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Junk food can be detected in blood and urine tests, reveals new research. Molecules in blood and urine samples can show how much ultra-processed food you eat, say American scientists.

Researchers used data from more than 700 people to discover biomarkers corresponding with ultra-processed food consumption. Sets of metabolites found in blood and urine "reliably

correspond" with how much energy from ultra-processed food a person consumes, according to the findings published in the journal PLOS Medicine. Ultra-processed foods, or UPFs, are

ready-to-eat or heat items made with ingredients extracted from foods or synthesised in labs, with little or no whole foods in their composition. They are often high in added sugar, fat and

salt, and low in protein and fibre. Common examples include bacon, sausages, breakfast cereals, ham, burgers, ice cream, crisps, mass-produced bread, canned baked beans, biscuits, fizzy

drinks, fruit-flavoured yoghurts, instant soups, and some alcoholic drinks, such as rum. UPFs can account for more than half of the calories consumed in the average diet, yet their impact on

human health remains unclear, in part because it is so difficult to accurately track exactly how many UPFs people eat. For the new study, American researchers analysed blood and urine

samples from 718 older adults, alongside diet details, to identify chemical fingerprints, called poly-metabolite scores, linked to UPF intake. The team found that hundreds of blood and urine

metabolites were associated with the percentage of energy someone consumes from UPFs. The researchers explained that a poly-metabolite score corresponding with UPF intake could be created

using 28 of the blood metabolites or 33 urine metabolites. The score was predictive of UPF intake among participants using self-reported dietary data. The research team then validated the

scores in a controlled feeding study, confirming the scores could distinguish, within subjects, between high-UPF and no-UPF diets among 20 patients with high-controlled diets. The scores

also "significantly differed" between a UPF-heavy diet and one without UPFs, according to the findings. Study leader Dr Erikka Loftfield, of the National Cancer Institute in

Maryland, said: “The identified poly-metabolite scores could serve as objective measures of UPF intake in large population studies to complement or reduce reliance on self-reported dietary

data. “Poly-metabolite scores should be evaluated and iteratively improved in populations with diverse diets and a wide range of UPF intake.” She added: “We developed and tested

poly-metabolite scores in blood and urine that were predictive of diets high in energy from UPF intake in an observational study of free-living adults and in a highly controlled feeding

trial, respectively. These poly-metabolite scores could serve as objective measures of UPF intake in large population studies to complement or reduce reliance on self-reported dietary data.

"Additionally, these findings could provide novel insight into the role of UPF in human health.”