Optifast vs OptiSlim: The Honest Referee

The short answer

On the published labels, Optifast is the stronger panel: more protein per serve (20g against 17.7g), more than four times the listed dietary fibre (3.6g against 0.8g), slightly less sugar (12.7g against 13.7g), a marine omega-3 source in the ingredients, and a gluten-free product. OptiSlim is the clear value pick: $44.99 for 21 sachets from its own site, which works out to $2.14 a meal against Optifast's $4.72 at recommended retail. Both are legitimate VLCD programs, and both are designed as a supervised phase rather than a permanent way of eating.

That is the referee's card. The rest of this page shows the working, row by row, from each brand's own published figures, all retrieved on 21 August 2026.

What these programs actually are

A very low calorie diet replaces normal meals with nutritionally engineered shakes, soups or bars for a defined period. It is a clinical tool, not a casual diet product. Optifast's own published materials put it plainly: the product is "for the dietary management of overweight and obesity and must be used under the supervision of a healthcare professional".

Optifast, made by Nestlé Health Science, is the pharmacy-channel option Australian clinics have used for decades. OptiSlim is the Australian direct-to-consumer alternative, sold from its own site, with directions to replace one, two or three meals a day depending on the program level. Same category, two different postures: one clinical, one flexible.

This article is general information, not medical advice. A VLCD is a clinical program, and decisions about starting, continuing or stopping one belong with your doctor or the health professional supervising it.

The label comparison

Chocolate shake against Chocolate shake, published panel against published panel. The final column is arithmetic on the two figures shown, so you can check every call.

Figures are each brand's published nutrition information for the Chocolate shakes: OptiSlim from the optislim.com.au product pages, and Optifast from the pack panel as reproduced on Australian pharmacy retail listings (Discount Chemist and Direct Chemist Outlet), cross-checked across two retailers. All figures retrieved 21 August 2026. Flavours vary and brands reformulate, so check the current label before buying.

This article uses nutrition information panel figures for both brands throughout, because the panel is the regulated document. Both brands' panels were re-retrieved from their own sites on 2 September 2026.

Where Optifast wins

Protein. 20g per serve against 17.7g, and if protein is your priority the gap widens: Optifast also sells a Protein Plus shake listing 28g per 63g serve, which its pages describe as "40% more than standard". OptiSlim's Classic range has no equivalent on the pages we retrieved.

Dietary fibre. 3.6g against 0.8g is the widest gap on the card. Fibre is not a side detail in this category: a diet made mostly of shakes carries very little incidental fibre from food, so what the sachet lists is close to what you get.

Sugars. 12.7g against 13.7g per serve, so the two sit close together. On a 165 to 203 calorie shake, sugars at that level are a meaningful share of either sachet, which is worth knowing before you buy, but it is not a real point of difference between these two.

Essential fats and allergens. Optifast lists fish oil, a marine omega-3 source, in its ingredients; OptiSlim's panel lists plant-derived essential fats (linoleic and alpha linolenic acid) with no marine source. Optifast is also sold as gluten free, while OptiSlim's Chocolate shake lists wheat protein. For coeliac or gluten-sensitive readers, that row alone decides it.

Where OptiSlim wins

Price, decisively. $44.99 for 21 sachets from its own site is $2.14 a meal. Optifast's recommended retail of $84.95 for 18 works out to $4.72, and even at the discounted pharmacy prices we found ($48.15 to $63.99), Optifast lands between $2.68 and $3.56 a serve. Over a multi-week program at recommended retail, that difference compounds into hundreds of dollars; at the deepest discounts the gap narrows to cents a serve.

Flexibility and access. OptiSlim sells direct online with directions to replace one to three meals a day, which suits people stepping a program up or down without a clinic visit. More sachets per box (21 against 18) also means fewer reorders.

A fairness note on protein. Optifast's protein edge partly reflects its bigger sachet. Per 100 calories, OptiSlim actually lists slightly more protein (10.7g against 10.0g), so on protein density the two are honestly level; it is fibre and sugar where the panels genuinely separate. We apply the same published-label method across this category; learn more in our review of The Lady Shake.

Which one should you pick

Pick Optifast if your VLCD is clinician-led, you want the strongest standard panel (fibre, sugars, marine omega-3) or the 28g Protein Plus option, or you need the gluten-free label. Its supervision requirement is a feature, not friction: this category works best with a professional watching the process.

Pick OptiSlim if cost per serve is the deciding constraint and you and your health professional are comfortable with a flexible, self-managed structure. The label trade-offs are real but the category job, a nutritionally supported very low calorie phase, is still being done.

Either way, take the decision to the GP or dietitian who is supervising your program. A VLCD is a medical intervention, and the right brand is the one that fits the program you are actually on.

