Metabolites in blood plasma offer news insights for measuring diet

Self-reporting is one of the primary ways that dietitians, medical doctors, and researchers assess people’s diets and their health effects. While useful, self-reporting, often through dietary records or questionnaires, creates a risk of inaccurate data.

To address these limitations, researchers analyzed metabolites (molecules like amino acids and peptides created during or after metabolic processes) in blood and determined that they have potential as objective biomarkers to evaluate the foods we consume.

“Typically, if we asked a person to eat a certain type of diet, they might say they did on their self-reported diet records, but maybe they didn’t actually consume the diet as well as they reported, so by analyzing metabolites in blood in controlled feeding studies, we may potentially be able to use these as biomarkers of dietary patterns in the future,” says Andrea J. Glenn, assistant professor of nutrition, at the NYU Steinhardt School of Culture, Education, and Human Development.

The researchers analyzed the metabolites in plasma samples of people who participated in two trials to measure their adherence to the portfolio diet, a diet designed to lower cholesterol levels through consumption of plant-based foods, such as soy protein, nuts, plant sterols and viscous fiber. In both trials, participants were provided with all of the diet plan’s foods at weekly clinic visits for four weeks (excluding fruits and vegetables, which participants bought separately). Plasma samples were collected at the start of the study, at week two, and week four.

For the first trial, 34 participants were placed in three groups: a portfolio diet group, a control diet group, and a control diet combined with a cholesterol-lowering medication. In the second trial, 25 participants were in two groups, a portfolio diet group and control group.

The results, published in the European Journal of Clinical Nutrition, found that of the 496 known metabolites, 145 (29%) of them changed significantly for the portfolio diet group in the first trial. For the second trial, 63 metabolites (12%) changed significantly with the portfolio diet. Across both trials, 52 metabolites (10%) changes significantly for those on the portfolio diet. These changed included increases in metabolites associated with plant-based diets such as N2-acetylornithine and lenticin, and decreases in metabolites associated with the low saturated fat content of the diet such as several C:18 lipids.

“These results are promising as these metabolites may be used to assess adherence to the portfolio diet or similar dietary patterns. However, further studies are needed to confirm or validate these metabolites as objective biomarkers given the limited research in this area,” says Glenn, the study’s lead author.

This study was supported by a Diabetes Canada End Diabetes 100 Award and the Canadian Institutes of Health Research.