The May 21 issue includes a profile of Dr Bill Sears and leads with a shot of 26-year-old Jamie Lynne Grumet feding her son Aram.
Grumet told the magazine that she was breastfed until she was 6 years old, and added: "I grew up this way and never thought about raising my kids differently.
"People have to realise this is biologically normal. The more people see it, the more it'll become normal in our culture. That's what I'm hoping. I want people to see it."
Broadcasters MSNBC and ABC chose to censor the image when discussing it during some programming.
Following the controversy surrounding the image, Time editor Stengel said: "It's certainly an arresting image. It's an image to get people's attention about a serious subject.
"Some people think it's great and some people are revolted by it. That's what you want, you want people talking."