01/09/2014 at 07:00 PM EST
loves her body and thinks you should love yours, too.
"I don't want to look like I did when I was 25," the actress, 41, tells PEOPLE. "I like the way that I look now better than when I was 25. I can't help that other people may be uncomfortable with that, but that's not my responsibility to make them feel okay with the fact that I'm getting older. I'm okay with it. I like it."
In her new tome
, The Body Book
, Diaz opens up about her own struggles with food, her beliefs about beauty and her suggestions for getting healthy in the New Year.
"There's no such thing as anti-aging," Diaz tells PEOPLE. "There's no such thing as turning back the hands of time, and it makes me crazy that we live in a society where that's sold to women – that we're supposed to believe that if we're getting older, we've failed somehow, that we have failed by not staying young."
"I wish that women would let other women age gracefully and allow them to get older and know that as we get older, we become wiser."
When she was younger, Diaz struggled with acne, which she eventually connected to all of the fast food that she was eating.
"I used to have really bad skin and that was absolutely due to the food that I was ingesting," she says. "I lived on processed fast food. I drank a ton of soda and I ate greasy, fatty, cheesy foods consistently. I went around with really bad acne well into my early 20s. Even into my 30s, when I was still eating a lot of dairy. I'd get those little white bumps all over my skin – I stopped eating dairy and it completely changed my skin."
But the Annie star
admits to splurging on French fries and other less-than-healthy food from time to time.
"I'm a total advocate for eating the things you love. For sure I splurge. Health is an equation. It just depends on how many times you pick good over bad. You need a higher ratio of good, and if you do [that], you're ahead of it."