The Medifast brand has been around for a number of decades, and at one time was only available via physicians. Nowadays the products can be ordered on-line and through a number of distributors.

Medifast offer a stable of meal replacement products - all generally formulated to be low-calorie and low-fat, and containing the optimum levels of vitamins. The formula will generally take users into a mild state of ketosis.

The most popular plan is called 5 and 1. This plan (800-1000 calories daily) comprises 5 meal replacements and one "real" meal containing a lean protein and vegetables and salad. Medifast claim a weight loss of 2-5 pounds per week on this plan.