Monique Coleman has lost 20 pounds, but she says “I didn’t notice I had gained 20 pounds until I saw myself in High School Musical 2.” “I got on the scale and it said 145, and I thought it was broken!” The 5-foot-3 Coleman has since lost 20 pounds and slimmed from a size 6 to a 2.

Plus, she has set her sights on a formidable fitness challenge: competing in the four-mile running leg of the Nautica Malibu Triathlon (alongside Jennifer Lopez). “It’s the hardest thing I’ve ever done,” says Coleman, who has been logging workouts of up to an hour and a half with trainers Rich and Helene Guzman of the gym L.A. Rox since June. “I’m doing it to feel good on the inside and look good on the outside.”

Here are the details about her diet and workout:

Monique Coleman’s sample diet It is pretty basic, but it is smart and easy to follow. Total calories: 1,600-1,700.

Breakfast: Protein shake with egg-white powder, almond milk and 1 tablespoon peanut butter.

Snack: One apple and a handful of almonds.

Lunch: One small chicken breast with asparagus spears and a small salad with nondairy dressing.

Snack: Hummus with celery, jicama and bell peppers, or radishes and carrots.

Dinner: Fish with steamed vegetables and brown rice.

Monique Coleman’s workout Our goal for her is to run eight-minute miles,” says her personal trainer Rich Guzman of their 90-minute sessions three to four times a week.

Their routine includes four miles on a treadmill (alternating running a mile with walking a half-mile at an incline), track work, stretching, strength training (biceps curls, chest flies) and core work (side planks, bicycles). Twice a week, they hit the pool to tread water, swim laps and lift weights. [via]