Sex differences and shifts in body composition, physical activity, and total energy expenditure across a 3-month expedition.

OBJECTIVES: An energetically demanding environment like a wilderness expedition can lead to potent stressors on human physiology and homeostatic balance causing shifts in energy expenditure and body composition. These shifts likely have consequences on overall health and performance and may potentially differ by sex. It is therefore critical to understand the potential differential body composition and energy expenditure changes in response to a novel and challenging environment in both males and female bodies. METHODS: Data were collected from 75 healthy individuals (female = 41; ages 18-53) throughout a 3-month long expedition in the American Rockies. Body mass, body fat, and lean muscle mass were measured before, during, and after the course. Physical activity intensity and energy expenditure were also measured in a subset of participants using the wGT3X-BT Actigraph wrist monitor and an accompanying Bluetooth heart rate monitor. RESULTS: Over the 3-month period, individuals initially experienced declines in body mass, body fat percentage, and lean muscle mass. Participants partially rebounded from these deficits to maintain overall body mass with a slight recomposition of body fat and lean muscle mass. Our data also demonstrated that sex moderated total energy expenditure, where females experienced a modest decline whereas males experienced an increase in energy expenditure from the beginning to the end of the course. CONCLUSIONS: Understanding changes in energy storage in the body and variation in energy expenditure between sexes during a 3-month expedition has critical implications for maintaining health and performance in an energetically demanding environment where resources may be scarce.

Feasibility of using infrared thermal imaging to examine brown adipose tissue in infants aged 18 to 25 months.

BACKGROUND: Recent studies in adults indicate that cold-induced temperature change of supraclavicular skin corresponds with brown adipose tissue (BAT) thermogenesis. AIM: This study examined the feasibility of using thermography to assess temperature changes in infants aged 18-25 months after mild cooling. Further, this study sought to evaluate whether cold exposure induces a thermal response suggestive of BAT activity underlying the supraclavicular region. SUBJECTS AND METHODS: Changes in maximum skin temperature at the supraclavicular and interscapular regions were determined using thermal imaging following a mild 5-minute cooling condition (by removal of clothes in a climate-controlled room) in 67 Samoan infants. Temperature changes of the forehead and hand, known BAT-free regions, served as indicators of cooling efficacy. RESULTS: Infants with increased hand and forehead temperatures after cold exposure were excluded from analysis, reducing the effective sample size to 19 infants. On average, forehead (p < 0.001), hand (p < 0.001) and back (0.029) temperatures dropped significantly while supraclavicular temperatures remained constant. Participants with greater decreases in forehead temperature tended to exhibit greater supraclavicular thermogenesis (p = 0.084), suggesting potential BAT activity in this region. CONCLUSIONS: While further work is necessary to develop a reliable cooling condition, this study provides proof-of-concept for non-invasive assessment of BAT activity in infants.

Body fat attenuates muscle mass catabolism among physically active humans in temperate and cold high altitude environments.

OBJECTIVE: Typical diet plans are based on an individual's body mass; however, body composition may be important to consider when an individual is in a negative energy balance. This study examines if high initial body fat and dietary macronutrient content reduce muscle mass catabolism during excursions in temperate and cold high altitude environments. METHODS: Subjects-53 healthy, un-acclimated volunteers (37 males and 16 females)-took part in 12-16 week-long outdoor education courses in moderately high altitude temperate and cold climates in the western United States. Body mass, body fat percentage, fat mass, and muscle mass were measured before and after each excursion. Total energy expenditure and dietary intake were also measured. RESULTS: In temperate and cold environments, both sexes lost significant amounts of body mass. In temperate climates both sexes lost a significant amount of fat mass, but not muscle mass. In cold climates, there was no significant change in fat mass for either sex; however, females gained muscle mass while males lost muscle mass. In both climates subjects with lower initial body fat percentages lost significantly more muscle mass than subjects with higher initial body fat percentages. There was no significant relationship between macronutrient intake and muscle mass loss for either sex. CONCLUSION: These results suggests that during a negative energy balance dietary macronutrient content cannot abate the loss of muscle mass, but body fat may have a protective effect. This information should be used to improve individualized diets based on body composition, not body mass.