Jillian Michaels Says These Are the 3 Major Mistakes Preventing You From Losing Weight

"The top mistake I see is not combining their workout with a calorie-controlled diet comprised of healthy foods," Jillian said. She explained that fat is stored energy and calories in our food are units of energy. "Eat more calories than you burn in a day and you will store those calories as fat."

You can monitor your food intake by measuring or weighing your food to ensure your portion sizes are accurate and track your calories in an app like My Fitness Pal or Lose It! It can be eye-opening to see exactly how many calories your meals and snacks add up to and to see what a portion size is. Make sure to track everything, including all those extra bites, handfuls, and add-ons like sauces and dips.

After several weeks of tracking and choosing healthy, whole foods most of the time, you'll have more experience counting calories in your head and won't need to be so strict about tracking every single calorie — you'll just know what works for you.

Another thing Jillian sees that can hinder weight loss is that people under-train. "They underestimate their abilities and do things like rest for long periods between sets, lift less than they could and should, jog more slowly, etc," Jillian said.

"All these things slow your progress and inhibit your best calorie burn," she added. Jillian said to push a little harder, and don't be afraid to get your heart rate up — to roughly 80 percent of your max.

You may find it challenging to push yourself when working out alone, so take a group fitness class, join a gym, or find a workout buddy to pump you up and push you out of your comfort zone. You'll feel encouraged to grab the heavier dumbbells, move a little faster, or do another set. That's when you'll start to see results.

Another mistake Jillian sees that prevents weight loss is having a workout routine or one type of workout or class as a go-to. "Be sure to mix it up. This is why all my workout programs in the My Fitness app are constantly changing exercises and progressing the user to ensure they don't plateau and results aren't compromised."

Jillian recommended changing up your workout regimen every two weeks to ensure you don't hit a wall. It'll keep your muscles guessing and help you burn more calories, get stronger, and will also prevent boredom that can make you want to stop working out.