Jennifer Aniston turned 40 this year and in the midst of filming several movies has maintained a lean, fit physique. When asked about her diet plan, Aniston is reportedly able to lose 5 pounds in 5 days with a protein packed low calorie diet. According to LIfe and Style weekly, Aniston eats nearly the same thing every day during the week-long fast.

Breakfast: A 250 calorie egg white omelet packed with vegetables and feta cheese.

Lunch: A 300-500 calorie salad, with a high protein fish such as tuna.

Dinner: A lean 500 calorie fish or chicken entree, and salad greens with no dressing.

The daily calorie intake, as estimated by Life and Style dietitian Joseph Mutz is a low 1050 to 1250 calories. The diet is also very low in carbohydrates. Aniston who is 5′ 5″ should consume approximately 2,200 calories per day to support her active lifestyle according to government health standards. By cutting a significant number of calories and limiting carbohydrates, Aniston may be able to slim down by dropping water weight, but the diet is probably not sustainable for an extended period of time.