Fasting plasma irisin is related to fat free mass and increases with normal protein overfeeding in humans

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 678-689-Adipocyte Biology
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-689
Mathias Schlögl*, Paolo Piaggi, Maximilian Hohenadel, Jonathan Krakoff and Marie S Thearle
National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, AZ
Background: Irisin, a recently identified myokine, is induced by endurance exercise in both mice and humans and increases energy expenditure (EE) in mice. Little is known of the determinants of fasting plasma irisin concentrations (FPIC), the relationship of irisin and 24 hour energy expenditure (24h EE) in humans, nor about the effects of overfeeding or protein content of the diet on FPIC in humans.

Methods: Both 24h EE and 24h respiratory quotient (RQ) were measured using whole room indirect calorimetry in 50 healthy subjects (8 NA/ 13 C/ 17 H/ 12 AA; 35M/ 15F; mean±SD: age 35.8±9.8 y; BMI 26.9±4.4 kg/m2; %body fat 29.6±11.5%, 24h EE 2502±306 kcal; FPIC 411.9 ± 171.1 ng/mL) during 24h of fasting, 24h of energy balance (EB), and during 3 separate occasions of 24h of overfeeding (OF) with 200% of energy requirements with 1)low protein (3%), high fat (46%), 2)normal protein (20%), high fat (60%) and 3)high protein (30%), high fat (44%) diets. A weight maintaining diet was given for 3 days between dietary interventions. Body composition was measured using DXA. Plasma for FPIC was collected before and after each dietary intervention and measured using an ELISA assay kit (Phoenix Pharmaceuticals, Inc., Burlingame, CA).

Results: Fat free mass (β=9.6±3.5; p <0.01) was the only significant predictor of FPIC in a stepwise regression analysis to assess for determinants of FPIC. FPIC did not explain additional variance of 24h EE during EB beyond known determinants including age, sex, race, fat mass and fat free mass (p= 0.7), nor was it associated with RQ (p=0.4). The 24h EE increased by 2.9±4.8%, 7.4±7.9%, and 14.9±7.0%, respectively, during the low protein, normal protein and high protein OF diets. FPIC increased after OF with both the normal protein, high fat diet (Δ67.8±131.4 ng/mL; 95% CI = 29.7 to 105.9; p<0.01) and the high protein, high fat diet (Δ31.4±61.7 ng/mL; 95% CI = 8.8 to 54.1; p<0.01), but not the low protein diet (p=0.3). In mixed models, FPIC changes during OF were neither related to the percent increase in EE (p=0.6) nor absolute diet induced EE (p=0.5) after accounting for age, sex, race and diet.

Conclusion: FPIC is strongly associated with fat free mass but is not an independent contributor to sedentary 24h EE during EB in humans. Although, 24h of increased protein intake led to increases in FPIC, FPIC was not associated with the EE response to OF.

Nothing to Disclose: MS, PP, MH, JK, MST

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