Non-Randomized Crossover Trial

C - Click here for explanation of classification scheme.

NEUTRAL: See Quality Criteria Checklist below.

To investigate whether lean and overweight subjects differ in cold-induced thermogenesis under mild cold conditions. 

• Healthy subjects
• Non-smoking
• Male
• Lean (BMI 17.9kg/m² to 23.4kg/m²) or overweight (BMI 24.7kg/m² to 33.2kg/m²)
• Written consent was obtained.

• Females 
• Smokers
• BMI less than 17.9kg/m² or >33.2kg/m².

Recruitment

Volunteers.

Design

Non-randomized crossover trial.

Blinding Used

Implied with measurements.

Intervention 

• Cold air exposure test followed by rewarming
• Thermoneutral condition was established:
  • Subjects lay on a chair, with legs supported in 15°C air and were covered with a duvet (375g per m²).
• Cold exposure was started:
  • Duvet was removed after 60 minutes of baseline measurement.
• Rewarming phase was started:
  • After 60 minutes of cold exposure, the duvet was replaced.
• The test was terminated after 60 minutes of rewarming
• Subjects wore standard clothing with insulative value of 0.71 clo (Icl = 0.109m² x °C per W)
  • Sweatpants, sweater, socks that covered only the feet and briefs
  • Face, hands and ankles were exposed directly to the environment.
• Heat production and body temperature were measured continuously 
• Subjects arrived at the laboratory by car or public transportation after overnight fasting
• Subjects instructed not to perform any strenuous activities the day before the experiment
• Body composition was determined on a separate visit within one week of the experiment.

Statistical Analysis

• Baseline values were calculated over minutes 21 to 50 of the first hour
• During cold exposure and rewarming, minutes 11 to 60 were used for calculations
• Data reported as means ± standard deviations
• Results considered statistically significant at P<0.05
• SPSS 11.5.0 was used
• Between-group differences were tested by unpaired T-tests
• Within-group changes were tested by paired T-tests
• Linear regression analysis was used to study the relation between skin temperature and fat percentage. 

Timing of Measurements

• Subjects exposed to thermoneutral condition for 60 minutes, followed by mild cold exposure for 60 minutes and then 60 minutes of rewarming
• Body composition was determined on a separate visit within one week of the experiment  

Dependent Variables

• Heat production
  • Oxygen consumption and carbon dioxide production were measured with an automated respiratory gas analyzer using a ventilated hood system (Omnical)
  • Gas analyzers were calibrated before the experiments
  • Heat production was calculated from these data according to Weir's method
• Body Temperature
  • Rectal temperature was measured continuously by a thermistor probe inserted 10 cm beyond the anal sphincter
• Skin temperature
  • Measured by surface thermistors placed on the dorsal side of the hand, forearm, upper arm, chest, abdomen, lower back, anterior thigh, posterior calf, and dorsal side of the foot
  • Temperatures were registered and recorded at 1-minute intervals
  • Mean skin temperature calculated according to Ramanathan's method
• Weighted body temperature
  • Calculated as a measure of rectal and mean skin temperatures according to Cunningham
• Trunk temperature
  • Calculated as the average of skin temperatures measured at the lower back, abdomen and chest
• Distal skin temperature
  • Measured at the hand and foot
• Shivering
  • Detected using electromyography
  • Electrodes were placed three cm apart on the skin at the musculus pectoralis major

Independent Variables

• Thermoneutral condition
• 15°C cold air exposure
• Rewarming to thermoneutral condition

 Control Variables

• Body composition
  • Calculated according to Siri's three-component model
  • Body density and total body water were determined using underwater weighing and deuterium dilution which was determined according to the Maastricht protocol

 

• Initial N: 10 lean and 10 overweight males
• Attrition (final N): 10 lean and 10 overweight males.

Age

• Lean: 23±4 years
• Overweight: 27±7 years
• Total group: 25±6 years.

Anthropometrics

• Height (m):
  • Lean: 1.82±0.08
  • Overweight: 1.80±0.06.
• Weight (kg):
  • Lean: 69.7±7.1
  • Overweight: 94.5±6.8.
• BMI:
  • Lean: 21.1±2.0
  • Overweight: 29.2±2.8.
• Fat mass (%):
  • Lean: 14.9±4.2
  • Overweight: 27.9±5.3.
• Fat-free mass (kg)
  • Lean: 58.8±5.0
  • Overweight: 70.0±5.5.

Location

Maastricht, The Netherlands.