What happens when the shakes stop

Here is the part neither label talks about: both programs end. While a VLCD runs, the sachet does the portion control and the nutrition maths for you. When it stops, appetite comes back before new habits do, and the food environment you return to is unchanged.

The clearest data on what follows medically induced weight loss comes from the medication side of the field. In the STEP 1 trial's extension study, people who stopped a GLP-1 medicine regained on average two-thirds of the weight they had lost within a year (Wilding et al, 2022). A VLCD is a different intervention, but it shares the mechanism that matters: the moment the structure is removed, everyday eating decides what happens next. If your weight loss was medication-led rather than shake-led, the same transition logic applies; learn more about nutrition support when coming off a GLP-1 medicine.

And everyday eating in Australia is not a high bar. Over 90% of Australian adults do not meet dietary guidelines (AIHW). The transition phase, when shakes step down and real food steps back in, is where protein, dietary fibre and micronutrient intake quietly fall away; learn more about the five gaps that open when intake drops.

General information, not medical advice. How and when to finish a VLCD, or any medication decision, belongs with your doctor.

Rebuilding everyday nutrition after a VLCD

First, the category line, stated plainly: HLTH+ is not a VLCD, it is not a weight-loss product, and it is not a substitute for either program above. A VLCD is a supervised phase with its own evidence base. HLTH+ is built for the ordinary daily eating that comes after, when the sachets stop and the nutrition maths becomes yours again.

HLTH+ is an Australian-owned and made Formulated Supplementary Food under the FSANZ Food Standards Code, supplying 30 essential daily nutrients in each serve. The label reads 30g protein per serve, 7g dietary fibre, 5g collagen, 10 billion CFU Lactobacillus Plantarum Postbiotic plus prebiotics, 60mg DHA, and a balanced multivitamin profile. Protein contributes to the maintenance of muscle mass, and dietary fibre contributes to regular laxation, which is exactly the territory a post-program diet has to keep covering. Sugar sits at 1.5g (Women's formulas) to 1.7g (Men's), with none added, and the product is dairy-free, gluten-free and low GI with a 5-star Health Star Rating.

Rather than one formula for everyone, HLTH+ is dietitian-formulated to the Nutrient Reference Values set by the National Health and Medical Research Council, the Australian Government Department of Health and Ageing and the New Zealand Ministry of Health, in life-stage versions: Women's, Women's 50+, Men's and Men's 50+. A serve is RRP $6.00, or $5.10 a day on a 28-serve subscription. It is sold at hlthplus.com and through Amazon AU and Chemist Warehouse online.

Finishing a program and not sure what your day-to-day nutrition is missing? The ✦ Find My Formula quiz takes 30 seconds and shows what your current routine is not giving you.

Frequently Asked Questions

What is the difference between Optifast and OptiSlim?

Both are Australian very-low-calorie-diet (VLCD) shake programs. Optifast is the pharmacy-channel clinical option, and its published materials state it must be used under healthcare supervision; its Chocolate panel lists 20g protein, 3.6g dietary fibre and 12.7g sugars. OptiSlim VLCD Classic sells direct at a lower price, listing 17.7g protein, 0.8g fibre and 13.7g sugars (panels retrieved 2 September 2026).

Is Optifast or OptiSlim cheaper?

OptiSlim. Its own site lists the VLCD Classic Shake at $44.99 for 21 sachets, which the brand states is $2.14 a meal. Optifast's recommended retail price is $84.95 for 18 sachets, about $4.72 a serve, though Australian pharmacy retailers commonly sell below that (prices retrieved 21 August 2026).

Which has more protein, Optifast or OptiSlim?

Optifast. Its standard Chocolate shake lists 20g protein per 53g serve against OptiSlim VLCD Classic's 17.7g per 43g serve, and its Protein Plus range lists 28g per serve. Per calorie the gap nearly closes: about 10.0g per 100 calories for Optifast and 10.7g for OptiSlim (published panels, 21 August 2026).

Do you need a doctor to start Optifast or OptiSlim?

Optifast's published materials state the program "must be used under the supervision of a healthcare professional". OptiSlim's product directions describe replacing one, two or three meals a day. A VLCD is a significant intervention either way, so involve your GP or dietitian before starting one. This is general information, not medical advice.

Is HLTH+ a VLCD like Optifast or OptiSlim?

No. HLTH+ is a Formulated Supplementary Food that supplements everyday meals with 30g protein per serve, 7g dietary fibre and 30 essential daily nutrients. It is not a weight-loss program and does not replace a VLCD. Its territory is everyday nutrition, including the months after a supervised program ends.

This article is general information, not medical advice. Decisions about a VLCD program or any medication belong with your doctor.