Low-plastic diets cut plastic-linked chemicals in urine within 7 days, study finds

In a recent study published in the journal Nature Medicine, researchers characterized urinary levels of plastic-associated chemicals (PACs) in healthy adults.

Plastics are common in everyday life, exposing us to harmful PACs. For instance, bisphenols and phthalates are established endocrine disruptors. Exposure to bisphenols and phthalates is associated with adverse health outcomes, including metabolic syndrome and cardiovascular disease. Most studies on the health effects of these PACs have been observational, and only a few trials have examined whether modifying exposure pathways could decrease urinary PAC levels.

PERTH Trial Design and Exposure Assessment

In the present study, researchers described the findings of the Plastic Exposure Reduction Transforms Health (PERTH) trial. They recruited 211 healthy adults (123 females and 88 males) in Australia for a longitudinal cohort study and included 60 of these subjects in a pilot randomized controlled trial (RCT). Nasal and urine samples were collected on non-consecutive days for both the cohort study and RCT.

Participants completed comprehensive health tests, including body composition, physiological, and biochemical measures. All cohort participants had at least six PACs in urine samples on any given day. Mono-methyl phthalate and bisphenol AP were detected in < 40% of participants. Bisphenol A (BPA) and di(2-ethylhexyl) phthalate (DEHP) were detected in 61.8% and 30.6% of nasal samples.

Further, the PAC exposure questionnaire, the 24-hour personal care product (PCP) recall questionnaire, and the 24-hour dietary recall-plastic exposure questionnaire were administered to assess dietary intake and PAC inhalation, dermal absorption, and ingestion. Single-exposure models showed that each additional serving of vegetables and fruits was associated with 1.82% reduction in mono-iso-butyl phthalate (MiBP) and 6.99% increase in bisphenol S (BPS) in urine.

In multi-exposure models, greater consumption of vegetables and fruits was associated with elevated urinary BPS, whereas higher consumption of oils and fats was associated with reduced urinary BPS. Next, the team calculated a total dietary plastic (TDP) score to estimate the number of plastic touchpoints of foods and beverages. The average TDP score was 41.6 per day, with females consuming more foods in plastic packaging than males.

Dietary Sources, Personal Care Products, and Body Composition Findings

Each unit increment in the TDP score was associated with nearly 0.09% increase in urinary mono(2-ethyl 5-hydroxyhexyl) phthalate. Similarly, urinary BPA increased by 14.3% for each additional canned item consumed. Further, increased use of PCPs, such as hair, makeup, and skin products, was associated with higher levels of low-molecular-weight phthalates in urine, including mono(3-carboxypropyl) phthalate (MCPP) and mono-ethyl phthalate (MEP).

Among body composition parameters, higher adiposity was associated with reduced urinary PACs; one standard deviation (SD) higher body mass index (BMI) was associated with 16.3% lower monobenzyl phthalate (MBzP), while one SD higher waist circumference was associated with 22% lower MCPP. Cross-sectional associations were also observed between elevated urinary levels of DEHP metabolites and cardiometabolic biomarker levels in this healthy cohort.

For instance, higher urinary levels of mono(2-ethyl-5-oxohexyl) phthalate were associated with a 30.5% decrease in lipoprotein(a) and a 24.7% reduction in high-sensitivity C-reactive protein (hsCRP). Likewise, higher MCPP levels were associated with lower fasting serum glucose levels, without establishing that higher PAC exposure is beneficial. In the seven-day pilot RCT, participants were randomized to one of five groups.

Low-Plastic Intervention Trial Results

Group 1, viz., low-plastic foods with minimal plastic touchpoints across production, processing, packaging, storage, and preparation, decreased urinary MBzP by 46.7%, mono-n-butyl phthalate (MnBP) by 31.5%, and bisphenols by 58.5% compared to controls (group 5; no intervention). Further, a low-plastic foods and plastic-free kitchenware intervention (group 2) resulted in greater decreases in urinary MBzP, MnBP, and BPA than in controls. A low-plastic PCP intervention (group 3) only reduced urinary MnBP by 35.3% relative to controls.

Notably, group 4, which included low-plastic foods, plastic-free kitchenware, and low-plastic PCPs, had the greatest reduction in urinary MnBP (-44.1%) compared with controls. Replacing foods and beverages with low-plastic alternatives had no impact on mean daily energy intake in groups 1, 2, or 4, or on saturated fat intake in groups 2 or 4. No adverse events or safety concerns emerged during the RCT.

Implications of Reducing Plastic Exposure

In sum, PAC exposure was ubiquitous in healthy adults, with packaged, processed, and canned foods contributing to exposure. In the short-term RCT, substituting diet with low-plastic alternatives, with or without low-plastic PCPs and/or plastic-free kitchenware, was associated with a significant reduction in urinary bisphenols, MBzP, and MnBP. Further research is required to investigate the causal links between PAC exposure and its impact on human health and whether lowering exposure improves long-term health outcomes.