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By: Melissa Mitri, MS, RD

Are you struggling to find an effective weight loss plan for yourself? If so, you may have heard about the OPTIFAST diet and are curious if it works. OPTIFAST is a medically supervised weight loss program that has risen in popularity over the years. 

The program is a comprehensive plan that provides you with medical, nutritional, and behavioral support throughout your journey. It utilizes a multi-disciplinary approach to help you lose weight and improve your overall healthy eating habits, which I appreciate, as many other programs use health coaches that may or may not be qualified to provide nutrition advice.

I’ve personally had my nutrition clients come to me with questions about how OPTIFAST works and what they can expect. So I’m digging into the facts today with a registered dietitian’s perspective on the OPTIFAST diet. I’ll discuss the pros and cons and what types of weight loss results you can expect with OPTIFAST. 

What is the Optifast Diet?

The OPTIFAST diet is a medically-supervised weight loss program that was developed over 40 years ago. It incorporates nutrition, exercise, and lifestyle interventions designed for weight loss. Eligibility for the program requires a BMI over 30 kg/m2 or over 25 kg/m2  with preexisting conditions such as diabetes or liver disease.

Owned by Nestle Health, OPTIFAST is one of the first physician-supervised weight loss programs on the market. The program is broken up into three key phases that are intended to be completed over six months. 

As you progress throughout the diet, the phases continuously get less restrictive.

Here is a brief overview of the three phases:

  • Phase 1: Active Weight Loss Phase (1-4 months, ~800 kcal/day): During this phase, your diet will consist of only OPTIFAST meal replacement products (about 5-6 products a day). You will begin the phase by meeting with your medical provider for monitoring and counseling.
  • Phase 2: Transition Phase (4-6 months, ~800-1000 kcal/day): Phase 2 is where you gradually transition off of the meal replacement products and start to add in self-prepared foods. You will typically still have around three OPTIFAST shakes or bars a day. 
  • Phase 3: Maintenance Phase (6-24 months, ~1000-1200 kcal/day): The final phase is the weight maintenance phase. During this phase, you are encouraged to get ongoing support to maintain any weight loss. You may choose to continue including partial meal replacements. 

Each phase also has an educational and support component consisting of both one-on-one and group coaching sessions. At these sessions, you are taught about various health topics to help you continue your weight loss journey after the program is over. This is an essential component of any weight loss program, as maintaining a weight loss is often one of the biggest challenges.

OPTIFAST diet program

All of the OPTIFAST products are gluten-free and low in sugar. According to their website, eating at least five servings of products will provide you with 100% of your daily vitamin and mineral needs. 

You can choose between the following:

  • OPTIFAST shakes. OPTIFAST shakes come in a few different forms. You can opt to drink either the ready-to-drink shakes or the shake mix depending on your preference.
    • Shake mixes: the shake mix can be combined with water and has 160 calories and 16 grams of protein. There is also a higher protein option if you have increased protein needs with 26 grams per mix. The flavors come in chocolate, vanilla, and strawberry.
    • Ready-to-drink shakes: ready-to-drink shakes are also 160 calories and 16 grams of protein. Flavors include vanilla, chocolate, and strawberry. 
  • OPTIFAST bars. These bars are a convenient option to eat at home or on the go. They are 160 calories per bar and contain 16 grams of protein. The flavor options include chocolate, peanut butter chocolate, and apple cinnamon. 
  • OPTIFAST soup mix. If you are looking for a hot meal replacement, OPTIFAST has soup mixes of varying flavors. Each mix has 16 grams of protein and should be limited to 1-2 servings/day. You can choose from tomato, chicken, or vegetable soup.

Pros of the Optifast Diet

OPTIFAST weight loss program

The OPTIFAST weight loss program does have some proven benefits to consider. 

Produces weight loss

It can be an effective weight loss solution for certain people. The OPITWIN study was conducted to test the effectiveness of OPTIFAST for weight loss in a study population. 

The study involved 273 participants ages 18-70 years old. After 26 weeks, participants lost an average of 30 lbs following the OPTIFAST diet. The program delivered double the amount of weight loss when compared to a placebo group following a standard reduced-calorie diet. 

However, it’s essential to note that this study was funded by Nestle Health Science, which owns the OPTIFAST program. When a study is funded by the industry itself, there is always a risk of bias in the study design and results to make them more favorable. This doesn’t mean they were intentionally deceptive, but it’s important to keep the possibility of bias in mind.

May help lower blood sugar

It may also be effective at lowering your blood sugar levels. Since the products are low in sugar, you will likely be intaking less sugar than you normally do. 

Medically supervised

Another benefit of the OPTIFAST diet is that it is medically supervised. There are many fad diets on the market that offer zero medical guidance or assistance. It is nice to have a team in your corner that you can trust and ask questions about during your weight loss journey. 

Gives you that “jumpstart” feeling of quick weight loss

Additionally, if you are looking to lose weight fast or in a short amount of time because of a medical condition, OPTIFAST may be an effective weight-loss option for you to try. Many of my clients look to this for that initial motivation, as it can be frustrating when you are trying and not seeing results right away.

