Behind the bikini-perfect bodies of Jessica Simpson, Katy Perry and Megan Fox is fitness guru Harley Pasternak.

Pasternak appeared on "Good Morning America" today to share his secrets for slimming down fast just in time for summer.

Jessica Simpson on Weight Loss: 'I Couldn't Believe What I Weighed'

The trainer says success can be had with these five small life changes:

Tip 1: Get up and walk. Using an activity monitor, Pasternak says, you should strive to stride a total of 14,000 steps a day. "Walking is one of the best ways that you can injury-free, and for the most part sweat-free, burn calories all day," he says.

Tip 2: Drink a gallon of water a day.

Tip 3: Follow the Fierce Five workout, which consists of four sets of 20 reps each of these: reverse lunges, single arm dumbbell rows, stiff leg dead lifts, lying dumbbell tricep extensions, plus four sets of minute planks to strengthen the core.

Tip 4: Say bye-bye to baked goods.

Tip 5: Embrace breakfast smoothies.

Harley Pasternak's Smoothie Recipes

Harley's Sweet Spinach Smoothie

Ingredients:

2 cups spinach leaves, packed 1 ripe pear, peeled, cored, and chopped 15 green or red grapes 6 ounces fat-free plain Greek yogurt 2 tablespoons chopped avocado 1 or 2 tablespoons fresh lime juice

Directions: In a blender or food processor, combine all the ingredients until blended to the desired consistency.

Harley's Breakfast Smoothie

Ingredients:

5 raw almonds 1 red apple 1 banana 3/4 cup nonfat Greek yogurt 1/2 cup nonfat milk 1/4 teaspoon cinnamon

Directions: In a blender or food processor, combine all the ingredients until blended to the desired consistency.

Harley's White Smoothie

Ingredients:

5 raw almonds, whole or chopped

1 red apple, unpeeled, cored and chopped

1 small banana, frozen and cut into chunks

3/4 cup fat-free plain Greek yogurt

1/2 cup fat-free milk

½ teaspoon ground cinnamon, or to taste

Directions: In a blender or food processor, blend the almonds until finely ground. (If your blender isn't powerful enough to grind almonds, you can buy chopped almonds or even almond meal instead.) Add the apple, banana, yogurt, milk, and cinnamon. Blend until of desired consistency.