Increasing similarity in diets worldwide is a threat to health and food security with many people forsaking traditional crops such as cassava, sorghum or millet, according to an international study.
The report, which detailed for the first time the convergence in crops towards a universal diet in more than 150 nations since the 1960s, showed rises for foods including wheat, rice, soybeans and sunflower.
Among shifts, Pacific islanders were eating fewer coconuts as a source of fat and many people in Southeast Asia were getting fewer calories from rice, it said.
Vulnerability to pests and diseases
"More people are consuming more calories, protein and fat, and they rely increasingly on a shortlist of major food crops ... along with meat and dairy products," Colin Khoury, leader of the study at the International Centre for Tropical Agriculture in Colombia, said in a statement.
Such diets have been linked to risks of heart disease, cancers and diabetes, the study said. Reliance on a narrower group of food crops also raises vulnerability to pests and diseases that might gain because of climate change.
Overall, diets had become 36% more similar in the past 50 years, judged by factors such as shifts in consumption of more than 50 crops for calories and protein, the study said.
The convergence "continues with no indication of slowing", according to the study in the US journal Proceedings of the National Academy of Sciences that included the Global Crop Diversity Trust, Wageningen University in the Netherlands and the University of British Columbia in Canada.
Soybean, sunflower oil and palm oil had become part of the "standard global food supply" alongside crops such as wheat, rice, maize and potato, the study showed.
Meat and sugary drinks
Rising wealth in emerging economies meant higher consumption of products such as meat and sugary drinks that are typical of Western diets. "We are seeing a rise in obesity and heart disease ... from Nigeria to China," Khoury told Reuters.
Even so, many national diets had become more varied.
"As the human diet has become less diverse at the global level over the last 50 years, many countries, particularly in Africa and Asia, have actually widened their menu of major staple crops, while changing to more globalised diets," a statement said.
The scientists urged diversification, including of crops that are falling from fashion, such as rye, yams or cassava, to bolster food security. They also called for preservation of genetic variety in all crops.
Read: Diet and exhaustion
Risks of single crop
"Genetic uniformity means more vulnerability to pests and disease," Khoury said. The Irish potato famine in the late 1840s, or southern corn leaf blight in the United States in the early 1970s, showed the risks of relying on a single crop.
John Kearney, of the Dublin Institute of Technology who was not involved in the study, said trends in diets could be reversed with greater awareness of health risks.
Some people in Northern Europe were adopting healthier Mediterranean diets with more fruit, vegetables and less meat, he said, even though many in Southern Europe were shifting to more meat and less olive oil.