Cargill Inc., the Minnesota-based company at the center of the global food chain, is stepping out of its usual low-key profile to fight attacks on trade and immigration.

“We have to turn the tide on some of the current themes that we are seeing,” Chief Executive David MacLennan said in a speech in St. Paul on Friday. “Geopolitics are shifting and we are standing at the crossroads of some really important issues for business and for society.”

The Wayzata-based company is the nation’s biggest food processor, shipper and trader, touching every step of the food chain, from seeds and feeds used by farmers to the processing and delivery of food to restaurants and grocery stores.

But the rise of protectionist sentiment and nationalism in the United States and other countries poses a threat to Cargill’s $100 billion business, which depends on relatively frictionless movement of goods and people.

The luncheon at the University of St. Thomas marked the third time that MacLennan has spoken publicly this week, a shift for both him and the company, which, despite its huge size, tends to avoid the spotlight because it is privately owned.

On Wednesday, he spoke before a congressional committee in Washington in support of new infrastructure spending. He spoke again on the topic before a legislative panel in St. Paul on Thursday.

But he used Friday’s appearance, before an audience of executives and students, to express worries about the trade and immigration stances of the new Trump administration.

“The events of the last two weeks and some of the policies that have been announced make it more compelling and more urgent that we be more public and more front-facing on things like trade, immigration, food innovation,” MacLennan said in an interview after the speech.

While Trump has met ­dozens of high-level executives since the November election and hosted a few CEOs in the White House on Friday, he hasn’t reached out to MacLennan or many other firms that are hugely dependent on trade.

“When it comes to U.S. trade policy, we need to be clear: we want to work productively and effectively with the U.S. Congress and the new Trump administration,” MacLennan said.

He tempered his concern by voicing optimism about Trump’s appointees to lead the Commerce and Agriculture departments and the U.S. Trade Representative. “Let’s let them get confirmed and get settled in, but I would expect that I meet all three of them in the next 90 days.”

While he devoted much of his remarks to trade, MacLennan also expressed concern about the signals the new administration is sending on immigration, seen in Trump’s executive orders and remarks.

“It causes some of the smartest people from outside the U.S. and those looking to come to the U.S. to question,” he said. “The world’s best and brightest may start looking at other countries as their land of opportunity and that would be profoundly un-American. It would weaken not only our food system but also the U.S. economy.”

MacLennan told the audience that Cargill was disappointed that Trump withdrew the United States from participation in the Trans-Pacific Partnership, a free-trade pact designed by the U.S. and Japan to lower barriers and shape rules in the Pacific Rim.

But the company is even more vulnerable to a potential U.S. withdrawal from the North American Free Trade Agreement, or NAFTA, which Trump threatened on the campaign trail and since taking office.

“We need to be mindful of the effect on jobs and the impact of trade on jobs in local communities, but it’s not an all-or-nothing approach,” MacLennan said. “If the U.S. steps back from our leadership role in the global economy, I can guarantee you other countries will very, very quickly fill the gap.”

Since NAFTA was implemented in 1994, U.S. agriculture exports to Mexico and Canada have quadrupled from $9 billion to $39 billion, while the broader U.S. economy grew about 80 percent in that period. It also brought more variety and consistent supply of products to American consumers. If supply chains that formed as a result of NAFTA are broken, the cost of food will go up, MacLennan said.

Critics of NAFTA say it weakened the economic power of individual farmers.

“I think, in general, that these trade agreements went too far in terms of empowering corporations and financial firms to move wherever they want, and play governments off each other and diminish the power of governments,” said Ben Lilliston, director of corporate strategies at the Institute for Agriculture and Trade Policy in Minneapolis.

Lilliston’s organization advocates changes to NAFTA but not its sudden demise.

“We are critics of NAFTA, but we are very concerned that if President Trump would pull the U.S. out of NAFTA, the disruption would be harsh and a lot of people would be hurt,” Lilliston said.

Asked if NAFTA could be reformed to benefit more people, MacLennan said, “I think by and large it’s working. Any deal can always be improved.”