Plus, the tennis star speaks for the first time about the "dark period" after her sister's death
Credit: John Parra/WireImage

Serena Williams – the outspoken winner of 22 Grand Slam titles – is rarely at a loss for words. But since the 2003 murder of her eldest sister, Yetunde, the tennis star has remained uncharacteristically quiet about her loss.

But Williams decided to write a memoir, On the Line, about her life – the fashion, the body image, her love life and how much she loves her sisters. Sitting with PEOPLE in the master suite of her Florida home, Williams spoke candidly about the ups and downs of her very public life.

What did you want to say in your memoir?
I wanted to explain how I see things. I wanted to talk about my body and my sisters, my career, what I’ve learned, what I’m still learning. I want women to know that it’s okay. You can be whatever size you are, and you can be beautiful both inside and out. We’re always told what’s beautiful and what’s not, and that’s not right.

Williams was devastated by the 2003 shooting death of Yetunde Price. The shooter, Robert Edward Maxfield, pleaded no contest to voluntary manslaughter and was sentenced to 15 years in prison.

The heart of the book is about the loss of your sister, Yetunde.
It was a real dark period in my life. I went through depression. I never even talked about it to my mom. No one knew I was in therapy, but I was. I was so close to her.

After Yetunde’s death, Williams gained about 20 lbs. Although she says she has always been ‘thick,’ Williams was the heaviest she’d ever been.

There were a lot of comments about your size. Was that strange?
Yes. For some reason, everyone is obsessed with weight. Are you bigger? Are you smaller? And everyone cares about that! It’s insane. Some days, I’ll be bigger. Other days, I’ll be smaller. It’s not a big deal.

You mention that in your memoir. But just a few sentences later, you say that you’re insecure about your body.
I think every female does that. We think we look good one day, and then the next day – or the next minute – we’re insecure about something. Sometimes I look at myself in the mirror and am like, ‘I want to lose my inner thigh. I’ve got to do an hour of cardio today,’ or whatever. I try not to do it, but the insecurity comes back sometimes. I do want to look good still; I do want to be healthy.

So what are your troublesome body parts?
My thighs. I think they’re too big. But also my arms. I think they’re too muscular. They’re too thick.

Your arms? I thought you’d consider those your best part.
I’m sensitive about them. I know that toned arms are in now. Look at Michelle Obama. She has great arms, and I think it’s wonderful that she shows them off like that! I love her for that. I’m like, ‘keep wearing strapless dresses!’ But I don’t like mine.

What’s your workout routine?

When I’m training, I just play a lot of tennis. But I’ll go to the gym, then I’ll run a lot of sprints. I spend a lot of time being physical, getting exercise. Sometimes, it’s an official workout. Other times, though, it’s just being active.

And what’s your diet like?
I don’t diet. I hate that word. Diets mean that you rob yourself of stuff that you like, and eventually you’re going to cave in and eat things that aren’t on your diet. You can’t deprive yourself forever. I eat what I like, but I try to eat it in proportion. There are things that aren’t healthy for me, so I try to eat less of them.

Williams, who has never publicly acknowledged her yearlong relationship with rapper Common, has had ups and downs in her love life.

In your book, you talk about a past relationship that didn’t work out, but you don’t name him. You just call him ‘So-and-so.’
The guy was a loser. That’s why I didn’t name him in the book. Everything is a learning experience. You learn about life; you learn about love. I wouldn’t trade the experience for anything, because it’s made me who I am. I enter relationships with my eyes wide open now. I’m not so na ve. ‘So and so’ actually had his own problems; he must have been 23 or 24. Looking back I’m like, ‘Oh my God, it was never going to work.’ At the time, you obviously can’t see that.

Are you an easy girlfriend to have?
No. I’m probably the worst girlfriend to have. I’m insecure; I think most girls are. I travel so much that it makes having a relationship hard. I can’t compromise my career for someone else, and that’s always difficult for guys to understand.

You’re dating someone in the public eye right now. What’s that like?
You can go on a Web site and there will be all sorts of gossip about them. They’re spotted hanging out with someone, and he’s suddenly ‘romantically linked’ with someone else. And you have all your friends calling you and asking what’s going on. That can be annoying. Really, it’s kind of stupid. You can’t let the media decide how your relationship is going to be. You have to communicate. Trust is very important to me, and I’m not going to get my information about my boyfriend from the media. Sometimes I read that I broke up with him, and I have to call and confirm. (Laughs) Which actually is my favorite part, because I love to make that phone call and be like, ‘Are we still together?’

Williams, who sells a line of apparel and skin care products on the Home Shopping Network, has always been interested in fashion.

You sometimes raise eyebrows with your choice of clothing. Does that bother you?
I’ve been on the worst dressed list several times, and I don’t care. I like what I like, and if I feel good wearing something, I’ll wear it.

And what makes you feel good?
A belt. I love belts. All my fashions tend to have belts. I’m obsessed with them. You can put a belt on any outfit and make it perfect.

Despite all the gossip about her clothes, weight and relationships, Williams claims not to know what people are saying about her.

What’s the weirdest thing you’ve read about yourself in the tabloids?
I don’t read about myself. I don’t bother anymore. It can really affect me. If they write something good, I don’t want to get all big headed, and let it change my attitude. It could change the way I walk. It’ll change the way I treat people. If it’s negative press, it can change your attitude for the negative and mess with your self esteem. So I just don’t read anything.

So you’ll never know what people are saying about you?
I have a great scrapbook. At the end of my career, I’ll read it. So I’ll get to read it; just not now.