The former first lady was speaking at the Partnership for a Healthier America conference in Washington, DC.
In case you don't remember, one of Obama's biggest initiatives while in the White House was the promotion of healthy lifestyles, especially for young people. This included her "Let's Move" initiative to combat childhood obesity.
But the Donald Trump administration has been dismantling some of Obama's work.
Trump starting going after Obama's healthy eating initiatives and her "Let Girls Learn" program for women's education at the beginning of May.
The Healthy, Hunger-Free Kids Act of 2010, supported by Obama, gave schools nutrition rules for the food they provided children through programs paid for by the government.
The rules included lowering the amount of calories, fat and sodium and increasing the amount of whole grains, fruits, vegetables and nonfat milk provided, according to the New York Times.
This affected 32 million students who get federally subsidized meals at school.
But in early May, Agriculture Secretary Sonny Perdue announced that schools didn't have to follow the nutrition rules anymore. States will get to decide about it in the next school year.
Obama addressed Trump undoing her healthy lunch work on Friday.
As is her norm, Obama did not mention Trump by name, but it was clear who she was talking about.
Obama said that taking away the healthy lunch regulations is basically "saying to you moms,"
You want to talk about nanny state and government intervention, well, you just buy the food and be quiet and you don't need to know what is in it.
The former first lady said parents should "think about why someone is OK with your kids eating crap."
"If we want to make this country great, our kids need to be healthy," Obama said.
This is not the first time Obama has slammed Trump.
She said the tape gave her a "sick, sinking feeling" that "hurts."
It doesn't seem like Obama's planning on letting up with her criticism of the president.
Citations: Michelle Obama Criticizes Trump School Lunch Decision (NBC Chicago), Do Healthy Lunches Improve Student Test Scores? (The Atlantic), How the quality of school lunch affects students' academic performance (Brookings)