ABC News' Juju Chang and Matt Knox report:

The hottest new trend for shedding extra pounds quickly includes one surprising no: no stepping on the scale.

"So many people are so obsessed with that number on the scale," said Melissa Hartwig, co-founder of Whole30. "The scale will blind you to all the amazing progress that you're seeing in your medical condition."

Hartwig and her husband, Dallas Hartwig, both certified sports nutritionists, created the Whole30 program in 2009 and co-authored the New York Times bestselling book "It Starts With Food." The Whole30 program, they say, is aimed at resetting your body's reaction to food.

On the 30-day plan, gone are any food that cannot be hunted or gathered, mimicking the Paleo diet or caveman diets that exclude post-agricultural foods. So, gone are grains like rice and wheat, beans, soy, dairy, alcohol, sugar and processed foods. What you can eat on the plan are fruits, vegetables and protein.

The key to the diet is slowly reintroducing the banned foods to your diet to see how your body reacts to gluten or dairy or sugar.

"We're not asking you to eat like this for the rest of your life 100 percent," said Hartwig. "We're saying, take 30 days, learn about yourself, how you interact with food and then create a plan that works for you based on what you've learned for the rest of your life."

Ashley Reeves, a 30-year-old mother of three from Utah, says she started the program when she didn't have the time or energy to get back into shape.

"I had done a few healthy eating things and I just wasn't, you know, losing the baby weight and I was getting pretty frustrated," Reeves said.

When Reeves followed the program last year, she says, she lost 16 pounds in the first 30 days without even working out.

"The first week I'd say is pretty rough because your body is just kind of like purging all of these things you've been eating for years," Reeves said. "But more than anything, my results were measured in energy.

"I felt amazing," Reeves added, saying she lost another 10 pounds when she tried the diet again more recently.

Reeves says she is able to "feel better" and be "more focused" after doing Whole30, although some dietitians have voiced concerns about eliminating food groups in one's diet.

"When you start eliminating food groups like dairy, legumes and whole grains, you start to miss out on important nutrients like calcium and vitamin D, B vitamins, fiber and antioxidants," New York City-based registered dietitian Lisa Drayer said.