It’s obvious to anyone who visits a U.S. supermarket — past displays brimming with Chilean grapes, Mexican berries and Vietnamese dragon fruit — that foreign farms supply much of our produce.

Imports have increased steadily, but the extent of the change may be surprising: More than half of the fresh fruit and almost a third of the fresh vegetables Americans buy now come from other countries. Local, seasonal and farm-to-table are watchwords for many consumers, but globalization has triumphed in the produce aisle. It raises questions about what it portends for U.S. consumers and farmers and what it means for Americans’ health. “I had no idea that more than half our fruit is imported, and it shocks me that this has happened so quickly,” said Michael Pollan, a professor at the University of California, Berkeley, whose bestselling books have analyzed the tensions between local and global food systems.

The surge in imports, mostly from Latin America and Canada, flows from changes in the past 40 years, starting with improvements in roads, containerized shipping and storage technology. Horticulturists developed varieties and growing practices adapted to warmer climates — enabling, say, blueberries and blackberries to be grown in central Mexico.

Growth in U.S. incomes spurred greater demand for fresh produce year-round. Immigrants brought tastes for the foods of their homelands, and in some cases (like avocados and mangoes) these tastes have became mainstream. Foreign growers took advantage of lower labor costs. International trade agreements reduced tariffs and other obstacles to imports, while many American farmers, facing regulatory hurdles at home, shifted production abroad, mainly to Mexico.

One crucial part of the story is little known: During the past two decades, the U.S. Department of Agriculture has issued roughly 100 new rules allowing specific crops to be imported from certain countries. Crops that previously would have not been approved because they might introduce invasive pests and diseases were allowed in through new “systems approaches” that combine methods like inspections, sprays and bagging of fruits.

As a result, the proportion of the imported fresh fruit eaten in the U.S. rose to 53.1 percent in 2016, from 23 percent in 1975, said the Agriculture Department’s Economic Research Service. Fresh vegetable imports rose to 31.1 percent from 5.8 percent. (Still, the U.S. remains a net agricultural exporter.)

Greater availability has led to a huge increase in per capita consumption of many crops, including mangoes (up 1,850 percent from 1975 to 2016), limes, avocados, grapes, asparagus, artichokes and squash. Yet consumption has fallen for peaches, oranges, cabbages and celery — which are still primarily grown in the U.S.

For consumers, the chief advantages of the import boom are the increased availability and variety of fresh produce.

“It’s easy to criticize food that comes from far away,” Pollan said. “But if the question is whether this is good for your health or not, in general it is.”

Many imports cost less and can be fresher than domestically grown equivalents. In spring, newly harvested Gala apples from New Zealand may be crunchier than the same variety from U.S. orchards, which were picked the previous fall.

But produce may suffer from transport. It may be picked less ripe. Varieties may be selected for durability at the expense of flavor, and treatments to kill pests (hot water for mangoes, cold temperatures for citrus) can degrade flavor or texture.

It might seem logical that older produce is less nutritious, and for some compounds such as vitamin C, levels do decline with time. But there does not appear to be any evidence that the overall nutrient content degrades significantly. From a public health standpoint, the benefits of increased availability and consumption of imported produce outweigh any such worries, nutritionists say. “ ‘Eat your veggies’ is good advice no matter what,” said Marion Nestle, a professor emerita of nutrition, food studies and public health at New York University.

For U.S. farmers, too, imports have had mixed consequences. The increased international trade in produce has benefited many (growers of Northwestern apples and California citrus) but harmed others (producers of Florida tomatoes and California asparagus).

Most growers’ organizations maintain that trade accords like the North American Free Trade Agreement have helped U.S. produce farmers on balance. “NAFTA overall has been positive, and we oppose U.S. withdrawal from the agreement,” said Ken Gilliland, director of international trade for Western Growers. “Eliminating NAFTA and implementing tariffs would have a negative impact on our members’ ability to export.”

Whatever the drawbacks or advantages, imports are likely to continue growing. An Agriculture Department report said fresh produce imports will rise 45 percent from 2016 to 2027, implying that a decade from now, three-quarters of our fruits and almost half of our vegetables will be imported.