Optislim vs Optifast: Which Meal Replacement Is Better? (2026)

The short version: no, Optislim and Optifast are not the same. Optifast is Nestle’s pharmacy product, built to be used with a doctor, at roughly 203 calories and 20 g of protein a serve. Optislim is an Australian brand sold in supermarkets and online, self-guided, at roughly 165 calories and 17.7 g of protein a serve, and about a third of the price per meal. Optifast has the longer research record. Optislim is cheaper and easier to start.

Updated 23 October 2026. Optislim pack prices re-checked against the brand’s own store on that date.

Optislim and Optifast are the two names almost everyone runs into when they start looking at meal replacement shakes in Australia. They sound similar, they sit on the same pharmacy shelf, and both promise fast weight loss. They are not the same thing, they are not owned by the same company, and the one that suits you depends mostly on whether you want a doctor involved. This guide compares them properly: what’s actually in the shakes, what each costs per meal, what the research does and doesn’t show, the side effects nobody mentions in the ads, and who each one genuinely suits.

Optislim vs Optifast: the Short Answer

What a VLCD Actually Is

Both brands sell what the research literature calls a formula total diet replacement. Instead of cooking, you drink nutritionally complete shakes (or eat bars and soups) that between them supply roughly 800 calories a day, along with the full daily requirement of protein, vitamins and minerals. Below about 800 calories a day it’s a very-low-calorie diet (VLCD); a bit above that it’s a low-calorie diet (LCD).

The reason this works isn’t magic: it’s a large, enforced calorie deficit, with the protein and micronutrients kept intact so you lose fat rather than muscle and don’t become deficient. After a few days your body shifts into mild ketosis, which blunts hunger, most people find days three to five are the hard part and it gets easier after that.

Optislim: What It Is

• Who owns it: an Australian company, on the market since 2001 and made in Australia.
• How you buy it: direct from optislim.com.au and in supermarkets and pharmacies. No referral, no appointment, no supervision required.
• The range: around 47 products. VLCD Classic and VLCD Platinum shakes, bars, soups, low-calorie snacks, plant-based options, separate “for Her” and “for Him” lines, and a newer range aimed at people on GLP-1 medications like Ozempic.
• The program: self-guided, in three phases, rapid weight loss, steady weight loss, then maintenance. You choose whether to replace one, two or three meals a day.
• A VLCD Classic shake (43 g sachet): 692 kJ / 165 calories, 17.7 g protein, 3.4 g fat, 17.4 g carbohydrate (13.7 g sugars), 0.8 g fibre, plus added vitamins and minerals. Contains milk; the Classic chocolate also contains wheat protein (gluten) and soy.

Optifast: What It Is

• Who owns it: Nestlé Health Science. Optifast has been used internationally for over 50 years and is sold in more than 30 countries.
• How you buy it: mainly through pharmacies, and the company’s own labelling states it “must be used under the supervision of a healthcare professional”. It’s positioned as a clinical product, not a supermarket one.
• The range: shakes in six flavours, ProteinPlus shakes, soups, bars, desserts.
• The program: four structured levels. Intensive (all three meals replaced), Active 2, Active 1 (fewer replacements as food returns), and Maintenance, with an app, recipes and healthcare-professional support.
• A VLCD shake (per serve): 850 kJ / 203 calories, 20 g protein, 4.6 g fat, 18.5 g carbohydrate (12.7 g sugars), 3.6 g fibre, 400 mg calcium and a full vitamin and mineral profile. Milk-based and gluten free.

Side-by-Side Comparison

Nutrition figures taken from each brand’s own current product labelling. Optislim pack pricing re-checked on 23 October 2026 directly against optislim.com.au, where the VLCD Classic Shake 21 meal pack is listed at a regular price of $45.00 across flavours. The Optifast per serve figure could not be verified the same way, because it sells through pharmacies rather than a public price list, so treat that one as an indicative range rather than a checked price.

What the Labels Actually Say, Allergens Included

Neither brand leads with this, and for some readers it decides the whole question. The statements below were read from the labelling on the retailers’ own product pages, not copied from another comparison. The OptiSlim wording was read from optislim.com.au on 1 November 2026. The Optifast wording was read on 3 November 2026 from two unrelated Australian pharmacies, Pharmacy Online and Chemist Warehouse, which print the same ingredient list and the same allergen sentences. Both comparisons use the chocolate shake, so the flavour is held still.

