Thinspired: Mara Schiavocampo's Amazing 90-Pound Weight Loss

— -- (Editor's Note: Mara Schiavocampo is an ABC News correspondent and author of the soon-to-be-released book “Thinspired: How I Lost 90 Pounds -- My Plan for Lasting Weight Loss and Self-Acceptance.” The book will be available Dec. 30.)

Most people don’t lose weight by accident. Especially not me.

I’m not naturally thin. I’ve never been athletic. I love sugar so much I have literally poured it down my throat.

I also have a very tortured and complicated relationship with food and my weight. As a child, a family member regularly ridiculed me and forced me to diet, including weekly weigh-ins.

As an adult, I’ve tried practically every diet and weight-loss program known to man. In my early 20s, I suffered a debilitating eating disorder, leading to depression. So, like I said, I’m definitely not the kind of girl who loses weight by accident.

But that’s exactly what happened. How much weight? Ninety pounds.

Ok, so it wasn’t completely by accident. I had a baby, and desperately wanted to lose the 40 pounds I’d gained, especially given that I was about 50 pounds overweight before the pregnancy. I refused to stay that size. So I made some major life changes, and didn’t give myself any outs or excuses.

The beginning was torturous. I mean, it was pure hell. But once I got through the initial phase, adopting new habits, it became effortless. The baby weight came off easily, and then more, and more, and more, all the way down to 90 pounds.

At some point, of course, people started to notice. I’d get questioned almost daily, by everyone from co-workers, to family members, to viewers sending emails.

“What are you doing?” everyone wanted to know. Though I didn’t start with a formal plan, looking back on my progress, I realized there was, in fact, a formula for lasting success.

Food: 70 percent

Sleep: 10 percent

Planning: 10 percent

Exercise: 10 percent

Food:This seems obvious, but what you eat and how much, is the single biggest factor in weight loss. Period. You will never exercise your way out of a bad diet. Never.

Conversely, if you make the right food choices, you can lose weight without any exercise at all. Don’t get me wrong, exercise is really good for you, for a number of reasons. But it plays a much smaller role in weight loss than so many of us believe.

Give yourself permission to focus on the food alone for a period of time. Changing your diet is hard enough as it is. For me, I eliminated all my trigger foods, including processed foods, flour, and dairy. My rule of thumb was, if I abuse it, it has to go altogether.

PHOTOS: See Mara Schiavocampo's amazing transformation!

Today, I eat mostly fruits, vegetables, chicken, fish, beans, nuts and whole grains. Once I made that change, losing weight felt like rolling downhill.

Sleep:Sleep is a necessity, not an indulgence. Studies suggest that when you give your body the sleep it needs, you’ll eat less. You’ll have stronger willpower. You’ll make better food choices. You’ll have more energy for exercise.

Adequate sleep is the one thing that makes an instant difference in how you feel. Most people need seven to nine hours, though it varies. If you feel tired during the day, you’re not getting enough sleep. It has to be a priority. Put the phone down, turn off the TV, and go to bed!

Planning:Failure to plan is planning to fail. A lot of your weight-loss challenges are simple logistical issues that are easily solved with a few minutes of thoughtful planning.

Make sure you have groceries in your kitchen. Schedule time to cook. Put your workouts in your calendar, just like other appointments. Wash gym clothes before you run out of clean socks. Pack a snack when you head out to run errands. Just think things through.

Exercise:These days, I love to exercise (I used to hate it). It gives me energy all day, is a great stress reliever, it’s empowering and, most of all, it’s fun.

My favorites are a spin class called SoulCycle, and interval training at Barry’s Bootcamp. Find an activity you love. You may have to kiss a lot of frogs, but find that sweaty prince!

It should be something you look forward to, not dread. If you get bored with one thing, move onto another. Variety is great for your body. Work really hard. Push yourself. Studies show most of us overestimate our intensity anyway.

My mantra these days is eat clean, train dirty.