Ever wonder how celebrities lose a ton of weight, got back into their skinny jeans a week after having a baby, or just seem to never gain weight? Strict diets, personal trainers and expensive diet plans are usually the answer. Here are some of the ways celebs have dropped the pounds.

Jennifer Hudson

Jennifer Hudson signed on as the WeightWatchers’ spokesperson in April 2010. Since then she has lost more than 80 pounds on the well-known diet plan. Since her weight loss, Hudson has launched the Lose for Good campaign, which teaches families how to prepare healthy and affordable meals.

Alison Sweeney

In The Mommy Diet, Alison Sweeney shares her own struggles with weight-loss. The host of “The Biggest Loser,” she lost 30 pounds by giving up sugar and sticking to a consistent exercise routine. She goes to a cycling class three or four times a week and also does strength training.

Mariah Carey

Mariah Carey is the latest celeb to be the face of Jenny, the program formerly known as Jenny Craig. Carey who recently had twins, says she’s lost more than 30 pounds since starting the diet. During a recent appearance on “The Rosie Show,” the 42 year-old singer also credited exercising with her dogs and doing workouts in the ocean.

Photo by AP

Kirstie Alley & Kelly Preston

After a stint as a spokesperson for Jenny Craig (and gaining the weight back), Kirstie Alley decided to start her own weight-loss program. Organic Liason promises to reduce cravings and boost energy. Alley’s friend, actress Kelly Preston, recently said that she lost 39 pounds on the program after giving birth to her and John Travolta’s son Ben. Preston has now signed on to be a spokesperson for the company.

Janet Jackson

Nutrisystem has a new program and a new spokesperson. Janet Jackson recently signed on with the company to promote Nutrisystem SUCCESS. The new program, which has its own iPhone app, includes protein shakes, prepared meals and activity plans. There are several plans to choose from and vegetarian and diabetic options are offered. Jackson says she’s already seen results on the program.

Drew Carey

“The Price Is Right” host Drew Carey now stays svelte by keeping to a strict no-carb diet and doing plenty of cardio. Carey, who lost more than 80 pounds, now says that water is the only thing he drinks. Carey who was once diabetic, no longer needs medication since the weight loss.

Photo by AP

John Goodman

Actor John Goodman has lost more than 100 pounds since hiring personal health coach, Mackie Shilstone. Shilstone, who also trains tennis pro Serena Williams, made Goodman cut out all the sugar from his diet and work out six days a week.

Photo by AP

Jordin Sparks

Singer Jordin Sparks lost 30 pounds by changing her eating habits and working out. She now eats smaller portions and eats her vegetables first at each meal. The former “American Idol” contestant does 30 minutes of high impact cardio and started taking hour-long Zumba classes up to five times a week.

For a show about weight loss, watch “The Biggest Loser,” Tuesdays on Halogen TV.

More Healthy Living in 2012 from HalogenTV.com:

1. Dr. Don Colbert Talks Health & Nutrition
2. Living Well in the New Year
3. A New You for the New Year