Nonshivering thermogenesis: responses to acute cold exposure in obese males

The studies in this thesis were to assess whether obese relative to non-obese individuals have blunted metabolic and non-shivering thermogenic responses in acute mild cold exposure, possibly established by a higher capacity to activate brown adipose tissue in the non-obese, resulting in greater energy expenditure. It was hypothesised that the obese would demonstrate a reduced non-shivering thermogenesis during acute mild cold exposure despite having lower skin temperatures and the same core temperature. The first study resulted in obese individuals having lower mean rate of oxygen consumption (p < 0.05), lower mean skin temperatures (p < 0.05), and lower mean heat flux (p < 0.05) during a 19°C exposure. There was no difference, however, in carbohydrate (p = 0.14) or lipid (p = 0.46) oxidation rates. The second study resulted in obese having lower mean supraclavicular skin temperatures (p < 0.001), lower mean supraclavicular heat flux (p < 0.05), lower mean surface temperatures from FLIR thermography (p < 0.05) and a lower mean metabolic response (p < 0.05). Non- shivering thermogenesis was achieved as there was minimal and no significantly different skeletal muscle activity between the two groups (p = 0.94). In conclusion, during acute mild cold exposure, obese individuals displayed a significantly lower non- shivering thermogenesis despite having lower skin temperatures and the same core temperatures relative to non-obese individuals. This possibly originates from a decreased capacity to activate brown adipose tissue depots in the obese that contributes to their lower energy expenditure in these conditions.