One thing to know about the OptiSlim page. It carries two different allergen statements. The ingredients block ends “CONTAINS GLUTEN, MILK, SOY AND CAFFEINE.” The summary under the nutrition panel on the same page ends “CONTAINS MILK.” A reader who checks only the line under the panel would not learn that the product contains gluten. Both were read from the same product page on the same day, 1 November 2026.

If you have coeliac disease, or you avoid gluten. Read the ingredients list rather than the summary line under the nutrition panel, because on this product the ingredients list names more allergens than the summary does. On the labelling we read, the OptiSlim VLCD Classic chocolate shake contains wheat protein and the Optifast chocolate shake is labelled gluten free. Labels change and ranges get reformulated, so check the pack in front of you, and if you are coeliac rather than simply avoiding gluten, take the pack or the ingredients list to your GP or dietitian before starting a diet that replaces every meal.

If you have phenylketonuria (PKU). The Optifast chocolate shake is sweetened with aspartame and its label carries the sentence “Contains Phenylalanine.” The OptiSlim chocolate shake lists sweetener 955 and carries no phenylalanine warning. Anyone managing PKU should treat that as the relevant line on the pack.

Pack Sizes, Serving Sizes, and Why Per Serve Figures Mislead

The two brands do not use the same serving size, which matters more than it sounds. Optislim’s VLCD Classic serving is 43 g, one sachet, 21 sachets to a pack. The VLCD range runs in three tiers: Classic and Platinum at 21 meals a pack, and Platinum Plus at 18. Optifast’s shake serving is 53 g, one sachet, and the chocolate shake is sold in both 12 sachet and 18 sachet packs by the pharmacies named above. Optifast also sells bars, soups and desserts alongside the shakes, which its own product description names as part of the range, so an Optifast week can be varied without leaving the program. Optislim’s VLCD range, as listed on its own site, is shakes.

So read the per serve rows in the table above with that in mind. A 43 g Optislim serve and a 53 g Optifast serve are not the same amount of powder, so comparing calories, protein or fibre per serve compares two different sized meals. The honest footing is per 100 calories, or per 100 g of powder. Try it on the protein row using the figures already in the table above: 17.7 g in a 165 calorie Optislim serve is about 10.7 g of protein per 100 calories, while 20 g in a 203 calorie Optifast serve is about 9.9 g. Per serve, Optifast looks like the higher protein shake. Per calorie, it is not. That is the same arithmetic trap in both directions, and it is why we are not adding more per serve rows until we can read both nutrition panels at their source, for the reason in the next paragraph.

What we could not check, said plainly. Neither pharmacy publishes the Optifast Nutrition Information table, and optifast.com.au does not serve pages to us at all, so we could not read Optifast’s per serve energy, protein, fat, carbohydrate, fibre or sodium figures at their source on 3 November 2026. Until we can, we are not adding more per serve rows to this comparison. If you want those numbers today, the back of the pack in the pharmacy is the authority, and it is worth two minutes in the aisle.

Working Out the Cost Yourself, Whatever the Price Is Today

Prices and promotions move, and a figure typed into an article ages badly. The arithmetic does not. On a full VLCD you replace three meals a day, so the only number that matters is the cost of one sachet, and both brands make that easy to work out from the pack in front of you.

• Cost per meal is the pack price divided by the sachets in the pack. Optislim VLCD Classic packs hold 21 sachets, Platinum Plus holds 18, and the Optifast chocolate shake comes in packs of 12 and 18.
• Cost per day on a full replacement is that figure times three.
• Cost per week is the daily figure times seven, and a 21 sachet pack is one week of three a day exactly, which is why 21 is the pack size it is.
• Then add the extras both programs expect: low starch vegetables, and for Optifast any GP or dietitian appointments, some of which may attract a Medicare rebate under a chronic disease management plan. Ask your GP rather than assuming either way.

