Optifast is an all liquid diet. It is intended for significant weight loss in a short period of time, is intended only for the extremely obese, and must be completed under the supervision of a trained physician.


Optifast product

Calories per serving

Protein (g)

Carbohydrates (g)

Fat (g)

Sodium (mg)

Potassium (mg)

Fiber (g)

% of DV vitamins and minerals

800 ready to drink









800 powder









HP powder









Nutrition bars









Amounts vary with product flavors



The Optifast diet generally consists of four phases, with the main program lasting 26 weeks. The phases are: screening, active weight loss, transition, and maintenance. Training is provided for physicians and other healthcare professionals who are going to be involved in monitoring and providing support to patients on the Optifast diet. General guidelines are also provided for administering the diet, but each clinic or physician may offer whatever specific program they chose. Therefore, no two experiences with Optifast will necessarily be the same, even though they follow the same basic overview.

The first phase of the Optifast diet is screening. Optifast is only appropriate for massively obese people, generally those who have at least 50 pounds to lose or are experiencing obesity-related complications. In most cases the diet is only recommended for patients between the ages of 20 and 50. The physician will do a general health screening and various lab tests to determine if Optifast is likely to pose any special risks to the patient. During this time the patient may be able to meet the various support staff that he or she will be working with while on the diet, including the physician, nurses, lab technicians, psychologists, counselors, registered dietitians, and anyone else who is going to be on the medical team.

After screening has been completed and it has been determined that the patient is suitable for the Optifast diet, the diet itself begins. This is the active weight-loss phase and generally lasts one to four months. During this phase, the patient is on a fluid-only diet using Optifast products. These are nutritional drinks that come in a variety of flavors, and generally provide a total of fewer than 800 calories per day. This means that the Optifast diet is considered a very low-calorie diet (a diet providing fewer than 800 calories a day). Generally, five Optifast drinks are consumed throughout the course of a day, and doing so provides the recommended daily allowance of vitamins, nutrients, proteins, and other substances necessary for good health.

During the active weight-loss phase, the patient meets with a physician once or more weekly to monitor progress and health. Lab tests may be repeated to check various levels such as cholesterol or blood glucose. As weight loss increases medication dosages may be altered, and the amount of Optifast consumed each day may be altered to fit changing caloric needs. Also during this time the patient will meet, usually in a group, with a trained psychologist or therapist to discuss any problems or obstacles he or she is facing. During these group meetings, patients learn new behaviors and eating patterns to help them maintain their weight when they begin eating self-prepared foods again.

After the active weight loss phase is finished, the transition phase begins. During this time the patient begins to replace the Optifast drinks with solid foods. Patients work with a nutritionist to help them choose meals high in fruits, vegetables, and whole grains and low in fats and simple carbohydrates. During this period the patient continues to meet with the physician regularly and attend group classes. This phase usually takes place during the fourth and fifth months.

Once the transition to solid foods is complete, the maintenance phase begins and can last from month 6 to beyond 24 months. During this phase the patient begins to practice the good eating and healthy living habits learned during the program. Exercise is emphasized as a way to help prevent the regaining of weight lost. Many clinics offer classes and meetings that patients can attend to help them as they try to keep the weight off.

Although the very low calorie diet was the original Optifast product, the line has begun to branch out and now offers a variety of diets. One diet is used for patients who are going to undergo bariatric surgery and can be administered both before and after the surgery. This can help reduce complications and smooth the transition into a fluid-only diet after the surgery. Another diet is an Optifast diet intended for very obese adolescents. Optifast also offers bars and other products, which are not associated with its original fluid-only diet. In addition to the very low-calorie diet, diet plans with a more moderate quantity of calories per day are also available.



Many possible benefits accompany significant weight loss for the obese. These benefits can include both looking and feeling better, as well as having more energy. In addition to these general benefits, some of the many specific health benefits include weight-loss, reduced blood pressure, improved cholesterol levels, and higher insulin sensitivity. These advantages tend to be even greater for people who are moderately or severely obese because a greater degree of obesity is generally associated with increased health risks.

Nestlé, the makers of Optifast, reports that in a study of 20,000 people who completed 22 weeks of the Optifast diet, the average weight loss was 52 pounds. This was a loss of 22% of body weight. They also report an average decrease of 29% in blood glucose levels, a 15% average decrease in total cholesterol, and an average decrease in blood pressure of 10%. Reductions in cholesterol and blood pressure can be especially significant in overall health gains from weight loss because they are important risk factors for heart disease.

Another possible benefit of the Optifast diet is an opportunity for the dieter to relearn food habits and behaviors while on the all-liquid phase of the diet. During this time, no food choices have to be made because the program is firmly outlined. Therefore, it may provide an opportunity for the dieter to take a more objective look at some negative eating habits and develop positive ways of dealing with potential problems before going back to eating self-prepared foods.

Some people also believe that Optifast may provide psychological benefits to dieters who have very significant amounts of weight to lose. It can be frustrating to lose one to two pounds a week if the eventual goal is a weight loss of 100 pounds or more. A program like Optifast that allows a large quantity of weight loss in a short period of time may encourage dieters by letting them see results more quickly, which can provide positive psychological benefits.


The Optifast diet is intended to be followed only under the supervision of a physician trained in administering the Optifast system. No very low-calorie diet should be undertaken without close medical supervision. It is also only intended for people who have large amounts of weight to lose or are experiencing significant complications from obesity. The Optifast diet can present significant health risks for people for whom it is not intended. The Optifast diet is not appropriate for pregnant or breastfeeding women.

