The Medifast diet consists of eating mainly prepackaged Medifast meal replacements until you reach your desired weight loss. For $300 you get a month’s worth of meal replacements, to be consumed five times per day. Medifast states that dieters can lose up to 20 pounds per month on their plan.

How Is This Diet Supposed to Work?

The premise of this diet is that by following a low-calorie diet the body will go into a state of mild ketosis. Ketosis occurs when the body does not have enough calories to use for fuel and turns to stored body fat and muscle to meet energy needs. According to Medifast, their meals contain a “proven combination of carbohydrates and protein” that helps the body to break down fat—not muscle—for fuel.

What’s Involved?

The Medifast diet is divided into three phases: 5 & 1 plan, transition, and maintenance.

The core part of the diet is the 5 & 1 plan, which you follow until you reach your desired weight loss. During this time you get to eat six times per day: five Medifast prepackaged meal replacements and one “lean and green” meal. Medifast provides over 70 meal replacements to choose from, such as soups, shakes, and bars.

All of these products are fortified with vitamins and minerals to help you meet your nutrient needs, which would otherwise be difficult to do since this diet only provides around 800-1,000 calories per day. You provide the daily “lean and green” meal, which consists of 5-7 ounces of lean meat, fish, or poultry, plus 1-2 cups of vegetables or salad. Meat-free recommendations are also made for vegetarians. Meals are supposed to be consumed every 2-3 hours so you won't feel too hungry.

After you reach your desired weight loss, you begin the transition phase, which gradually reintroduces you to “regular” food and increases your calorie intake. The final phase of this diet is maintenance, during which you are encouraged to eat mostly regular foods along with some Medifast meals and work continuously to balance the calories you eat with those that you expend. This is done so that you maintain your current weight.

This diet plan offers programs for both women and men, as well as specific populations:

  • Women who are nursing
  • Seniors
  • Teenagers
  • People with gout
  • People with diabetes
  • Postbariatric surgery patients
You can sign up by phone or online, and the meals will be delivered to your home on a monthly basis. The cost is about $150 for two weeks or $300 per month, but it costs a bit more if you want to choose your own meals.

The Medifast plan recommends that its subscribers also engage in regular exercise. Specifically, they recommend low to moderate exercise, such as walking, swimming, or biking starting at 10 minutes per day for three days a week and increasing as tolerated.

Additional Features of This Diet

  • Free online meal planner, weight-loss tracker, and support
  • Access to registered dietitians via phone or online
  • One-on-one counseling sessions with health coaches trained in the Medifast diet plan

Maryland, California, Texas, Minnesota, Arizona, and Florida also have weight-loss centers where you can receive in-person, customized support.

What Does the Research Say?

Research suggests that going on a meal replacement diet can be a safe and effective way to lose weight for people if they can stick with the diet. Moreover, studies have found that these diets can help people keep the weight off and thereby lower their risk of weight-related conditions. Also, one study found that women on a meal replacement diet were more likely to meet their vitamin and mineral requirements than those on a food-based, calorie-restricted diet. A study sponsored by Medifast, also found that the diet may promote fat loss, not muscle loss.

There is also some research suggesting that meal replacement diets, such as Medifast, may be helpful for people with diabetes who need to lose weight. A study conducted at John Hopkins University found that a diet consisting of portion-controlled meal replacements helped obese people with diabetes lose weight and maintain that loss for one year. It can also help diabetic patients with their blood sugar control.

However, there is no research to support the idea that you should avoid certain healthful foods, such as whole grains, low-fat dairy products, and fresh fruit, to help promote weight loss. These foods are still an important source of nutrients, and fruits and whole grains are naturally high in fiber. The diet does include these foods in the transition and maintenance phase of the program, but not in the 5 & 1 plan. Also the plan's meals are nutrient-fortified, so you are still getting some essential vitamins from the meals.

Are There Any Concerns With This Diet?

This is a low-calorie diet. Therefore, talk to your doctor before starting this diet. Because it is so low in calories, it should not be followed by certain groups of people, including women who are pregnant and very active individuals. Medifast warns of potential side effects, such as constipation, dizziness or lightheadedness, fatigue, feeling cold, and dry skin or hair.

Bottom Line

While the Medifast diet is not recommended for everyone because it is so low in calories, it may help some individuals with their desired weight loss. Before investing in this diet, consider meeting with a registered dietitian to help you determine what type of diet is best for you.