Blood lactose after dairy product intake in healthy men.

The absence of a dedicated transport for disaccharides in the intestine implicates that the metabolic use of dietary lactose relies on its prior hydrolysis at the intestinal brush border. Consequently, lactose in blood or urine has mostly been associated with specific cases in which the gastrointestinal barrier is damaged. On the other hand, lactose appears in the blood of lactating women and has been detected in the blood and urine of healthy men, indicating that the presence of lactose in the circulation of healthy subjects is not incompatible with normal physiology. In this cross-over study we have characterised the postprandial kinetics of lactose, and its major constituent, galactose, in the serum of fourteen healthy men who consumed a unique dose of 800 g milk or yogurt. Genetic testing for lactase persistence and microbiota profiling of the subjects were also performed. Data revealed that lactose does appear in serum after dairy intake, although with delayed kinetics compared with galactose. Median serum concentrations of approximately 0·02 mmol/l lactose and approximately 0·2 mmol/l galactose were observed after the ingestion of milk and yogurt respectively. The serum concentrations of lactose were inversely correlated with the concentrations of galactose, and the variability observed between the subjects' responses could not be explained by the presence of the lactase persistence allele. Finally, lactose levels have been associated with the abundance of the Veillonella genus in faecal microbiota. The measurement of systemic lactose following dietary intake could provide information about lactose metabolism and nutrient transport processes under normal or pathological conditions

URINARY AND SERUM BIOMARKERS OF MILK AND CHEESE INTAKE ASSESSED BY METABOLOMICS APPROACH

Biomarkers of food intake are currently intensively investigated in the frame of the European Project `Food Biomarker Alliance` (FoodBAll) for a wide range of foods. In the future, validated biomarkers will serve as a tool for dietary assessment enabling the objective link between diet and disease outcomes in epidemiological studies.The randomized, controlled crossover study presented here aimed to identify urinary and serum biomarkers for the intake of two products of public health relevance, milk and cheese, in addition to a soy-based control. Eleven healthy volunteers (five women, six men) participated in the acute intervention study. Urine and serum samples were collected in the fasted state and up to 24 hours postprandially and were further analysed using a multiplatform approach combining untargeted gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR).Using multivariate analysis, several urinary and serum biomarkers for milk, cheese as well as for soy drink after their acute intake have been identified. The majority of metabolites that specifically reflected the intake of milk were derived from lactose/galactose metabolism whereas an amino acid derivative was indicative of cheese intake. The kinetics of the biomarkers from the two dairy products was different when compared to biomarkers of the plant-based control (soy drink). Comparing urine and serum, the majority of identified biomarkers were discriminative in both biofluids but urine seemed to contain a higher number of biomarkers for the intake of these three food items. Overall, the outcomes of this study will serve as a basis for future validation studies under free-living conditions.Acknowledgements: Swiss National Science Foundatio

POSTPRANDIAL SERUM LACTOSE AFTER ACUTE INTAKE OF MILK AND YOGHURT

The use of dietary lactose as a source of energy requires its prior hydrolysis at the intestinal brush border into glucose and galactose. Indeed, as a disaccharide, intact lactose cannot be actively absorbed. Therefore, the presence of unhydrolysed lactose in plasma or urine has mostly been associated with specific cases such as lactating women or altered gastrointestinal permeability. Nevertheless, lactose has also been detected in the blood and urine of healthy men, indicating that the presence of lactose in the circulation of healthy subjects is not incompatible with normal physiology. The present crossover study monitored, in 14 healthy men, the postprandial appearance of lactose in serum after a single intake of 800 g of milk or yoghurt. Genetic testing for lactase persistence and microbiota profiling of the subjects were also performed in order to investigate their potential contribution to postprandial lactose serum levels. Data revealed that lactose does appear in serum after dairy intake, and with delayed kinetics when compared to the actively absorbed galactose. A notable inter-individual variability was observed and, although lactose levels were inversely correlated with galactose levels, the presence of the lactase persistence allele could not explain this variability. Finally, lactose levels have been associated with the abundance of the Veillonella genus in faecal microbiota. The measurement of systemic lactose following dietary intake could provide information about lactose metabolism and nutrient transport processes under normal or pathological conditions

Serum and Urine Metabolites in Healthy Men after Consumption of Acidified Milk and Yogurt

The identification of molecular biomarkers that can be used to quantitatively link dietary intake to phenotypic traits in humans is a key theme in modern nutritional research. Although dairy products (with and without fermentation) represent a major food group, the identification of markers of their intake lags behind that of other food groups. Here, we report the results from an analysis of the metabolites in postprandial serum and urine samples from a randomized crossover study with 14 healthy men who ingested acidified milk, yogurt, and a non-dairy meal. Our study confirms the potential of lactose and its metabolites as markers of lactose-containing dairy foods and the dependence of their combined profiles on the fermentation status of the consumed products. Furthermore, indole-3-lactic acid and 3-phenyllactic acid are two products of fermentation whose postprandial behaviour strongly discriminates yogurt from milk intake. Our study also provides evidence of the ability of milk fermentation to increase the acute delivery of free amino acids to humans. Notably, 3,5-dimethyloctan-2-one also proves to be a specific marker for milk and yogurt consumption, as well as for cheese consumption (previously published data). These molecules deserve future characterisation in human interventional and observational studies