Structured and organized

OPTIFAST can be a good option if you like to have structure and organization. The outline of the diet is clearly defined on the website and can be easily followed. Since your food plan is being provided to you, this takes much of the guesswork out of the program. 

Provides accountability and support

During the initial phase, you are encouraged to meet once a week with your advisor. This can help increase your adherence to the diet and offer support if you need it. 

Sense of community

OPTIFAST offers optional peer support groups that you can attend. If you want to ask questions and connect with others, these group settings are a great place to do that. Being able to connect with others in a group environment may help you feel more comfortable during your journey.

Cons of the Optifast Diet


Despite the benefits of OPTIFAST, some downsides should be discussed. 

Food options are limited

One potential con is the lack of variety in the program, especially during the first four months when you are only eating OPTIFAST bars and shakes. 

Eating the same few foods every day can feel repetitive and boring. You are also not able to eat out in social settings, such as with family and friends at restaurants. This can feel isolating and lead to a lower quality of life. 

May lead to nutrient deficiencies

You need variety in your diet to get the number of nutrients that your body needs. Studies show that people who eat very low-calorie and restrictive diets are at a greater risk for nutrient deficiencies

Can trigger disordered eating behaviors

If you have a history of disordered eating, OPTIFAST is likely not a good choice for you. The restrictiveness and rigid rules can lead to disordered eating thoughts or guilt if you don’t follow it perfectly. 

This is especially true if you tend to have an all-or-nothing mentality around dieting.

Additionally, if you prefer a diet with more variety and balance, you’ll probably get bored pretty quickly with the OPTIFAST plan. 

May not be sustainable

Lastly, the sustainability of the OPTIFAST weight loss program should be considered. How likely are you to keep the weight off that you lose? This is a hard question to answer and will likely vary based on many factors. Sustainability is more likely if you continue healthy habits, exercise, and most importantly, continue to get support from a dietitian coach.

Optifast Weight Loss Results to Expect

If you are considering trying the OPTIFAST diet, you may wonder what sort of weight loss results you can expect. 

As I mentioned above, studies that have been done on the program show an average weight loss of around 30 pounds after 26 weeks. This equals out to about 1 pound/per week of weight loss. 

However, since the beginning of the diet is the most restrictive, majority of the weight was likely lost during this initial phase, therefore you may lose 3-4 pounds per week during this phase, and then as time goes on, it may level off to 0.5-1.0 pounds per week. 

It is also important to note that this initial fast weight loss was likely water weight loss vs fat loss. When you lose weight very quickly (especially if you are not exercising or doing strength training) you tend to lose water weight and muscle, which is not ideal. This should be taken into account, as the ideal scenario would be to lose fat.

All in all, if you were to stay on OPTIFAST for four weeks, you could expect to see anywhere from 4-10 pounds of initial weight loss. This will depend on a variety of factors including your starting weight, gender, height, and more. 

What my clients had to say:

I have had a few of my nutrition clients try out OPTIFAST for weight loss before working with me. Most found it helpful in the beginning but then started to gain the weight back after the initial stage. I think part of the reason for weight gain is that they stopped getting the 1:1 accountability and support from the OPTIFAST team, and transitioned on their own without guidance.

Even so, most of my clients say that it doesn’t really teach you how to eat healthy long-term, as you are prescribed a set list of their products to eat.  While it helped give them an initial jumpstart of motivation, it wasn’t necessarily sustainable.

After following it, most of them then came to me with some knowledge but were looking for a long-term, less restrictive plan.

A Registered Dietitian’s Perspective


OPTIFAST offers a different approach to weight loss that can be effective for some and not for others. The restrictive guidelines of the program can promote weight loss in certain people but may be a challenge for others. 

If you need to lose weight quickly or have tried other methods of weight loss and failed, OPTIFAST could be worth the try. Also if you’re someone who likes structure and just wants someone to tell you what to eat, it may be a good starting place. The educational and medical support components of the program make it stand out from other weight loss programs. 

However, it is not uncommon to feel deprived of variety and nutrients while on a very low-calorie diet such as OPTIFAST. There is also the risk of weight regain once the program is finished if appropriate lifestyle and eating habits aren’t continued.

If you are considering trying the OPTIFAST program, I recommend talking to your healthcare provider or working with a registered dietitian while following the program. Together you can decide if the OPTIFAST diet is a good fit for you moving forward. 

Bottom Line – Should You Try the Optifast Diet?

OPTIFAST is one of the only medically-supervised weight loss programs on the market that provides you with all the food you need for the initial stage of the program. Medifast is a similar meal replacement weight program that is the parent company of Optavia. 

Optavia is based on similar principles as OPTIFAST but is not medically supervised. Instead, you are working with Optavia coaches who may or may not be qualified nutrition experts. Stay tuned for more info on Optavia in an upcoming review.

Overall, OPTIFAST can be a good option if you are looking for support, structure, and fast results with your weight loss plan. Especially if you can adhere to the guidelines of the diet for the entire duration of the program. 

However, the program lacks variety and may not be suitable for you if you have a history of disordered eating. If you do decide to try OPTIFAST, it is best to continue receiving ongoing support even after the initial phases are completed.

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