The impact of heat treatment of bovine milk on gastric emptying and nutrient appearance in peripheral circulation in healthy females: a randomized controlled trial comparing pasteurized and ultra-high temperature milk.

BACKGROUND: Heat treatments of dairy, including pasteurization and ultra-high temperature (UHT) processing, alter milk macromolecular structures, and ultimately affect digestion. In vitro, animal, and human studies show faster nutrient release or circulating appearance after consuming UHT milk (UHT-M) compared with pasteurized milk (PAST-M), with a faster gastric emptying (GE) rate proposed as a possible mechanism. OBJECTIVES: To investigate the impact of milk heat treatment on GE as a mechanism of faster nutrient appearance in blood. We hypothesized that GE and circulating nutrient delivery following consumption would be faster for UHT-M than PAST-M. METHODS: In this double-blind randomized controlled cross-over trial, healthy female (n = 20; 27.3 ± 1.4 y, mean ± SD) habitual dairy consumers, consumed 500 mL of either homogenized bovine UHT-M or PAST-M (1340 compared with 1320 kJ). Gastric content volume (GCV) emptying half-time (T50) was assessed over 3 h by magnetic resonance imaging subjective digestive symptoms, plasma amino acid, lipid and B vitamin concentrations, and gastric myoelectrical activity were measured over 5 h. RESULTS: Although GCV T50 did not differ (102 ± 7 min compared with 89 ± 8 min, mean ± SEM, UHT-M and PAST-M, respectively; P = 0.051), GCV time to emptying 25% of the volume was 31% longer following UHT-M compared with PAST-M (42 ± 2 compared with 32 ± 4 min, P = 0.004). Although GCV remained larger for a longer duration following UHT-M (treatment × time interaction, P = 0.002), plasma essential amino acid AUC was greater following UHT-M than PAST-M (55,324 ± 3809 compared with 36,598 ± 5673 µmol·min·L-1, P = 0.006). Heat treatment did not impact gastric myoelectrical activity, plasma appetite hormone markers or subjective appetite scores. CONCLUSIONS: Contrary to expectations, GE was slower with UHT-M, yet, as anticipated, aminoacidemia was greater. The larger GCV following UHT-M suggests that gastric volume may poorly predict circulating nutrient appearance from complex food matrices. Dairy heat treatment may be an effective tool to modify nutrient release by impacting digestion kinetics. CLINICAL TRIAL REGISTRY: www.anzctr.org.au (ACTRN12620000172909).

Circulatory amino acid responses to milk consumption in dairy and lactose intolerant individuals.

BACKGROUND/OBJECTIVES: Self-reported digestive intolerance to dairy foods is common. As dairy can be an important source of dietary protein, this study aimed to identify whether milk protein digestion is compromised in individuals with digestive intolerance. SUBJECTS/METHODS: Adult women (n = 40) were enroled in this double-blinded, randomised cross-over trial, with digestive symptoms characterised using a lactose challenge and self-reported digestive symptom questionnaire. Participants were classified as either lactose intolerant (LI, n = 10), non-lactose dairy intolerant (NLDI, n = 20) or dairy tolerant (DT, n = 10). In a randomised sequence, participants consumed three different kinds of milk (750 ml); conventional milk (CON), a2 Milk™ (A2M), and lactose-free conventional milk (LF-CON). Circulatory plasma amino acid (AA) concentrations were measured at baseline and every 30 min until 3 h post-ingestion. RESULTS: In all participants across all milk types, plasma AA concentrations (AUC0-180) increased after milk ingestion with no significant differences in responses observed between milk types or participants (P > 0.05), with the exception of the suppressed lysine response in the DT group following A2M ingestion, relative to the other two groups and milk types (P < 0.05). CONCLUSION: Milk protein digestion, as determined by circulatory AAs, is largely unaffected by dairy- and lactose- intolerances.

Postprandial lipemic response in dairy-avoiding females following an equal volume of sheep milk relative to cow milk: A randomized controlled trial.

Background: Sheep milk (SM) is an alternate dairy source, which despite many similarities, has both compositional and structural differences in lipids compared to cow milk (CM). Studies are yet to examine the apparent digestibility of SM lipids, relative to CM, and the potential impact on the plasma lipidome. Objective: To determine the response of the circulatory lipidome to equal volume servings of SM and CM, in females who avoid dairy products. Method: In a double-blinded, randomized, cross-over trial, self-described dairy avoiding females (n = 30; 24.4 ± 1.1 years) drank SM or CM (650 mL; 33.4 vs. 21.3 g total lipid content; reconstituted from spray dried milk powders) following an overnight fast. Blood samples were collected at fasting and at regular intervals over 4 h after milk consumption. The plasma lipidome was analyzed by LC-MS and fatty acids were quantified by GC-FID. Results: The overall postprandial triglyceride (TG) response was similar between SM and CM. TG concentrations were comparable at fasting for both groups, however they were higher after CM consumption at 30 min (interaction milk × time p = 0.003), well before any postprandial lipemic response. This was despite greater quantities provided by SM. However, there were notable differences in the postprandial fatty acid response, with SM leading to an increase in short- and medium-chain fatty acids (MCFAs) (C6:0, C8:0, and C10:0) and several long-chain fatty acids (LCFAs) (C18:1 t11, c9, t11-CLA, and C20:0; interaction time × milk p < 0.05). This corresponded to a greater postprandial response for medium chain triglycerides (MCTs) C10:0, including TG(10:0/14:0/18:1), TG(16:0/10:0/12:0), and TG(16:0/10:0/14:0) (interaction time × milk p < 0.05). Conclusions: Despite a higher fat content, SM ingestion resulted in a greater circulating abundance of MCTs, without increasing total postprandial triglyceride response, when compared to CM. The greater abundance and postprandial appearance of MCTs may provide advantageous metabolic responses in children and adults. Unique identifier and registry: U1111-1209-7768; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=375324.

Growth Factor Concentrations in Human Milk Are Associated With Infant Weight and BMI From Birth to 5 Years.

Background: Human milk bioactives may play a role in infant health and development. Although the variability in their concentrations in milk is well-established, the impact of differential milk profiles on infant growth outcomes remains unclear. Thus, the aim of the present study was to investigate whether different concentrations of metabolic hormones are associated with different weight and BMI in infants beyond the first year of life. Methods: Milk samples at 2.6 (±0.4) months after birth and anthropometric measures at 13 months, 2, 3, and 5 years were collected as part of the Finnish STEPS cohort study from 501 mothers and the respective 507 infants. Leptin, adiponectin, insulin-like growth factor (IGF)-1 and cyclic glycine-proline (cGP) in milk were analyzed. Multiple regression models and a repeated measures mixed model were used to examine associations between milk hormone concentrations and weight and BMI z-scores across time, at each time-point, and weight gain from birth to each follow-up visit. All models were corrected for birth weight, infant sex, duration of exclusive and total breastfeeding, time of introduction of solid foods and maternal pre-pregnancy BMI. Results: Higher milk IGF-1 was associated with higher weight at 13 months (p = 0.004) but lower weight at 3 (p = 0.011) and 5 years of age (p = 0.049). Higher cGP was associated with lower weight across the 5 years (p = 0.019) but with higher BMI at 5 years (p = 0.021). Leptin and adiponectin did not display associations with infant growth at this time. Sex interactions were also absent. Conclusions: Our results suggest that the interplay between human milk-borne IGF-1 and cGP is similar to that reported in other mammals and may have an important role in defining infant growth trajectories beyond the first year of life. Further research should explore the determinants and origins of these milk-borne compounds and evaluate their effect on infant growth and metabolism.