"Phosphorus is an essential element to all life – it's in our bones, and it comes from the plants and animals we eat," said Geneviève Metson of McGill in a video abstract for Environmental Research Letters (ERL). "Because it's an essential nutrient, it is a fertilizer we use in agricultural production to ensure high yields. The phosphorus we use as fertilizer mostly comes from mines, and thus it is a non-renewable resource."

From 1961 to 2007, global phosphorus demand rose 198%, from 5.9 Tg to 17.6 Tg. Population growth alone would have increased phosphorus demand to 12.7 Tg, Metson and colleagues calculated. So a shift in diet was responsible for almost 28% of the rise.

Meat, dairy and egg consumption accounted for 72% of the global average dietary phosphorus footprint, with beef the most phosphorus-intensive meat.

"On a national level the amount of phosphorus needed to satisfy diet choices varied greatly – more developed countries [used] larger amounts of mined phosphorus," Metson told environmentalresearchweb. "This is the most spatially and temporally detailed analysis of the relationship between diet and phosphorus requirements."

As countries develop, their inhabitants tend to eat more meat. In 2007, the Democratic Republic of Congo had the lowest phosphorus footprint with an average of 0.35 kg consumed per head per year. Luxembourg led the table with 7.64 kg, closely followed by the US at 6.89 kg. China’s footprint, one of the lowest in 1961, increased almost 400% by 2007, while Canada’s decreased.

Throughout the study period, footprints tended to be highest in North America, Oceania and parts of South America. Most of Europe, the ex-USSR and South America had footprints of moderate size – between 3 and 5 kg per head per year. Asia and Africa consistently showed the lowest phosphorus footprints.

"While phosphorus is a scarce resource globally, it is also overabundant in some areas," said Metson. "When phosphorus is lost through runoff and erosion from agricultural fields or lost through sewage systems, it can pollute waterways downstream. Human management of phosphorus is key to ensure future long-term food security and clean waterways."

By 2050, phosphorus demand could increase by 68–141% if diets continue to change and population increases, said the researchers. But if people ate pulses instead of meat and population grew in line with the lowest projected rise, the global average phosphorus footprint would decrease by a fifth compared to 2007 and the total global phosphorus use for food production would drop by 10%.

"Diet changes, especially moderating meat consumption, can be part of a suite of strategies to increase the sustainability of phosphorus management through the food system," said Metson, who believes a vegetarian diet would also be less intensive with regards to land, water and energy.

The researchers hope their method for calculating dietary phosphorus footprint at the national level can be used to include diet more accurately in sustainable phosphorus management strategies. They reported their work in Environmental Research Letters (ERL).