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

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.

Organ-specific fuel rewiring in acute and chronic hypoxia redistributes glucose and fatty acid metabolism

Oxygen deprivation can be detrimental. However, chronic hypoxia is also associated with decreased incidence of metabolic syndrome and cardiovascular disease in high-altitude populations. Previously, hypoxic fuel rewiring has primarily been studied in immortalized cells. Here, we describe how systemic hypoxia rewires fuel metabolism to optimize whole-body adaptation. Acclimatization to hypoxia coincided with dramatically lower blood glucose and adiposity. Using in vivo fuel uptake and flux measurements, we found that organs partitioned fuels differently during hypoxia adaption. Acutely, most organs increased glucose uptake and suppressed aerobic glucose oxidation, consistent with previous in vitro investigations. In contrast, brown adipose tissue and skeletal muscle became "glucose savers," suppressing glucose uptake by 3-5-fold. Interestingly, chronic hypoxia produced distinct patterns: the heart relied increasingly on glucose oxidation, and unexpectedly, the brain, kidney, and liver increased fatty acid uptake and oxidation. Hypoxia-induced metabolic plasticity carries therapeutic implications for chronic metabolic diseases and acute hypoxic injuries.

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.

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.

Effect of ghrelin on hypoxia-related cardiac angiogenesis: involvement of miR-210 signalling pathway

OBJECTIVE

Hypoxia is the main stimulus for angiogenesis. Hypoxia-inducible factor (HIF)-1α, vascular endothelial growth factor (VEGF), and miR-210 are involved in the hypoxia-induced angiogenesis. This study examined the effects of hypoxia and/or ghrelin on miR-210, HIF-1α, and VEGF levels in the heart of rats.

METHODS

Wistar rats were randomly divided into 4 groups (n = 6): control; ghrelin, received daily intraperitoneal injections of ghrelin; hypoxia, was exposed to hypoxic condition; hypoxia + ghrelin, was exposed to hypoxic condition and received intraperitoneal injections of ghrelin, for 2 weeks. Myocardial angiogenesis, the expression level of miR-210, and protein levels of HIF-1α and VEGF were assayed in the heart samples.

RESULTS

Hypoxia increased myocardial angiogenesis and cardiac levels of miR-210, HIF-1α, and VEGF. However, ghrelin inhibited these hypoxia-induced changes. Interestingly, ghrelin had no significant effect on miR-210, HIF-1α, and VEGF levels in normoxic condition.

CONCLUSION

Ghrelin may be useful as an anti-angiogenic factor.

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.

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.

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.

Additive Effects of Intermittent Hypobaric Hypoxia and Endurance Training on Bodyweight, Food Intake, and Oxygen Consumption in Rats

Cabrera-Aguilera, Ignacio, David Rizo-Roca, Elisa A. Marques, Garoa Santocildes, Teresa Pagès, Gines Viscor, António A. Ascensão, José Magalhães, and Joan Ramon Torrella. Additive effects of intermittent hypobaric hypoxia and endurance training on bodyweight, food intake, and oxygen consumption in rats. High Alt Med Biol. 19:278-285, 2018.-We used an animal model to elucidate the effects of an intermittent hypobaric hypoxia (IHH) and endurance exercise training (EET) protocol on bodyweight (BW), food and water intake, and oxygen consumption. Twenty-eight young adult male rats were divided into four groups: normoxic sedentary (NS), normoxic exercised (NE), hypoxic sedentary (HS), and hypoxic exercised (HE). Normoxic groups were maintained at an atmospheric pressure equivalent to sea level, whereas the IHH protocol consisted of 5 hours per day for 33 days at a simulated altitude of 6000 m. Exercised groups ran in normobaric conditions on a treadmill for 1 hour/day for 5 weeks at a speed of 25 m/min. At the end of the protocol, both hypoxic groups showed significant decreases in BW from the ninth day of exposure, reaching final 10% (HS) to 14.5% (HE) differences when compared with NS. NE rats also showed a significant weight reduction after the 19th day, with a decrease of 7.4%. The BW of hypoxic animals was related to significant hypophagia elicited by IHH exposure (from 8% to 12%). In contrast, EET had no effect on food ingestion. Total water intake was not affected by hypoxia but was significantly increased by exercise. An analysis of oxygen consumption at rest (mL O₂/[kg·min]) revealed two findings: a significant decrease in both hypoxic groups after the protocol (HS, 21.7 ± 0.70 vs. 19.1 ± 0.78 and HE, 22.8 ± 0.80 vs. 17.1 ± 0.90) and a significant difference at the end of the protocol between NE (21.3 ± 0.77) and HE (17.1 ± 0.90). These results demonstrate that IHH and EET had an additive effect on BW loss, providing evidence that rats underwent a metabolic adaptation through a reduction in oxygen consumption measured under normoxic conditions. These data suggest that the combination of IHH and EET could serve as an alternative treatment for the management of overweight and obesity.

