A study carried out in Japan showed that in rats, the physiological responses to the ingestion of a glucose solution varied dramatically depending on the temperature of the solution. The study measured blood sugar, blood insulin and brown adipose tissue activity following the ingestion of a 1M glucose solution at either 4 degrees Celsius or 25 degrees Celsius (Fridge temperature and room temperature respectively).
The key results were as follows: Both groups exhibited similar blood sugar responses. However, the ‘warm’ group showed a rise in insulin 3 minutes after ingestion whereas the ‘cold’ group showed a corresponding rise after 15 minutes. Perhaps more importantly, the ‘warm’ group showed an increase in brown adipose tissue activity whereas the ‘cold’ group did not, which implies that the thermic effect of ingesting sugars is absent if the solution is cold.
Bottom line: warm drinks raise insulin faster than cold drinks. Ingesting sugars warm raises the metabolic rate, whereas ingesting them cold does not.
Link to the article on PubMed: http://www.ncbi.nlm.nih.gov/pubmed/18262576