Effects Of Increased Energy Availability On Energy Metabolism And Blood Indices In Healthy Young Men

Abstract

Previous studies showed that low energy availability (low EA) condition affects resting energy expenditure (REE) and blood indices such as insulin-like growth factor-1 (IGF-1). Skipping breakfast may lead to low EA, as it reduces daily energy intake. In addition, skipping breakfast reduces protein intake, which may affect blood nutrition markers and muscle protein breakdown. PURPOSE: To examine the effects of increased EA on energy metabolism and blood indices in healthy young men. METHODS: Ten healthy young men who are habitually skipping breakfast participated in this study (age: 24 ± 4 years). Two conditions of EA-adjusted meals with low EA (LEA) and high EA (HEA) were provided one week each. In the LEA condition, the subjects skipped breakfast as usual and consumed meals of EA less than 30 kcal/kg FFM/day. Then, the subjects consumed three meals per day of EA more than 45 kcal/kg FFM/day in the HEA condition. All measurements were conducted after ingestion of each EA diet. REE was measured using the Douglas bag method (REEm), predicted REE (REEp) was calculated using the formula for Japanese people, and the ratio of REEm to REEp was calculated (REEratio). Early morning fasting blood indices were measured, and 3-methylhistidine (3-MH) as an indicator of muscle protein breakdown was measured using 24-hour urine storage. RESULTS: IGF-1 (LEA: 170.7 ± 43.0 ng/mL, HEA: 198.1 ± 43.2 ng/mL, p < 0.05) and transthyretin level (LEA: 23.4 ± 3.4 mg/dL, HEA: 27.1 ± 4.0 mg/dL, p < 0.05) were significantly higher in the HEA than the LEA condition. Retinol-binding protein level was below the reference value (2.7 - 6.0 mg/dL) in the LEA condition, however, significantly increased after the HEA condition (LEA: 2.5 ± 0.5 mg/dL, HEA: 2.9 ± 0.5 mg/dL, p < 0.01). REEratio (LEA: 0.92 ± 0.08, HEA: 0.99 ± 0.09) showed a tendency to improve after the HEA condition. CONCLUSIONS: This study indicated that adequate EA with three meals per day, even for a short period of time, might improve blood protein indices and IGF-1 level. Examination of adequate EA on energy metabolism and muscle protein breakdown requires long-term intervention.