Role of leptin in energy expenditure and substrate utilization during lactation

The role of leptin, prolactin and insulin in energy expenditure and substrate utilization during lactation was investigated. Data were collected from 29 postpartum women: 1 and 4 months exclusive lactation and 2 weeks post-lactation (PL) (N = 16). Changes in fasting and post-meal serum leptin, prolactin and insulin associated with alterations in resting energy expenditure (REE), respiratory quotient (RQ) and energy substrates; glucose, triglycerides (TG) and free fatty acids (FFA) were determined. Changes in percent body fat (PBF), and regional body fat were determined using DEXA. Height, weight, skinfolds (suprailiac, thigh, triceps and biceps), waist and hip circumferences were measured. Energy intake was determined from 3-day diet records. REE and RQ were determined by indirect calorimetry, hormones by radioimmunoassay and energy substrates by spectrometry.; PBF decreased from 1-month (34.4 ± 1.5) to 4-months lactation (32.9 ± 1.5) to PL (29.6 ± 1.6) (p < 0.05) Trunk PBF decreased from 1-month to 4-months to PL. Skinfolds did not change during lactation; a significant decrease in all four sites was observed PL. Waist circumference decreased during lactation; no change in hip circumference was observed.; Energy intake (kcal/day) decreased (p < 0.05) from 1-month (2364 ± 102) to 4-months lactation (2188 ± 103) to PL (1939 ± 120). REE (kcal/day) at 1-month (fasting 1417 ± 27; post-meal 1577 ± 30) and 4-months lactation (fasting 1425 ± 27; post-meal 1568 ± 30) was lower (p < 0.05) than PL (fasting 1458 ± 33; post-meal 1616 ± 33). Leptin (ng/ml), adjusted for variation in PBF, decreased (p < 0.05) from 1-month (fasting 12.15 ± 0.70; post-meal 11.28 ± 0.78) to 4-months lactation (fasting 10.17 ± 0.70; post-meal 8.96 ± 0.78). TG (mg/dl) at 4-months lactation (fasting 61.8 ± 7.2; post-meal 89.6 ± 12.3) was lower (p < 0.05) than 1-month lactation (fasting 83.1 ± 11.6; post-meal 123.9 ± 19.6) and PL (fasting 73.1 ± 7.6; post-meal 116.7 ± 13.4). Decrease in TG was significantly correlated with decrease in leptin only during lactation (r = 0.4, p < 0.05). Significant post-meal increase in REE, RQ, insulin and TG and decrease in FFA during lactation and PL was observed. A significant post-meal decrease in leptin and an increase in prolactin was observed only during lactation. REE during exclusive lactation could be predicted by leptin, fat mass and energy intake and only by lean mass PL.; Thus lowered REE and leptin-associated changes in serum TG are part of a possible energy utilization mechanism for successful lactation with decreased energy intake and body fat.