 

Key Findings

• Cold exposure:
  • Heat production increased significantly for both groups compared to baseline:
    • Lean group: P=0.004
    • Overweight group: P=0.006
    • The increase was significantly larger in the lean group (17.2% average) compared to overweight (6.4% average) (P=0.04).
• Weighted body temperature (WBT):
  • Decreased significantly during cold exposure (P=0.002 for lean and P<0.001 for overweight subjects)
  • During rewarming, WBT increased by did not return to baseline (P=0.01 for lean and P=0.003 for overweight groups) compared to baseline.

Other Findings

• Subject characteristics: Weight, BMI, fat mass and fat-free mass were all significant between the lean and obese groups (P<0.05)
• Baseline:
  • No significant differences between lean and overweight subjects in energy expenditure 
  • Only trunk temperature was lower in overweight men (P=0.02)
• Cold exposure:
  • Heat production increased significantly for both groups compared to baseline:
    • Lean group: P=0.004
    • Overweight group: P= 0.006
    • The increase was significantly larger in the lean group (17.2% average) compared to overweight (6.4% average) (P=0.04).
• Rewarming:
  • Heat production decreased in both groups:
    • Returned to baseline in the overweight group
    • Remained significantly higher compared with baseline in lean group (P=0.003)
    • Difference in heat production between rewarming and baseline was greater in the lean group compared to overweight group (P=0.01).
• Temperatures:
  • Rectal temperature:
    • Not significantly different between groups at any stage of the experiment
    • Did not change significantly compared with baseline.
  • Trunk temperature:
    • Significantly lower in overweight group compared with lean group during the three stages (P=0.02, P=0.007 and P=0.006, respectively)
    • Within groups, trunk temperature decreased significantly during cold exposure (P<0.001) in both groups
    • During rewarming, trunk temperature was not significantly different from baseline in overweight group but stayed significantly lower compared with baseline in lean group (P=0.03).
  • Mean skin temperature:
    • Decreased significantly during cold exposure (P<0.001) in both groups
    • During rewarming, did not return to baseline in the two groups (P<0.001) compared to baseline.
  • Weighted body temperature (WBT):
    • Decreased significantly during cold exposure (P=0.002 for lean and P<0.001 for overweight subjects)
    • During rewarming, WBT increased by did not return to baseline (P=0.01 for lean and P=0.003 for overweight groups) compared to baseline.
  • Distal skin temperature:
    • Decreased significantly during cold exposure (P<0.001)
    • Increased during rewarming 
    • Did not return to baseline values in both groups (P<0.001 for both groups) compared to baseline.
  • Trunk temperatures:
    • Negatively related to fat percentage at baseline (R²=0.32, P=0.009)
    • Similar relationship during cold exposure (R²=0.40, P=0.003)
    • Similar relationship during rewarming (R²=0.36, P=0.005).
  • Distal skin temperature:
    • Positively related to fat percentage at baseline (R²=0.28, P=0.02)
    • During cold exposure (R²=0.25, P=0.03)
    • During rewarming (R²=0.29, P=0.01).

Heat Production and Body Temperatures at Baseline, During Cooling and Rewarming

Temperature and Group	Baseline	Cooling	Rewarming
Heat production (W per m)
Lean	44.7±3.1	53.4±7.2*	50.0±4.2*
Overweight	44.7±3.9	47.5±4.5*	45.9±4.7
Rectal temperature
Lean	36.8±0.2	36.9±0.2	36.8±0.2
Overweight	36.9±0.2	36.9±0.2	36.9±0.2
Mean skin temperature
Lean	32.4±0.4	29.6±0.8*	30.5±0.6*
Overweight	32.6±0.6	29.9±0.7*	30.6±0.7*
Trunk skin temperature
Lean	34.6±0.2§	32.7±0.4*§	34.3±0.3*§
Overweight	33.9±0.8	32.0±0.6*	33.5±0.8
Distal skin temperature
Lean	30.5±0.8	26.6±1.2*	27.0±1.1
Overweight	31.5±1.3	28.0±1.9*	28.2±1.9*
Weighted temperature
Lean	36.8±0.2	36.5±0.2*	36.5±0.3*
Overweight	36.9±0.2	36.6±0.2*	36.6±0.3*

*P<0.05 vs. baseline.

§P<0.05 overweight vs. lean.

This study demonstrated that overweight subjects showed a blunted cold-induced thermogenesis, but there was no difference in the insulative cold response between lean and overweight subjects. The results indicate that the overweight subjects preserved heat more efficiently through a smaller heat loss compared with body size.

University/Hospital:

Maastricht University and Technical University Eindhoven

Small numbers of subjects in groups. Questionable validity of indirect calorimeter.