Jennifer Aniston and the Zone

When watching Friends on DVD, it's difficult to miss Jennifer Aniston's transformation. The curvaceous, round-faced waitress became the slim and toned fashion executive right before our eyes. Years later, after her marriage and divorce, and from sitcom to movies, Aniston is still trim. So, how did the reported lover of margaritas and tortilla chips drop the weight?

Jennifer Aniston reportedly follows one of the most popular and healthy celebrity diets: the Zone. While the Zone can initially appear a bit complicated, its basic premise is relatively simple: 40 percent of calories come from complex carbohydrates, 30 percent from protein, and 30 percent from fat. In addition, Zone creator Dr. Barry Sears recommends eating several light meals daily rather than three large ones. Other reported followers of this plan include:

* Sandra Bullock
* Cindy Crawford
* Brad Pitt
* Charlie Sheen
* Renee Zellweger

Kirstie Alley and Jenny Craig

In the 80s and 90s, Emmy award winning actress Kirstie Alley was known just as much for her sexy body as for her sassy wit. After a hiatus from acting, Kirstie flaunted a shocking new form in 2005. The one-time sex symbol now topped the scales at over 200 pounds. Even more surprising, she made the weight gain the focus of a brand-new sitcom. In Fat Actress, Kirstie plays an overweight woman struggling to succeed in weight obsessed Hollywood. Later, Kirstie took a new approach to her weight and vowed to slim down. She joined Jenny Craig as a spokeswoman and lost 75 pounds in one year. Though she also works out with a fitness trainer, Alley attributes much of her success to the prepackaged meals and counseling program. Kirstie Alley even paraded her new bikini bod on Oprah.
All-Natural Celebrity Diets

With access to personal chefs, nutritionists, and gourmet grocers, some celebrities choose to go the all-natural route.

Vegetarian Celebrities

Whether for ethical considerations or for weight loss, many of the most famous celebrities have chosen a vegetarian lifestyle. Bright-eyed country singer Carrie Underwood was voted 2005's Sexiest Vegetarian. Pamela Anderson, another high profile vegetarian, frequently makes headlines for her views on animal rights. Still other famous veggie lovers include:

* The late Linda McCartney
* Alyssa Milano
* Amber Valetta
* Alannis Morrisette
* Brooke Shields
* Claudia Schiffer
* Anne Hathaway
* Dustin Hoffman
* Fiona Apple

Raw Food Diet

Supermodel Carol Alt attributes her youthful appearance to a more extreme form of vegetarianism: the raw food diet. As the name suggests, Alt and other followers eat only non-cooked, natural foods. This, of course, leads to a diet high in nutrient-dense fruits, vegetables, grains, nuts, and herbs. Other proponents of a raw food diet include Demi Moore and Alicia Silverstone.
Macrobiotic Diet

The macrobiotic diet takes healthy eating even further by instructing followers to eat foods native to the land. This means no processed foods and no imported foods. Macrobiotics also eat very little dairy, eggs, poultry, and meat. Although golden girl Gwyneth Paltrow has long been the most famous of macrobiotic diet followers, recent reports indicate that she may have abandoned the lifestyle. Other reported macrobiotics include Madonna and Joe Pesci.

Celebrity Diets Gone Awry

One of the most tragic side effects of super stardom is the incredible pressure to be ultra skinny. We've all heard that the camera adds 10 pounds, and many celebrities combat this by forcing their bodies into unrealistically thin proportions.

Nicole Richie

Although Nicole Richie repeatedly denies that she suffers from an eating disorder, rumors still abound. After months of insisting that her weight loss is the result of stress, the painfully thin star sought medical help for her drastic weight loss.

Kate Bosworth

During her Blue Crush days, Kate Bosworth showed off a healthy, athletic beach-ready physique. In the years following that 2002 hit, Bosworth grew increasingly thin and frail. Photos taken in 2006 of the beautiful blonde clearly show protruding shoulder blades, spine, and collarbone. Where Kate once flaunted sporty curves, she now shows off a visible breastbone.