One warning about per meal figures printed in marketing, including the per meal figure on Optislim’s own product page. On 1 November 2026 that page stated one per meal cost in its bullets and in a block headed THE MATHS, while the pack price in its own selector divided out to a different figure, and the collection listing showed a third. None of them was wrong exactly; they were different offers and pack sizes. Run the division on the price you are actually being charged.

What Optifast’s Label Says About Supervision and Who Should Not Use It

Both pharmacy listings carry the same classification sentence, and it is a clearer statement of what the product is than anything in either brand’s advertising: “OPTIFAST VLCD is classified as a very low energy diet (VLED) and not a formulated meal replacement. A VLED can be used as a total diet replacement, meaning you can replace all 3 meals with specially formulated VLED products, such as OPTIFAST VLCD. With a formulated meal replacement, you can only replace 1-2 meals per day.”

The same listings carry the product’s own cautions. One states: “Unsuitable for use by Pregnant or Lactating Women, Infants, Children, Adolescents or People Older than 65 years of age.” The other adds that a very low energy diet “should not be used by people with acute heart disease, advancing renal disease, advanced hepatic disease or overt psychosis”, and that people over 65 or with existing medical conditions should consult a healthcare professional before use. Both also instruct an additional two litres of calorie free fluid a day. These are the manufacturer’s own words, quoted from the retailer pages linked above and read on 3 November 2026. They apply to the Optifast product; they are not our clinical advice, and they are a good reason to involve a GP whichever brand you pick.

Buying From New Zealand

There is no separate New Zealand Optislim store. We checked optislim.co.nz on 1 November 2026 and it redirects to the Australian site, so a New Zealand buyer orders from Australia and any free shipping threshold advertised there is an Australian offer. Check what shipping to New Zealand costs before you compare per meal prices, because on a three a day program the freight is not a rounding error.

The Study Optislim Cites, Read at Source

Optislim’s product page attaches a citation to two of its weight loss claims, crediting “Logue et al. (2014)” and giving “PubMed 25586630”. We looked up that record. It is a real paper and its weekly weight loss is in the same range as the claim, so the number is not invented. Four things about it do not match the page, and a reader deciding between two products deserves to know them.

• Different authors and year. PubMed 25586630 is Rolland and colleagues, published in Clinical Obesity in October 2013, not Logue in 2014.
• Different number of people. The paper reports 710 participants, 355 with type 2 diabetes matched to 355 without. The page describes a study based on more than 1,200 participants.
• Different kind of study. It is a retrospective analysis of a community program run in the United Kingdom, not a trial of a product.
• It is not a study of this product, and the shakes were not the only ingredient. The program was about 550 kcal a day plus group support and behaviour therapy from trained facilitators. Weight change at 12 weeks was 18.3 kg in the diabetes group and 19.9 kg in the group without, which is roughly 1.5 to 1.7 kg a week.

We are not calling that citation dishonest, and we are not softening it either. The useful reading is the last point: the results that formula diets produce in published research usually come from a supervised program with support built in, not from shakes on their own. That is true of the Optifast literature as well, and it is the single best argument for treating either brand as a program rather than a product.

What the Research Actually Says

This is where the two brands genuinely differ, and where the marketing on both sides needs a second look.

Formula diets do work: that part isn’t in doubt

The evidence for total diet replacement as a category is strong. In the landmark DiRECT trial, published in The Lancet in 2018, people with type 2 diabetes who followed a formula diet of 825 to 853 calories a day for three to five months lost an average of 10 kg, and 46% were in diabetes remission at one year, compared with 4% on usual care. At two years, more than a third were still in remission. The DROPLET trial in the BMJ found much the same in general practice: people referred to a total diet replacement programme lost 10.7 kg at one year versus 3.1 kg with usual care.

A 2017 systematic review in the International Journal of Obesity found that formula diets produce about 0.5 to 0.6 kg of weight loss per week, and, usefully, that people with type 2 diabetes lose just as much as people without it, contrary to the old assumption that diabetes makes weight loss harder.

