Role of the Healthcare Professional

Managing side effects

Careful management of the side-effects during the Intensive level of the OPTIFAST VLCD can greatly increase the success of the program as well as the patient’s compliance.

It is important to note that some initial side-effects, especially during the first 3 days of the program, are normal and can be easily managed. Please see the list below for tips on how to manage the more common side-effects

3 day Challenge

The first few days on the OPTIFAST VLCD Program Intensive level are commonly known as the 3 day challenge.

As the body transitions into ketosis, your patient may experience some transient side effects such as;

  • fatigue
  • hunger
  • lack of concentration
  • nausea
  • headaches.

Typically, only mild ketosis occurs during the Intensive level of the OPTIFAST VLCD program and most symptoms pass by days 4-6.

Encourage your patients to stick to the program as prescribed and to avoid eating any extra food during this initial 3 days, otherwise they will just prolong the uncomfortable feeling. If your patient has quite an intensive type job, recommending starting the program on a weekend where they have more time to rest may assist with them managing their symptoms.

Headaches can be managed by recommending some over the counter pain relief.


It is normal to feel hungry for the first few days of the program as the body transitions into ketosis. If possible encourage your patient not to eat any extra food to compensate for the fatigue or hunger. However if they are struggling then recommending to add in a small serve of lean protein each day may help manage their hunger feelings whilst they adjust to ketosis.

It is very important that they avoid foods that contain carbohydrates, as this will stop ketosis from occurring. If hunger is a problem whilst on the OPTIFAST VLCD Program, make sure fluid intake is adequate as we sometimes mistake hunger for thirst or recommend they distract themselves with another activity such as going for a walk or taking a bath.

If all else fails use the foods listed in the Additional Allowances table, such as increasing the allowed quantity of vegetables, diet fluids, diet jelly or some sugar free lollies.


A complete meal replacement program is usually a dramatic change of intake for most people, and this can cause changes in bowel habits. In addition, if the recommended fluid and low starch vegetables are not consumed, a lack of fibre (dietary bulk) and fluid can result in constipation.

It’s important to know the difference between going less frequently and true constipation. It is normal to go less frequently when you are consuming less food, whereas true constipation is when the consistency is also affected.

If your patient is experiencing constipation, recommend they consume more than the 2 cups of low starch vegetables per day, drink 2-3 litres of fluid, and ensure they are exercising daily to help keep the bowels healthy and regular.

If they still find they are constipated suggest a fibre supplement such as Benefiber, or Metamucil. Benefiber is sugar free, has no flavour and dissolves completely, so is ideal to add into the OPTIFAST VLCD Shakes. Benefiber is available from pharmacies and supermarkets.


Diarrhoea can be a temporary side effect of taking OPTIFAST VLCD and should pass with time (refer to leaflet in carton under 'Adverse Reactions'). If diarrhoea continues for more than a week you may need to investigate for further causes.

Bloating /flatulence

There could be several explanations to explain bloating or an increase in flatulence. Bloating / increase flatulence maybe caused by the change in diet. If there is more fibre in the new regimen due to increased intake of vegetables, this may result in the bloating.

Some people find that they feel bloated because they are drinking a lot more fluid than usual. The bloating /increased flatulence is usually transient and resolves quickly so it is recommended to keep progressing with the program.

Alternatively if your patient is lactose or fructose intolerant, the OPTIFAST VLCD products may cause bloating as they contain both lactose and fructose. If the symptoms don’t improve within a week it may be worth doing some further investigation.


Estimated fluid requirements are 35-45mL/kg Adjusted IBW/day.

For most patients greater than 80kg this will equate to approximately 2.5-3.0 L/day.

As 3 sachets of OPTIFAST VLCD provides approximately 600mL per day, most patients on OPTIFAST VLCD will require an additional 2 L per day of fluid preferably water.

Nutritional Deficiencies / Supplementation


The OPTIFAST VLCD Intensive level (minimum of 3 OPTIFAST VLCD products plus 2 cups of vegetables) is designed to meet the recommended dietary intake for most people. Therefore additional supplementation is not necessary unless there has been a pre-existing nutritional deficiency diagnosed when starting the OPTIFAST VLCD Program. If additional supplementation is desired, care would need to be taken to ensure that recommended safe levels of vitamins, minerals and trace elements are not exceeded.

Fish Oils

Fish oil supplementation is considered relatively safe and there is substantial research regarding the benefits of Omega-3, particularly in the area of cardiovascular health. The Australian dietary target to reduce chronic disease is 430mg for females and 610mg for males. Therefore the National Heart Foundation has set the recommendation of 500mg per day for all adults to help reduce the risk of heart disease. The OPTIFAST VLCD Shakes and Tomato Soup contain on average 60mg of Omega-3 (combined EPA/DHA) per serve and the Mixed Vegetable Soup contain on average 75mg per serve. If additional fish oil supplementation is desired for health benefits then this will be safe to include as part of the OPTIFAST VLCD Program.


Rapid weight loss may induce the formation of gallstones. Fat intake is low with a VLCD, therefore the addition of fat (i.e. 1 tsp vegetable oil per day) to the OPTIFAST VLCD Program Intensive level is recommended to stimulate the emptying of the gallbladder and prevent the formation of gallstones. Formation of gallstones can also be prevented with ursodeoxycholic acid in predisposed individuals.


Bad breath or halitosis can occur whilst using OPTIFAST VLCD. This is caused by ketosis and generally due to an increase in acetone levels. This is characteristic of ketogenic type diets and indicates compliance to the program. The halitosis will only last whilst they are following the Intensive level of the OPTIFAST VLCD Program. Recommending chewing on a low-calorie mint or sugar free chewing gum can help. Chewing fresh parsley can also be very effective.