On the exterior, Katherine Heigl looks like a perfectly manicured poolside goddess. She's tan, she's fit, she's beautiful, she's blonde - and will you check out that engagement rock on her finger?

But don't be fooled. This 28-year-old actress knows how to get down and dirty. Glamour sat down with the star on the eve of her movie breakthrough to talk about her fearless ride to the top.

GLAMOUR: Now you're starring in Knocked Up with Paul Rudd and Seth Rogen, as a woman who gets pregnant after a one-night stand. What was it like to work with those funny guys?

Katherine Heigl: Oh, it was the best experience. I constantly had to be on my toes, because some of the scenes were improvised and the stuff they came up with was so outrageous. In one scene, I got into a fight with [Rogen] about the way my body was changing. He said something like, "Don't worry, we'll pay for vaginal reconstruction." That's what came out of his mouth, unscripted!

GLAMOUR: Was it weird to feel pregnant?

Katherine Heigl: No, because the prosthetic belly felt so fake. Plus, my character in Knocked Up was a super-in-shape reporter, so I had to lose 10 pounds for the role. When I do get pregnant, I highly doubt I'll be one of those women who don't look pregnant from behind â€" I'll look pregnant from the ankles up!

GLAMOUR: Was it hard to lose weight for a role?

Katherine Heigl: It was awful! I remember once reading an article about Jessica Alba â€" the most beautiful, most in-shape person alive â€" and how committed she was to her regimen. And I thought, There's no way in hell that will ever be me. I can't eat only fish and vegetables or work out seven days a week. Then suddenly I was that person and I was shocked. But I could never maintain it. I like food too much!

GLAMOUR: You seem to have a very healthy attitude toward your body. Do you own a scale?

Katherine Heigl: No, because it can make you kind of crazy. I used to weigh myself every day at a certain time of day. Then I would write down the number and measure my body fat. It wasn't a healthy way to live. Now I can tell if I've gained or lost weight just by the way my clothes are fitting. But it's tempting to buy a scale, because I'd love to know what I weigh. Whatever. I just lie and say 120. [Laughs]

Katherine Heigl: When I see some of the people who are glorified in magazines these days â€" who are so thin it's bordering on sickness â€" I just feel exhausted. I would hate to think that young girls in high schools across America think that's what they're supposed to look like.

GLAMOUR: Who do you think has a healthy-looking body?

Katherine Heigl: Jennifer Aniston and Halle Berry are both in amazing shape. They look phenomenal but they don't look sick. Then there's Kate Winslet. She's confident, beautiful, talented and sexy and she owns it. Early in my career, I read an interview she gave about how the industry wanted her to lose weight; she basically gave them the finger and said no. I remember thinking, I can do that too. I don't have to look like one of these genetically superior people in order to work.

GLAMOUR: Your fiancé is Josh Kelley. The two of you met when you starred in the video for his song, "Only You." How quickly did you know he was the one for you?

Katherine Heigl: We definitely had chemistry at first sight. In the beginning, I was a little intimidated because I thought I was more into him than he was into me. But I was tired of games, tired of playing it cool, tired of trying to remain in control of my relationships. So I was honest about how I felt, he was honest right back, and within a month and a half I was completely in love with this guy.

GLAMOUR: Do you ever have to deal with groupies?

Katherine Heigl: Yes, and I don't particularly like it. About a year ago I called him on his tour bus and heard giggling voices in the background. After that I said, "No more girls on the bus." If the boys in the band want to meet girls they can go to a local bar.

GLAMOUR: Don't the other guys in the band ever say, "Hey, we want to have girls on the bus â€" what's the problem?"

Katherine Heigl: [Laughs.] They'll get over it.

GLAMOUR: What do you and Josh tend to fight about?