Dietary supplement—
A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual's diet with the expectation that it will improve health.
Stones that form in the gallbladder or bile duct from excess cholesterol or salts.
Pertaining to a surgical procedure that uses an instrument that can be inserted into the body to view structures within the abdomen and pelvis.
An inorganic substance found in the earth that is necessary in small quantities for the body to maintain health (e.g., zinc, copper, iron).
Type 2 diabetes—
Sometime called adult-onset diabetes, this disease prevents the body from properly using glucose (sugar).
Very low-calorie diet—
A diet of 800 calories or fewer per day.
A nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet.


Every diet carries possible risks, but the dangers associated with a very low-calorie diet can be more serious. Optifast is designed to be a complete replacement for all meals, so it contains the daily recommended amounts of vitamins and minerals. Because these recommendations are made for the average, healthy adult, however, they are not necessarily right for everyone. Because severe obesity has many common complications, daily requirements of vitamins and nutrients should be considered carefully for each person thinking of beginning the Optifast diet. Also each dieter needs to learn to live a healthy lifestyle by following the doctor's dietary advice. If the guidelines are not followed, the patient risks regaining the lost weight and struggling with health problems.


Another risk of following a very low-calorie diet is an increased risk of gallstone formation. Gallstones are more likely to occur in women than men, and are more likely to occur during rapid weight loss or when following a very low-calorie diet such as Optifast. Other side effects of a very low-calorie diet can include nausea, fatigue, constipation, or diarrhea. In most cases these problems resolve in a few weeks and are not very severe.

Whenever a person loses a very large amount of weight in a very short time there are certain risks. Many medication dosages are prescribed based on a person's weight. Therefore, what might be the right amount of medication when beginning the Optifast diet may be too much only a few weeks later after weight has been lost. In some cases, this may cause an overdose. This is one of many reasons that it is critical to be under medical supervision during the Optifast diet, so medications can be adjusted appropriately as weight is lost.

Research and general acceptance

Optifast has been used in many studies investigating the impact of very low-calorie diets. Asof 2018, it was being tested for efficacy against a standard weight-loss intervention over a one year period as part of the Opti-WIN trial. Optifast has been shown to have many positive outcomes, such as lowered cholesterol levels and reduced risks of cardiovascular disease. It has also been shown that if patients who are going to undergo laparoscopic adjustable gastric banding (a procedure in which a band is placed around the upper part of the stomach causing patients to feel full with less food) follow the Optifast diet for six weeks prior to the procedure, they can reduce liver size and fat content, allowing surgeons better access and reducing the possibility of complications.

Although many benefits have been documented for the Optifast diet, some researchers have suggested there may be other, more beneficial diets with fewer possible negative side effects. As for other weight loss diets, the challenge with very low-calorie diets, such as Optifast, is in avoiding weight regain in the long run. This suggests that for some people the risks and benefits of a very low-calorie diet should be assessed in regard to the long-term effects and not just the speed of original weight loss. Another reason that some people may prefer more traditional diets is that the Optifast diet can be expensive, depending on the clinic at which it is administered and how long the active weight loss and transition phases last.

See also Bariatric surgery ; Liquid diets ; Obesity .



Kazaks, Alexandra, and Judith S. Stern. Nutrition and Obesity: Assessment, Management, and Prevention. Burlington, MA: Jones & Bartlett, 2013.

Nix, Staci, and Lillian Mowry. Williams' Basic Nutrition and Diet Therapy. 15th ed. St. Louis, MO: Elsevier, 2017.


Kanders, B. S., G. L. Blackburn, P. Lavin, et al. “Weight Loss Outcome and Health Benefits Associated with the Optifast Program in the Treatment of Obesity.” International Journal of Obesity 13, suppl 2 (1989): 131–4.

Lewis, Mark C., Madeleine L. Phillips, J. P. Slavotinek, et al. “Change in Liver Size and Fat Content after Treatment with Optifast Very Low Calorie Diet.” Obesity Surgery 16, no. 6 (2006): 697–701.

Nuijten, Mark, Agnieszka Marczewska, Krysmaru Araujo Torress, et al. “A Health Economic Model to Assess the Cost-Effectiveness of OPTIFAST® for the Treatment of Obesity in USA.” Journal of Medical Economics (April 20, 2018): 1–20.

Van Wyk, Hamish. “What is Nestleé OPTIFAST ®?” Diabetes Lifestyle 2017, no. 2 (December 11, 2017): 54–5.


Optifast. “About the Optifast Program.” https://www.optifast.com/about-the-optifast-program (accessed May 19, 2018).


Academy of Nutrition and Dietetics, 120 S. Riverside Plaza, Ste. 2190, Chicago, IL, 60606-6995, (312) 899-0040, (800) 877-1600, amacmunn@eatright.org, http://www.eatright.org .

American Society for Nutrition, 9211 Corporate Blvd., Ste. 300, Rockville, MD, 20850, (240) 428-3650, Fax: (240) 404-6797, http://www.nutrition.org .

Center for Food Safety and Applied Nutrition, Food and Drug Administration, 5001 Campus Dr., HFS-009, College Park, MD, 20740-3835, (888) 723-3366, https://www.fda.gov .

Center for Nutrition Policy and Promotion, U.S. Department of Agriculture, 3101 Park Center Dr., 10th Fl., Alexandria, VA 22302, (202) 720-2791, support@cnpp.usda.gov, http://www.cnpp.usda.gov .

Weight-Control Information Network, National Institute of Diabetes and Digestive and Kidney Diseases Health Information Center, 9000 Rockville Pike, Bethesda, MD, 20892, (800) 860-8747, healthinfo@niddk.nih.gov, https://www.niddk.nih.gov/health-information/communication-programs/win .

Helen Davidson
Revised by Anne P. Nugent, PhD RNutr

  This information is not a tool for self-diagnosis or a substitute for professional care.