The New Year brings new resolutions to slim down and shape up, but if you are one of the 50 percent of women in the U.S. classified as petite - 5'4? or under - you face unique challenges when trying to lose weight.

Fitness expert Jim Karas wrote his new book, The Petite Advantage Diet, to help shorter women left wondering, in frustration, why regular diets don't work for them, as they watch their taller friends drop the pounds.

Karas appeared on " Good Morning America" today to share his top diet and exercise tips for petite women.

1) Allow Yourself Carbs

People forget that carbohydrates are not just breads and pasta, but items like fruits and vegetables too, Karas says.  Healthy carbs, especially those with a high water content, are needed to help people stay full and lean in the midsection.

2) Watch the Small Stuff

Karas estimates petite women who overeat by as few as 28 calories a day will gain 30 pounds over the course of one decade.  A 45-year-old woman who weighs 160 pounds and is 5'9," for example, can eat 2,013 calories per day to maintain her weight.  A petite, 5'3? woman of the same weight and age would only be able to consume 1,973 per day without gaining weight.

If the petite woman were to take in those extra 40 calories per day, she'd gain 4.2 pounds of fat each year, which would mean 42 pounds each decade and an extra 128 pounds over the course of 30 years.

3) Eat High-Calorie and High-Fat Foods Sparingly

Karas says petite women should watch out for three foods in particular when counting their calories: olive oil, avocado and juice.

Just one tablespoon of olive oil, for instance, contains 120 calories and is 100 percent fat, so Karas recommends using it sparingly, no more than one serving per day.  Juice, meanwhile, has 25 percent more calories than soda and twice as many calories as liquid sports drinks, so petite women should watch their intake.  Commercial juice products are also pasteurized, which kills valuable nutrients and vitamins.

4) Swap Your Meals

Eaters in the U.S. typically start the day with their smallest meal, breakfast, and then work their way up to the largest, dinner.  Petite woman in particular, Kass says, should do just the opposite.  To start off, he recommends flipping breakfast and lunch servings in order to better balance the day calorie-wise.

5) Skip the Treadmill, Pick Up the Weights

Karas says cardio can actually cause petite women to gain weight because it increases their appetites.  Instead, petite women should focus on strength training, which fulfills their cardio needs while also increasing their caloric burn, enhancing their posture and strengthening and flattening their core muscles.