If you’re looking to lose weight the chances are that you’ve looked into various weight loss programs, from Atkins to Weight Watchers and everything in between.

The OPTIFAST Diet, developed in 1974, is a very low calorie diet that claims to support people through their weight loss journey with a combination of personalized support, nutritional products and group support.

But what is the OPTIFAST Diet and how does it work? We’ve taken an insider look to explain everything you need to know about the OPTIFAST Diet including what it entails, if it works and if it is safe to follow.

What Is The OPTIFAST Diet?

The OPTIFAST Diet is a minimum 26-week plan that promises significant weight loss; as much as 5 pounds per week in the ‘active weight loss’ time period.

The speed of the weight loss has been criticized by health professionals as too quick, but the diet was designed for people with over 50 pounds to lose and so it may be that the health benefits of weight loss outweigh the disadvantages of losing weight quickly.

The diet is split into three sections – the ‘active weight loss’ phase of a minimum 12 to a maximum of 16 weeks consuming only OPTIFAST products and non starchy vegetables; an eight week phase of transitioning back to self prepared foods while attending nutrition classes and a maintenance phase lasting from six months to over two years.

Some people have criticized the diet for its extended period of extreme calorie deficit, while others believe that the long term support is helpful for dieters wanting to make long term health and lifestyle changes.

The Basic Premise Of OPTIFAST

The idea behind the OPTIFAST Diet is that long term health improvement and weight loss needs to be supported with thorough monitoring, education, nutritional changes and exercise regimens.

There is also an emphasis on an extreme calorie deficit in order to kick start weight loss at a rate that motivates the participant to keep up their lifestyle changes once the ‘active weight loss phase’ has been completed.

This is why OPTIFAST has three distinct stages and incorporates a very low calorie diet, group support, personalized plans, medical monitoring and long term planning in its weight loss program.

Phases Of The OPTIFAST Diet 

Phase 1 – Active Weight Loss

The first part of the OPTIFAST Diet, the ‘active weight loss’ phase, runs for a duration of a minimum of 12 weeks and a maximum of 16 weeks.

During this time participants are expected to consume nothing but non starchy vegetables from a specified list and six daily OPTIFAST branded meal replacements, which are available in the form of shakes (ready to drink or make at home), soups and bars. These each provide between 130 and 140 calories, amounting to a total daily calorie intake of around 800.

Vegetables on the ‘free allowance’ list that dieters are allowed to consume on top of their OPTIFAST products include broccoli, cabbage, lettuce, leeks, squash and eggplant. Stock cubes and miso are also allowed so dieters can make their own vegetable soups. Diet, oil free and fat free dressings are also permitted during the active weight loss phase, as well as natural herbs and spices.

Medical professionals have criticized the size of the calorie deficit due to the recommended minimum calorie intake of 1200 for adults. Possible side effects of consuming just 800 calories a day include a slowed metabolism, headaches, fatigue, dizziness and skin problems as well as extreme hunger.

The expected rate of weight loss during this period is between two and five pounds. Dieters are required to attend weekly medical check ups as well as group counseling for the entirety of the ‘active weight loss’ phase and can personalize their weight loss plan using online tools. The OPTIFAST branded products contain 100% of the recommended daily values of 24 vitamins and minerals in five daily servings.

Phase 2 – Transition Phase

The second part of the OPTIFAST Diet is the ‘transition’ phase. This is where participants move gradually from consuming only OPTIFAST meal replacements to starting to eat self prepared food.

Participants should still consume two OPTIFAST products each day plus a serving of fruit, one serving of dairy and at least two cups of low starch vegetables, as well as a low calorie (400 kcal) meal consisting of one serving of grains, one serving of protein and half a plate of low starch vegetables or salad.

Note: one serving of grains is equal to three quarters of a cup of cooked rice, one cup of cooked pasta, one medium potato or corn cob, one slice of bread or half of a bread roll.

You may also add one tablespoon of dressing or sauce as long as the total calorie value of the meal does not exceed 400. People in the ‘transition’ phase should also consume at least two liters of water each day and continue with their weekly group support and medical check ups until week 18 of the OPTIFAST Diet plan.

Phase 3 – Maintenance Phase

The ‘maintenance’ phase of the OPTIFAST Diet focuses on keeping off excess weight and maintaining healthy lifestyle, eating and exercising habits that have been formed in the first two stages of the plan. Participants are re-educated on healthy cooking and eating habits and are encouraged to eat at their basal metabolic rate (exactly how many calories your body needs to function and maintain weight without any activity) and increase their metabolism by eating a high protein diet and exercising regularly.

