In the past 50 years, what's on dinner plates has grown more similar the world over - with major consequences for nutrition and global food security, researchers say.
"Diversity enhances the health and function of complex biological systems," the researchers wrote in the Proceedings of the National Academy of Sciences. But the world of food had become homogeneous, to the point of suggesting a global standard food supply.
In the past 50 years, "national per capita food supplies expanded in total quantities of food calories, protein, fat and weight," they said. But at the same time, there had been "a decline in the total number of plant species upon which humans depend for food".
More people were relying on "a short list of major food crops", such as wheat, corn and soy, dairy and meat, lead researcher Colin Khoury said. "These foods are critical for combating world hunger, but relying on a global diet of such limited diversity obligates us to bolster the nutritional quality of the major crops."
Khoury and his colleagues used data from the United Nations Food and Agriculture Organisation to look at the composition of food supplies in 152 countries from 1961 to 2009. The total supply has increased, with animal products becoming "increasingly important in contribution to protein and oil crops dominating fat food supplies".
That reliance on a few foods may also accelerate the rise in obesity, heart disease and diabetes, Khoury said. And those diet-related diseases are growing even in countries with significant hunger problems.
"One of the worrying issues is that as we tend toward a homogeneous diet, the regionally important crops" such as sweet potatoes, yams, sorghum, oca and maca, are declining," Khoury said.
Wheat is a major staple in 97.4 per cent of countries, rice in 90.8 per cent and soy is significant to 74.3 per cent.
The lessening of diversity of food crops also makes the food supply more vulnerable to drought, insects or disease.
In some parts of the world, Asia and Africa in particular, the diversity of food crops has grown, as staples such as wheat and potatoes have gained importance. But that has meant many minor crops that had been important have lost ground.