The average person could be ingesting 2000 tiny pieces of plastic every week - the equivalent of a credit card - with drinking water the largest source.
The No Plastic in Nature report from the University of Newcastle, commissioned by the World Wildlife Fund, suggests people around the world are consuming about five grams of microplastics a week, or just over 250 grams annually.
The study combines data from more than 50 studies on the ingestion of microplastics, which are plastic particles under five millimetres in size.
Drinking water is the largest contributor, with the plastic particles found in bottled, tap, surface and groundwater all over the world.
Shellfish, beer and salt are the consumables with the highest recorded levels of plastic.
WWF International's director general Marco Lambertini says the findings should serve as a wake-up call to governments.
"Not only are plastics polluting our oceans and waterways and killing marine life - it's in all of us and we can't escape consuming plastics," he said in a statement.
"Global action is urgent and essential to tackling this crisis."
The University of Newcastle study, released on Wednesday, found water in the United States and Lebanon had on average 4.8 and 4.5 fibres per 500 millilitres respectively, compared to 1.9 fibres per 500ml in both Europe and Indonesia.
Since the year 2000, the world has produced as much plastic as all preceding years combined, with a third ending up in nature, the report states.
In 2016, some 100 million metric tonnes of plastic waste ended up in the natural world.
Mr Lambertini said the issue was a global problem which could only be solved by addressing the root cause of plastic pollution.
"If we don't want plastic in our bodies, we need to stop the millions of tonnes of plastic that continue leaking into nature every year," he said.
"In order to tackle the plastic crisis, we need urgent action at government, business and consumer levels, and a global treaty with global targets to address plastic pollution."