But “clinically proven” doesn’t always mean what you think

Almost none of that research tested these specific brands. Optislim’s product pages describe “our 12-week clinical study, based on 1,200+ participants” and cite a PubMed ID. We looked the reference up: PMID 25586630 is Rolland and colleagues, published in Clinical Obesity in 2013, a retrospective analysis of 710 people following a 550-calorie community VLCD programme with group support and behaviour therapy. It’s a real and reasonable piece of research about VLCDs in general, but it isn’t a 1,200-person trial of Optislim’s own shakes.

Optifast is on firmer ground: it appears by name in published clinical research, is used in hospital and pre-surgical weight-loss protocols, and the wider evidence base for its style of medically supervised program is the one that produced results like DiRECT. That’s the practical difference between the two, not that one works and the other doesn’t, but that one has been formally studied and the other leans on the category’s research.

Worth saying plainly: both brands are nutritionally complete formula products. A calorie deficit is a calorie deficit. If you follow either properly, you will lose weight.

Cost: What You’ll Actually Spend

On a full VLCD you’re replacing three meals a day, so the per-meal price matters more than the pack price. Every figure below is in Australian dollars, read from Australian retailers on the dates given.

• Optislim: a 21-meal VLCD Classic pack is around $45, roughly $2.14 a meal, about $45 a week on three replacements a day, with multi-pack discounts and free shipping over $99.
• Optifast: sold by the box through pharmacies at a higher per-serve price, typically in the $3 to $4 range depending on the product and any promotion, so roughly $65 to $85 a week on three replacements, before any consultation fees.
• Don’t forget the extras: both programs expect you to add low-starch vegetables, and Optifast’s structure may involve GP or dietitian appointments (some of which may attract a Medicare rebate under a chronic disease management plan, ask your GP).
• The honest comparison: against a typical grocery and takeaway spend, a VLCD isn’t necessarily more expensive. It just moves the money.

Taste and Day-to-Day Reality

“What tastes better, Optifast or Optislim?” is one of the most searched questions about these two, and the honest answer is that it’s personal, but a few patterns come up consistently in user reviews and pharmacy feedback:

• Optislim is generally described as sweeter, with more flavour variety (chocolate, vanilla, strawberry, banana, mango, choc mint, coffee, salted caramel).
• Optifast is described as more “clinical” tasting and thinner, though the ProteinPlus and dessert formats give you more texture to work with.
• Both are far more tolerable made with icy-cold water, blended rather than shaken, and left to sit for a few minutes.
• Flavour fatigue is the real enemy on a full VLCD. Variety packs and mixing formats (shake, soup, bar) matters more than which brand you start with.

Side Effects and Safety

These apply to both brands, because they’re features of very-low-calorie dieting rather than of any particular shake:

• The first week is unpleasant. Headache, fatigue, irritability, feeling cold and bad breath are normal as you shift into ketosis, and usually settle by day five.
• Constipation is very common. This is where Optifast’s 3.6 g of fibre per serve has a practical edge over Optislim Classic’s 0.8 g. Add the permitted vegetables, drink at least two litres of water a day, and ask a pharmacist about a fibre supplement.
• Gallstones. Rapid weight loss increases the risk of gallstone formation. It’s one of the main reasons VLCDs are meant to be supervised and time-limited.
• Muscle loss is minimised but not eliminated by the high protein content. Keep doing some resistance exercise.
• Medication changes. If you take insulin, sulfonylureas or blood pressure medication, doses often need adjusting quickly once you start, this must be managed by your doctor, not by you.
• Not suitable in pregnancy or breastfeeding, for children and teenagers, for people with a history of eating disorders, or for anyone with significant kidney, liver or heart disease unless a specialist says otherwise.
• Regaining weight is the usual outcome if the maintenance phase is skipped. Both programs include one for good reason: the shakes are the easy part, and the transition back to food is where the result is won or lost.

Which Should You Choose?

• Lots of weight to lose, or a health condition in the mix: Optifast. Supervision isn’t red tape here, it’s medication adjustment, monitoring and someone checking the maintenance phase actually happens.
• Pre-surgery weight loss: Optifast, because that’s the protocol most Australian surgical teams already use.
• 5 to 15 kg to lose and otherwise healthy: Optislim, replacing one or two meals a day rather than all three, is cheaper and easier to live with.
• You struggle with constipation or need gluten-free: Optifast’s higher fibre and gluten-free formulation is the easier fit.
• Budget is the deciding factor: Optislim, and put the difference towards the maintenance phase, where most people fall down.
• You’re on a GLP-1 medication (Ozempic, Wegovy, Mounjaro): both brands now market nutrition support ranges for this. The concern with GLP-1s is protein and micronutrient intake while appetite is suppressed, that’s a conversation for your prescriber, not a reason to add a VLCD on top.

