposures do not seem to differentially affect appetite regulation via hormonal pathways in this cohort. Given the lack of experimental data, future well-controlled acute and prolonged studies are warranted to expand our understanding of hypoxia-induced hormonal appetite modulation and its kinetics in health and disease.

Does hypoxia play a role in the development of sarcopenia in humans? Mechanistic insights from the Caudwell Xtreme Everest Expedition

Objectives

Sarcopenia refers to the involuntary loss of skeletal muscle and is a predictor of physical disability/mortality. Its pathogenesis is poorly understood, although roles for altered hypoxic signaling, oxidative stress, adipokines and inflammatory mediators have been suggested. Sarcopenia also occurs upon exposure to the hypoxia of high altitude. Using data from the Caudwell Xtreme Everest expedition we therefore sought to analyze the extent of hypoxia-induced body composition changes and identify putative pathways associated with fat-free mass (FFM) and fat mass (FM) loss.

Methods

After baseline testing in London (75 m), 24 investigators ascended from Kathmandu (1300 m) to Everest base camp (EBC 5300 m) over 13 days. Fourteen investigators climbed above EBC, eight of whom reached the summit (8848 m). Assessments were conducted at baseline, during ascent and after one, six and eight week(s) of arrival at EBC. Changes in body composition (FM, FFM, total body water, intra- and extra-cellular water) were measured by bioelectrical impedance. Biomarkers of nitric oxide and oxidative stress were measured together with adipokines, inflammatory, metabolic and vascular markers.

Results

Participants lost a substantial, but variable, amount of body weight (7.3±4.9 kg by expedition end; p<0.001). A progressive loss of both FM and FFM was observed, and after eight weeks, the proportion of FFM loss was 48% greater than FM loss (p<0.008). Changes in protein carbonyls (p<0.001) were associated with a decline in FM whereas 4-hydroxynonenal (p<0.001) and IL-6 (p<0.001) correlated with FFM loss. GLP-1 (r=−0.45, p<0.001) and nitrite (r=−0.29, p<0.001) concentration changes were associated with FFM loss. In a multivariate model, GLP-1, insulin and nitrite were significant predictors of FFM loss while protein carbonyls were predicted FM loss.

Conclusions

The putative role of GLP-1 and nitrite as mediators of the effects of hypoxia on FFM is an intriguing finding. If confirmed, nutritional and pharmacological interventions targeting these pathways may offer new avenues for prevention and treatment of sarcopenia.

Very Low Volume Sprint Interval Exercise Suppresses Subjective Appetite, Lowers Acylated Ghrelin, and Elevates GLP-1 in Overweight Individuals: A Pilot Study

High-intensity exercise has been shown to elicit a transient suppression of appetite and create a more anorexigenic profile of appetite-associated hormones. It is yet to be fully elucidated whether such a response is observed following very low-volume, intermittent exercise at supramaximal intensity in those who are overweight. Eight overweight individuals (BMI 27.7 ± 1.7 kg·m²) completed resting (REST) and exercise (EX) trials in a counterbalanced order. EX consisted of 4 × 30 s “flat-out” cycling on an ergometer (adapted Wingate test). Two hours post-exercise (or REST), participants were presented with an ad libitum meal. Subjective appetite measures and blood samples were obtained throughout. Subjective appetite, measured using VAS, was significantly lower immediately after exercise compared with REST (38.0 ± 28.5 mm vs. 75.1 ± 26.2 mm, p = 0.018, d = 1.09). This difference remained significant 30 min post-exercise. Acylated ghrelin concentration was suppressed in EX compared with REST immediately post-exercise (113.4 ± 43.0 pg·mL⁻¹ vs. 189.2 ± 91.8 pg·mL⁻¹, p = 0.03, d = 1.07) and remained lower until the ad libitum test-meal. Area-under-the-curve for GLP-1 concentration was significantly greater for EX, versus REST. There was no difference in absolute adlibitum intake or relative energy intake. As little as 4 × 30 s of “flat-out” cycling was sufficient to elicit a transient suppression of appetite and an enduring suppression of plasma acylated ghrelin. Nonetheless, food intake 2-h post-exercise was unaffected.

