Their analysis of amino acid and metabolite concentrations in blood samples from obese or overweight patients identified notable differences in fasting and postprandial concentrations that could impact interpretations of health status.
For example, elevated α-hydroxybutyrate, β-hydroxyisobutyrate, and α-ketoglutarate were reported 60 minutes after ingesting a light breakfast, compared to fasting levels, and likely reflect increased postprandial catabolism of amino acids such as glutamate and valine that denote insulin sensitivity.
“These findings indicate that elevated concentrations of these candidate biomarkers of insulin sensitivity should be interpreted with caution if the prandial status of the subject is not known,” they write in 'BMC Nutrition'.
Prandial status is rarely considered when analysing biomarkers for health and disease risk, with blood typically sampled from patients in a fasting state or following a light meal, the authors explain.
“Inconsistent observations in epidemiological studies investigating biomarkers in relation to various health and disease outcomes may be linked to differences in blood collection protocols.
“Especially, it is unclear how the time interval between last meal and blood draw may affect biomarker concentrations in blood.”
The present study therefore examined the effects of a light meal on patients’ metabolic activity (from catabolic to anabolic status), including serum concentrations of amino acids, kynurenine pathway metabolites, and metabolites involved in glucose regulation. Researchers also compared all biomarkers between male and female participants.
Amino acid concentrations
Sixty-three healthy adults were recruited for the study, including 36 women. Blood samples were collected at the fasting state and intermittently up to 120 minutes following consumption of a light, low protein, breakfast. Serum samples were compared using the T test.
Amino acid concentrations increased significantly after 60 minutes in 13 out of the 20 amino acids measured – and particularly alanine (up 34%) and proline (45%) - and did not reflect the amino acid composition of the breakfast.
Serum concentrations of histidine and phenylalanine (EAAs) significantly increased postprandial; leucine, isoleucine and valine were unchanged, while threonine and methionine initially increased after 60 minutes then dropped back to fasting levels.
Male participants displayed higher fasting serum concentrations of EAAs isoleucine, leucine, methionine, tryptophan, valine, glutamate, and tyrosine, compared to women, and hence increases after meal consumption were considerably higher in the latter case.
“For glycine, methionine, glutamine, threonine and phenylalanine, the ratios of postprandial to fasting serum concentrations were marginally but statistically significantly higher in women compared to men at either 60 or 120 minutes, post breakfast, whereas both ratios for the other 13 amino acids were similar between the genders,” they write.
Researchers observed relative changes to α-hydroxybutyrate, β-hydroxyisobutyrate, and α-ketoglutarate metabolites involved in glucose regulation 60 minutes after ingestion (up 25%, 20% and 22%, respectively).
They note that men had higher fasting concentrations of β-hydroxyisobutyrate, suggesting poor insulin sensitivity and higher risk for type 2 diabetes.
“Hence, relative to the women in our study, male participants had an unfavourable fasting amino acid profile that has been associated with insulin resistance,” they assert.
Further tests revealed a considerable decline in seven kynurenine metabolites (kynurenic acid, anthranilic acid, 3-hydroxykynurenine, xanthurenic acid, 3-hydroxyanthranilic acid, picolinic acid and quinolinic acid) two hours post-consumption, compared to fasting levels, although postprandial kynurenine and tryptophan were unaffected.
The kynurenine pathway is crucial for tryptophan catabolism, which has anti-cancer and anti-inflammatory properties, and observed increases in glucose concentrations may contribute to reduced catabolism through this pathway, the authors’ say.
They add: “The possible inhibitory effect of glucose on the kynurenine pathway underscores the importance of investigating if the prandial status can impact the concentrations of the metabolites in this pathway.”
Source: BMC Nutrition
Published online, January 11, 2023: http://doi.org/10.1186/s40795-022-00661-1
‘Serum concentrations of amino acids and tryptophan metabolites are affected by consumption of a light breakfast: a clinical intervention study in adults with overweight or obesity’
Authors: Ingrid V. Hagen, Anita Helland, Marianne Bratlie, Oivind Midttun, Adrian McCann, Arve Ulvik, Gunnar Mellgren, Per M. Ueland and Oddrun A. Gudbrandsen