Whichever programme you pick, it helps to know what the first few weeks actually look like before you start. Our guide to what really happens on a very low calorie diet covers why week one flatters the scale, what the trials achieved, and the regain figures that decide whether any of this lasts.

Both of these programmes are often started because of a blood sugar result rather than a number on the scale. If that is the reason, the food and habit changes in our guide to lowering blood sugar naturally are worth reading alongside whichever programme you choose.

Frequently Asked Questions

Is Optislim the same as Optifast?

No. They’re competing brands from different companies. Optislim is Australian and independent, Optifast belongs to Nestlé Health Science. The similar names and similar products cause a lot of confusion, but they’re separate ranges with different formulations, prices and distribution.

Which is better for weight loss, Optislim or Optifast?

For pure kilos lost, neither has a proven advantage, weight loss on a VLCD is driven by the calorie deficit, and both supply roughly the same. Optifast has the stronger clinical track record and the supervision that makes a full very-low-calorie diet safer, so it’s the better choice for larger or medically complex weight loss. Optislim is the better everyday option for smaller, self-managed goals.

What’s the difference between Optifast and Optislim shakes?

Per serve, Optifast has more calories (203 vs 165), more protein (20 g vs 17.7 g), considerably more fibre (3.6 g vs 0.8 g) and more calcium (400 mg vs 279 mg), and is gluten free. Optislim is cheaper per meal, comes in more flavours and is easier to buy without a pharmacy visit.

What tastes better, Optifast or Optislim?

Most people find Optislim sweeter and more dessert-like, and Optifast plainer. Taste is the single biggest reason people abandon these programs, so if you can, buy a variety pack or a couple of single sachets before committing to a month’s supply.

How much weight can you lose on Optislim or Optifast?

Research on formula diets shows roughly 0.5 to 1 kg a week on average, with trials of full total diet replacement producing around 10 kg over three to five months. Both brands advertise faster figures; the first week always looks dramatic because much of it is water and glycogen.

Can you buy Optifast without seeing a doctor?

It’s sold in pharmacies and the pharmacist can advise you, but the labelling states it should be used under healthcare supervision. For a full three-meal-replacement VLCD, that supervision matters, particularly if you take any regular medication.

Can you buy Optislim or Optifast outside Australia?

Optifast is sold in more than 30 countries, though the formulation and program differ by market (in the US it’s typically offered through clinic-based programs). Optislim is an Australian brand and sold mainly in Australia.

How long can you stay on a VLCD?

Total meal replacement is usually limited to around 12 weeks, after which you step down through the program’s transition phases. Staying on one indefinitely without supervision isn’t safe or necessary.

The Bottom Line

Optifast is the clinical option: more research behind it, more fibre and protein per serve, a more structured program, more expensive, and designed to be run with a healthcare professional. Optislim is the accessible option: cheaper, tastier to most people, easy to buy, flexible about how many meals you replace, and fine for a healthy adult with a moderate goal.

The thing that determines whether either works isn’t the brand on the sachet. It’s whether you complete the maintenance phase and change what you eat afterwards. Choose the one you can actually stick to, and plan the way back to real food before you start.

Related Reading

• Natural Ozempic Alternatives: what the evidence says about the supplements people try first
• Diet and Nutrition: all our nutrition guides
• Lifestyle and Wellness: sleep, stress and everyday habits

This article is for educational purposes only and is not medical advice, and we have no commercial relationship with either brand. Very-low-calorie diets are a medical intervention: speak to your GP, pharmacist or dietitian before starting one, especially if you take regular medication, are pregnant or breastfeeding, or have diabetes, kidney, liver or heart disease. Nutrition and price details were taken from each brand’s own published information in September 2026 and may change. See our medical disclaimer.