Appetite Suppression and Altered Food Preferences Coincide with Changes in Appetite-Mediating Hormones During Energy Deficit at High Altitude, But Are Not Affected by Protein Intake

Karl, J. Philip, Renee E. Cole, Claire E. Berryman, Graham Finlayson, Patrick N. Radcliffe, Matthew T. Kominsky, Nancy E. Murphy, John W. Carbone, Jennifer C. Rood, Andrew J. Young, and Stefan M. Pasiakos. Appetite suppression and altered food preferences coincide with changes in appetite-mediating hormones during energy deficit at high altitude, but are not affected by protein intake. High Alt Med Biol. 19:156-169, 2018.-Anorexia and unintentional body weight loss are common during high altitude (HA) sojourn, but underlying mechanisms are not fully characterized, and the impact of dietary macronutrient composition on appetite regulation at HA is unknown. This study aimed to determine the effects of a hypocaloric higher protein diet on perceived appetite and food preferences during HA sojourn and to examine longitudinal changes in perceived appetite, appetite mediating hormones, and food preferences during acclimatization and weight loss at HA. Following a 21-day level (SL) period, 17 unacclimatized males ascended to and resided at HA (4300 m) for 22 days. At HA, participants were randomized to consume measured standard-protein (1.0 g protein/kg/d) or higher protein (2.0 g/kg/d) hypocaloric diets (45% carbohydrate, 30% energy restriction) and engaged in prescribed physical activity to induce an estimated 40% energy deficit. Appetite, food preferences, and appetite-mediating hormones were measured at SL and at the beginning and end of HA. Diet composition had no effect on any outcome. Relative to SL, appetite was lower during acute HA (days 0 and 1), but not different after acclimatization and weight loss (HA day 18), and food preferences indicated an increased preference for sweet- and low-protein foods during acute HA, but for high-fat foods after acclimatization and weight loss. Insulin, leptin, and cholecystokinin concentrations were elevated during acute HA, but not after acclimatization and weight loss, whereas acylated ghrelin concentrations were suppressed throughout HA. Findings suggest that appetite suppression and altered food preferences coincide with changes in appetite-mediating hormones during energy deficit at HA. Although dietary protein intake did not impact appetite, the possible incongruence with food preferences at HA warrants consideration when developing nutritional strategies for HA sojourn.

"Living High-Training Low" improved weight loss and glucagon-like peptide-1 level in a 4-week weight loss program in adolescents with obesity: A pilot study

BACKGROUND

"Living High-Training Low" (LHTL) is effective for the improvement of athletic ability; however, little is known about the effect of LHTL on obese individuals. The present study determined whether LHTL would have favorable influence on body composition, rebalance the appetite hormones, and explore the underlying mechanism.

METHODS

Adolescents with obesity [body mass index (BMI) >30 kg/m] were randomly assigned to "Living Low-Training Low" (LLTL, n = 19) group that slept in a normobaric normoxia condition and the LHTL (n = 16) group slept in a normobaric hypoxia room (14.7% PO2 ∼2700 m). Both groups underwent the same aerobic exercise training program. Morphological, blood lipids, and appetite hormones were measured and assessed.

RESULTS

After the intervention, the body composition improved in both groups, whereas reductions in body weight (BW), BMI, and lean body mass increased significantly in the LHTL group (all, P < .05). In the LLTL group, cholecystokinin (CCK) decreased remarkably (P < .05) and CCK changes were positively associated with changes in BW (r = 0.585, P = .011) and BMI (r = 0.587, P = .010). However, in the LHTL group, changes in plasma glucagon-like peptide-1 (GLP-1) and interleukin-6 (IL-6) levels, positively correlated with each other (r = 0.708, P = .015) but negatively with BW changes (r = -0.608, P = .027 and r = -0.518, P = .048, respectively).

CONCLUSION

The results indicated that LHTL could induce more weight loss safely and efficiently as compared to LLTL and increase the plasma GLP-1 levels that may be mediated by IL-6 to rebalance the appetite. Thus, an efficient method to treat obesity and prevent weight regain by appetite rebalance in hypoxia condition was established.

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.

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.