Katherine Heigl: Stupid stuff. I'll call him on tour and say, "When should I expect you?" And he'll say, "I'll check that out." Two days before he's supposed to arrive I'll say, "Do you know yet?" And he'll say, "No, I haven't gotten that e-mail yet." And I'm like, "Oh my God â€" figure it out!" But what's wonderful about our relationship is that when it comes to the bigger things, like values, we see very eye-to-eye.

GLAMOUR: Let's talk about your childhood. You were raised Mormon; do you still practice the religion?

Katherine Heigl: Not to the extent I did growing up â€" I'm having a glass of white wine right now; that's not exactly being a good Mormon! But I am really supportive of the Mormon church and so profoundly grateful for the childhood I had. It's hard work to grow and change and be honest with yourself about your mistakes, and I think the Mormons handle that beautifully. The faith I grew up with has influenced every decision I've made in my life â€" well, except for the bad ones! [Laughs]

GLAMOUR: So would you raise your kids in the religion?

Katherine Heigl: I haven't decided yet. I've always thought I would raise them Mormon because I had such a wonderful childhood. In today's world you look around and the decisions 14-year-olds are making about sex just horrify me: I wasn't thinking about any of that as a kid. So I'd like to give my children the same sense of security and ease.

GLAMOUR: But your childhood wasn't all rosy: When you were seven, your teenage brother, Jason, was killed in a car accident. How does that still affect you today?

Katherine Heigl: I think about what our lives would be like now if he were still alive: what he'd be doing, where he'd be living, whether I'd see him often, whether he'd have kids. These are the things you think about when someone dies â€" all the potential that never was. It stays with you forever.

GLAMOUR: Your parents donated his organs and you're a spokeswoman for organ donation.

Katherine Heigl: I'm sure it's the last thing my parents were thinking about when my brother was on life support, but my mother [Nancy Heigl] stated it beautifully at the time. She said, "If I can spare another mother what I'm going through, then [donating his organs] is the most important thing I can do in Jason's memory." It's phenomenal when you meet someone whose life was saved because someone made that choice.

NOTE: [For more information on how to become an organ donor, please visit shareyourlife.org]

GLAMOUR: Where do you see yourself 10 years from now?

Katherine Heigl: I hope to have children and the sort of family traditions where we eat together every night. But my career is also super important to me. I don't think I could ever be a stay-at-home mom. So I'll have to find a way to combine the two in a healthy and productive way. Joshua will be an amazing father, so I won't have to do it alone. Most importantly, I don't want life to spin by so fast I can't hold onto it, or remember it, or enjoy it. Because I'm loving life right now.

GLAMOUR: So you've had a pretty crazy year at Grey's Anatomy. What prompted you to chastise Isaiah Washington?

Katherine Heigl: At the time, I was a girl whose best friend had been hurt. I was mad, I'd had a glass or two of champagne, and an interviewer asked me about it. Later, when I watched it on the news, I thought, I'm totally going to get in trouble for this. I knew I wasn't playing the political game â€" the network wants us to promote a healthy, happy environment, and I'm usually all for that â€" but that particular incident really infuriated me, and I couldn't hold my tongue. I think it's pathetic there's still so much bigotry in 2007, and I would speak out again if the situation arose.

GLAMOUR: How did people react to your statement?

Katherine Heigl: There was so much encouragement, so much gratitude. The man who designed my engagement ring, Ryan, and his partner, Ken, wrote me a letter thanking me for standing up for them. And when I read that letter I realized the issue was larger than what happened to T.R. Knight, and I started to understand how very alone so many people have felt.

GLAMOUR: Isaiah Washington basically received a slap on the wrist; he went to rehab for a month. Do you feel he should have been treated more harshly, like Don Imus was?

Katherine Heigl: People make mistakes â€" they say things they shouldn't have or didn't necessarily mean. But I believe in consequences. If there are none, someone might feel like they've gotten away with something, or that what they said couldn't have been that bad. Those female basketball players needed the community and this country's support more than Don Imus did. The same goes for my feelings about T.R. Knight.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.