The OPTIFAST Program before bariatric surgery

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Pre-Bariatric Surgery Diet

Two to six weeks before bariatric surgery, you may be advised by your healthcare professional to commence a pre-bariatric surgery diet.

Why is this diet necessary?

The pre-bariatric surgery diet prescribed is usually a Very Low Energy Diet (VLED), which is known as the Intensive Level of the OPTIFAST VLCD Program. The aim of the diet is to improve the safety of surgery by reducing the size of the liver, as well as fat around the organs, to allow greater access to the surgical area. A VLED is designed to meet your nutritional requirements, whilst being low in carbohydrates and providing less than 800kcal per day.

Following a VLED program for as little as 2 weeks prior to bariatric surgery has been shown to result in a reduction of liver size, reduction of fat tissue and weight loss, therefore making the bariatric surgery easier for your surgeon and a safer procedure which you will recover from more quickly afterwards1.

What does the diet involve?

You will be required to replace all your meals with three OPTIFAST VLCD products per day (choosing either OPTIFAST VLCD Shakes, Meal Replacement Bars, OPTIFAST Desserts, OPTIFAST Soups or a combination of these products), in addition to 2 cups of low starch vegetables, 1 teaspoon of oil and 2 litres of calorie free fluids.


Intense level - up to 12 weeks

See here for the list of permitted low starch vegetables and other permitted foods on the Intensive Level.

It is important to follow the items on this list to maintain a low carbohydrate intake, enabling your body to utilise fat stores as a source of energy. This is known as ‘ketosis’. Find out more about ketosis.

The Three Day Challenge

Some people can experience some mild side effects during the first few days of following the Intensive Level of the OPTIFAST VLCD Program such as:

  • Tiredness
  • Nausea
  • Constipation/diarrhoea
  • Headaches
  • Hunger
  • Poor concentration

These side effects normally resolve by day 4, when you achieve the mild state of ketosis.

After surgery

Following your bariatric procedure, you may be asked to continue to consume OPTIFAST VLCD products as they are nutritionally complete. Your dietitian will advise you what is appropriate as you progress from a clear fluid diet through to a solid diet again over a few weeks. OPTIFAST VLCD Shakes, OPTIFAST Soups and Desserts are all suitable to be used during “full-fluid” diet stages unless you are otherwise advised by your healthcare professional.

For further advice on the use of OPTIFAST VLCD products and bariatric surgery, please speak to your dietitian or surgeon.




  1. Colles, S., et al., Am J Clin Nutr, 2006. 84: p.304-311.



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