The effect of moderate versus severe simulated altitude on appetite, gut hormones, energy intake and substrate oxidation in men

Acute exposure to high altitude (>3500 m) is associated with marked changes in appetite regulation and substrate oxidation but the effects of lower altitudes are unclear. This study examined appetite, gut hormone, energy intake and substrate oxidation responses to breakfast ingestion and exercise at simulated moderate and severe altitudes compared with sea-level. Twelve healthy males (mean ± SD; age 30 ± 9years, body mass index 24.4 ± 2.7 kg·m^-2) completed in a randomised crossover order three, 305 min experimental trials at a simulated altitude of 0 m, 2150 m (∼15.8% O₂) and 4300 m (∼11.7% O₂) in a normobaric chamber. Participants entered the chamber at 8am following a 12 h fast. A standardised breakfast was consumed inside the chamber at 1 h. One hour after breakfast, participants performed a 60 min treadmill walk at 50% of relative V˙O_2max. An ad-libitum buffet meal was consumed 1.5 h after exercise. Blood samples were collected prior to altitude exposure and at 60, 135, 195, 240 and 285 min. No trial based differences were observed in any appetite related measure before exercise. Post-exercise area under the curve values for acylated ghrelin, pancreatic polypeptide and composite appetite score were lower (all P < 0.05) at 4300 m compared with sea-level and 2150 m. There were no differences in glucagon-like peptide-1 between conditions (P = 0.895). Mean energy intake was lower at 4300 m (3728 ± 3179 kJ) compared with sea-level (7358 ± 1789 kJ; P = 0.007) and 2150 m (7390 ± 1226 kJ; P = 0.004). Proportional reliance on carbohydrate as a fuel was higher (P = 0.01) before breakfast but lower during (P = 0.02) and after exercise (P = 0.01) at 4300 m compared with sea-level. This study suggests that altitude-induced anorexia and a subsequent reduction in energy intake occurs after exercise during exposure to severe but not moderate simulated altitude. Acylated ghrelin concentrations may contribute to this effect.

Effects of prolonged hypoxia and bed rest on appetite and appetite-related hormones

Environmental hypoxia and inactivity have both been shown to modulate appetite. To elucidate the independent and combined effects of hypoxia and bed rest-induced inactivity on appetite-related hormones and subjective appetite, eleven healthy, non-obese males underwent three experimental interventions in a cross-over and randomized fashion: 1) Hypoxic confinement combined with daily moderate-intensity exercise (HAMB, F_iO₂ = 0.141 ± 0.004; P_iO₂ = 90.0 ± 0.4 mmHg) 2) Bed rest in normoxia (NBR, F_iO₂ = 0.209; P_iO₂ = 133.1 ± 0.3 mmHg) and 3) Bed rest in hypoxia (HBR, F_iO₂ = 0.141 ± 0.004; P_iO₂ = 90.0 ± 0.4 mmHg). A mixed-meal tolerance test (MTT), followed by an ad libitum meal were performed before (Pre) and after 16-days (Post) of each intervention. Composite satiety scores (CSS) during the MTT were calculated from visual analogue scores, while fasting and postprandial concentrations of total ghrelin, peptide YY (PYY), glucagon-like peptide-1 (GLP-1) and leptin were quantified from arterialized-venous samples. Postprandial CSS were significantly lower at Post compared to Pre in NBR only (P < 0.05) with no differences observed in ad libitum meal intakes. Postprandial concentrations and incremental area under the curve (AUC) for total ghrelin and PYY were unchanged following all interventions. Postprandial GLP-1 concentrations were only reduced at Post following HBR (P < 0.05) with resulting AUC changes being significantly lower compared to HAMB (P < 0.01). Fasting leptin was reduced following HAMB (P < 0.05) with no changes observed following NBR and HBR. These findings suggest that independently, 16-day of simulated altitude exposure (∼4000 m) and bed rest-induced inactivity do not significantly alter subjective appetite or ad libitum intakes. The measured appetite-related hormones following both HAMB and HBR point to a situation of hypoxia-induced appetite stimulation, although this did not reflect in higher ad libitum intakes.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02293772.