The OPTIFAST Product Range

OPTIFAST has a selection of meal replacement products to choose from during the ‘active weight loss’ phase. These include:

  • Ready to drink shakes in strawberry, chocolate and vanilla flavors (individual 8 oz carton servings)
  • Ready to drink high protein shakes in chocolate and vanilla flavors (individual 8 oz bottle servings)
  • Shake mixes to be prepared at home in strawberry, chocolate and vanilla flavors (packs of seven individual sachets)
  • High protein shake mixes to be prepared at home in chocolate and vanilla flavors (packs of six individual sachets)
  • Meal replacement bars including chocolate, peanut butter and chocolate, or apple and cinnamon flavors (packs of seven individually wrapped 47g servings)
  • Soup mixes to be prepared at home in tomato, chicken or vegetable flavors (packs of seven individual sachets)
  • Optisource very high protein drink for post bariatric surgery in strawberry or caramel flavors (cartons of two 4 oz servings)
  • Optisource chewable vitamin and mineral supplements in citrus flavor (bottle of 120 tablets)
  • Nutrisource fiber (tub of 51 servings)
  • Beneprotein instant protein powder (pack of 14 individual sachets)

Other Rules of the OPTIFAST Diet

People following the OPTIFAST are also given other rules to follow, including:

  • Only two cups coffee are allowed per day with 30ml skimmed milk and no sugar
  • No full sugar soda is allowed
  • Only two cans of diet soda are allowed per day

The Importance Of Water in The OPTIFAST Diet

Advocates of the OPTIFAST Diet recommend drinking eight to ten glasses of water a day, as well as the diet soda and coffee if desired. This can reduce the feeling of hunger and well as hydrating the body, decreasing the risk of headaches from hunger. Soda is high in sodium and so can make people retain water weight which is why only two cans of diet soda are allowed per day.

Exercise On The OPTIFAST Diet

Although exercise is an important part of maintaining a healthy lifestyle and weight, the OPTIFAST Diet is too low in calories and nutrients for people following it to be able to participate in any meaningful physical activity.

Dieters will only be consuming 800 calories a day which is less than the amount of energy burned through day to day activities, so there is not energy left for exercise.

This is one of the factors that leads to muscle loss on the OPTIFAST Diet as muscle building activity has to be avoided through necessity.

How Do I Start The OPTIFAST Diet?

To start the OPTIFAST Diet you need to attend an OPTIFAST clinic near you for a complimentary consultation to establish if this is the right diet plan for you.

You can find your nearest clinic on the OPTIFAST website; there are over 450 clinics across the US.

How Much Does The OPTIFAST Diet Cost?

The cost of the OPTIFAST Diet varies from city to city and is dependent on the clinic.

How Effective Is The OPTIFAST Diet?

The OPTIFAST Diet appears to be very effective as a method of losing weight rapidly. On average, OPTIFAST participants lose between 2.2lb and 5lb each week during the ‘active weight loss’ phase.

Examples Of Daily OPTIFAST Meal Plans

Here are two examples of how an OPTIFAST day during the ‘active weight loss’ phase can look for two different participants:

OPTIFAST Diet Meal Plan 1:

  1. Breakfast: One apple and cinnamon OPTIFAST bar plus one cup of hot water with fresh lemon juice
  2. Snack: One chocolate OPTIFAST shake mixed with iced coffee
  3. Lunch: Salad made with lettuce, tomatoes, watercress, cucumber and capsicum with a fat and oil free dressing, plus an OPTIFAST tomato soup
  4. Snack: One OPTIFAST chocolate bar
  5. Dinner: OPTIFAST chicken soup with Konjac noodles, mushrooms and onions
  6. Snack: One OPTIFAST vanilla shake

OPTIFAST Diet Meal Plan 2:

  1. Breakfast: One chocolate OPTIFAST bar plus a coffee with milk and sweetener
  2. Snack: Glass of diet cordial with an apple and cinnamon OPTIFAST bar
  3. Lunch: Grilled vegetable mix of peppers, carrots, squash, beets and shallots with soy sauce, plus an OPTIFAST vegetable soup
  4. Snack: OPTIFAST peanut butter and chocolate bar
  5. Dinner: OPTIFAST vanilla shake and a cup of ginger tea
  6. Snack: OPTIFAST chicken soup


The OPTIFAST Diet is a potential option for people who wish to lose a lot of weight rapidly and who can commit to a period of discomfort for long term health benefits.

The OPTIFAST Diet provides creative solutions and long term guidance for weight loss and maintaining a healthy weight.

The foods suggested by the OPTIFAST Diet in the maintenance phase are everyday items that require no specialist knowledge of nutrition or cooking, making this program a possible solution for people wanting to lose weight quickly before learning health and nutrition information for long term benefit.

Hannah Canavan
Hannah Canavan
Researcher at DietProbe
Hannah is a health and lifestyle journalist with a passion for veganism and nutrition.
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