Lower core body temperature and greater body fat are components of a human thrifty phenotype

Abstract

Background/objectives: In small studies, a thrifty human phenotype, defined by a greater 24-hour energy expenditure (EE) decrease with fasting, is associated with less weight loss during caloric restriction. In rodents, models of diet-induced obesity often have a phenotype including a reduced EE and decreased core body temperature. We assessed whether a thrifty human phenotype associates with differences in core body temperature or body composition.

Subjects/methods: Data for this cross-sectional analysis were obtained from 77 individuals participating in one of two normal physiology studies while housed on our clinical research unit. Twenty-four-hour EE using a whole-room indirect calorimeter and 24-h core body temperature were measured during 24 h each of fasting and 200% overfeeding with a diet consisting of 50% carbohydrates, 20% protein and 30% fat. Body composition was measured by dual X-ray absorptiometry. To account for the effects of body size on EE, changes in EE were expressed as a percentage change from 24-hour EE (%EE) during energy balance.

Results: A greater %EE decrease with fasting correlated with a smaller %EE increase with overfeeding (r=0.27, P=0.02). The %EE decrease with fasting was associated with both fat mass and abdominal fat mass, even after accounting for covariates (β=-0.16 (95% CI: -0.26, -0.06) %EE per kg fat mass, P=0.003; β=-0.0004 (-0.0007, -0.00004) %EE kg(-1) abdominal fat mass, P=0.03). In men, a greater %EE decrease in response to fasting was associated with a lower 24- h core body temperature, even after adjusting for covariates (β=1.43 (0.72, 2.15) %EE per 0.1 °C, P=0.0003).

Conclusions: Thrifty individuals, as defined by a larger EE decrease with fasting, were more likely to have greater overall and abdominal adiposity as well as lower core body temperature consistent with a more efficient metabolism.

Figure 1.

Correlation of 24 h-energy expenditure responses to fasting and overfeeding (r = 0.27, P = 0.02). Filled circles represent subjects with a wide BMI range (17.8─50.0) participating in study NCT00523627; open triangles represent 12 obese individuals (BMI range: 30.0─50.0) that with evaluation prior to their participation in a CR weight loss study (NCT00687115; details can be found here).

Figure 2.

(a, b) Correlation of fat mass, abdominal fat and percent change in 24 h energy expenditure in response to fasting (r = −0.36, P = 0.001; ρ = −0.34, P = 0.003, respectively). (c, d) Correlation of fat mass, abdominal fat and percent change in 24 h energy expenditure in response to fasting after adjustment for fat-free mass, age, sex, race and ambient temperature (β = −0.16%EE per kg, P = 0.003, (−0.26, −0.06); β = −0.0004%EE per kg, P = 0.03, (−0.0007, −0.00004), respectively). Filled circles represent subjects with a wide BMI range (17.8─50.0) participating in study NCT00523627; open triangles represent 12 obese individuals (BMI range: 30.0─50.0) evaluated prior to participation in a caloric restriction weight loss study ((NCT00687115; details can be found here).

Figure 3.

Correlation between the EE response to fasting in men and average 24 h core body temperature during fasting (a; r = 0.36, P = 0.03, N = 36), energy balance energy balance (b; r = 0.42, P = 0.01, N = 34), overfeeding (c; r = 0.56, P = 0.0008, N = 32) and the combined average 24 h core body temperatures during fasting, energy balance and overfeeding (d; r = 0.59, P<0.0001, N = 44).