Breaking up prolonged sitting time with walking does not affect appetite or gut hormone concentrations but does induce an energy deficit and suppresses postprandial glycaemia in sedentary adults

Breaking up periods of prolonged sitting can negate harmful metabolic effects but the influence on appetite and gut hormones is not understood and is investigated in this study. Thirteen sedentary (7 female) participants undertook three 5-h trials in random order: (i) uninterrupted sitting (SIT), (ii) seated with 2-min bouts of light-intensity walking every 20 min (SIT + LA), and (iii) seated with 2-min bouts of moderate-intensity walking every 20 min (SIT + MA). A standardised test drink was provided at the start of each trial and an ad libitum pasta test meal provided at the end of each trial. Subjective appetite ratings and plasma acylated ghrelin, peptide YY, insulin, and glucose were measured at regular intervals. Area under the curve (AUC) was calculated for each variable. AUC values for appetite and gut hormone concentrations were unaffected in the activity breaks conditions compared with uninterrupted sitting (linear mixed modelling: p > 0.05). Glucose AUC was lower in SIT + MA than in SIT + LA (p = 0.004) and SIT (p = 0.055). There was no difference in absolute ad libitum energy intake between conditions (p > 0.05); however, relative energy intake was lower in SIT + LA (39%; p = 0.011) and SIT + MA (120%; p < 0.001) than in SIT. In conclusion, breaking up prolonged sitting does not alter appetite and gut hormone responses to a meal over a 5-h period. Increased energy expenditure from activity breaks could promote an energy deficit that is not compensated for in a subsequent meal.

Ghrelin, GLP-1, and leptin responses during exposure to moderate hypoxia

Severe hypoxia has been indicated to cause acute changes in appetite-related hormones, which attenuate perceived appetite. However, the effects of moderate hypoxia on appetite-related hormonal regulation and perceived appetite have not been elucidated. Therefore, we examined the effects of moderate hypoxia on appetite-related hormonal regulation and perceived appetite. Eight healthy males (21.0 ± 0.6 years; 173 ± 2.3 cm; 70.6 ± 5.0 kg; 23.4 ± 1.1 kg/m(2)) completed two experimental trials on separate days: a rest trial in normoxia (FiO2 = 20.9%) and a rest trial in hypoxia (FiO2 = 15.0%). The experimental trials were performed over 7 h in an environmental chamber. Blood samples and scores of subjective appetite were collected over 7 h. Standard meals were provided 1 h (745 kcal) and 4 h (731 kcal) after initiating exposure to hypoxia or normoxia within the chamber. Although each meal significantly reduced plasma active ghrelin concentrations (P < 0.05), the response did not differ significantly between the trials over 7 h. No significant differences in the area under the curves for plasma active ghrelin concentrations over 7 h were observed between the two trials. No significant differences were observed in glucagon-like peptide 1 or leptin concentrations over 7 h between the trials. The subjective feeling of hunger and fullness acutely changed in response to meal ingestions. However, these responses were not affected by exposure to moderate hypoxia. In conclusion, 7 h of exposure to moderate hypoxia did not change appetite-related hormonal responses or perceived appetite in healthy males.

Hypoxic Conditioning as a New Therapeutic Modality

Preconditioning refers to a procedure by which a single noxious stimulus below the threshold of damage is applied to the tissue in order to increase resistance to the same or even different noxious stimuli given above the threshold of damage. Hypoxic preconditioning relies on complex and active defenses that organisms have developed to counter the adverse consequences of oxygen deprivation. The protection it confers against ischemic attack for instance as well as the underlying biological mechanisms have been extensively investigated in animal models. Based on these data, hypoxic conditioning (consisting in recurrent exposure to hypoxia) has been suggested a potential non-pharmacological therapeutic intervention to enhance some physiological functions in individuals in whom acute or chronic pathological events are anticipated or existing. In addition to healthy subjects, some benefits have been reported in patients with cardiovascular and pulmonary diseases as well as in overweight and obese individuals. Hypoxic conditioning consisting in sessions of intermittent exposure to moderate hypoxia repeated over several weeks may induce hematological, vascular, metabolic, and neurological effects. This review addresses the existing evidence regarding the use of hypoxic conditioning as a potential therapeutic modality, and emphasizes on many remaining issues to clarify and future researches to be performed in the field.