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Optifast is a branded diet plan that incorporates varying meal replacement products.
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You may be considering Optislim versus Optifast if you're thinking about trying a fast weight loss diet. Each plan has its own set of benefits and drawbacks, so it's important to know the difference between Optifast and Optislim when making a decision.


Here's a breakdown of the two diets, plus whether or not you should try Optifast or Optislim in the first place.

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What Is Optifast?

The Pros and Cons of Optifast



Its medically supervised.

It may not provide the calories or nutrition you need.

It can help you lose weight.

It doesn’t provide calories in the form of whole foods.

Optifast is a branded diet plan that incorporates varying meal replacement products like bars, soups and 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).

Optifast Diet Program

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 up to two years, broken down into three segments:

  1. Active Weight Loss Phase:‌ The first stage lasts four months, and involves 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 takes place during months four to six, and consists of slowly returning self-prepared foods to mealtimes (as opposed to consistent meal replacements). This occurs while you still attend classes that aim to help you change your relationship with food and how you view your dietary habits.
  3. Maintenance Phase:‌ The third and final phase is also the longest phase — it can last up to a year and a half 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 this three-stage weight-loss plan is a highly effective form of weight loss, and clinical evidence may corroborate this claim.


For instance, a November 2019 study in the journal ‌Obesity‌ carried out the largest U.S.-based, year-long randomized clinical trial of behavioral weight loss intervention with total meal replacement. 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.


What Is Optislim?

The Pros and Cons of Optislim



It may help you lose weight.

It doesn't provide the calories, nutrition or protein you need.

It doesn’t provide calories in the form of whole foods.

It’s not medically supervised.

It’s only available in Australia.

Optislim is another meal replacement program that claims to support weight loss.

So what is the difference between Optifast and Optislim? Optislim is similar to Optifast in the sense that it offers branded meal replacement products, but it differs in that it does not offer a medically supervised program to go alongside the supplements.


Optifast, in contrast, 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, which occurs without medical supervision.


Optislim Diet Program

According to the National Health Service (NHS), 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 essential nutrients.

However, studies have challenged these claims. A September 2016 study in ‌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 people they did provide enough protein to were the youngest and smallest people assigned female at birth 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, as these diets can deprive you of necessary nutrients, per the NHS.

Are Meal Replacement Shakes Safe?

VCLDs originated as a form of obesity treatment, but they are still not widely used for obesity management, according to the NHS. 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, per the NHS.

Aside from persistent hunger and tiredness from your body not receiving the energy it needs, side effects of programs like Optislim and Optifast can also include:

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

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


But fast weight loss isn't safe or sustainable, according to the Mayo Clinic. Indeed, it can lead to the side effects listed above, and may also cause you to lose water or muscle weight instead of fat, which doesn't contribute to weight loss in the long term.


You should not try a VLCD if you're under 18 years old, pregnant, breastfeeding or have an eating disorder, per the NHS.

Last Word on Optifast vs. Optislim

When it comes to deciding between Optislim versus Optifast, safety is paramount.

While the Optifast plan appears to be more beneficial due to medical supervision and hands-on classes, it can be time-consuming, pricey and provide little nutrition in the form of whole foods. It can also be difficult to stick with all three segments of the diet program over the long term.

Clinical evidence also suggests that Optislim is not as nutritionally beneficial as it boasts, meaning it may be dangerous to try the diet on your own.

Your best bet? Talk to your doctor about trying Optislim versus Optifast to see if either of these diets are safe for you in the first place. Diets like these can be risky, and when it comes to fast weight loss, safety is most important.


Losing weight at a pace of 1 to 2 pounds per week through a combination of eating a nutritious diet and exercising regularly is the most safe and sustainable way to shed pounds, per the Mayo Clinic.




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