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June 20 (UPI) -- A blood sample detecting small molecules might reveal whether a person is following a prescribed diet, according to a new study. Scientists at Johns Hopkins Bloomberg School of Public Health studied how dozens of metabolites can show adherence to a diet. They say their findings, which were published Monday in the American Journal of Clinical Nutrition, could provide an easy measure of dietary adherence.
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They found that the metabolites in the blood differed significantly between treatment and control groups enrolled in a clinical trial of the Dietary Approaches to Stop Hypertension diet. The DASH diet, which is designed to lower blood pressure, emphasizes fruits and vegetables while restricting red meat, sodium and sweets.
"We can now consider these metabolites as candidate biomarkers for assessing adherence to the DASH diet in future nutrition research studies, and one day clinicians might use these markers to monitor what their patients eat," lead author Dr. Casey M. Rebholz, an assistant professor in the Department of Epidemiology at Hopkins, said in a press release.
In the past, researchers have had difficulty determining health impacts of diets because of poor adherence to them.
They have relied on asking participants to keep track of what they eat but that is not always accurate.
Another method is testing urine samples from participants, but they say it's a burden to ask them to collect samples over several days. In addition, a urine analysis detects limited nutrients.
Hopkins researchers tested frozen blood samples that had been drawn from participants during the landmark 1997 study of the DASH diet that showed it significantly reduced blood pressure. Participants were provided with all meals.
The Hopkins scientists analyzed blood samples from 329 DASH trial participants for levels of metabolites. These include lipids, amino acids and other small-molecule byproducts of the body's biochemical activity that reflect food consumption.
They used an advanced "untargeted metabolomics" approach to examine all known metabolites.
They found 97 metabolites levels that differed significantly between the DASH diet-assigned participants and the control group.
In addition, they identified 67 metabolites in which average levels differed significantly between the DASH diet group and a third group of mainly fruits and vegetables but not as rich in low-fat dairy.
In each dietary comparison, they found 10 metabolites with the sharpest diet-related differences to distinguish the two groups.
"We don't think a single metabolite will be enough to detect a dietary pattern," Rebholz said. "It really needs to be a combination of metabolites."
The top 10 discriminator metabolites were N-methylproline, stachydrine, tryptophan betaine, theobromine, 7-methylurate, chiro-inositol, 3-methylxanthine, methyl glucopyranoside, β-cryptoxanthin and 7-methylxanthine.
The researchers believe these metabolites could be used in future studies as well as ordinary clinical setting to assess adherence to the DASH diet.
"This approach certainly could be adapted for other dietary patterns, and I hope it will be," Rebholz said.
