About this Research Topic
Obesity represents a principal health and economic burden for the modernized societies. 50-100% increase in all cause-mortality is observed when body mass index is above 30 kg.m-2. Considering the morbidity as well as social and economical burdens related to the escalating obesity prevalence, effective prevention strategies are clearly required. Current strategies, tackling obesity include dietary, pharmacological, surgical and activity/exercise interventions. Recently, exposures to altitude/hypoxia have been suggested to provide an alternative strategy.
In particular, anecdotal and scientific observations of weight loss and appetite reduction at high altitudes led to the suggestion that incorporating hypoxic/altitude exposures might be beneficial for weight management programmes. The aetiology, as well as the underlying mechanisms, of the so called “altitude anorexia” phenomenon currently remains unresolved. Altitude-related anorexia has been attributed to hypoxia-induced appetite reduction, resulting from increases of appetite-reducing and satiety signalling peptides (i.e. leptin and cholecystokinin) on the one hand and reductions of the hunger-stimulating agents (i.e. ghrelin) on the other. In addition both, hypoxia-related increase in energy expenditure as well as shifts in the structure and function of the gut microbiome have been suggested to play an important role. It is of note, however that the degree and the duration of hypoxia significantly modulates metabolic and other physiological systems adaptation.
Given that physical activity is one of the cornerstones of effective weight loss programs, the addition of exercise to hypoxic exposure might offer a novel approach for treating obesity and related comorbidities. Indeed, recent evidence suggests that combining altitude exposure and physical exercise might provide a cost effective strategy for reducing body weight and improving metabolic health. However, very few studies to date have scrutinized the combined effects of both factors in both normal-weight and obese individuals. Studies investigating the effects of intermittent hypoxic exposures in combination with exercise have demonstrated greater weight loss compared to the same training in normoxia. Moreover exercising in hypoxia has been shown to increase the activity of glycolytic enzymes, enhance mitochondria density and glucose transporter GLUT-4 levels as well as improve insulin sensitivity. It is important to note, that under hypoxic conditions the mechanical load can be significantly reduced to achieve the same metabolic effect (i.e. same relative load). This is especially important in the light of decreased risk of orthopaedic injuries with lower mechanical load and potential higher adherence to exercise training as a consequence of reduced perceived-exertion. Regardless of the above, while combining exercise with hypoxic exposure might result in negative energy balance and thereby reduce weight and improve metabolic fitness the scientific data is lacking.
Accordingly, this Research Topic aims to provide a platform for original research and review contributions that further elucidate the effects of hypoxia and combined hypoxia and exercise in overweight and obese individuals. We welcome contributions that will shed more light on the following research questions:
• Does altitude (hypoxic) anorexia exist in both normal weight and obese individuals?
• What are the safe limits of altitude exposure of obese individuals?
• Does hypoxia and/or exercise induce any detrimental physiological effects in obese individuals?
• What are the key mechanisms that underlie altitude related anorexia and what are the threshold altitude levels in both normal weight and obese individuals?
• What strategies combining hypoxia and exercise would be optimal for treating obesity and related comorbidities?
• How does hypoxia and exercise interact with diets incorporating different macronutrient composition?
• Do exposures to hypobaric (terrestrial) or normobaric (simulated) altitudes provoke clinically relevant differences in obese cohort?
The studies scrutinising the effects of hypoxia or hypoxic exercise on the key modulators of obesity related clinical conditions such as metabolism, gut microbiome, sleep architecture and oxidative stress, are also welcome.
Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.