Even so, it would be interesting to run some tests during these events, though I can not see anyone willing to agree to this. Calorific value of food intake is easy to record. Metabolic rate can be measured using a respiratory monitor and oxygen analyzer. Mobilisation of body fat stores can be detected by measuring the ketones in a blood or urine sample using a simple test. Water loss can be measured by weighing the subject.
Rectal temperature is a good indication of how dehydrated a subject has become.
Blood sugar, blood pressure and pulse rate might also be interesting to measure. The usefulness of the above data is reduced slightly since I have not had time to compile a detailed set of references. Manual of Nutrition , M.A.F.F. pub.