Medifast is a structured weight loss program built around portion-controlled meal replacements, designed to keep daily intake between 800 and 1,000 calories. Founded in 1980 by William Vitale, a medical doctor, the program was originally sold through physicians who prescribed the products alongside behavioral counseling. It has since evolved into a direct-to-consumer brand with an independent coaching network, and today operates primarily under the name OPTAVIA.
How the 5 and 1 Plan Works
The core of Medifast is its signature “5 and 1” plan. You eat five pre-packaged Medifast meals throughout the day (shakes, bars, soups, and similar products), plus one homemade “Lean and Green” meal that you prepare yourself using a lean protein and non-starchy vegetables. That structure creates a predictable calorie range of roughly 800 to 1,000 calories per day, which is well below what most adults normally eat and low enough to be classified as a very low-calorie or low-calorie diet depending on individual needs.
The appeal is simplicity. You don’t count calories, weigh portions, or plan most of your meals. The packaged foods are designed to be nutritionally balanced, so the program handles macronutrient math for you. Your one self-prepared meal each day is the only part that requires cooking or decision-making, and even that follows specific guidelines for portion size and food choices.
Weight Loss Results From Clinical Trials
A randomized controlled trial published in the International Journal of Obesity tested the 5 and 1 plan against a food-based diet in 120 adults with a BMI between 35 and 50. After 26 weeks, participants on the Medifast plan lost an average of 7.5 kilograms (about 16.5 pounds), compared to 3.8 kilograms (about 8.4 pounds) in the food-based group. That’s roughly double the weight loss.
The more telling number comes from the follow-up. After a full year, which included 26 weeks of active weight loss and 26 weeks of maintenance, the Medifast group had kept off an average of 4.7 kilograms (about 10.4 pounds) versus 1.9 kilograms (about 4.2 pounds) in the comparison group. The results were statistically significant at both time points, but they also illustrate a common pattern with structured diet programs: some weight tends to return during the maintenance phase once the rigid meal plan loosens.
What It Costs
Medifast is not cheap. A three-week supply of the pre-packaged meals runs between $385 and $430, depending on which plan you choose. That works out to roughly $515 to $575 per month just for the program foods. On top of that, you still need to buy groceries for your daily Lean and Green meal, which adds another layer of expense. For many people, the total monthly cost lands somewhere around $600 or more when everything is factored in.
Whether that feels reasonable depends on what you’re comparing it to. If your current grocery and dining-out budget is already high, the switch may feel less dramatic. But for most households, it represents a significant increase in food spending, especially since the program is designed to be followed for months.
The Shift to OPTAVIA
If you search for Medifast products today, you’ll mostly find them marketed under the OPTAVIA brand. The company, still publicly traded as Medifast, Inc. on the New York Stock Exchange, shifted its consumer-facing identity to OPTAVIA over the past several years. The structured meal replacement plans remain the foundation of the business, but the company now frames its mission more broadly around “metabolic health” rather than weight loss alone.
In 2025, Medifast announced a further strategic pivot, introducing a concept it calls “Metabolic Synchronization” with new products planned for 2026. The company describes this as a holistic approach combining personalized plans, scientifically developed products, and habit-building, all supported by a network of independent coaches. In practice, the coaching model means you’ll likely be paired with a personal coach (often someone who has used the program themselves) who guides you through the process and earns a commission on product sales.
Practical Considerations
At 800 to 1,000 calories per day, the 5 and 1 plan is restrictive enough that some people experience side effects during the first week or two. Common complaints include fatigue, headaches, irritability, and digestive changes as your body adjusts to the lower calorie intake. These typically ease as you settle into the program, but the calorie level is low enough that the plan isn’t appropriate for everyone, particularly people who are pregnant, nursing, or managing certain medical conditions.
The biggest practical challenge tends to be sustainability. The program works well for initial weight loss precisely because it removes most food decisions from your day. But that same rigidity makes it hard to transition back to normal eating. The clinical trial data reflects this: participants regained some weight during the maintenance phase even within the controlled setting of a study. Building lasting eating habits alongside or after a meal replacement program is the piece that determines whether the results stick long-term.
The coaching component is meant to address this gap, helping with accountability and behavioral change. But because coaches are independent contractors who earn income from product sales, the quality and objectivity of coaching can vary widely. Some people find the support invaluable, while others feel the relationship is more transactional than therapeutic.