Abstract
Background:
Positive energy balance within individuals that is sustained for extended periods has lead to epidemic rates of obesity occurred around the world. The accurate measurement of both Energy Expenditure (EE) and Energy Intake (EI) which comprise the energy balance equation are critical tools for any obesity intervention or prevention programme development. Environmental conditions, particularly ambient temperature, may be able to influence energy balance through modulation of EE or EI. The development of an environmental simulation suite and accompanying physiological laboratory provided an opportunity to craft a combined research facility able to address these areas of interest.
Objectives:
The overall aim of this these was to assess whether modification of ambient temperature could be used as an interventional tool to influence energy balance in a New Zealand (NZ) context. However, both newly purchased technology and physiological responses to temperature changes required validation before interventions could be developed.
Firstly, I had to validate the reliability and precision of a newly acquired Dual Energy X-ray Absorptiometry (DXA) scanner in healthy and overweight populations.
Secondly, I needed to build and test an environmental simulation suite before I could examine the presence of a Thermoneutral Zone (TNZ) that has been reported in previous work with select populations, and whether this applied to the NZ population. This was critical because large variability has been observed in other populations.
Thirdly, the impact of ambient temperature modulation on EI needed to be considered in the context of ambient temperatures that are also shown to alter EE.
Results:
High levels of precision were demonstrated during repeat DXA scanning protocols. This precision was somewhat reduced for those with higher Body Mass Index (BMI) but still well within acceptable margins of error for scientific and clinical research needs. In an experiment within the environmental suite, exposure to cooler temperatures increased EE as others have reported. Furthermore, this study identified temperature ranges where EE had increased but participants still reported to be thermally comfortable. No increase in EE was observed at warmer temperatures though distinct sex differences were seen for both EE and comfort levels. In my final experiment, EI was not significantly affected by either warm or cool temperatures despite increases in EE during cold exposure.
Conclusion:
The findings of this thesis support the hypothesis that under controlled experimental conditions, modification of ambient temperature within a comfort range does result in changes in EE without compensatory increases in EI. This then supports further investigation or interventions being developed to use cold ambient temperature exposure as a possible intervention for obesity. It also lays the groundwork and confidence that this type of research could be conducted in a NZ context using cutting edge technology.