Leptin Levels Are Higher in Whole Compared to Skim Human Milk, Supporting a Cellular Contribution

Abstract

Human milk (HM) contains a plethora of metabolic hormones, including leptin, which is thought to participate in the regulation of the appetite of the developing infant. Leptin in HM is derived from a combination of de novo mammary synthesis and transfer from the maternal serum. Moreover, leptin is partially lipophilic and is also present in HM cells. However, leptin has predominately been measured in skim HM, which contains neither fat nor cells. We optimised an enzyme-linked immunosorbent assay for leptin measurement in both whole and skim HM and compared leptin levels between both HM preparations collected from 61 lactating mothers. Whole HM leptin ranged from 0.2 to 1.47 ng/mL, whilst skim HM leptin ranged from 0.19 to 0.9 ng/mL. Whole HM contained, on average, 0.24 ± 0.01 ng/mL more leptin than skim HM (p < 0.0001, n = 287). No association was found between whole HM leptin and fat content (p = 0.17, n = 287), supporting a cellular contribution to HM leptin. No difference was found between pre- and post-feed samples (whole HM: p = 0.29, skim HM: p = 0.89). These findings highlight the importance of optimising HM leptin measurement and assaying it in whole HM to accurately examine the amount of leptin received by the infant during breastfeeding.

Associations between Maternal Body Composition and Appetite Hormones and Macronutrients in Human Milk

“…Interestingly, longitudinal changes observed in concentrations of skim milk leptin in this study were not confirmed in whole HM. Caution in the interpretation of leptin concentrations measured in skim HM should be exercised, as whole milk measures are more indicative of the level of hormone consumed by the infant [28]. The consistent concentrations of adiponectin and leptin in whole HM over the first 12 months of life may be indicative of a continuing roles of appetite programming, priming neural connections involved in the appetite circuitry, thereby contributing to long-lasting enhanced appetite control and BC of breastfed infants throughout life.…”

“…Leptin concentrations in whole and skim HM were measured using the DuoSet Human Leptin enzyme-linked immunosorbent assay (ELISA) (R&D Systems, Minneapolis, MN, USA) as described previously [28]. The detection limit was 0.05 ng/mL with a recovery of 96.3% ± 1.2% ( n = 10) for skim milk and 97.1% ± 9.1% ( n = 10) for whole milk leptin and an inter-assay coefficient of variation (CV) of <7.2%.…”

“…Investigations between the relationship of maternal BMI and leptin have been conducted predominantly in skim HM, which excludes the fat and cellular components of HM [21,24]. Further, leptin concentrations have been shown to be higher in whole HM compared to skim HM [20,23,28]. …”

Effect of Human Milk Appetite Hormones, Macronutrients, and Infant Characteristics on Gastric Emptying and Breastfeeding Patterns of Term Fully Breastfed Infants

“…In animal models (rat, mouse), injection of leptin into the fourth ventricle has been shown to delay GE [ 30 ] and oral administration reduced food intake [ 31 ]. Leptin in HM is by far the most studied appetite hormone, but predominantly in skim milk [ 32 ]. Leptin measured in skim HM was not associated with time between feeds [ 33 , 34 ] or GE [ 34 ] in term breastfed infants, emphasizing the need for studies including whole milk leptin, where the levels of leptin are shown to be higher [ 32 ].…”

“…Leptin in HM is by far the most studied appetite hormone, but predominantly in skim milk [ 32 ]. Leptin measured in skim HM was not associated with time between feeds [ 33 , 34 ] or GE [ 34 ] in term breastfed infants, emphasizing the need for studies including whole milk leptin, where the levels of leptin are shown to be higher [ 32 ]. Adiponectin has the highest concentration of any appetite hormone in HM.…”