Optislim Vs. Optifast

Optifast is a brand that provides a diet plan that incorporates varying meal replacement products.
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Optislim vs. Optifast may be a competition you find yourself considering when you're thinking about trying a fast weight loss diet. Each plan has its own set of benefits and drawbacks, so it's important for you to be informed when you're making a decision.

Read more: Healthy Ways to Lose Weight Fast

What Is Optifast?

Optifast is a brand of diet plan that incorporates varying meal replacement products, from bars to soups to the more conventional options such as shakes. Its distinguishing factor rests in the fact that Optifast is more than a variety of weight loss products — it is a regimented program as well.

It is a medically supervised program offered at weight loss clinics, which allows for heightened safety when undergoing a very low calorie diet (which can be dangerous if not carried out with due caution).

This program consists of replacing your everyday meals with three liquid substitutes in the forms of shakes and soups, with the aim of encouraging weight loss. In total, the diet can last anywhere between 26 and 52 weeks. The program is broken down into three segments:

  1. Active Weight Loss Phase: This is the first stage and is comprised of 12 to 16 weeks of total meal replacement using the Optifast products. This is also when a client will meet with an assigned medical provider for monitoring and counseling.
  2. Transition Phase: The second stage is ordinarily four to six weeks long and consists of slowly returning self-prepared foods to mealtimes, as opposed to consistent meal replacements. This occurs while you still attend classes in the hope of changing your relationship with food and how you view your dietary habits.
  3. Maintenance Phase: The third and final phase is the maintenance phase, and it is also the longest phase. It can last up to 52 weeks in total; this is when clients are advised to attend support sessions to consolidate what they have learned in previous sessions regarding positive eating habits and sustain their weight loss. There is partial use of meal replacements during this time.

Optifast claims that these three phases together make a highly effective form of weight loss, and clinical evidence may corroborate this claim.

A study published in November 2019 in the journal Obesity carried out the largest year-long randomized clinical trial of behavioral weight loss intervention with total meal replacement conducted in the U.S. It found significant benefits in the use of Optifast.

These benefits included the magnitude of weight lost by the participants as well as the proportion of test subjects who achieved clinically meaningful results by the 26- and 52-week points. The study concluded that the 135 participants who followed the Optifast meal replacement diet showed a greater loss of fat mass than the 138 participants who used the more conventional diet.

Read more: Recommended Caloric Intake for Weight Loss

What Is Optislim?

Optislim is similar to Optifast in the sense that it is a brand offering meal replacement products, but it differs in that it does not offer a medically supervised program to go alongside the meal replacements. Optifast is a medically supervised program offered at weight loss clinics, whereas Optislim is an Australian brand of weight loss foods. Optislim is only available for delivery in Australia through its official website.

Optislim provides shakes, bars and soups as meal replacements. These products come in a variety of flavors and types (including Optislim Platinum) but they all fall into two distinct categories: VLCD and LCD. These acronyms stand for "very low calorie diet" and "low calorie diet," respectively.

VCLDs and LCDs provide the basis of both Optifast and Optislim diets, but it is important to understand the risks associated with these types of diets, particularly in the case of Optislim — in which the diets are not monitored.

The National Health Service of the United Kingdom explains that VLCDs (sometimes referred to as very low energy diets or VLEDs) consist of a medically supervised diet plan with a daily intake of 800 calories or fewer. They are usually categorized by diets that replace full, nutritious meals with liquid substitutes, such as shakes, that claim to contain all the required nutrients.

However, studies have challenged these claims. A study published in the September 2016 issue of the journal Healthcare found that even the very low energy diets that boasted the highest protein concentration still did not provide enough protein to participants.

In fact, the only participants they did provide enough protein to were the youngest and smallest women of the group, excluding a large portion of subjects. One of the high-protein diets was Optislim, providing a logical reason to doubt its nutritional effectiveness.


It is strongly advised that VLCDs be conducted under medical supervision and not on your own.

Are Meal Replacement Shakes Safe?

VCLDs originated as a form of obesity treatment, but they are still not used as the very first step of obesity management. They can be a challenging and potentially harmful diet to maintain, and often do not provide the results desired once completed.

Because of the low calorie count and general lack of nutrition provided by these meal replacements, following a VLCD can be exceptionally difficult. Aside from persistent hunger and tiredness from your body not receiving the energy it needs, side effects can also include:

  • Dry mouth
  • Constipation
  • Diarrhea
  • Headaches
  • Dizziness
  • Cramps
  • Hair thinning

Meal replacement diets are desirable because they can have quick results. Weight loss occurs quickly due to the low calorie intake, so results are achieved at a much faster rate than with more conventional weight loss plans.

However, these plans carry with them their own set of risks that must be considered before you decide to take them on. There are a variety of individual factors that can complicate these diets, including age, lifestyle and personal health.

When it comes to Optislim vs. Optifast, it really depends on your own personal schedule. While the Optifast plan appears to be more beneficial, thanks to its monitoring and classes, it can be time consuming and does not necessarily fit in with an individual's busy lifestyle — which may make Optislim a preferable option. However, easier is not always better, and clinical evidence suggests that Optislim is not quite as nutritionally beneficial as it boasts.


If you are tempted to try a VLCD or similar meal replacement plan, contact your health care provider for advice beforehand. Diets such as these can be risky, and when it comes to fast weight loss, safety is paramount.