Medifast Diet Plan: What You Can Eat continued...

Alcohol, fruit, dairy, grains, sweets, and most fats are also prohibited. Dieters are encouraged to drink 64 daily ounces of non-calorie beverages, including water, coffee, tea, diet sodas, and other sugar-free drinks. Caffeinated beverages are limited to three servings daily because the low-calorie diet "may make you more sensitive to caffeine."

Optional snacks include three celery stalks, sugar-free gelatin or popsicles, sugar-free gum, and two dill pickle spears.

Total daily carbohydrates are limited to 80-85 grams per day until the transition to maintenance phase, when they are slowly added back into the diet.

Sample Menu

8 a.m.: Medifast oatmeal

10 a.m.: Medifast caramel nut bar

Noon: Medifast chili

3 p.m.: Medifast strawberry creme shake

Dinner: Three servings of raw, steamed, grilled, baked or boiled vegetables, plus one "lean," "leaner" or "leanest" protein choice.

Leanest: 7 ounces cod, flounder, grouper, crab, shrimp, or lobster; a Boca Burger or 2 cups Egg Beaters, plus two additional fat servings

Leaner: 6 ounces swordfish, trout, skinless chicken breast, pork tenderloin, or 99% lean ground meat; 15 ounces firm tofu, or two eggs plus

four egg whites, plus one additional fat serving

Lean: 5 ounces salmon; mahi-mahi; lean beef, lamb, pork chop or 80%-

98% lean ground meat, three eggs, or 15 ounces soft tofu, with no additional fat.

8 p.m.: Medifast chocolate pudding

The Medifast Diet Plan: How It Works

Losing weight is essentially a mathematical formula: When you cut calories sufficiently, you will lose weight. The Medifast plan cuts calories severely, but, according to the company, helps dieters manage hunger. According to the Medifast literature, the meals and replacements are formulated for the highest fullness index (a calculation of fiber, protein and calories).

"Successful weight loss comes from eating a high-protein meal every few hours, which helps modulate blood sugar levels, control hunger [and] cravings, and preserve muscle mass while burning fat," says Davis.

Experts agree that when you manage hunger, it is much easier to stick to a weight loss plan. But the adjustment to the very low-calorie Medifast plan may not be easy. Program literature warns: "Until you reach the fat-burning state, you may feel hungry, tired, or slightly irritable. You may also experience headaches and light headedness."

Once you reach your weight loss goal, there is a 4-16 week "transition to maintenance" phase in which you slowly add back high-carb vegetables, fruit, nonfat or low-fat dairy foods, whole grains, and additional lean meat. The length of the transition phase depends on how much weight was lost. This phase aims to help dieters adjust to eating more calories, controlling portions, and choosing and preparing healthy foods.

Mild to moderate exercise is recommended on the Medifast program, but dieters are warned not to engage in activity beyond their normal levels during the first few weeks of the weight loss plan.

"Energy levels may be low due to fewer carbs and the adjustment to the very low-calorie intake," says Davis. She suggests increasing physical activity after three weeks on the program.

Exercise is recommended five days a week during the transition to maintenance phase.