2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
312
METABOLIC RESPONSES TO MILD COLD AND OVEREATING.
ROLE OF MITOCHONDRIAL UNCOUPLING
Sander Wijers, Patrick Schrauwen, Wim Saris, Wouter van Marken Lichtenbelt,
Department of Human Biology, NUTRIM, Maastricht University, The Netherlands
Contact person: s.wijers@hb.unimaas.nl
INTRODUCTION
Mild cold exposure and overfeeding are known to elevate energy expenditure, the so-called
adaptive thermogenesis. Large individual variation in adaptive thermogenesis might explain
why some people are more prone to obesity than others. In rodents, adaptive thermogenesis is
caused by mitochondrial uncoupling in brown adipose tissue and regulated via the
sympathetic nervous system. In adult humans, skeletal muscle tissue is a key candidate tissue.
Therefore, we hypothesized that both diet induced and cold induced adaptive thermogenesis
in humans is caused by mitochondrial uncoupling in skeletal muscle tissue.
METHODS
The metabolic response to mild cold and overeating in 13 lean adult male subjects was
measured in a respiration chamber in three situations:
1. Baseline: 36 hours at 22°C with feeding in energy balance;
2. Overfeeding: 84 hours overeating at 22°C with overfeeding of 160% of energy balance;
3. Mild cold: 84 hours at 16°C with feeding in energy balance.
After each respiration chamber measurement a muscle biopsy was taken, in which
mitochondrial uncoupling was measured using the Oxygraph-2K (Oroboros, Austria). The
uncoupling ratio was defined as state 4 respiration (substrates + ADP + ATP-synthase
blocker) divided by state 3 respiration (substrates + ADP).
RESULTS
Total daily energy expenditure (TDEE) increased after overfeeding with 6.6% (0.76 MJ/day)
and after mild cold exposure with 5.1% (0.59 MJ/day). The increase in TDEE after
overfeeding (overfeeding – baseline) was significantly related to the increase in TDEE after
mild cold exposure (mild cold – baseline) (r=0.63, p