Metabolism
on-line - the virtual tutorial room
copyright © 2008 - 2015 David A Bender
Weight loss in a patient with advanced cancer
AB is an 80 year old man who has metastatic cancer of the pancreas. He is 170 cm tall, and weighs 49 kg. He has lost 2 kg in body weight over the last 4 weeks - the condition of cancer cachexia.
What is his body mass index, and how would you classify it?
height ^2 = 1.7 x 1.7 = 2.89
BMI = weight / (height m^2) = 49 / 2.89 = 16.96
He is undernourished
His mean skinfold thickness is 1.9 mm, suggesting that he has negligible reserves of adipose tissue, and he shows considerable wasting of muscle, so we can assume that most of his weight loss is muscle.
The composition of muscle is:
79% water
17% protein (at 17 kJ /gram)
3% fat (at 37 kJ /gram)
What was his overall energy deficit over the last 4 weeks?
1 kg muscle =
170 g protein at 17 kJ /g = 2890 kJ
30 g fat at 37 kJ /g = 1110 kJ
Total = 4000 kJ = 4 MJ / kg muscle loss
He has lost 2 kg over 4 weeks = 8 MJ total deficit = 8000/28 = 286 kJ /day
For his
age and weight we would expect his basal metabolic rate (BMR) to be between
4.7 - 4.9 MJ /day. His oxygen consumption at rest was measured and was found
to be 11.2 L /hour.
Regardless of the fuel being consumed, 1 L of oxygen is equivalent to energy expenditure of 20 kJ.