Microplastics in our food and water may increase how much fat we digest and absorb, potentially heightening the risk of obesity, heart disease and other conditions associated with consuming too much fat.
When plastics are degraded by sunlight, water, landfill incinerators and other processes, they can form microplastics 鈥� fragments less than 5 millimetres long. 鈥淎s they degrade, they become smaller and smaller, going down into the nanoscale,鈥� says at Rutgers University in New Jersey. 鈥淎 nano is one-billionth of a metre. So, at that tiny of a size, you can鈥檛 even see it.鈥�
The smaller the fragments become, the easier it is for them to leach into food and water. From there, they make their way into our bodies, though the exact amount we wind up digesting is unclear. Demokritou and his colleagues looked at how nanoplastics affect digestion using a small intestine model made from three different types of human epithelial cells, which line membranes.
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The team added nanoplastics to a slurry that contained proportions of protein, fat, carbohydrates, sugar and fibre comparable to the average US diet. The researchers then added heavy cream to boost the fat content. To simulate digestion, they passed this solution through three other liquids containing enzymes and molecules present in the mouth, stomach and small intestine.
The final product contained about 100 micrograms of nanoplastics per millilitre. Estimates of the average concentration of nanoplastics in food and water vary widely, but the researchers assume it is closer to 240 micrograms per millilitre.
Demokritou and his colleagues coated the solution onto the small intestine model. Two hours later, they measured the concentration and breakdown of fat. They found that the presence of nanoplastics boosted the breakdown of fat, increasing digestion by 33 per cent compared with a similar solution that didn鈥檛 contain nanoplastics. The microplastic mixture also increased the amount of fat the tissue absorbed by 145 per cent. The nanoplastics did not, however, appear to be toxic to epithelial cells or to decrease gut permeability.
鈥淥ur experience so far with microplastics is that they are not really toxic in the gut,鈥� says Demokritou, who presented these findings on 3 March at a meeting of the American Association for the Advancement of Science in Washington DC. Though he adds, 鈥渋t鈥檚 very alarming that they can interfere with the digestion and absorption of nutrients鈥�.
He believes this is because nanoplastics act like life rafts for fat molecules, increasing the surface area they can glom onto. This makes it easier for digestive enzymes to break down fats and absorb more of them.
at the University of Rome Tor Vergata in Italy says that these findings in an organ model may not completely translate to humans. 鈥淏ut still, I think this paper is very important because it gives us a new perspective on the potential hazards of these particles.鈥�
Demokritou says it鈥檚 important to keep in mind that not all microplastics are the same. Some have different properties, which may affect digestion differently. 鈥淭here might be some differences between saturated and unsaturated fats [too],鈥� he says.
Environmental Science & Technology
Article amended on 31 March 2023
We removed an erroneous statistic on the amount of nanoplastics humans consume each week
